Compensated Neutron(1)

Coompe om m ppen ens nsa n sat ed Ne N Neut eut utrr on

Objectives Compensated Neutron

• JFE JFE wil willl gat gathe herr suf suffi fici cien entt kno knowl wled edge ge to effic efficie ient ntly ly operate compensated neutron tool and explain its operational basic theory. • JEF JEF will will revi review ew stan standa dard rd proc proced edur ures es for for han handl dlin ing g the neutron sources. • JFE JFE will will be be able able to to cal calib ibra rate te the the comp compen ensa sate ted d neutron tool. • JEF JEF will will iden identif tify y dif diffe fere rent nt neut neutro ron n log log resp respon onse ses. s.

Objectives Compensated Neutron

• JFE JFE wil willl gat gathe herr suf suffi fici cien entt kno knowl wled edge ge to effic efficie ient ntly ly operate compensated neutron tool and explain its operational basic theory. • JEF JEF will will revi review ew stan standa dard rd proc proced edur ures es for for han handl dlin ing g the neutron sources. • JFE JFE will will be be able able to to cal calib ibra rate te the the comp compen ensa sate ted d neutron tool. • JEF JEF will will iden identif tify y dif diffe fere rent nt neut neutro ron n log log resp respon onse ses. s.

Benefits Compensated Neutron

1.You will improve your skills 2. After this chapte chapter, r, you be able to operate operate one one of the most popular Open Hole tool in the Oil Industry. 3.Finally, all this represent money ($.. ($..)… )… for for you. ou.

Agenda Compensated Neutron Module 1.

Introduction Neutron Radiation Neutron Source Neutron Interaction.

Module 2.

Compensated Neutron

Module 3

Hardware

Module 4

Calibration / Verification

Module 5

Logging Operation

Introduction Compensated Neutron

Compensated Neutron instrument is a radiation logging device that indicates formation porosity in open or cased hole. Use an induced chemical radioactive source that emits neutrons. Two proportional counters act as detectors.

Introduction Compensated Neutron

• Neutron logs respond to the fundamental formation property of hydrogen richness. • If all of the formation's hydrogen is contained in the form of liquids, and if these liquids completely occupy the total pore volume, hydrogen richness is an index of porosity. • Hence, a neutron log is used to determine Porosity Index.

Neutron Radiation Compensated Neutron

Neutron radiation is induced or man-made and occurs when a very excited nucleus emits a neutron in order to become more stable. Neutrons have the following physical characteristics: • Mass of 1 • No charge • Varying speed

→

varying kinetic Energy Ek = 1/2 m v 2

Neutron Radiation Compensated Neutron

Neutrons are classified by the amount of energy they possess. This energy is directly related to their speed of travel. 1. Fast neutrons > 100 KeV of energy 2. Intermediate neutrons - between 100 KeVand 100 eV of energy 3. Slow neutrons < 100 ev of energy a) Epithermal neutrons - between .1 and 100 eVof energy b) Semi-epithermal neutrons c) Thermal neutrons - < 0.025 eVof energy

Neutron Source Neutron Radiation

• Typically neutron logging sources are mixtures of isotopes, which when combined decay in such a manner that neutrons result. • The chemical source most commonly used contains Beryllium (Be) and Americium 241 (Am) which is an alpha emitting radioactive element.


9 inches / 22.7 cm Neutron Source Am-241/Be - 666 GBq(18 Ci)

Neutron Source Containers (WEP)


As Americium spontaneously decays to neptunium, it emits sizeable quantities of alpha particles.

Americium Decay : 95 Am 241 → 2 α 4 + 93 Np 237 – This decreases the atomic weight by 4 and the atomic number by 2. – The alpha particle is captured by the Be which becomes C13 (Carbon 13). – The carbon 13 atom is very unstable and emits a 4.5 MeV neutron, which is a Fast neutron.


α

241 95

Am

237 Np 93

+

4 2

+ 4.5 Mev


4 2

α

+

9 4 Be

13

→ 6 C* →

12 6C

1

+0

n

Isotopic Neutron Sources Mixing Alpha emitter with an appropriate target material.

Features of the neutron source Neutron Radiation

– Isotope: • Americium241- Beryllium (Am241Be)

– Source Type: • S17S20

– Activity: • 666 GBq (18 Ci) activity - produces about 40 million n/sec,

– Energy level • 4.5 MeV.

– Radioactive half life • 432 years.


decays

Am241 95

α42 + Np237 93 Captured by Be to become

C13 (unstable) 6

decays

FAST + C126 NEUTRONS

Compounds: Americium 241 - Beryllium (Am 241 Be) Denomination: S17S20 Activity: 18 Ci

Energy: 4.5 MeV

Radioactive 1/2 life: 432 years

Neutron Interaction Neutron Radiation

• The Neutron source emits high energy neutron radiation. • Immediately upon entering the borehole-formation environment, neutrons start undergoing a continuous de-energizing process. • This energy reduction occurs when the neutron collides with nucleus of borehole and formation elements. • A neutron loses some of its total kinetic energy each time it is involved in either an elastic or inelastic collision. • Neutrons with low energy can be absorbed or capture by the target nucleus become a excited stated.

Elastic Collision Neutron Interaction

Remember your last billiard game

1

V1

1

Before

E k = E k 1 =

m1v1

2

2

V’1

2

=

After

V2

E k = E k '+ E k 2 E k =

m'1 v'1

2

2

+

m2 v2

2

2


Head-on collision between particles of the same masse: neutron and hydrogen

N

V1

V1 = V2 H

The neutron transfer 100 % of its Energy to the Hydrogen


• Conservation of the kinetic Energy. • The best transfer appears with a particle of same masse: HYDROGEN. • Hydrogen is primarily responsible for the reduction of the neutron energy. • The matrix has a significant effect.

Inelastic Collision Neutron Interaction

V1’ emitting emitting -ray -ray

1

V1

1

≠

Before

E k = E k 1 =

2

m1v1

2

After

2

E k = E k 1 '+ E k 2 Atom Atom 22 is is in in an an excited excited state state

V2

Inelastic Collision Neutron Interaction

• No conservation of the kinetic energy. • The struck nucleus is left in an excited state. • Emission of -ray so the excited nucleus comes back to its ground state.

Neutron Capture Neutron Interaction

The Neutron incident has low energy

N

V1

V2 = 0 2

The neutron is absorbed by the target nucleus, and this nucleus, emits instantaneously a gamma ray

Neutron Interaction Compensated Neutron

Since hydrogen atoms are both relatively abundant and nearly equal in mass to the neutron, they are primarily responsible for reducing high energy neutrons to their thermal state.

Compensated Neutron – Module 2 • Detecting Hydrogen and relation sheet with Porosity • Reading with high porosity and low porosity conditions. • Position of detectors • Ratio SSN/LSN • Eccentricity • Lithology Effects • Gas Effects

Compensated Neutron The two thermal neutron detectors are positioned at different spacing from an 18 Curie Americium 241 – Beryllium neutron source. - The near detector is referred to as the "short-spaced" (SS) detector. - The far detector is referred to as the "long-spaced" (LS) detector.

Compensated Neutron • The neutron source continuously emits fast neutrons. • When fast neutrons collide with the various nuclei in the formation they lose energy, slowing to an epithermal energy level, then to a thermal energy level.

Compensated Neutron • Therefore a decreasing detector count indicates an increasing amount of hydrogenous material between the source and the detectors. • This in turn indicates a higher formation porosity. • The count rates from the long-spaced detector and the short-spaced detector are each processed in the instrument and transmitted to the surface.

Compensated Neutron • Whether the detector type used is responsive to capture gamma rays or to slow neutrons – the measurement is indicative of the relative amount of hydrogen in the formation. • When formation liquids are the primary source of formation hydrogen – neutron measurements are correlative to the quantity of liquid existing in the pore space.

Compensated Neutron

Compensated Neutron • In high porosity, liquid-filled formations, the neutron flux is thermalised close to the source, so that relatively few neutrons or capture gamma rays are detected. – Thus high porosity is indicated by a low neutron counting rate. – The reverse reasoning will relate low porosity to a high count rate.

Compensated Neutron Can Can be be divided divided in in 3 3 zones zones

More porosity, more hydrogen COUNTS DECREASE QUICKER

Higher porosity, More Hydrogen around the source, Neutrons thermalized closer from the source, Detector is closed to the source Higher

Further away from the source LESS COUNTS

count rate

High reading, Reading decrease when porosity decrease

SAME READING whatever value is the porosity

Reading INCREASE when porosity DECREASE

Compensated Neutron The far spacing zone provides: 1. Increased depth of investigation • formation porosity is emphasized over borehole effects.

2. Improved porosity resolution • fractional change in count rate per unit porosity change.

Compensated Neutron • The Compensated Neutron tool is the standard used for open hole logging. – A fast neutron source is located near the bottom of the tool, – and two thermal neutron detectors are spaced ~1 and ~1.5 ft above it, both are in the far field. • The ratio of the count rates from the near and far detectors, SSN/LSN is related to formation porosity

Compensated Neutron • The ECLIPS acquisition system uses the ratio of the short-spaced (SS) count rate to the long-spaced (LS) count rate to compute an apparent limestone porosity curve. • The computed curve may be further corrected for environmental and formation effects.

2435 CN Porosity Response Compensated Neutron

• SSN / LSN is presented on the X-axis.

• THE RATIO INCREASES WITH POROSITY. • Remember : both SSN and LSN decrease with porosity but LSN decreases more. • Need to be link to porosity

Tool Eccentricity Compensated Neutron

Neutron count rates increase as the tool approaches contact with the borehole wall from a center hole position. – To aid in this the tool is normally run with a decentralizer in place.

Lithology Effects Compensated Neutron

While the SSN/LSN ratio depends primarily on porosity, there is also a significant dependence on lithology because the matrix contributes some to the slow down and capture of the neutrons. Therefore to derive porosity from the count ratio with any accuracy the lithology must be known.


The ratio-porosity relationship used to derive CN is normally limestone matrix, and is referred to as: Apparent Limestone Porosity – For different lithology such as sandstone and dolomite correction charts have been derived.


Gas Effect Compensated Neutron

• The measurement of porosity is only valid in rocks filled with oil or water – both fluids have the same volumetric hydrogen contents. • Gas filled formations will show too low a value for porosity – the number of hydrogen atoms per unit volume in gas is much lower than that of water or liquid hydrocarbons.

Hardware – Module 3 Compensated Neutron

• Detectors SS SSN and and LS LSN • Elec lectron tronic – Main components – Data transmission – Subset – Sample rate – Computed Curves – General parameters • Compe ompens nsated ated Neu Neuttron Log’s Log’s presen presenttation ations s

LS and and SS detect detector detectors detectoors rss Compensated Neutron - Hardware The detectors are proportional counters encased in nylon moderator sleeves. – The counters consist of two electrodes mounted in a metal cylinder and pressurised with active helium gas (He3).

Proportional Counter Compensated Neutron - Hardware

– Similar to ionization chamber. The operating voltage between the anode (center wire) and cathode (cylinder) is more than 1000 volts. – Primarily used as epithermal and thermal neutron detectors. – The cylinder is filled with an active gas (He ) pressurized to 10 atmospheres. – The cylinder is encased in a nylon sleeve which acts as a moderator and has a cadmium shield. – Detection begins with the absorption of neutrons by the atoms of He .

Proportional Counter Compensated Neutron - Hardware

Advantages • Fairly rugged and temperatures to 400 F tolerated • Signal pulses large enough to be easily counted • Pulse strength proportional to the energy level of the radiation particles detected by the counter. Disadvantage • Dead Time Application • 2418, 2435, 2438, 2446 Compensated Neutron

Deadtime of detectors Compensated Neutron - Hardware

• It’s defined simply as the amount of time that must elapse before another event can be detected. • Any events that occur during the deadtime of a detector are missed. • The deadtime for 2446XA’s detectors is 20 microseconds for the short space and 24 microseconds for the long space. • Deadtime correction is applied to 2446XA’s detectors using the next formula: count rate raw/(1-count rate raw*t)= count rate deadtime corrected

where “ t ” is the deadtime known for each detector.

H L E C B A M

B00

H Micro R BZ0 123906 E L Controller O UDI 8 R LSCNT NEUTRON WTS M2 comms WTS M2 comms 1 T 1 PREAMP 0 N +5 Voltage monitor Voltage monitor 5 O 5 1 C Frequency +24V Frequency counter counter O R D V V GND 4 C I Boost the pulses N H 2 M G + + T N C S L

T N C S S

133913 NEUTRON SIGNAL PROCESSOR

LS DETECTOR

Detectors low low output output signal signal

SSCNT 133906 SS NEUTRO DETECTOR Signal Processing board N 1. Buffer 1. Buffer PREAMP

2. 2. Voltage Voltage reference reference 3. 3. Discriminator Discriminator 4. 4. Scaler Scaler (( SS/16 SS/16 LS/4) LS/4) 5. 5. Pulse Pulse shaping shaping

DIAGRAM OF THE CIRCUIT – Compensated Neutron - Hardware

Neutron Curves Compensated Neutron - Hardware

• Raw curves

ssnr : raw short space count lsnr : raw long space count count • Computed curves

Presented

CN : compensated neutron porosity CNC : borehole size corrected CN CNCF : Field normalized CNC (made (made to to look look like like Schlumberger Schlumberger curve curve for for high high porosity) porosity)

Data Transmission Compensated Neutron - Hardware

All data is transmitted to surface via the 3514 using the WTS telemetry scheme. – The total long space/short space counts and diagnostic curves are sent to surface via M2. – The tool commands are sent from surface to the tool via M2.

Subset Compensated Neutron - Hardware

The tool can acquire only one subset: – Subset #0: • LSN (Long space counts), • SSN (Short space counts), • W0AF (flask temperature) and • W0AP (+24V power supply).

– M2 telemetry only.

Sample Rate Compensated Neutron - Hardware

Data is typically acquired at – 4 samples/foot (13.12 samples/meter), • which is a finer resolution than the vertical bed resolution of the instrument.

– Other sample rates are available as defined by the ACT’s available within the OCT being used, these are normally 2/ft or 8/ft.

General Parameters in Eclips Compensated Neutron

Limestone Matrix

Limestone Matrix

Sandstone Matrix

Sandstone Matrix

Calibration and Verification – Module 4 Compensated Neutron

• API neutron calibration pit • 2437XB Calibrator Tank • 2446XA Rod Moderators used in the calibrator tank. • Normalized Ratio for 2446XA • Normalized Ratio for 2438XA • Primary Calibration, Primary Verification • Safety Procedures handling Neutron source. • Inserting the Radioactive Source • Extracting the Source • Emergency Removal Procedure

Compensated Neutron • The standard unit of measurement for neutron logs is the API Porosity Unit. • Test pit in Houston university. • 3 references: 1.9%, 19%, 26%.

2437XB CN Calibrator • We use a calibrator and moderator rod. • It is filled with water/propylene glycol.

2446XA Compensated Neutron



• C arrangement. • Reading depends of tool series. • Ratio SSN / LSN is 8.31 (2438XA). • Tolerance is +/- 0.15. • Corresponds to a porosity of 25.738 % API.

2435XA Compensated Neutron READ THE TOOL ANSWER

•

y y t t i i s s o o r r o o P P

Read a value for SSN/LSN with the Rods in the C arrangement.

7.9 in this case

Ratio Ratio SSN/LSN SSN/LSN

2435XA Compensated Neutron CHECKS THE RATIO IS IN TOLERANCE

•


Acceptable Ratio Range : 7.63 to 9.09

7.9 in this case


2435XA Compensated Neutron NORMALIZES THE ANSWER


•

SHIFT THE POINT

•

Determination of the multiplicative calibration factor

•

MCF = Nominal Ratio

•

Normalized ratio = tool reading * MCF

SSN / LSN Normalized Normalized ratio ratio


Primary Calibration

Primary Calibration

Primary Verification

Primary Verification

Compensated Neutron

Compensated Neutron

Compensated Neutron

Compensated Neutron

Compensated Neutron (Source Insertion)



Com ompensate pensatedd Neut utro ronn (Sour ource ourc ou rce cee Ext xtracti xtra xtrraction) actio ct ion) on) n)




Comp ompeensate nsated nsa ns ated ted Ne Neutr utron on sour s ource ce sub sid sidee doo doorr scre sc screws rews ws

P/N f091715000

Compensated Neutron source sub side door screws

P/N F097409000.

Compensated Neutron (Emergency Removal Procedure)

Order material # f091715000!

Screw damaged and can not be released? Use source-sub punch and hammer to shear screws!

Do not pry on source door !!!

Logging Operation – Module 5 Compensated Neutron

• Main Factors – Matrix – Mud Salinity – Hole Diameter – Mud Density – Mud Cake Thickness – Gas – Casing. Curves Matching Neutron and Density Scales Neutron Density curves response

OPERATION Factor affecting the log

Solution

•

Tool position :

•

A neutron Decentraliser must be used.

•

Any gaps between the formation and tool housing will cause reading error. (Higher values of porosity).

•

Exists in different sizes.

•

It has a SPECIFIC position.

Attach it where you install the tool clamp (Hex head)

Neutron Decentralizer Compensated Neutron

The decentralizer must be below or above of neutron tool, and when run with z-density, the decentralizer must be aligned with the arm of z-density tool, not confuse with the pad !!!


•

THE MATRIX :

Solution

•

Parameter : select the matrix (limestone, sandstone, dolomite).

•

the matrix contribute to the slowdown and capture of the neutron.

•

Curve is recorded in the APPARENT MATRIX POROSITY

•

Depending of the formation the reading need to be corrected

Correction

If If the the matrix matrix is is Limestone Limestone is Sandstone If the the matrix matrix is formation Sandstoneis the If porosity of the the porosity of 15 the % formation is 19 %is If the the matrix matrix is Dolomite Dolomite the porosity of the formation is 8%

For a 15 % reading


• MUD SALINITY • •

Solution •

PARAMETER section :

•

found the value of NaCl in the mud report.

•

Enter Cl- concentration calculated from chart.

Cl- capture thermal neutron very well. There could be a high content in the mud.

OPERATION Factor affecting the log •

PARAMETER section :

•

use CALIPER for correction if available

Large borehole will show a false high porosity.

•

Use FIXED Size if not caliper is run in combination or failed.

CN tool is calibrated in a 7-7/8 in hole.

•

FIXED Size = BIT SIZE.

• HOLE DIAMETER : •

•

Solution


• MUD DENSITY •

High density mud will show a slightly lower porosity.

Solution •

POST PROCESSING:

•

use environmental correction menu.

•

Most of the time negligible.

Software to use


•

MUD CAKE THICKNESS

•

Thick mud cake might show a slightly lower porosity.

Solution

•

Most of the time negligible


Solution

•

GAS

•

None, sign of a gas zone.

•

Neutron will read very low.

•

If plotted with ZDEN , this separation is known as “Negative Separation”


• CASING : •

Iron is a good neutron absorber.

•

Cement behind casing affecting counts.

Solution •

PARAMETER section :

•

Select casing correction ON and casing parameter.

•

Select Bit Size behind casing.

•

Set the expected casing thickness.

Where To Enter The Correction?

Default Default values values

Other Corrections

Affect Affect the the neutron neutron processing processing

Default Default values values

Neutrons Curves Compensated Neutron

• Raw curves

ssnr : raw short space count lsnr : raw long space count count • Computed curves

Presented

CN : compensated neutron porosity CNC : borehole size corrected CN CNCF : Field normalized CNC (made (made to to look look like like Schlumberger Schlumberger curve curve for for high high porosity) porosity)

Neutron Curves Compensated Neutron cnc nplm

cncf nphi

y t i s o r o P

+/- 25 % Ratio ss/ls

No Magic How to match neutron and density scale?

Formula of porosity

ρma - ρ bulk ma bulk φ= ρma - ρfluid ma fluid

• For limestone, limestone, Density Density curve is is presented presented from 1.95 1.95 to 2.95 2.95 g/cc g/cc • We want with the density one in water want the the neutron neutron curve to to stack stack with water..

φ

2.71 -- 2.95 1.95 = -0.4444 0.1403very veryclose closetoto45- 15 %%

=

2.71 -- 1

Few Value To Remember

Recorded in limestone matrix and presented on limestone scale

• Sandstone

read

- 4 pu lower

• dolomite

read

+ 7 pu higher

• anhydride

read

- 2 pu

• Salt

read

- 3 pu

Neutron / Density Curve Response

MOST LOGS ARE RECORDED ON LIMESTONE SCALES WITH A LIMESTONE MATRIX

Because a the CN tool is calibrated for water filled limestone, the CNC curve will read the porosity of limestone correctly

MOST LOGS ARE RECORDED ON LIMESTONE SCALES WITH A LIMESTONE MATRIX

For example: 10% porosity water filled limestone reads 10 p.u.’s 25% porosity water filled limestone reads 25 p.u.’s

HOW DOES THIS LOOK ON A LOG?

LETS LOOK AT THE CNC SCALE 45 pu 0 pu 30 pu

-15 pu

15 pu

EACH CHART DIVISION IS 3 PU’S


Limestone 10% Water Filled Limestone 20% Water Filled REMEMBER THE SCALES ARE SUCH Limestone 30%THAT THE ZDEN AND Water CNC FilledCURVES OVERLAY IN A WATER FILLED LIMESTONE

HOW DOES HYDROCARBON LOOK?

Limestone 10% Gas Filled Limestone 10% Oil Filled HYDROCARBON WILL AFFECT BOTH Limestone 10% THE CNC AND ZDEN RESPONSES Water Filled LET’S LOOK AT A 10% POROSITY LIMESTONE FORMATION

HOW DOES HYDROCARBON LOOK?

This is large negative Limestone 10% separation and indicates gas Gas Filled Limestone 10% This is known Oil Filled as negative separation Limestone 10% Water Filled

WHY DOES IT BEHAVE IN THIS WAY? Here, pore space is filled LETS HAVE A LOOK AT THE gasLOOK – CNCAT tends NOWwith LETS THE ZDEN RESPONSE FIRST towards zero p.u. CNC RESPONSE ρ=

Limestone 10% Gas Filled

(0.9 x 2.71) + (0.1 x 0) = 2.44 g/cc

Limestone 10% Oil Filled

ρ=

(0.9 x 2.71) + (0.1 x 0.8) = 2.52 g/cc

Limestone 10% Water Filled

Limestone Matrix in the pore space Limestone Oil Scales reduces the CN porosity ZDEN overlays CNC at 10 pu

WHAT ABOUT INCREASED POROSITY? AN INCREASE IN POROSITY INCREASES THE SEPERATION CAUSED BY H-C Limestone 20% 10% Gas Filled Limestone 20% 10% Oil Filled Limestone 20% 10% Water Filled

HOW DOES A SANDSTONE LOOK? LET’S BRING UP THE CORRECTION CHART FOR LITHOLOGY Sandstone 15% Gas Filled Sandstone 15% Oil Filled Sandstone 15% Water Filled

HOW DOES A SANDSTONE LOOK? 15 % WATER FILLED SANDSTONE READS 10 P.U. BY THE CNC CURVE Sandstone 15% Gas Filled Sandstone 15% Oil Filled Sandstone 15% Water Filled

15%

CNC=10 pu

HOW DOES A SANDSTONE LOOK? WATER FILLED HERE’S THE1515%PU SANDSTONE READS 10 P.U. LINE BY THE CNC CURVE Sandstone 15% Gas Filled zden = (0.85 x 2.65) + (0.15 x 1) = 2.4 g/cc

Sandstone 15% Oil Filled

Sandstone 15% Water Filled

HOW DOES A SANDSTONE LOOK?

Sandstone 15% Gas Filled Sandstone 15% Oil Filled Sandstone 15% Water Filled

THE 2.5 CHART DIVISION SEPERATION IS A TYPICAL WATER FILLED SANDSTONE RESPONSE ON LIMESTONE MATRIX/SCALES

HOW DOES A SANDSTONE LOOK?


2.25 g/cc

2.37 g/cc

2.4 g/cc

WHAT ABOUT OTHER FORMATIONS?

Salt

2.08 g/cc

SHALE Anhydrite Dolomite 15% Water Filled

Salt: Zden = 2.08 g/cc Cnc = -3 pu

-3 pu


2.08 g/cc

Salt SHALE Anhydrite Dolomite 15% Water Filled

High

-3 pu 2.3-2.7 g/cc

Shale: Zden = 2.3 -2.7 g/cc Cnc = High


2.08 g/cc

Salt SHALE

High

-3 pu 2.3-2.7 g/cc

Anhydrite Dolomite 15% Water Filled

•Positive separation •High water content


2.08 g/cc


-3 pu 2.3-2.7 g/cc

High 2.98 g/cc

Anhydrite: Zden = 2.98 g/cc Cnc = -2 p.u.

-2 pu


2.08 g/cc


-3 pu 2.3-2.7 g/cc

High 2.98 g/cc

•Type of evaporite •Hence very dense

-2 pu

WHAT ABOUT OTHER FORMATIONS? FOR DOLOMITE LET’S BRING UP THE CORRECTION CHART FOR LITHOLOGY AGAIN 2.08 g/cc


High 2.98 g/cc

-3 pu 2.3-2.7 g/cc -2 pu

WHAT ABOUT OTHER FORMATIONS? 15 % WATER FILLED DOLOMITE READS 22 P.U. BY THE CNC CURVE 2.08 g/cc

Salt SHALE

High

-3 pu 2.3-2.7 g/cc -2 pu

2.98 g/cc

Anhydrite 15% Dolomite 15% Water Filled

CNC=22 pu


2.08 g/cc

Salt SHALE

High

-3 pu

15% Dolomite: Zden = 2.58 g/cc 2.3-2.7 g/cc Cnc = 22 p.u.

Anhydrite

2.98 g/cc

Dolomite 15% Water Filled

22 pu

-2 pu

2.58 g/cc


2.08 g/cc

Salt SHALE

High

-3 pu

Coal (Anthracite): Zden = 1.6 g/cc 2.3-2.7 g/cc Cnc = 46 p.u.

Anhydrite

2.98 g/cc

Dolomite 15% Water Filled

22 pu

-2 pu

2.58 g/cc


LETS LOOK AT THE CNC SCALE 60 pu 15 pu 45 pu

30 pu

EACH CHART DIVISION IS 3 PU’S

0 pu



OTHER LITHOLOGIES?

SHALE Dolomite 15% Water Filled Limestone 15% Water Filled Sandstone 15% Water Filled

Using the Lithology Correction Chart

OTHER LITHOLOGIES?

SHALE Dolomite 15% Water Filled Limestone 15% Water Filled Sandstone 15% Water Filled

8 cd’s +ve separation 2.5 cd’s +ve separation

Cnc-zden Crossplots

Cnc-Zden crossplots are used to determine two important factors: 1. Lithology 2. Porosity They can also give an indication to how much shale is in the formation

Cnc-zden Crossplots

For Lithology, three lines are drawn on the crossplot relating to: Sandstone Limestone Dolomite

Sandstone Limestone Dolomite

Cnc-zden Crossplots

For Lithology, three lines are drawn on the crossplot relating to: Where the CN vs ZDEN points plot indicates the type of lithology, or combination of lithologies


Cnc-zden Crossplots

Gas or light hydrocarbon pushes the points up


H-C effect Shale effect

Shale pulls the points down:

Compensated Neutron(1)

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