UNIVERSITI TEKNOLOGI MARA FACULTY OF CHEMICAL ENGINEERING GEOLOGY AND DRILLING LABORATORY (CGE 558)
GROUP MEMBERS
:
MUHAMMAD ZULHILMI B. AHMAD FAUZI NIK KHAIRUL IKHWAN B. FAUZI MUHAMMAD NAZIM B. MOHAMAD FAUZI MUHSIN BIN IBRAHIM NAZIRUL MUBIN BIN SAMSUDIN
EXPERIMENT DATE PERFORMED SEMESTER PROGRAMME / CODE SUBMIT TO GROUP
: : : : : :
MUD VISCOCITIES AND OTHER RHEOLOGICAL PROPERTIES 1st OCTOBER 2013 SEPT 2013 – JAN 2014 BACHELOR OF ENGINEERING (HONS.) OIL AND GAS (EH223) SIR HOSSEIN HAMIDI 4
No.
Title
Allocated marks %
1 Abstract/Summary
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2 Introduction
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3 Aims/Objectives
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4 Theory
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5 Apparatus
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6 Procedures
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7 Result
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8 Calculations
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9 Discussion
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10 Conclusion
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11 Recommendations
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12 References
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13 Appendices TOTAL MARKS
Remarks:
Checked by:
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(2012887124) (2012895986) (2012651824) (2012464662) (2012299766)
Marks %
Table of Contents SUMMARY ............................................................................................................................................... 2 INTRODUCTION ....................................................................................................................................... 3 OBJECTIVE ............................................................................................................................................... 5 THEORY ................................................................................................................................................... 6 PROCEDURES........................................................................................................................................... 7 APPARATUS ............................................................................................................................................. 8 RESULTS .................................................................................................................................................. 9 SAMPLE CALCULATIONS.......................................................................................................................... 9 SAMPLE OF CALCULATION OF ERRORS ................................................................................................. 10 DISCUSSION........................................................................................................................................... 11 CONCLUSION......................................................................................................................................... 19 RECOMMENDATION ............................................................................................................................. 20 REFFERENCES ........................................................................................................................................ 21 APPENDICES .......................................................................................................................................... 22
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SUMMARY The objective of this study is to determine the viscosity, gel strength and yield point of each of the samples. Rheological measurements made on fluids help to determine how well this fluid will flow under a variety of different conditions. This information is important in the design of circulating systems required to accomplish certain desired objectives in drilling operations.
For the results that we had calculated is plastic viscosity= 26cp and apparent viscosity = 43cp. For the results that we had obtained, shows that the gel strength is 12cp. The yield point is 47lb/
. At the same time, we had calculated that the
percentage error from the experiment. The percentage error for gel strength is 4.76% whereas the percentage error for yield point is 374.74%. The higher percentage error of yield point may occur due to parallax error. To measure the funnel viscosity of drilling mud is the second objective Funnel viscosity is defined as time, in seconds for one quart of mud to flow through a Marsh funnel which has a capacity of 946 cm 3. From our experiment we used 200ml of mud and the time taken for mud finish to flow out from funnel is 70s. In a nutshell, we can said that the point at which a material can no longer deform elastically known as yield point and gel strength is the shear stress of drilling mud that is measured t low shear rate after the drilling mud is static for a certain period of time. Funnel viscosity is time, in seconds for one quart of mud to flow through a Marsh funnel. The funnel viscosity is useful only for relative comparison. There are few precautions taken place in order to increase the accuracy of the data such as ensure the viscometer is clean and set up correctly and make sure the viscometer is switched off before change the speed of the viscometer.
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INTRODUCTION PART A: MUD RHEOLOGY DETERMINATION USING VISCOMETER Rheology is the study of flow and deformation of materials under applied forces. The measurement of rheological properties is applicable to all materials – from fluids such as dilute solutions of polymers and surfactants through to concentrated protein formulations, to semi-solids such as pastes and creams, to molten or solid polymers. Rheological properties can be measured from bulk sample deformation using a mechanical rheometer. Many commonly-used materials and formulations exhibit complex rheological properties, whose viscosity and viscoelasticity can vary depending upon the external conditions applied, such as stress, strain, timescale and temperature. Internal sample variations such as protein concentration and stability, and formulation type for biopharmaceuticals, are also key factors that determine rheological properties. In the drilling operations knows that muds behave with non-Newtonian fluid flow properties as their viscosity is not only influenced by temperature and pressure but is also strongly related to the velocity at which the mud flows through the hydraulic system. The drilling fluid velocity and the resulting rate of shear at the walls of the conduits play an important role on the viscosity of the fluid pumped. For this reason, it is important to know the viscosity in the full range of shear rate usually considered for hydraulic calculations. There is a well characterized minimum stress, called yield point, below which flow does not occur. At low shear rates there is a typical non-linear relationship between shear stress and shear rate, which tends to be attenuated with the increase of shear rate.
A) Viscosity
Viscosity is a measure of a fluid's resistance to flow. It describes the internal friction of a moving fluid. A fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction. A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion.
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Gases also have viscosity, although it is a little harder to notice it in ordinary circumstances.
Viscosity is due to friction between neighbouring parcels of the fluid that are moving at different velocities. When fluid is forced through a tube, the fluid generally moves faster near the axis and very slowly near the walls, therefore some stress (such as a pressure difference between the two ends of the tube) is needed to overcome the friction between layers and keep the fluid moving. For the same velocity pattern, the stress required is proportional to the fluid's viscosity. A liquid's viscosity depends on the size and shape of its particles and the attractions between the particles.
B) Gel strength Gel strength is the shear stress of drilling mud that is measured at low shear rate after the drilling mud is static for a certain period of time. The gel strength is one of the important drilling fluid properties because it demonstrates the ability of the drilling mud to suspend drill solid and weighting material when circulation is ceased. The Fann viscometer is a concentric cylinder viscometer capable of measuring the shear stress at two or more shear rates. This is by far the most common device used at the rig site and in the laboratories to measure the rheological properties of drilling fluids. The Fann viscometer was designed specifically for use with drilling fluids and the various constants in the rheological models can be measured rather easily. C) Yield point This is the measure of the electro-chemical or attractive forces in the mud flow (dynamic) conditions. These forces depend on (1) surface properties of the mud solid, (2) volume concentrations of the solids and (3) electrical environment of the solids. The yield point of the mud reflects its ability to carry drilled cutting out of the hole.
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PART B: MUD RHEOLOGY DETERMINATION USING VISCOMETER Viscosity is measured using a Marsh funnel, a conical-shaped funnel, fitted with a small-bore tube on the bottom end through which mud flow under a gravity head. A screen over the top removes large particles that might plug the tube. In the test standardized for evaluating water-base and oil-base muds, the funnel viscosity measurement is the time (in seconds) required one quart of mud to flow out of a Marsh funnel into a graduated cup. This test is quick and simple. This test is quick and simple. Unfortunately, the Marsh funnel gives no useful quantitative information about the rheological properties of the drilling fluid. Fluids with widely varying rheologies may all have the same funnel viscosity. A reasonable hydraulics program cannot be developed based on funnel viscosity, although it may be the only flow property specified in the drilling fluids program.
OBJECTIVE PART A: MUD RHEOLOGY DETERMINATION USING VISCOMETER
1. To determine the viscosity, gel strength and yield point of a sample.
PART B: MUD RHEOLOGY DETERMINATION USING VISCOMETER
1. To measure funnel viscosity of drilling fluid.
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THEORY Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress. It is measured as the ratio of the shearing stress to the rate of shearing strain. In this experiment, the viscosity was measured by using Fann Viscometer. ⁄ = Viscosity (centipoise) = Shear stress = Shear rate
Gel strength is a function of inter-particle forces. Gel strength was measured by using the Fann Viscometer, in lb/100sq.ft. First mix the water-based mud under 600rpm for 3 minutes, then rest for 3 minutes, then mix again under 3 rpm. The first reading deflected was taken as the gel strength reading. Yield Point (YP) is resistance of initial flow of fluid or the stress required in order to move the fluid. Simply put that the Yield Point (YP) is the attractive force among colloidal particles in drilling mud. Yield Point can be calculated by using this formula:
Yield Point (YP) = Reading from a viscometer at 300 rpm – Plastic Viscosity (PV)
A unit of YP is lb/100 ft2. In water-based mud, the YP will be increased with following items; • High temperature– the high temperature environment tends to increase the YP in the water base mud. • Contaminants such as carbon dioxide, salt, and anhydrite in the drilling fluids. • Over treatment the drilling mud with lime or caustic soda.
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PROCEDURES PART A: Mud Rheological Determination Using Viscometer. Viscosity: 1. Test Fluid is stirred at low speed for 5 minutes by using the Hamilton Beach Mixer. 2. The drilling fluid is then poured into the sample cup to the level corresponding to the predetermined bob length. 3. With drilling fluid in the cup properly placed in the viscometer, the rotor sleeve is immersed exactly to the scribed line. 4. The test fluid is sheared at 600 rpm until torque reading reaching a steady value, after which the stabilized dial reading is recorded in descending order at 600 and 300 rpm. 5. Each dial reading is recorded just before shifting to the lower speed.
Gel Strength: 1. Water-based mud is stirred at 600 rpm about 1 minute. 2. Then, the mud is allowed to stand undisturbed for 1 minute. 3. The rpm knob is switched to 3 rpm. 4. The maximum reading attained after the start of the rotation is recorded.
Yield Point: 1. The dial reading of water-based mud is recorded at 600 rpm and 300 rpm by using Fann Viscometer. 2. Then, the yield point is calculated by using the formula as follow: Yield Point: The reading at 600 rpm – The reading at 300 rpm
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PART B: Determination of Marsh Funnel Viscosity
1. With the funnel in an upright position, the orifice is covered with a finger and the water-based mud is poured through the screen until the mud exactly reached the bottom of the screen. 2. Then, the finger is removed immediately from the outlet and the time required is measured in seconds for 200 ml of mud to flow out of the funnel. 3. The reading from stopwatch is recorded. 4. The experiment is repeated for three times in order to obtain average value. 5. The number of seconds is reported as funnel viscosity.
APPARATUS Part A 1. Baroid viscometer 2. Mud sample (water-based mud) 3. Mud mixer Part B 1. Marsh funnel with receiving cup 2. Mud sample (water-based mud) 3. Mud mixer
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RESULTS A) Mud Rheology Determination Using Viscometer By using a Fann Viscometer, these results were obtained: Viscometer Speed (rpm)
Viscosity (Centipoise)
3
12
6
14
100
35
200
51
300
60
600
86
B) Determination of Marsh Funnel viscosity Time taken for
mud to flow through Fann Marsh funnel:
SAMPLE CALCULATIONS GEL STRENGTH Initial reading of viscometer (5 minutes) : 86 cP Gel Strength: 12 cp YIELD POINT Plastic viscosity (cp) = 600 rpm reading – 300 rpm reading = 86-60 = 26 cP Apparent viscosity = 600 rpm reading/2 = 86/2 = 43 cP 9
Yield point = 300 rpm reading – plastic viscosity x (0.5) N/m2 = 60 – 26(0.5) = 47 lb/ft3
SAMPLE OF CALCULATION OF ERRORS GEL STRENGTH
YIELD POINT
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DISCUSSION This experiment is carried out to determine mud viscosities and other rheological properties, which are gel strength and yield point. This experiment can be divided into two parts. The first part is the determination of mud rheology using viscometer while the second one is the determination of marsh funnel viscosity. For the first part, it is then divided into three, which are, viscosity, gel strength and yield point. Firstly, viscosity is a measurement of the resistance of a fluid which is being deformed by either shear stress or tensile stress. First of all, the Baroid Rheometer is a coaxial cylindrical rotational viscometer, used to determine single or multi-point viscosities. It has fixed speeds of 3, 6, 100, 200, 300 and 600 rpm that are switch selectable with the RPM knob. First of all, place a recently agitated sample in the cup, tilt back the upper housing of the rheometer, locate the cup under the sleeve (the pins on the bottom of the cup fit into the holes in the base plate), and lower the upper housing to its normal position. Turn the knurled knob between the rear support posts to raise or lower the rotor sleeve until it is immersed in the sample to the scribed line. Stir the sample for about 5 minutes at 600 RPM, and then select the RPM desired for the best. Wait for the dial reading to stabilize (the time depends on the sample's characteristics). Record the dial reading and RPM. Secondly, for gel strength, at first, stir a sample at 600 RPM for about 5 minutess. Turn the RPM knob to the STOP position. Wait the desired rest time (for 5 minutes). Switch the RPM knob to the slowest gear position that is 3 RPM. Record the maximum deflection of the dial before the Gel breaks, as the gel strength in lb/100 ft2 (lb/100 ft2 x 5.077 = Gel strength in dynes/cm2). Lastly, for the yield point, we use the Baroid Rheometer to obtain dial readings at 3, 300 and 600 RPM. By means of the rheological calculations procedure, the Apparent and Plastic Viscosities, Yield Point and initial 10 sec. and final 5-minute Gel Strength parameters are determined. All the results are tabulated. For the second part, marsh funnel is used to determine mud viscosity. Firstly, with the funnel in an upright position, cover the orifice with a finger and pour the freshly collected mud sample through the screen into a clean, dry funnel until the fluid level reaches the bottom of the screen (1500ml). Immediately remove the finger from the outlet and measure the time required for the mud to fill the receiving vessel to the 1-quart (946 ml) level. The time is required to the nearest second. 11
From the experiment that we have conducted, based on all the result and all the calculation that we had done, for the first part, the viscosity for 3, 6, 100, 200, 300 and 600 rpm are 12, 14, 35, 51, 60 and 86 cP respectively. The plastic viscosity is 26 cp while apparent viscosity is 43 cp. The gel strength is 12 cP and the yield point is 47 lb/ft3. For the second part, the time taken for 200 ml mud to flow through Fann Marsh funnel is 70 seconds. Primarily, all drilling fluids, especially drilling mud can have wide range of chemical and physical properties. These properties are specifically designed for drilling conditions and the special problems that must be handled in drilling a well. The purposes of drilling fluids include cooling and lubricate the drill bit. Besides that, it also removes cuttings from the well. Moreover, it controls the pressure to prevent blowout. Drilling mud also solve some drilling problems include lost circulation and stuck pipe. Plastic viscosity (PV) controls the magnitude of shear stress develops as one layer of fluid slides over another. It is a measure of friction between layers and provides a scale of the fluid thickness. With liquid, plastic viscosity decreases with the increasing in temperature but reverse with gasses. Any increase in solid content in drilling mud as Bartie, drill solid, lost circulation material, etc will result in higher the plastic viscosity. In order to lower the PV, you must reduce the solid content that can be achieved by using solid control equipment and/or diluting drilling mud with base fluid. With increasing temperate while drilling deeper, the plastic viscosity of the drilling mud will decrease because the viscosity of the base fluid decreases. Normally, the higher mud weight, the higher PV will be. However, if you have an increasing trend of PV without mud weight change, it means that there is an increase in ultra-fine drill solid content in the mud system. Moreover, if you use oil base mud, please keep in mind that emulsified water in oil base drilling fluid will act like a solid, and it will increase the plastic viscosity dramatically. Effective viscosity depends on fluid velocity flow pattern. It is difficult to measure but can be calculated. The gel strength is the shear stress of drilling mud that is measured at low shear rate after the drilling mud is static for a certain period of time. The gel strength is one of the important drilling fluid properties because it demonstrates the ability of the drilling mud to suspend drill solids and weighting material when circulation is ceased. If the mud has the high gel strength, it will create high pump pressure in 12
order to break circulation after the mud is static for long time. Furthermore, increasing in a trend of 30-minute gel strength indicates a build-up of ultra-fine solid. Therefore, the mud must be treated by adding chemicals or diluting with fresh base fluid. Yield point is a resistance of an initial flow of fluid or the stress required in order to move the fluid. In other words, yield point (YP) is the attractive force among the colloidal particles in drilling mud. Yield point is influenced by the concentration of solids, their electrical charge and other factors. If not at the proper value, it can also reduce drilling efficiency by cutting penetration rate, increasing circulating pressure, and posing the danger of lost circulation. Lastly, based on the experiment that has been carried out, the percentage error for gel strength is 4
whereas the percentage error for yield point is
. This error may occur due to parallax error, error in timing the mud coming out from the marsh funnel. Besides that, error may also occur when eyes of the observer is not perpendicular to the scale while taking RPM reading. Other errors are encountered from other carelessness during the experiment.
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QUESTIONS 1. (a) What is Plastic Viscosity? Plastic viscosity (PV) is a parameter of the Bingham plastic rheological model. PV is the slope of the shear stress-shear rate plot above the yield point (See Figure 1). Viscometer is equipment to measure Plastic Viscosity. Plastic Viscosity is derived from the 600 rpm reading minus the 300 rpm reading and PV is in centipoises (cP).
Figure 1: Bingham plastic model describe Plastic Viscosity and Yield Point
1. (b) What does it characterize? A low PV indicates that the mud is capable of drilling rapidly because of the low viscosity of mud exiting at the bit. With increasing temperate while drilling deeper, the plastic viscosity of the drilling mud will decrease because the viscosity of the base fluid decreases. High PV is caused by a viscous base fluid and by excess colloidal solids. To lower PV, a reduction in solids content can be achieved by dilution. Our group is using oil-based mud as the mud sample, thus the emulsified
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water in oil base drilling fluid will act like a solid, and it will increase the plastic viscosity dramatically.
(c) What is the difference between the Plastic Viscosity and Apparent Viscosity of a drilling fluid? Plastic viscosity is the slope of the shear stress line above the yield point. Plastic viscosity can control the magnitude of shear stress develops as one layer of fluid slides over another. Plastic viscosity also can provide a scale of full thickness besides it will decrease with increasing temperature; with liquids: but reverse with gasses. The apparent viscosity is the slope of the dashed line in figure 2, it is the shear stress divided by the shear strain rate at a particular point in the curve. The apparent viscosity depends on the point chosen. Apparent viscosity (AV) is one-half of the dial reading at 600 rpm (1022 sec-1 shear rate) using a direct-indicating, rotational viscometer.
Figure 2: Relationship of stress to shear train for a Bingham plastic, illustrating the difference between plastic viscosity and apparent viscosity
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2. Which role does Gel Strength play in the drilling process? Gel strength is the ability of the mud to develop gel structure. The gel strength is the shear stress of drilling mud that is measured at low shear rate after the drilling mud is static for a certain period of time. The gel strength is one of the important drilling fluid properties because it demonstrates the ability of the drilling mud to suspend drill solids and weighting material when circulation is ceased. With proper gel strength can help suspend solids in the hole and allow them to settle out on the surface, excessive gel strength can cause a number drilling problems. Gel strengths are usually classified as progressive (strong) or as fragile (weak) type gels.
3. What type of fluids does drilling fluids belong to? The drilling fluid can be air, foam (a combination of air and liquid or a liquid). Liquid drilling fluids are commonly called drilling mud. All drilling fluids, especially drilling mud, can have a wide range of chemical and physical properties. These properties are specifically designed for drilling conditions and the special problems that must be handled in drilling a well.
4. What is the Yield Point? Yield point is a resistance of an initial flow of fluid or the stress required in order to move the fluid. In another words, yield point (YP) is the attractive force among colloidal particles in drilling mud. YP is calculated from 300- and 600-rpm viscometer dial readings by subtracting PV from the 300-rpm dial reading. The YP indicates the ability of the drilling mud to carry cuttings to surface. The Bingham plastic fluid plots as a straight line on a shear-rate (x-axis) versus shear stress (y-axis) plot, in which YP is the zero-shear-rate intercept (PV is the slope of the line).
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Figure 2: Bingham Plastic models describe PV and YP
4. (b) What does it characterize? A high Yield Point implies a non-Newtonian fluid, one that carries cuttings better than a fluid of similar density but lower YP. Moreover, frictional pressure loss is directly related to the YP. If you have higher YP, you will have high pressure loss while the drilling mud is being circulated. In water-based mud, the YP will be increased as the temperature of the environment getting higher. Presence of the contaminants also one of the factors that the water based will increase in yield point. As for the oil-based mud, the more drill solid it contains, the more yield point will be. Lower temperature of the op based will increase the viscosity and the yield point. 4. (c) What is the difference between Gel Strength and Yield Point of drilling mud? Gel strength measurements denote the thixotropic properties of the mud. They are a measure of the attractive forces under static or-non-flow conditions. Yield point on the other hand is a measurement of attractive forces under flowing conditions and should not be confused with gel strength. However, since both gel strength and yield point are a measure of the force of flocculation as yield point decreases the gel strength will usually decrease. A low yield point does not necessarily indicate a condition of 0/0 gels, but without any appreciable reduction in apparent viscosity. 17
5. Explain what you know about one point and two point curve fluids? Give one example of each type of fluid.
6. Discuss the difference between Plastic Viscosity and Funnel Viscosity. Marsh funnel is a great advantage is its simplicity and reliability under field conditions. There is, however, no recognized method of converting Marsh funnel times to viscosity in conventional units. Moreover, since drilling muds are generally highly non-Newtonian in character, their flow characteristics cannot be defined by a single viscosity. Besides, the viscosity given by the Marsh Funnel is not a true viscosity, but serves as qualitative measure of how thick the mud sample is. The Funnel viscosity is useful only for relative comparisons. It indicates the changes in viscosity and cannot be used to quantify the rheological properties such as Yield Point and Plastic Viscosity. The funnel viscosity measures at only one rate of shear but the temperature each time of measurement is not constant. This is the reason why the viscosity measured from the Marsh Funnel does not represent the true mud viscosity. 18
CONCLUSION The main objective of this experiment is to measure the rheology properties of the mud samples which is the viscosity, yield point and also the gel strength of the mud sample. As for the Marsh funnel experiment, the objective is to measure the funnel viscosity and then we can compare it with the plastic viscosity that we get during the experiment. The purposes of drilling fluids are good for cooling and lubrication. As the drill bit drills into the rock formation, the friction caused by the rotating bit against the rock generate heat. Besides, drilling fluids may also be a cutting removal as it is an important function of the drilling fluid is to carry rock cuttings removed by the bit to the surface. Furthermore, it will also act as a pressure control as it can prevent against the “kick” or loss of well control caused by formation pressures. That why it is important to control the viscosity of mud during the drilling well activity. Next, based on the experiment that has been carried out, the percentage error for gel strength is 4
whereas the percentage error for yield point is
.
This error may occur due to parallax error, error in timing the mud coming out from the marsh funnel. Besides that, error may also occur when eyes of the observer is not perpendicular to the scale while taking RPM reading likes we mention before. Here, we already listing the precaution should be takes during the experiment to avoid the errors happened. For the last, the objectives for this experiment has achieved for both part.
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RECOMMENDATION Part A 1. Before start the experiment, we have to make sure that each of our member wearing laboratory coat, safety goggle, gloves and enclosed shoes. This is really important to keep our member in safe from any unexpected incident that could happen. 2. Make sure that calibration of the viscometer is being checked properly before run the experiment. If there some error happen, adjust the meter in correct position and if it cannot be adjusted, record the error (+/- ) of the value. 3. Check the bob and rotor and make sure both of it are in good condition and clean either before or after experiment. This is important because to prevent any impurities mixing with the muds. 4. The timing also must be correct and need to be monitored well so that we can get the most accurate result. 5. The experiment should be repeated a few time so that we can get the average value for the experiment.
Part B
1. Make sure the starting timing that been taken by stopwatch is simultaneous with the mud that start to flow out from funnel.
2. When pouring mud into a funnel, make sure that the mud will pour on marsh. This is because to prevent any larger substance from clog or blocking the hole at the end of funnel.
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REFFERENCES 1. Laboratory Manual; Geology And Drilling Laboratory (CGE 558), Faculty of
Chemical Engineering, UiTM Shah Alam.
2. Doughlas, J. F. (2010). Fluid Mechanic, 5th Edition. New York: Pearson
Prentice.
3. 13B-1 Recommended Standard Procedure for Field Testing Water-Based
Drilling Fluids, Dallas: American Petroleum Institute, 1990
4. http://www.glossary.oilfield.slb.com/Display.cfm?Term=apparent%20viscosity
5. http://www.drillingahead.com/profiles/blogs/gel-strength
6. http://www.glossary.oilfield.slb.com/Display.cfm?Term=viscosity
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APPENDICES
Figure 4: Viscometer
Figure 3: Water based Mud
Figure 6: Stopwatch
Figure 5: MIxer
Figure 7: Marsh and Funnel
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