The Mudlogger’s Bible North Sea specific
ORDER CODE: 648.NC.365
TABLE OF CONTENTS
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CONTENTS
SECTION 1 – Sample Catching Basics SECTION 2 – Cuttings Analysis Basics SECTION 3 – Basic well monitoring SECTION 4 – Basic well control SECTION 5 – Gas Detection Basics
Appendix A – Oil field Glossary Appendix B – Useful Formulas and Calculations
TABLE OF CONTENTS
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CONTENTS
SECTION 1 – Sample Catching Basics SECTION 2 – Cuttings Analysis Basics SECTION 3 – Basic well monitoring SECTION 4 – Basic well control SECTION 5 – Gas Detection Basics
Appendix A – Oil field Glossary Appendix B – Useful Formulas and Calculations
SECTION 1 – Sample Catching
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1. Sample Catching Basics Introduction
The purpose of collecting rock cuttings from the well is to provide geological data for that particular part of a well. From these cuttings, information such as rock type, properties of the rock, age of the rock, chemical composition of the rock and presence of flora/fauna can be obtained. Although some analysis is performed at the well site the majority of clients require a sample for additional specialist tests. If there are a number of partners involved on the well it is common for them to require a sample for their own purposes. In the UK the DTI (government) also requires a sample. This can mean you could be catching a number of samples for each drilled interval Practical Safety in the shaker house
To be honest, sample catching is such an easy task a monkey (or Frenchman) could be trained to perform the task. However on your first trip offshore the shale shakers can be a little intimidating. As long as you do not put your hands or any other part of your body actually on the shakers there should be nothing to worry about, also remember that the shaker house is a very noisy work area so hearing protection should always be worn. During some parts of a well it is also common for the shaker house to contain a lot of vapour and this can sometimes feel uncomfortable, if you are having some problems with regard to the vapour or fumes inside the shakers, just leave the area and request (either from the data engineer or the rig store man) a filter mask. On some rigs you may be required to wear a filter mask before going into the shakers anyway. Please do not panic about this, the fumes in the shakers are usually only harmful either on a short term basis or after a prolonged exposure to them and as mud loggers we do not spend enough time in the shakers at anyone time to be aversely affected by this.
SECTION 1 – Sample Catching Collecting your first sample
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So now you are ready to catch your first sample, first of all you need a few small tools, a trowel (to scoop up cuttings), sieves (to filter out and sort small and large cuttings), sample bags (to put the sample in) and a bucket (for detergents/cleaning of samples). In the shakers there should be a board or plate situated at the front of one or more of the shakers, in order to collect a sufficient quantity of cuttings for you to take your sample from. To collect an unwashed wet sample simply use the trowel to shovel cuttings from this plate into a wet sample bag (usually a cloth bag with a plastic insert). Two scoops from a trowel are usually sufficient. A washed wet sample involves putting cuttings from the board into a sieve and washing the excess mud from the cuttings before putting the cuttings into a wet sample bag. Washing samples (Water based Mud)
To wash cuttings in a sieve when drilling with water based mud you can either partly submerge the sieve in a bucket filled with freshwater (try to avoid seawater as it can contaminate the sample) and just swill the contents of the sieve around gently. The other method is a little more fun, simple take the hose the shaker man uses for cleaning, put the sieve on the floor and wash the sample using the hose. Take care not to use too much pressure or you will only displace the entire sample from the sieve. When drilling through a large section of Salt/Halite you will have to wash the sample in a bucket of salt saturated water, simply get some salt from the mud engineer or derrick man (Sodium Chloride) and mix it with water in a bucket, the more salt you use the better but if you have time add the salt to the water continuously until the salt no longer dissolves. Washing samples (Oil based mud)
To wash cuttings in Oil based mud you will need 2 buckets. In the first bucket you will need to use base oil, which can be obtained from the shaker man or the derrick man and the second bucket needs to be filled with a mixture of Rig wash and water. Use about 1/3 rig wash to 2/3 water in the mixture. Rig wash can be found somewhere on the deck of the rig but if you aren’t sure just ask one of the drill crew or the data engineer. Wash your sample in the base oil first and then in the rig wash solution, remembering to wear oil work gloves that cover your forearms up to your elbows. If your skin does come into contact with base oil or rig wash then wash it off with clean water as soon as you can as these substances can give you a slight rash. Dry samples
Dry samples are taken from the sample you gathered in the sieve for your microscope analysis and should always be washed (even if the client asks for unwashed dried samples) as fumes from Oil based mud could set of smoke
SECTION 1 – Sample Catching
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detectors in the unit. Basically the samples should be dried in an oven or microwave (but not baked!) so try to keep the temperature between 60 and 80 degrees Celsius. Additional Info – Tips
Be careful not to drop your sieve into the void where the cuttings are dumped, as this is very easy to do if you aren’t paying attention. If you do happen to drop your sieve down this gap please tell the shaker hand immediately as this can cause a blockage and lead to the shakers being swamped. I have heard of this happening and the Mudlogger was not in the good books of the drill crew who had to spend 2 days digging out the shakers. The same applies to the trowel. An easy way to remove excess fluid from the sieve after washing is to press the side gently against the side of the shaker for a few seconds; this is especially useful when using a finer sieve. Cavings
Cavings are basically abnormally sized and shaped fragments of rock that have not been drilled by the drill bit. There are a number of reasons for the appearance of cavings but one of the most serious is as a result of the well being under balanced. For this reason alone always report any sign of cavings to the well site geologist and data engineer. Pressure cavings do differ in appearance from cavings resulting from mechanical sources, in that pressure cavings tend to have a sharp splintery form and a concave cross-section. The diagram below shows the difference between pressure cavings (on the left) and cavings caused by other means (on the right), however there are some much better comparison charts (especially the schlumberger one) around.
SECTION 2 – Cuttings Analysis Basics
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2. Cuttings Analysis Basics Introduction
Although a number of mud loggers have a strong geological background there are a number of us who don’t. This is not usually a problem as the geological knowledge actually required for mudlogging is very basic. The first analysis task we are required to perform is a description of the cuttings using a microscope. This is at first daunting for both geologists and non geologists as rock formations tend to look rather different after they have been carved up by a drill bit and pushed up a vertical tube at high velocity. Other analysis usually required by mud loggers tend to consist of a number of simple tests using “sophisticated” apparatus. These are actually very straightforward to use and you will always be able to receive help from the data engineer or a more experienced. The most common of these analysis techniques are fluorescence (use of UV light to detect hydrocarbons) and Calcimetry (a test of how much calcium carbonate is present in a rock). Looking at and describing samples
In the North Sea area there are really only 5 main rock types you will need to identify; sandstone, claystone, limestone, salt (halite) and siltstone. Once you become used to looking at the cuttings it should be pretty easy to identify each main group, however siltstone is normally quite difficult to identify as you can have silty claystones and formations where the difference between claystone, siltstone and fine sandstone can be a little debatable but just take your best guess. The following dummies guide should help you work out what you need to describe and what terms to use in your descriptions:
SECTION 2 – Cuttings Analysis Basics
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Dummies Guide to Cuttings Descriptions Cuttings descriptions should be done in a consistent order, thus minimising the chance of missing something out. A conventional order is laid out below, although some operating companies have peculiarities of their own. The common rocks found while drilling oil wells can be split into three categories, namely: Claystone and Siltstone Carbonates and Evaporites Sandstone
The method of description varies slightly for each category.
Claystone and Siltstone a) Rock Name: Self explanatory but be aware that what looks like a Siltstone, is often a micro-micaceous Claystone b) Colour : Colour or combination of colours (e.g. pinkish brown) can be used with qualifiers such as pale, light or dark. c) Hardness: Typical terms used are: Soft. Firm, Moderately Hard, Hard . These have specific meanings. Soft grains offer no resistance to the probe when prodded. Firm grains break apart easily; moderately hard grains break with some difficulty. Hard grains are difficult to break at all, and tend to jump out from under the probe. Brittle is sometimes used, particularly when describing Coal or Salt, to describe relatively hard rocks that break easily along fracture planes. d) Break: A term used to describe the morphology of the cuttings. Examples are Blocky (breaking into rectangular fragments), Angular (majority of corners are less that 90"), Splintery (pointed, elongated cuttings), Fissile and subfissile (having more or less well-developed laminar or platy structure), Amorphous means having no form, and is commonly used to describe soft cuttings. e) Swelling: This describes the tendency of cuttings to absorb water over a period of time. It is not often described in oil-based mud as oil on the cuttings surface can affect absorption. Conversely, washing with detergent sometimes gives an over enthusiastic reaction. Common terms used are Hydro- or Hygro-turgid (swelling in a random manner), Hygro-fissile (swelling into small flakes) and are usually qualified by ‘slightly’, 'moderately’ or 'very'. The term Crypto-fissile may be used, this describes a similar reaction to hvgro-fissile but is induced by 10% HCL. f) Modifiers: Not all rocks are composed of one grain type. Argillaceous is used with non-Claystones with recognisable clay content. Similarly the terms Silty and Sandy can be used. (Arenaceous is interchangeable with Sandy).
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g) Carbonate content: Calcareous with the qualifiers ' Non', 'Slightly ', 'Moderately ' or 'very ’, describe the way in which a cutting reacts in I0% HCL. Dolomitic is used to describe a cutting that reacts only after several minutes’ immersion or after warming. Be aware that oil based mud residue also inhibits reaction times therefore cuttings should be crushed to expose fresh surfaces. h) Accessories: These are the small quantities of other minerals present in the major lithology. Examples are Pyrite (which may be described as disseminated i.e. fine grains scattered throughout the rock, or nodular i.e. a crystalline mass), Glauconite, Mica, (which nay be prefixed with micro to describe the fine disseminated form.) and Carbonaceous. The usual qualifiers of quantity can be used with these minerals (i.e. slight etc.); also used are common, locally (specific to some horizons) and occasionally (scatted randomly throughout).
Carbonates and Evaporites Carbonates are rocks composed of lime mud and/or biogenic debris (shell fragments, algal structures etc.), or their re crystallisation products. Evaporites are rock deposited either by the direct evaporation of a body of water, or by a continuous process, whereby minerals are deposited at or near a terrestrial surface, as water evaporates from that surface. Both Limestone and Gypsum/Anhydrite are prone to conversion to Dolomite after burial, when subjected to Mg rich ground waters. In the Zechstein sequence of the Southern North Sea, intergrown masses of Anhydrite and Dolomite are commonly seen, in which it is difficult to determine the dominant constituent. a) Rock Name: Self-explanatory. Identification of more obscure evaporite minerals can be difficult. Most Calcium Sulphate is Anhydrite at bottom hole temperature and pressure, but tends to hydrate due to bit and mud action. b) Colour : In addition to the terms outlines above, some minerals are described as Colourless. These, and some coloured minerals, also allow the transmission of light and can be further described as Transparent (clear) or Translucent (semi-opaque). c) Hardness: As above. d) Break: As above e) Texture: This is used to describe the internal structure and/or composition of the cuttings. Terms used include Microcrystalline (having a crystal structure that is not visible except under the higher power lenses of the microscope), Crystalline (having an easily seen crystal structure) Cryptocrystalline (crystalline in appearance but having no visible structure, commonly applied to Chert). Sucrosic can be used to describe a fine-grained rock that has a sugary appearance. Texture in Limestones can be described using Dunham's classification (Wackestone, Packstone etc.), which can be found in manuals and is based on the proportions of lime mud lo skeletal fragments. The term Oolitic may also be used when Limestone contains spheroids of algal origin.
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f) Modifiers: Limestones can contain significant quantities of sand or clay and are described as Argillaceous or Arenaceous respectively. They may also be Dolomitic , which decreases the rapidity of the reaction with HCL. Halite also commonly contains clay laminations. g) Accessories: As Above. Limestone often contains carbonaceous laminations. h) Porosity: Carbonates may exhibit porosity and should be examined thoroughly. While inter-granular porosity may be seen in Oolitic Limestones, the principle type is fracture porosity. Vuggy porosity may also be seen where elements of the original fabric have been leached away by groundwater. Porosity is usually qualified by nil, poor, fair or moderate, good and very good or excellent . The terms visible or estimated are also usually applied, as visually porosity estimation can be very subjective. i) Shows: Although carbonate reservoirs are not commercially important in the UK, they often contain hydrocarbon shows. These should be observed and noted. Be aware that minerals in the carbonates con also fluoresce.
Sandstone The description of Sandstone can be split into two parts, the properties of the whole rock, and the properties of the grains that make up that rock. a) Rock Name: Sandstone or Sand . Sandstone is composed of cemented Sand grains, but be aware that bit action can reduce even reasonably well-cemented Sandstone to a tray full of grains. Also be aware that PDC bits can turn well-cemented Sandstone into a silica paste often referred to as rock flour . If the cement is calcareous, testing with acid may also give the false impression of drilling Limestone. Look for tell tale grains of sand trapped within the paste, by rubbing the probe or tweezers against the plate you can often encounter a sandy texture. b) Colour : This deals specifically with the colour of the rock. c) Hardness: The term Friable is used in place of soft and firm in the scheme above. Loose is used where only Sand grains are observed. d) Break: In addition to the scheme as outlined above, the term Crumbly is used to describe a cutting of irregular outline.
SECTION 2 – Cuttings Analysis Basics
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e) Grains: Grain descriptions are split into the following sub divisions: Type - Usually Quartz but maybe Feldspar (although this is difficult to distinguish from cuttings alone) or Lithic (a re-deposited grain of a pre-existing rock type). The following grain description categories should be applied to each type if they occur in significant quantities. Colour - Grain colour should be described, and an estimate made of light transmission properties (transparent translucent, etc.). The term Frosted is also used to describe grains with an abraded outer surface; these are commonly found in wind blown sand deposits. Size - Grain size should be measured using a relative comparison to a known size. Not by guessing (although if you must…) Roundness - Grain roundness is an estimate of the surface smoothing of the grain and is independent of the grain shape. Sphericity - Conversely sphericity is an estimate of the grain shape. Aids to the type of sphericity and roundness are commonly combined on grain size comparison charts. Sorting - Sorting is a visual estimation of the variety of grain sizes in a Sandstone. This is usually straightforward i.e. if there is little variation then the sample is well sorted . Be aware that some sandstones consist of well-sorted laminated layers of Two different grain sizes, but these may appear poorly sorted in a cuttings sample.
f) Cementation: Cementation is described both in terms of degree and type. The terms poor, moderate, well , etc., are used to describe the difficulty with which the cement bond can be broken, not the degree to which the pore spaces are filled with cement The common cement types are silica, calcite and dolomite , but iron oxide, pyrite, anhydrite and rarely barite, may be encountered. g) Modifiers: Once again, Sandstones can contain significant quantities of clay, and the term Argillaceous can be used. Sandstones containing significant quantities of Feldspar are often referred to as Arkosic and those with significant rock fragments as Lithic . Conglomerate Sandstones are often found, particularly at channel bases in fluvial or sub-sea fan systems. While easy to see in cored sections, they are often missed in cuttings, due to the break up of constituent pebbles by the drill action. Look for angular shards of quartz with one rounded facet. h) Accessories: As previously discussed. i) Porosity: Porosity estimation in cuttings is extremely subjective, principally; because as grain size decreases the apparent pore space diminishes. Consequently porosity is commonly under estimated. Estimates can also be affected by the deposition of drilling fluid residue in the pore space.
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Using a Fluoroscope to identify hydrocarbon shows
The most important bit last! Does the rock contain hydrocarbons? Shows should be considered in the following way: 1) Examine the cuttings for oil staining under the microscope. 2) Examine the cuttings under UV light of Fluoroscope and describe the colours seen. Colours range from: Bluish white in condensates Yellow, orange and brown in crude Black in bitumen and dead oil . Be aware that base oil usually exhibits a pale bluish white fluorescence so a comparative sample of the mud should be kept on a sample tray inside the fluoroscope. Oil base mud can invade and flush the formation considerably affecting show quality. Try to pick out some representative cuttings and place them in a spotting tray. Examine these under the microscope and check that they are Sandstone, as some minerals, particularly Calcium Carbonate also exhibit fluorescence. 3) Place the spot tray back in the UV box, and while watching, immerse the cuttings in a solvent (e.g. Propan-2-ol). Describe the rapidity, character and colour of the hydrocarbon as it is leached from the rock. This gives an indication of the permeability of the cuttings and mobility of the oil. If leaching is very slow, then crush the cuttings and observe the changes in the fluorescence. 4) Describe the colour of the oil stained solvent under natural light. Allow the solvent to evaporate and describe the colour of the residual ring in the tray. Darker colours indicate heavier crudes.
Using a Calcimeter (Geoservices)
1) First of all you need to take some of your dried sample from the oven and crush it into a fine powder, using a pestle and mortar then you need to place a small disc of either filter or ordinary paper on a set of scales (electronic ones work best…usually). Then add between 0.95 and 1.05 grams (aim for 1 gram) of sample to the paper as shown in the diagram below.
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2) Switch on the calcimeter (or make sure it’s switched on) and select main menu by pressing the F1 button on the calcimeter (as shown below) then select analysis by pressing F1 again once you have weighed your sample press the weight (F3) button and input your weight using the numeric keypad and press F3 again.
3) You then need to insert the sample into the reaction chamber, insert the acid and then close the reaction chamber:
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a) Check control knob is in purge position and the valve turned to the back of the bowl. b) Take the bowl in one hand and insert the sample into the reaction chamber, preferably on the sample cup (if it hasn’t been lost or broken) c) Fill the acid chamber up to the filling groove d) Insert the back of the bowl into the support e) Hold the clamp open, lift the bowl and engage the hook f) Turn the handle clockwise to fasten the bowl into position g) Check the ‘O’ ring is seated on the support (a black line 1mm thick should be visible from the side).
4) Press the F1 button on the Calcimeter and then turn the control knob to the Run position; the system should then start measuring. Record the values for the 1 minute reading and the 3 minute reading on the lithology worksheet and then turn the knob to the purge position, press F2 to reset, clean out the bowl and you are ready for the next sample.
SECTION 2 – Cuttings Analysis Basics
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Other Geological tests Phenolphthalein – This is used to test for cement after we start drilling again after a casing run. The reaction turns cement cuttings a pink colour. Shale Density – Very rarely we use a microsol to measure shale density. It is not common in the North Sea but some clients may ask for it. The instructions found in the manual are very good so just follow this, as my experience with this equipment is limited.
Sample boxes and Logistics
Basically as a Mudlogger you are responsible for ensuring there are sufficient sample boxes and sample bags available until the end of the well so be sure to check the drilling programme for sample intervals, and proposed depths. Be sure to keep a record of which samples are in which box, e.g. 100ft to 600ft in box #1. Write the box number and the sample type (usually a letter e.g. A, B, C) on the outside of the box but only write the depths on the outside of the boxes with the clients permission as some operators can be a little protective of their data. At the end of each section the boxes should be taped up and the address of their destination taped to the outside of the box. Always make sure that every time you arrive on a new rig / well site you read the sample requirements in the drilling programme very carefully and ask the well site Geologist to clarify anything you are uncertain of. Any spares you require, e.g. a new sieve, gloves, bags, boxes, tape, rags e.t.c. you need to inform the data engineer so he/she can put in an order. Chemicals
The amount of chemicals we have stored and use in the mudlogging unit is only very small but there are still risks involved. Ensure that you have read the Chemical Safety Data Sheets and COSHH procedures carefully before using any chemical unfamiliar to you. Chemicals should be stored appropriately and always store Calcium Carbide away from all other chemicals and any source of water as Calcium Carbide produces acetylene when it reacts with water. Calcium Carbide MUST be stored away from ACIDS and CALCIUM CHLORIDE. If in doubt read the Data Sheets, which must be present in the logging unit, by law. If you notice any missing datasheets for any chemical then ask the base to fax you a copy of the missing sheet. It is also a good idea to keep an inventory of the chemicals in the unit and update at least every 2 weeks, this will ensure you will not run short of chemicals.
SECTION 3 –Basic Well Monitoring
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3. Basic Well Monitoring Introduction
Although monitoring the well is for the most part the job of a data engineer, there are times when they cannot be in the unit and therefore it is necessary for the Mudlogger to keep an eye on things.
PIT VOLUMES – gain/loss GAS LEVELS – high gas (1% and Above) and H2S (5ppm +) DEPTH TRACKING – based on HK Height and WOH.
Why these 3? Pit levels – a significant gain in the pit levels can be an indication of either fluids or gas invading the well from the formation. This can cause the well to become unstable and unless it is spotted and reported can potentially lead to a blow out which is extremely dangerous. A significant decrease or loss in the pit levels can be an indication of downhole losses which can lead to the reduction in the productivity of a potential reservoir or even the total loss of all mud on the rig and the consequent invasion of unwanted fluids/gas into the well, the hydrostatic pressure of the well can also be affected by losses and could eventually lead to a kick. Gas – Hydrocarbon gasses are highly flammable in certain concentrations and a large volume of gas coming out of the hole can create an explosive environment on the rig. In addition if the volume of gas in the mud is at a significantly high level then it can lower the mud weight and cause instability in the well leading to a blow out. Gas that appears from the lagged time of the rig pumps being off can also indicate well instability and lead to a blow out. H2S Gas is a highly toxic gas that can be lethal in relatively small concentrations. If more than 5ppm H2S gas is detected it must be reported.
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Depth Tracking – It is best to think of depth tracking as a “map” of the well, we need our depth tracking to be accurate in order to identify where we are with regards to the stratigraphy of the well. If we know where we are then we are able to see things such as where we are aiming to get to and any potential obstructions or hazard areas that may be coming up. Our depth tracking affects all of our data including our gas data and other lagged parameters. If it is accurate then it can allow us to record correctly the depths at which certain events occurred for future reference.
There are other important parameters that need to be monitored during the process of drilling such as SPP and RPM for example. However, none are as critical as the 3 described above. Be aware that monitoring these parameters is as good as useless if you fail to report any observed changes to the Driller and the Company Man, so please remember that Communication is absolutely essential. Do not be afraid of being incorrect or raising a false alarm, if you have any doubts whatsoever then call the Driller and report it . IF IN DOUBT - ASK
ALWAYS REPORT ANY UNEXPLAINED INCREASE/ DECREASE IN PIT LEVELS AND TOTAL GAS SHOWS OF 1% and ABOVE. ALWAYS REPORT THE PRESENCE OF H2S GAS AT 5PPM and ABOVE
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A Guide to Monitoring for Mudloggers Drilling
Whilst drilling there are 2 essential parameters that you need to observe very carefully. The Active pit (Act Pit) and the Total Gas (Tot GAS) are both essential indicators of how stable the well is. Most of the time it is the Data Engineer who will be monitoring these parameters, however as Data Engineers are people as well they do need to leave the unit from time to time leaving you to monitor the well. Pit Level Monitoring
The active pit is basically the mud pit that is being used to pump mud down the hole and receive the mud returning from the hole. The pit is the part of the circulating system where we measure the volume of mud and are able to notice changes in this system. The Circulating System
In theory, this is a closed system (whilst not drilling) and therefore if the well is stable the Volume measured in the Active pit should remain static. On the Geoservices graphic display it should be represented as a straight line. Whilst drilling, however the
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volume of the hole is continuously increasing and this is represented by a steady gradual decline in the Active pit volume (fig 1) Fig 1- Pit volume decrease due to filling of hole whilst drilling
There are 2 major deviations from this trend, which can occur whilst drilling: a Pit gain or a Pit loss. A gain seen in the active pit can be caused by 3 main events; a pit transfer, when the pumps are turned off (or reduced) or an influx from the formation. The latter of these causes is the main reason why we monitor the pit levels as it can result in a potentially dangerous situation.
PIT LEVEL GAINS A pit transfer can be identified by observing a decrease in another pit at the same time as an increase in the Active pit (Fig. 2). If this is seen it is a good idea to call the Derrickman and check, as not all transfers are intentional.
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Figure 2
You will also see a gain in the Active pit if the Pumps are switched off; this is due to mud flowing back to the pit and the system reaching a new equilibrium. Eventually this will stabilise and the volume will appear stable. Figure 3 – Effect of turning off the flow pumps on Pit levels
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If an increase in the active is seen and both the above possibilities can be ruled out then it is possible that an influx has entered the well from the formation. If this is the case – CALL THE DRILLER IMMEDIATELY it would then be sensible to contact the Data Engineer (either by phone or the P.A/Radio system) to verify. Figure 4– If the pumps are on and at a steady rate and no pit transfers are occurring – CALL THE DRILLER
It is absolutely essential that any unexplainable change in the level of the active pit is communicated to the Driller immediately. Do not be afraid of being wrong, everyone on the rig would rather you gave a false alarm than keep potentially vital information to yourself. IF IN DOUBT – ASK!
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PIT LEVEL LOSSES A reduction in the level of mud in the active pit. This can be caused by 4 main factors; Increase in ROP, increase in Flow rate, Transfer of mud out of the active and Downhole losses. Again it is the latter of these factors that requires immediate action (calling the Driller). Fig 1 – Increase in ROP (Rate of Penetration)
An increase relating to Rate of penetration is usually quite subtle and occurs due to the increase in the rate at which the hole size is increased and the amount of fluid required to fill the new hole.
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Figure 2 – Pit level decrease due to increased Flow Rate
This decrease usually only occurs for a short period of time until the system equalises and the trend resumes it’s normal path.
Fig 3 – Mud transfer from the Active Pit
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If you see another pit increasing at the same rate as the Active decreases then it is highly likely that there is a transfer between the 2 and you should call the Derrickman to check. Fig 4 – Active decrease due to losses to formation
If you see a decrease in the Active pit and the Flow, ROP and other pits are all constant then it is likely that mud is being lost to the formation and therefore you should
CALL THE DRILLER IMMEDIATELY.
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GAS LEVELS Generally if you see the Total Gas increase by more than 1% then call the Driller immediately. 1% Total Gas and 5% Total gas are critical points when dealing with rig safety so at these values inform the Driller and the Company man. If the Gas level suddenly drops the most likely cause is a problem with the equipment and you should try to contact the Data Engineer.
CHECK LIST Pit level increase
Has the flow rate changed (Decreased)? – Yes = pumps off and flowback Are any of the other pits decreasing at a similar rate – Yes = Pit Transfer Call Derrickman If the answer is no to both these – CALL THE DRILLER IMMEDIATELY Pit Level decrease
Has the ROP increased dramatically – Yes = see if level stabilises Are other pits increasing at same time – Yes = Call Derrickman (Transfer) Has the Flow rate increased – Yes = see if level stabilises If the answer to all these is no or if the levels do not stabilise – CALL THE DRILLER IMMEDIATELY
Gas Level increases
If the Total gas increases by at least twice it’s previous value or when the levels reach 1% and 5% total gas then – CALL THE DRILLER IMMEDIATELY and then call the Company Man. If the level dramatically decreases then try to contact the Data Engineer, as there is probably a problem with the equipment.
This info is just the very basics of monitoring and is useful mostly for very new mudloggers when monitoring the well in the engineer’s absence (lunch breaks, meetings e.t.c.) As your knowledge increases you will find that other factors can contribute to changes in pit levels but the ones above are the most common.
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PIT DRILLS
A pit drill is when the driller transfers mud between the trip tank and pits as a test to check if both the Mudloggers and Derrickman are paying attention. If you see either the trip tank move at all whilst drilling CALL THE DRILLER IMMEDIATELY. H2S
Most if not all Geoservices Units will be monitoring for the presence of H2S. Alarms are usually set at around 6-10ppm although this varies from rig to rig. If you do see any H2S you must CALL THE DRILLER IMMEDIATELY and then CALL THE COMPANY MAN. H2S is a deadly gas in high concentrations and is taken very seriously; so do not be afraid of looking stupid for reporting only a few ppm of H2S. It is better to be wrong than dead!
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4. Basic Well Control Introduction
Well control is one of the most important aspects of drilling a well. If your well is not stable then you are not in control of your well and this can be a highly dangerous situation, which can, not only, result in the loss if a well but also a loss of life. As far as mudlogging is concerned we are in a good position to identify any warning signs of well instability and it is a large part of our job (especially for the data engineer). The main warning signs we can identify as a mudlogging crew are pit level gains / losses, increases in the gas level, increases in the level of flow out of the well, pressure cavings within the cuttings and identifying an increase in the trip tank volume during a flowcheck. Pressure Concepts
In order to understand well control it is essential that you understand some basic pressure concepts and how they relate to a well. Hydrostatic Pressure: Pressure exerted by the weight of a static column of fluid. It is a function of fluid specific gravity and of vertical height of the fluid. In API, the formula is: Ph = 0.052 * H * d
With
Ph= hydrostatic pressure (psi) d = Fluid specific gravity (ppg) H = Vertical height of fluid (ft)
The hydrostatic pressure is related only to the vertical depth of the well and as such measured depth becomes less relevant as the well becomes more horizontal. Consequently, in the following sketches, the Hydrostatic Pressure is always the same:
H
‘U tube’ effect:
SECTION 4 –Basic Well Control
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If the mud weight in the pipes and in the annulus is different, the ‘U tube’ effect is the difference of Ph in the 2 branches of the ‘U tube’ formed by annulus and pipes
Pore Pressure / Formation (fluid) Pressure: This is the pressure exerted by the fluids within the formations being drilled. Sedimentary rocks contain fluid due to their mode of formation, which is as accumulations of rock debris or organic matter underwater. As the depth of the sediments increases due to deposition over the top of them, water is squeezed out and becomes progressively saltier as the smaller water molecules travel between the pore spaces of the rock while the larger salt molecules are retained. Formation pressure has been determined to increase at a gradient of 0.465 psi/ft by the Yanks but for the North Sea the gradient is closer to 0.455 psi/ft. Formation Fracture Pressure: This is the pressure required to fracture or rupture a formation so that whole mud will flow into it. Fracture pressure is usually determined by performing a Leak off Test (LOT) just after a casing point. A Leak Off Test is performed by shutting in the well and increasing the pressure by pumping a set volume of drilling fluid and monitoring the point where the formation fractures and a drop in pressure is observed. This is then calculated and recorded as an equivalent mud weight. Equivalent Circulating Density: This is basically the mud weight equivalent of the pressure exerted at the bottom of the whole when circulating. Annular Pressure Losses: When the pumps are on they are exerting pressure on the mud in order to push it around the system. All of this pressure is expended in this process, overcoming friction losses between the mud and whatever it is in contact with. A small amount of this pressure loss, or friction loss, is used in moving mud up the annulus. Since the annular space is quite large, the mud moves relatively slowly, thus using very little energy. Annular pressure loss acts as a “back pressure” on formations exposed to the annulus and this causes a slight increase in the total pressure exerted upon them when the pumps are circulating mud around the system. The effect of this is that the bottom hole pressure exerted when circulating is increased over the hydrostatic bottom hole pressure and as such the ECD is calculated as: ECD = Hydrostatic Pressure + Annular Pressure Loss . Annular pressure loss can be calculated by using a variety of calculation methods, each one suited to different mud properties and including Bingham Law, Power Law, Alternative Method and Hughes model. Normally this is performed by the Hydraulics programme on the TDX (Data Engineer Workstation). A removal of the ECD (pumps off) will in the situation of drilling a well that is close to balance (where formation pressure is close to the pressure being exerted on the well bore) result in becoming more underbalanced (formation pressure higher than pressure exerted on the well) and greatly increase the chance of an Influx or Kick . This is the reason why flowchecks are performed, as the ECD can mask downhole pressure conditions whilst drilling.
I SECTION 4 –Basic Well Control Primary Well control: Primary well control is simply the process of ensuring the
well conditions remain as stable as possible and is effectively a balancing act between ensuring the Hydrostatic pressure remains higher than the formation pressure and the ECD does not exceed the formation fracture pressure. The ideal situation is one in which no losses or influxes are observed. However things do not always go according to plan and when a kick or influx is observed entering the well bore then secondary well control needs to come into place. Secondary Well Control
This is basically the actions and processes required to deal with an influx into the well and bring the situation back under control. This is performed essentially by closing the Blow Out Preventers (BOPs), which are a series of large valves that can shut in the well and control the flow out of the well. The mud weight is then increased and the well is displaced to remove the intruded substance (fluid or gas) and replace the lighter mud with a heavier mud. This is known as killing the well and there are a number of different methods used to perform this operation. The BOPs There are typically 3-4 parts to standard BOP stack, the annular preventer , the pipe rams, blind rams and the shear rams. The annular preventer consists of a ring (packer) of synthetic rubber sandwiched between 2 steel compression plates. These plates are compressed together using hydraulic pressure and this squeezes the packer into the well bore. If there is drill pipe in the hole the packer conforms around it effectively sealing off the annulus. The Annular Preventor is usually the top most part of the BOP. The pipe rams use packing elements with semi-circular cut outs that match the external diameter of the drill pipe in use, if the diameter of pipe is to be changed then the packer in the pipe rams must also be changed accordingly and if 2 or more sizes of drill pipe are to be run then there must be a separate pipe ram for each size of pipe. Blind rams contain a packer that fits tightly together when the rams are closed and are used to shut in the well when no pipe is in hole. Shear rams contain a packer that has 2 steel blades attached to each part and are used only as a last resort to shut in the well with pipe in the hole and this cuts through the drill string (resulting in the inability to circulate the well and the need for a fishing trip. The diagram below shows a typical BOP stack.
SECTION 4 –Basic Well Control
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Methods of Killing a Well
When the signs of a kick are first observed then usually a flowcheck is performed. If this flowcheck shows a gain, the well is shut in by closing the BOP
SECTION 4 –Basic Well Control
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stack. There are 2 methods of shutting in the well, the soft shut in (choke line open) and hard shut in (choke line closed). The drilling programme specifies the method used. Once the well has been shut in the influx pressure compresses the mud until equilibrium is reached and the Shut in Drill Pipe Pressure (SIDPP) and Shut in Casing Pressure (SICP) are recorded. SIDPP is basically the standpipe pressure (SPP) reading and the SICP is basically the Choke Pressure or Wellhead Pressure (WHP). These figures are used to calculate the formation pressure and the required mud weight increase needed to kill the well. There are 3 main well kill methods used in the oil industry each one differs in the starting weight of the kill mud at the beginning of the kill operation. The 3 methods are known as The Driller’s Method (where kick is circulated out and then the new mud is circulated – requires at least 2 full circulations), the Wait and Weight Method (where influx is circulated out in same cycle as kill mud is circulated) and the Concurrent Method (where the mud weight is increased in stages). There are advantages and disadvantages to each method and the choice of method is either predetermined in the drilling programme or at the operators discretion. This is just a very basic introduction to well control. It is strongly advised that you attend a training course or seminar for a more in depth understanding of well control. There are also a lot of very good manuals around either provided by your company or pirated from somewhere else but it is definitely worth your time learning about well control as it is a very significant part of drilling a well.
SECTION 5 – Gas Detection Basics
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5. Gas Detection Basics Introduction
Hydrocarbon gas detection and analysis is (in my opinion) the single most important aspect of our role as a mudlogging crew and although the majority of this responsibility falls upon the Data Engineer, it is necessary for mudloggers to know at least the basics. The reason for the high importance of gas detection is mainly for the reason that we are the only people on the rig who are monitoring and recording gas levels. From a safety aspect hydrocarbon gases are highly flammable and in an environment where activities such as welding and electrical work occur on a daily basis it is vital that we know how the quantity of gas coming from the well. The other reason for the importance of the gas is that it can be an excellent indicator of the quality and quantity of a potential reservoir. Hydrocarbon gases are formed in much the same way as oil in that accumulated sediments of rock debris, water and organic matter are buried, compacted and matured over millions of years under conditions of high temperatures and pressures. There are different types of Hydrocarbon gases and the classification is based on the number and proportion of H (hydrogen) and C (carbon atoms). With regard to mudlogging we are primarily interested in saturated hydrocarbons or alkanes. These include Methane (CH4), Ethane (C2H6), Propane (C3H8), iso and normal Butane (C4H10) and iso and normal Pentane (C5H12). In the oilfield we tend to classify these hydrocarbon gases by the number of Carbon (C) atoms so for example Methane = C1, Ethane C2 and so on. The highest quantity of gas we usually see in the field is of Methane. How gas data is obtained
Mudloggers collect their gas data from a gas trap, which is situated somewhere in the flow line (as close to the bell nipple as possible) or in the header box at the shakers. The gas trap usually extracts gas from the mud by beating it with agitator blades (rather like beating an egg – if you do it fast enough you can see gas bubbles) and this gas is then transported to a gas detector in the mudlogging unit by means of a pump (located in the gas equipment). The diagram below shows the typical location of a gas trap.
SECTION 5 – Gas Detection Basics
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Gas Trap Maintenance
As mudloggers are usually in the shaker house more often than data engineers the tendency is for the responsibility of checking the condition of and the general maintenance of the gas trap to fall upon the Mudlogger. To be perfectly honest the majority of gas traps are extremely simple items of equipment and the maintenance is also relatively simple (GZ1, GZ2 and GZ11 – in Geoservices). The ones that are more complicated tend to be of the volumetric variety (GZG) but these are also more efficient and reliable. The diagram on the following page describes very nicely the best maintenance practices for a GZ11 type degasser (diagram courtesy of Ani Sathe ☺)
SECTION 5 – Gas Detection Basics
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Don’t ignore my presence in the shakerhouse…remember Check my breather hole…don’t let it get blocked and choke me or I’ll choke your FID
Check that my Altuglass is still dry, I don’t like sucking mud & water with gas
Is my level in the mud OK? Don’t let me drown!!! Very Important
Oh No Full Flood…I need air to pass through the outlet
The Flow out from my outlet should never be flooded completely or else you won’t see heavy gases or even C1 on your Gas machine…reduce the air pressure to adjust this or raise my level above the mud.
SECTION 5 – Gas Detection Basics
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If you are working with a GZG degasser then the maintenance is a little more involved. The main points though are, the pump rubber (often ruptures and leaks mud from weep hole – due to wear and also high temperatures), the torque limiter (check that when you hold the driven assembly still the disc still turns – if it is stiff add some WD40 to unfreeze it) and check the probe is clear of cuttings and the rotating blade is rotating. Some of these maintenance techniques are shown below.
SECTION 5 – Gas Detection Basics
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SECTION 5 – Gas Detection Basics
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Gas Detectors / Analysers
There are a number of different machines with various methods of Hydrocarbon gas detection and analysis (thermal conductivity, mass spectrometer) but the most common one found in a mudlogging unit is a Flame Ionisation Detector or FID for short. In an FID a hydrogen flame burns hydrocarbons and produces ions and the flow ions is picked up by electrodes. The number of ions produced is proportionate to the number of carbon atoms. The operating principle of an FID is shown in the diagram below and shows how a gas is broken down and converted to an electrical signal. Basically in gas detection the higher the quantity of hydrocarbon gas then the more ions are produced and the greater the electrical signal given by the gas detector.
SECTION 5 – Gas Detection Basics
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There are usually 2 types of FID detection used in mudlogging in conjunction with each other. One is for the measurement of the total hydrocarbon gas in air and is an instantaneous measurement the other measures the chromatographic breakdown of the hydrocarbon gas (i.e. measures the quantity of different alkanes in the sample, C1, C2, C3 e.t.c.). The chromatograph cycle of an FID can vary from 40 seconds (Reserval, GFF – Geoservices) to around 240 seconds and above (Geo FID – Geoservices). The best data is usually given by the Chromatographs with a shorter cycle time. Take the time to learn how the FID system you are using works and what it’s strengths and weaknesses are, as these machines tend to vary and oil company representatives always ask a lot of questions about the gas data gathered by mudloggers. Gas Data Analysis
When drilling a well there are a number of different reasons for Hydrocarbon gasses being observed, here are some of the main ones: Liberated Gas: During drilling the bit action of breaking up the formation releases gas trapped in the pore space. This mixes with the mud and is transported to the surface after a lag time. Normally the hydrostatic pressure is slightly more than the formation pressure. Recycled Gas: Part of the gas in the mud, if not degassed, will be pumped back into the hole. This gas will surface out after one cycle time. The amount of recycling depends on factors like the type of gas, type of mud and type of degassing equipment. Note: Oil in the mud will enhance the recycling of gas
SECTION 5 – Gas Detection Basics
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Produced Gas: If the formation pressure is greater than the hydrostatic pressure then there will be gas influx into the borehole. Influx may be from the reservoir or from poor permeability zones in form of seepage or the caving of shales. Contaminated Gas: Thermal break down can also generate gas, break down of some mud additives. The heat is produced due to the mechanical action and jetting action of the bit
I SECTION 5 – Gas Detection Basics Background Gas: Continuous steady gas in mud that forms a low steady line -a
background trend on recorder against which gas peaks can be viewed. The background gas is generally from shale or from any other lithology. Increase/ decrease in BG: Change in the gas content –silty shale, carbonaceous shale, compact limestone, changes in differential pressure, changes in mud flowrate, increase / decrease in ROP. hole size, mud properties e.t.c.
Connection Gas: Gas recorded one lag time after the completion of connection. Connection gas appears because of a) Swabbing b) under-balanced conditions Trip Gas: Gas recorded one lag-time after completion of a trip or a wiper trip
Other factors affecting Gas levels
increase in ROP ROP will lead lead to an increase increase in the amount amount of liberated liberated ROP – An increase gas as shown below.
SECTION 5 – Gas Detection Basics
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Hole Size – In theory if the ROP and flow rate remain the same then a larger hole size will show a higher quantity of gas as the larger surface of the bit is able to liberate more cuttings and therefore gas per foot/meter drilled.
SECTION 5 – Gas Detection Basics
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increase in mud mud flow rate rate decreases decreases the amount amount of gas gas Mud Flow Rate – An increase liberated.
Although Although we use gas level level increases increases as an indicator indicator of a potential potential kick it is possible possible for high gas levels to be observed without a kick situation:
SECTION 5 – Gas Detection Basics
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As a mudlogger this is again the very basics of what is occurring with regard to hydrocarbon gas detection and as you expand your knowledge and start to work as a Data Engineer you will need to learn how to perform and interpret more in depth gas analysis, such as Wetness, character and balance, gas ratios and other characteristics. Also bear in mind that other gases such as Carbon Dioxide and H2S are usually monitored by different types of sensor and usually require little interpretation (it’s either present or it’s not).
Appendix A – Oil Field Glossary
I
Oil Field Terminology Drilling Terms On Bottom = This is when the bit is in contact with the bottom of the hole. On Slips = This is when the total weight of the drill string is being supported by the Slips. Bit Depth = The depth at which the bit is currently at Total Depth = The depth of the bottom of the hole based on the measured depth of the hole. TVD = Total Vertical Depth; the depth of the bottom hole based on a vertical measurement. Lag Depth = The depth from which the current cuttings on surface originated. Lag time = The time required for the cuttings at the bottom of the hole to reach the surface WOB = Weight on Bit; The amount of weight being applied on the bit from the surface. WOH = Weight on Hook; The weight of the drill string. RPM = Rotations per Minute; The speed at which the drill pipe is rotated SPP = Stand Pipe Pressure; The amount of pressure exerted by the mud pumps when pumping mud down the drill string. Sometimes called “Pump Pressure”.
Mud Pit Terms: Active Pit = The mud pit(s) that is being used to circulate the well. Trip Tank = A mud tank which is taller and narrower in shape to the rest in order to observe smaller changes. It is mainly used whilst tripping or flowchecking Flowcheck = A period of 20-30 mins (ideally) when the pumps are switched off and the well is observed for signs of losses or gains. ROP = Rate of Penetration; the speed at which the formation is being drilled. Pump Strokes = Each stroke represents a single action of a pump. Pump strokes can be used to measure the flow of volume as each stroke will push a certain volume of mud. The flow in value is calculated using this method.
Appendix A – Oil Field Glossary
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Flow In (FLWpmp) = The volume of mud being pushed into the well per minute. Flow Out = The volume of mud returning from the hole per minute. Sometimes given as a percentage of the Flow in. Transfer = A pit transfer is when mud is taken from one pit and put into a different one. Bleeding = Bleeding is the same as transferring, except it is slower. Slug = A slug is a heavier batch of mud usually used to force lighter mud out of the drill pipe during tripping operations. You may hear the term “Pumping Slug”. Pill = The same as a Slug, only a pill can sometimes be of a lighter weight or of a different viscosity. Chase Pill = Refers to pumping down mud after the pumping the pill Slug Pit = A mud pit (usually a small one) designated for making and storing a slug. Pit Drill = A Test performed by the driller where he will usually transfer between the Trip Tank and one of the pits without informing the Mudloggers and the derrickman. This is to check that we are monitoring carefully and if we see this happen we should call the Driller immediately.
Well Control Terms: WHP = Well Head Pressure; The amount of pressure exerted on the well head (BOPs), sometimes called “Casing Pressure”. BOP = Blow Out Preventers; Basically a series of safety valves that can close in and contain a well. E.M.W = Equivalent Mud Weight; a measurement of pressure using mud weight as opposed to psi or bar. ECD = Equivalent Circulating Density; This is basically what the equivalent mud weight is during circulation (As pressure down hole increases during circulation the actual mud weight downhole will also increase to give the ECD)
KICK = An entry of water, gas, oil or any other fluid from the formation into the well. This is identified by a gain in the active pit volume. A kick occurs when the pressure exerted by the mud in the hole is less than the pressure exerted by the formation. KILL = To control a kick by taking suitable measures. Shut the BOPs, circulate out the kick and increase the mud weight.
Appendix A – Oil Field Glossary
I
Drill Pipe Terms: BHA = Bottom hole Assembly; this is a collection of Heavy drill pipe, motors, drill collars, MWD tools and mud motors that make up the lower part of the drill string. Single = A single length of Drill Pipe, usually about 30ft (10m) in length. Double = 2 Singles Stand = 3 singles around 90ft (30m) in length. This is normally what most rigs use whilst drilling. DC = Drill Collars; Part of the BHA they are used to help guide the bit and add weight to the Drill string. HWDP = Heavy Weight Drill Pipe; used to add weight to the BHA. Drill String = Collective term for all of the pipe and BHA that is currently in the hole. p/u = Pick Up; used in reference to Drill pipe or BHA it just refers to picking up pipe from the Deck to use as part of the Drill String. m/u (Make Up) means exactly the same. L/d = Lay Down; Again used in reference to the dismantling of the BHA and laying it down on the deck. N/u = Nipple up; refers to connecting the BOP stack to the diverter line where the the returns go to Shakers / Trip tank.
Tripping Terms: Tripping = The movement of the Drill string either into the hole or out of the hole. POOH = Pull Out Of Hole; the process of removing the drill string from the hole to the surface. RIH = Running In Hole; the process of sending the drill string from the surface to the bottom of the hole. Pumping Out of Hole = The same as Pulling out of hole only with the pumps on. This is usually done to control the start of the trip during unstable formations. Washing Down = Is basically Running in the Hole with the pumps on, usually only performed on the last stand before reaching bottom.
Other Terms:
Appendix A – Oil Field Glossary
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WBM = Water Based Mud OBM / LTOBM = Oil Based Mud / Low Toxicity Oil Based Mud. S.C.Rs = Slow Circulating Rates; Basically these are just measurements the driller takes from time to time to aid with well control. F.I.T = Formation Integrity Test; After a new casing has been set a small amount of formation is drilled and a pressure test is performed to a set value to check if the formation can withstand that pressure without breaking. L.O.T = Leak Off Test; Similar to an F.I.T but the pressure is increased to the point of fracturing the formation and the point at which the formation fractures is recorded for future reference. Bottoms Up = Where the mud and cuttings at the bottom of the hole are circulated to the surface. Is basically the same as the lag time/ lag depth. Annulus = The space between the Drill pipe and the sides of the hole. Slip and Cut = Basically, this is an operation where the drill line (cable) is replaced with new cable. As the cable has to support a lot of weight and tension it suffers from wear and tear and needs to be replaced every so often.
Appendix B – Formulas and Calculations
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Formulas and Calculations
Pressure gradient
psi/ft = mud weight, (ppg) x 0.052 psi/ft = mud weight, (SG) x 0.433 Hydrostatic pressure using ppg and feet as the units of measure
HP = mud weight (ppg) x 0.052 x TVD (ft) Example: mud weight = 13.5 ppg
true vertical depth = 12,000 ft
HP = 13.5 ppg x 0.052 x 12,000 ft HP = 8424 psi Hydrostatic pressure, psi, using meters as unit of depth
HP = mud weight, ppg x 0.052 x TVD, m x 3.281 Example: Mud weight = 12.2 ppg
true vertical depth = 3700 meters
HP = 12.2 ppg x 0.052 x 3700 x 3.281 HP = 7,701 psi Convert pressure, psi, into mud weight, ppg using feet as the unit of measure
mud weight, ppg = pressure, psi ÷ 0.052 + TVD, ft Example:
pressure = 2600 psi
true vertical depth = 5000 ft
mud, ppg = 2600 psi ÷ 0.052 ÷ 5000 ft mud = 10.0 ppg Convert pressure, psi, into mud weight, ppg using meters as the unit of measure
mud weight, ppg = pressure, psi ÷ 0.052 ÷ TVD, m + 3.281 Example: pressure = 3583 psi
true vertical depth = 2000 meters
mud wt, ppg = 3583 psi ÷ 0.052 ÷ 2000 m ÷ 3.281 mud wt = 10.5 ppg
Appendix B – Formulas and Calculations
I
Specific gravity using mud weight, ppg
SG = mud weight, ppg + 8.33
Example: 15..0 ppg fluid
SG = 15.0 ppg ÷ 8.33 SG = 1.8 Convert specific gravity to mud weight, ppg
mud weight, ppg = specific gravity x 8.33
Example:
specific gravity = 1.80
mud wt, ppg = 1.80 x 8.33 mud wt = 15.0 ppg Equivalent Circulating Density (ECD) (API)
ECD, ppg = (annular pressure, loss, psi ) ÷ 0.052 ÷ TVD, ft + (mud weight, in use, ppg) Example: annular pressure loss = 200 psi
true vertical depth = 10,000 ft
ECD, ppg = 200 psi ÷ 0.052 ÷ 10,000 ft + 9.6 ppg ECD = 10.0 ppg Annular velocity (AV), ft/min
AV = pump output, bbl/min ÷ annular capacity, bbl/ft Example: pump output = 12.6 bbl/min annular capacity = 0.126 1 bbl/ft
AV = 12.6 bbl/min ÷ 0.1261 bbl/ft AV = 99.92 ft/mm Capacity of tubulars and open hole: drill pipe, drill collars, tubing, casing, hole, and any cylindrical object
a) Capacity, bbl/ft = ID in. 2 Example: Determine the capacity, bbl/ft, of a 12-1/4 in. hole: 1029.4 Capacity, bbl/ft = 12 25 2 1029.4 Capacity
= 0. 1457766 bbl/ft
Appendix B – Formulas and Calculations
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Capacities, bbl/ft, displacement, bbl/ft, and weight, lb/ft, can be calculated from the following formulas:
Capacity, bbl/ft = ID, in. 2 1029.4 Displacement, bbl/ft = OD, in. 2 — ID, in. 2 1029.4 Weight, lb/ft = displacement, bbl/ft x 2747 lb/bbl
Example: Determine the capacity, bbl/ft, displacement, bbl/ft, and weight, lb/ft, for the following:
Drill collar OD = 8.0 in.
Drill collar ID = 2-13/16 in.
Convert 13/16 to decimal equivalent:
13 : 16 = 0.8125
a) Capacity, bbl/ft = 2.8125 2 1029.4 Capacity
= 0.007684 bbl/ft
b) Displacement, bbl/ft = 8.0 2 — 2.81252 1029.4 Displacement, bbl/ft = 56.089844 1029.4 Displacement
= 0.0544879 bbl/ft
c) Weight, lb/ft = 0.0544879 bbl/ft x 2747 lb/bbl Weight = 149.678 lb/ft
Convert temperature, °Fahrenheit (F) to °Centigrade or Celsius (C)
°C = (°F — 32) 5 9
OR
°C = °F — 32 x 0.5556
Appendix B – Formulas and Calculations
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Example: Convert 95 °F to °C:
°C = (95 — 32) 5 9 °C =35
OR
°C = 95 — 32 x 0.5556 °C = 35
Convert temperature, °Centigrade or Celsius (C) to °Fahrenheit
°F = (°C x 9) ÷ 5 + 32
OR
°F = 24 x 1.8 + 32
Example: Convert 24 °C to °F:
°F = (24 x 9) ÷ 5 + 32 °F = 75.2
OR
°F = 24 x 1.8 + 32 °F = 75.2
Drill string volume, barrels
Barrels = ID, in. 2 x pipe length 1029.4, Annular volume, barrels
Barrels = Dh, in. 2 — Dp, in.2 1029.4 Strokes to displace: drill string, Kelly to shale shaker and Strokes annulus, and total circulation from Kelly to shale shaker.
Strokes = barrels ÷ pump output, bbl/stk Example:
Determine volumes and strokes for the following:
Drill pipe — 5.0 in. — 19.5 lb/f Inside diameter = 4.276 in. Length = 9400 ft Drill collars — 8.0 in. OD Inside diameter = 3.0 in. Length = 600 ft Casing — 13-3/8 in. — 54.5 lb/f Inside diameter = 12.615 in. Setting depth = 4500 ft Pump data — 7 in. by 12 in. triplex Efficiency = 95% Pump output = 0.136 @ 95% Hole size = 12-1/4 in. Drill string volume
a) Drill pipe volume, bbl:
Barrels = 4.2762 x 9400 ft 1029.4 Barrels = 0.01776 x 9400 ft Barrels = 166.94
Appendix B – Formulas and Calculations
b) Drill collar volume, bbl:
I
Barrels = 3.0 2 x 600 ft 1029.4 Barrels = 0.0087 x 600 ft Barrels = 5.24
c) Total drill string volume:
Total drill string vol., bbl = 166.94 bbl + 5.24 bbl Total drill string vol. = 172.18 bbl
Annular volume
a) Drill collar / open hole:
Barrels = 12.25 2 — 8.02 x 600 ft 1029.4 Barrels = 0.0836 x 600 ft Barrels = 50.16
b) Drill pipe / open hole:
Barrels = 12.25 2 — 5.02 x 4900 ft 1029.4 Barrels = 0.12149 x 4900 ft Barrels = 595.3
c) Drill pipe / cased hole:
Barrels = 12.615 2 — 5.02 x 4500 ft 1029.4 Barrels = 0.130307 x 4500 ft Barrels = 586.38
d) Total annular volume:
Total annular vol. = 50.16 + 595.3 + 586.38 Total annular vol. = 1231.84 barrels
Strokes
a) Surface to bit strokes:
Strokes = drill string volume, bbl ÷ pump output, bbl/stk
Surface to bit strokes = 172.16 bbl ÷ 0.136 bbl/stk Surface to bit strokes = 1266 b) Bit to surface (or bottoms-up strokes): Strokes = annular volume, bbl ÷ pump output, bbl/stk Bit to surface strokes = 1231.84 bbl ÷ 0.136 bbl/stk Bit to surface strokes = 9058
Appendix B – Formulas and Calculations
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c) Total strokes required to pump from the Kelly to the shale shaker: Strokes = drill string vol., bbl + annular vol., bbl ÷ pump output, bbl/stk Total strokes = (172.16 + 1231.84) ÷ 0.136 Total strokes = 1404 ÷ 0.136 Total strokes = 10,324
Tank Capacity Determinations Rectangular Tanks with Flat Bottoms
SIDE
END
Volume, bbl = length, ft x width, ft x depth, ft 5.61 Example 1: Determine the total capacity of a rectangular tank with flat bottom using the following data:
Length = 30 ft
Width = 10 ft
Depth = 8 ft
Volume, bbl = 30 ft x 10 ft x 8 ft 5.61 Volume, bbl = 2400 5.61 Volume = 427.84 bbl Example 2: Determine the capacity of this same tank with only 5-1/2 ft of fluid in it: Volume, bbl = 30 ft x 10 ft x 5.5 ft 5.61 Volume, bbl = 1650 5.61 Volume
= 294.12 bbl
Rectangular Tanks with Sloping Sides:
SIDE
END
Appendix B – Formulas and Calculations
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Volume bbl — length, ft x [depth, ft (width, + width 2)] 5.62 Example: Determine the total tank capacity using the following data:
Length = 30 ft
Width, (top)
= 10 ft
Depth
= 8 ft
Width 2 (bottom) = 6 ft
Volume, bbl = 30 ft x [ 8ft x ( 10 ft + 6 ft)] 5.62 Volume, bbl = 30 ft x 128 5.62 Volume
= 683.3 bbl
Circular Cylindrical Tanks: side
Volume, bbl = 3.14 x r 2 x height, ft 5.61 Example: Determine the total capacity of a cylindrical tank with the following dimensions: Height = 15 ft Diameter = 10 ft
NOTE:
The radius (r) is one half of the diameter:
Volume, bbl = 3.14 x 5 ft 2 x 15 ft 5.61 Volume bbl =1177.5 5.61 Volume
= 209.89 bbl
r = 10 = 5 2
Appendix B – Formulas and Calculations
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Tapered Cylindrical Tanks:
a) Volume of cylindrical section:
Vc = 0.1781 x 3.14 x Rc 2 x Hc
b) Volume of tapered section:
Vt = 0.059 x 3.14 x Ht x (Rc 2 + Rb2 + Rb Rc)
where Vc = volume of cylindrical section, bbl Hc = height of cylindrical section, ft Ht = height of tapered section, ft
Rc = radius of cylindrical section, ft Vt = volume of tapered section, bbl Rb = radius at bottom, ft
Example: Determine the total volume of a cylindrical tank with the following dimensions: Height of cylindrical section = 5.0 ft Height of tapered section = 10.0 ft
Radius of cylindrical section = 6.0 ft Radius at bottom = 1.0 ft
Solution: a)Volume of the cylindrical section: Vc = 0.1781 x 3.14 x 6.02 x 5.0 Vc = 100.66 bbl b) Volume of tapered section:
Vt = 0.059 x 3.14 x 10 ft x (6 2 + 12 + 1 x 6) Vt = 1.8526 (36 + 1 + 6) Vt = 1.8526 x 43 Vt = 79.66 bbl
c) Total volume:
bbl = 100.66 bbl + 79.66 bbl bbl = 180.32
Horizontal Cylindrical Tank:
a) Total tank capacity:
Volume, bbl =3.14 x r 2 x L (7.48) 42
b) Partial volume; Vol. ft3 = L[0.017453 x r 2 x cos-1 (r — h : r) — sq. root (2hr — h 2 (r — h)) ] Example I: Determine the total volume of the following tank;
Appendix B – Formulas and Calculations
Length = 30 ft a)
I
Radius = 4 ft
Total tank capacity;
Volume, bbl = 3.14 x 422 x 30 x 7.48 48 Volume, bbl = 11273.856 48 Volume
= 234.87 bbl
Conversion Tables
TO CONVERT FROM
TO
MULTIPLY BY
Area Square inches
Square centimetres
6.45
Square inches
Square millimetres
645+2
Square centimetres
Square inches
0.155
Square millimetres
Square inches
1.55 x 10 -3
Circulation Rate Barrels/min
Gallons/min
42.0
Cubic feet/min
Cubic meters/sec
4.72 x 10 -4
Cubic feet/min
Gallons/min
7.48
Cubic feel/mm
Litres/min
28.32
Cubic meters/sec
Gallons/min
15850
Cubic meters/sec
Cubic feet/min
2118
Cubic meters/sec
Litres/min
60000
Gallons/min
Barrels/ruin
0.0238
Gallons/min
Cubic feet/min
0.134
Gallons/min
Litres/min
3.79
Gallons/min
Cubic meters/sec
6.309 x 10 -5
Litres/min
Cubic meters/sec
1.667 x 10 -5
Litres/min
Cubic feet/min
0.0353
Appendix B – Formulas and Calculations
Litres/min
Gallons/min
I
0.264
Impact Force Pounds
Dynes
4.45 x 10 -5
Pounds
Kilograms
0.454
Pounds
Newtons
4.448
Dynes
Pounds
2.25 x 10 -6
TO
MULTIPLY BY
Pounds Pounds
2.20 0.2248
TO CONVERT FROM
Kilograms Newtons
Length Feet Inches Inches Centimetres Millimetres Meters
Meters Millimetres Centimetres Inches Inches Feet
0.305 25.40 2.54 0.394 0.03937 3.281
Mud Weight Pounds/gallon Pounds/gallon Pounds/gallon Grams/cu cm Pounds/cu ft Specific gravity
Pounds/cu ft Specific gravity Grams/cu cm Pounds/gallon Pounds/gallon Pounds/gallon
7.48 0.120 0.1198 8.347 0.134 8.34
Power Horsepower Horsepower Horsepower Horsepower (metric) Horsepower (metric) Kilowatts Foot pounds/sec
Horsepower (metric) Kilowatts Foot pounds/sec Horsepower Foot pounds/sec Horsepower Horsepower
1.014 0.746 550 0.986 542.5 1.341 0.00181
Appendix B – Formulas and Calculations
I
Pressure Atmospheres Atmospheres Atmospheres Kilograms/sq. cm Kilograms/sq. cm Kilograms/sq. cm Pounds/sq. in. Pounds/sq. in. Pounds/sq. in. TO CONVERT FROM
Pounds/sq. in. Kgs/sq. cm Pascals Atmospheres Pounds/sq. in. Atmospheres Atmospheres Kgs/sq. cm Pascals TO
14.696 1.033 1.013 x 10 5 0.9678 14.223 0.9678 0.680 0.0703 6.894 x 10 -3 MULTIPLY BY
Velocity Feet/sec Feet/mm Meters/sec Meters/sec
Meters/sec Meters/sec Feet/mm Feet/sec
0.305 5.08 x 10 -3 196.8 3.28
Volume Barrels Cubic centimetres Cubic centimetres Cubic centimetres Cubic centimetres Cubic centimetres Cubic feet Cubic feet Cubic feet Cubic feet Cubic feet Cubic inches Cubic inches Cubic inches Cubic inches Cubic inches Cubic meters Cubic meters Cubic meters
Gallons Cubic feet Cubic inches Cubic meters Gallons Litters Cubic centimetres Cubic inches Cubic meters Gallons Litters Cubic centimetres Cubic feet Cubic meters Gallons Litres Cubic centimetres Cubic feet Gallons
42 3.531 x 10 -3 0.06102 10-6 2.642 x l0 -4 0.001 28320 1728 0.02832 7.48 28.32 16.39 5.787 x 10-4 1.639 x 10-5 4.329 x 10 -3 0.01639 106 35.31 264.2
Appendix B – Formulas and Calculations
Gallons Gallons Gallons Gallons Gallons Gallons
I
Barrels Cubic centimetres Cubic feet Cubic inches Cubic meters Litres
0.0238 3785 0.1337 231 3.785 x 10 -4 3.785
Weight Pounds Tons (metric) Tons (metric)
4.535 x 10 -4 2205 1000
Tons (metric) Pounds Kilograms
Displacement and Capacity Volumes API Drill Pipe Size OD
Size ID
in.
in.
2-3/8 2-7/8 3-1/2 3-1/2 4 4-1/2 4-1/2 5 5 5-1/2 5-1/2 5-9/16 6-5/8
1.815 2.150 2.764 2.602 3.340 3.826 3.640 4.276 4.214 4.778 4.670 4.859 5.9625
WEIGHT lb/ft
6.65 10.40 13.30 15.50 14.00 16.60 20.00 19.50 20.50 21.90 24.70 22.20 25.20
CAPACITY bbl/ft
0.01730 0.00449 0.00742 0.00658 0.01084 0.01422 0.01287 0.01766 0.01730 0.02218 0.02119 0.02294 0.03456
DISPLACEMENT bbl/ft
0.00320 0.00354 0.00448 0.00532 0.00471 0.00545 0.00680 0.00652 0.00704 0.00721 0.00820 0.00712 0.00807
Table A-2 HEAVY WEIGHT DRILL PIPE AND DISPLACEMENT Size OD
Size ID
in.
in.
3-1/2 4
2.0625 2.25625
WEIGHT lb/ft
25.3 29.7
CAPACITY bbl/ft
0.00421 0.00645
DISPLACEMENT bbl/ft
0.00921 0.01082
Appendix B – Formulas and Calculations
4-1/2 5
2.75 3.0
41.0 49.3
I
0.00743 0.00883
0.01493 0.01796
Additional capacities, bbl/ft, displacements, bbl/ft and weight, lb/ft can be determined from the following: Capacity, bbl/ft = ID, in. 2 1029.4 Displacement, bbl/ft = Dh, in. — Dp, in. 2 1029.4 Weight, lb/ft = Displacement, bbl/ft x 2747 lb/bbl
METRIC Drill Pipe Size OD
Size ID
in.
in.
2-3/8 2-7/8 3-1/2 3-1/2 4 4-1/2 4-1/2 5 5 5-1/2 5-1/2 5-9/16 6-5/8
1.815 2.150 2.764 2.602 3.340 3.826 3.640 4.276 4.214 4.778 4.670 4.859 5.965
WEIGHT lb/ft
6.65 10.40 13.30 15.50 14.00 16.60 20.00 19.50 20.50 21.90 24.70 22.20 25.20
CAPACITY ltrs/ft
1.67 2.34 3.87 3.43 5.65 7.42 6.71 9.27 9.00 11.57 11.05 11.96 18.03
DISPLACEMENT ltrs/ft
1.19 1.85 2.34 2.78 2.45 2.84 3.55 3.40 3.67 3.76 4.28 3.72 4,21
Appendix B – Formulas and Calculations
I
Drill Collars I.D. 1½” 1¾” 2” 2¼” 2½” 2¾” 3” 3¼” 3½” 3¾” 4” 4¼” Capacity .0022 .0030 .0039 .0049 .0061 .0073 .0087 .0103 .0119 .0137 .0155 .0175 OD 4”
4¼” 4½” 4¾” 5” 5¼” 5½” 5¾” 6” 6¼” 6½” 6¾” 7” 7¼” 7½” 7¾” 8” 8¼” 8½” 8¾” 9” 10”
#/ft 3 6.7 Disp. .0 133 #/ft 34.7 Disp. .0126 #/ft 48.1 Disp. .0175 #/ft 54.3 Disp. .0197 #/ft 60.8 Disp. .0221 #/ft 67.6 Disp. .0246 #/ft 74.8 Disp. .0272 #/ft 82.3 Disp. .0299 #/ft 90.1 Disp. .0328 #/ft 98.0 Disp. .0356 #/ft 107.0 Disp. .0389 #/ft 116.0 Disp .0422 #/ft 125.0 Disp. .0455 #/ft 134.0 Disp. .0487 #/ft 144.0 Disp. .0524 #/ft 154.0 Disp. .0560 #/ft 165.0 Disp. .0600 #/ft 176.0 Disp. .0640 #/ft 187.0 Disp. .0680 #/ft 199.0 Disp. .0724 #/ft 210.2 Disp. .0765 #/ft 260.9 Disp. .0950
34.5 32.0 29.2 .0125 .0116 .0106 42.2 .0153 45.9 .0167 52.1 .0189 58.6 .0213 65.4 .0238 72.6 .0264 80.1 .0291 87.9 .0320 95.8 .0349 104.8 .0381 113.8 .0414 122.8 .0447 131.8 .0479 141.8 .0516 151.8 .0552 162.8 .0592 173.8 .0632 184.8 .0672 106.8 .0716 268.0 .0757 258.8 .0942
40.0 .0145 43.4 .0158 49.5 .0180 56.3 .0214 62.9 .0229 70.5 .0255 77.6 .0282 85.4 .0311 93.3 .0339 102.3 .0372 111.3 .0405 120.3 .0438 129.3 .0470 139.3 .0507 149.3 .0543 160.3 .0583 171.3 .0623 182.3 .0663 194.3 .0707 205.6 .0748 256.3 .0933
37.5 .0136 40.6 .0148 46.8 .0170 53.3 .0194 60.1 .0219 67.3 .0245 74.8 .0272 82.6 .0301 90.5 .0329 99.5 .0362 108.5 .0395 117.5 .0427 126.5 .0460 136.5 .0497 146.5 .0533 157.5 .0573 168.5 .0613 179.5 .0653 191.5 .0697 202.7 .0738 253.4 .0923
43.6 .0159 50.1 .0182 56.9 .0207 64.1 .0233 71.6 .0261 79.4 .0289 87.3 .0318 96.3 .0350 105.3 .0383 114.3 .0416 123.3 .0449 133.3 .0485 143.3 .0521 154.3 .0561 165.3 .0601 176.3 .0641 188.3 .0685 199.6 .0726 250.3 .0911
53.4 .0194 60.6 .0221 68.1 .0248 75.9 .0276 83.8 .0305 92.8 .0338 101.8 .0370 110.8 .0403 119.8 .0436 129.8 .0472 139.8 .0509 150.8 .0549 161.8 .0589 172.8 .0629 194.8 .0672 196.0 .0714 246.8 .0898
56.8 .0207 64.3 .0234 72.1 .0262 80.0 .0291 89.0 .0324 98.0 .0356 107.0 .0389 116.0 .0422 126.0 .0458 136.0 .0495 147.0 .0535 158.0 .0575 169.0 .0615 181.0 .0658 192.2 .0700 242.9 .0884
67.9 .0247 75.8 .0276 84.8 .0308 93.8 .0341 102.8 .0374 111.8 .0407 121.8 .0443 131.8 .0479 142.8 .0520 153.8 .0560 164.8 .0600 176.8 .0613 188.0 .0685 238.8 .0869
63.4 .0231 71.3 .0259 80.3 .0292 89.3 .0325 98.3 .0358 107.3 .0390 117.3 .0427 127.3 .0463 138.3 .0503 149.3 .0543 160.3 .0583 172.3 .0697 183.5 .0668 234.3 .0853
93.4 .0340 102.4 .0372 112.4 .0409 122.4 .0445 133.4 .0485 144.4 .0525 155.4 .0565 167.4 .0609 178.7 .0651 229.4 .0835
88.3 .0321 97.3 .0354 107.3 .0390 117.3 .0427 123.3 .0467 139.3 .0507 150.3 .0547 162.3 .0590 173.5 .0632 224.2 .0816
122.8 .0447 133.8 .0487 144.8 .0527 156.8 .0570 168.0 .0612 118.7 .0796