well logging mind build-up

Quantitative Well Log Analysis

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Intro to Logging Tools

• Gamma Ray Tool ( GRT )

• Compensated Sonic Tool ( CST )

• Litho Density Tool ( LDT )

• Compensated Neutron Tool ( CNT )

• Phased Induction Tool (ILM, ILD - PIT)

• Spherical Focused Log (SFL –PIT)

• Spontaneous Potential (PIT)

Gamma Ray

• Counts natural Gamma Ray emits by formation

• Tool measurements are counts per second (cps)

• Convert to API :

Secondper CountsRay GammaGR

UnitsAPIRay GammaGR

: Where

)(

cps

API

BackgroundMeascpsMeasJig

APIValueJigGRGR cpsAPI

Compensated Sonic

• Measures the delta-T of a compressional sound wave through the formation.

• Delta-T Formulation :

R2

R1

T1

T2

4

)24()13( TTTTTTTTT

TT1

TT2

TT4

TT3

TT1

TT2

TT3

TT4

3ft

2ft

3ft

Litho Density

• Cs 137 (2 curie) radioactive source emits medium-energy gamma rays (662 Kev) into the formation.

• These GR interact (collide) with the electrons of the atoms in the formation and loses some of its energy to the electron, known as Compton Scattering.

• The number of Compton-scattering collisions is related directly to the number of electrons in the formation, and determined essentially by the electron density.

• Electron density is related to the true bulk density, b , which,

depends on the density of the rock matrix material and fluids filling the pores

Litho Density

• In addition to the bulk density measurement, b, the tool also measures the photoelectric absorption index of the formation, Pe.

• The Pe can be related to lithology.

• The b measurement responds primarily to porosity and secondarily to rock matrix and pore fluid.

• The Pe responds primarily to rock matrix (lithology) and secondarily to

porosity and pore fluid.

Litho Density

• Source ( Cesium-137 ) emits Gamma Ray to formation

• 3 Ways G-ray interact with matters in formation : – Photoelectric ( to calculate PEF )

– Compton Scattering ( to calculate RHOB )

– Pair Production

SS

LS

Source

Compensated Neutron

• Fast neutrons(16 curie) emitted from a radioactive source in the sonde.

• Neutrons interact with the nuclei of the formation through Nuclear Scattering (Inelastic & Elastic), Capture.

• Each collision ,the neutron loses some energy.

• During the Elastic Collision, the greater energy loss occurs when the neutron strikes a nucleus of practically equal mass, i.e. a hydrogen nucleus.

• The large hydrogen concentration surrounding the neutron source, the most of the neutrons are slowed and captured within a short distance of the source.

• Accordingly, the counting rate at the detector increases for decreased hydrogen concentration and vice versa.

Compensated Neutron

Phased Induction

• The induction tool generates a 20 kHz magnetic field around the tool by passing an alternating current (AC) into a transmitter coil array.

• The alternating magnetic field induces an alternating voltage and current in formation which is 90° out phase with original transmitter current. The strength of formation current will depend on the formation conductivity.

• The alternating magnetic field (X) associate with the 90° formation current (R) induces another alternating voltage and current in receiver coil array which is 180° out of phase with original transmitter current.

Spherical Focused Log

• The SFL sending current out the A0 electrode and returning to the tool body.

• Focusing is accomplished by sending a bucking current IB from A0 to A1.

• In the bucking system, two monitor electrodes, M1 and M2 are used to measure the potential drop in the borehole.

• If there is a voltage present between these electrodes, the IB current is boosted to compensate until the M1-M2 voltage is driven to zero.

M1 = M2

• The voltage between M0 (B) and M1M2 (C) is measured and is used as the reference voltage.

𝑅𝑠𝑓𝑙 =𝑘(𝑉𝐵 − 𝑉𝐶)

𝐼0

(M1,M2) Bucking Current Monitoring electrode

(M1,M2) Bucking Current Monitoring electrode

(A1) Bucking Current Return electrode

(A1) Bucking Current Return electrode

(M0) Monitoring electrode (M0) Monitoring electrode

(A0) Current electrode (A0) Current electrode

Spontaneous Potential

• Potential difference recorded between electrode in current depth and a ground electrode

• SP source is the solutions of formation water and mud salinity differences in porous formation

• SP deflection : – if Rmf > Rw , SP (-)

– if Rmf < Rw , SP (+)

– If Rmf = Rw , no SP deflection

WELL LOG ANALYSIS AND

INTERPRETATION

WELL LOG ANALYSIS AND

INTERPRETATION

Well : mywell-26

Interpretation Goals

• Porosity Effective (Phie)

• Water Saturation (Sw)

• Lithology

Well header completion, Define formations

Well header completion, Define formations Data Preparation Data Preparation

Editing & Correction Editing & Correction

Zone Screening Zone Screening

Petrophysics Petrophysics

Pay Summary Pay Summary

Well header contains all important parameters for next process, i.e. mud properties, tool specs, well info etc.

Each formation will process in different way and parameters while its spesific lithology are difference

Data Check Data Check





Log Patching

Log Patching

Log patching Log patching

Shale baseline shift (SP) Shale baseline shift (SP)

Some logs in casing are invalid and must be removed to prevent intruding in analysis. So do with another invalid logs interval caused by tool error or else.






Shale baseline shift

Shale baseline shift

Log patching Log patching

Shale baseline shift (SP) Shale baseline shift (SP)

To get SP log in ideal scale by theory, it must be regulated where on shale interval, SP reading is zero.






Zone Screening

Zone Screening

• Zones must be defined as far as the physical properties changed in formation, i.e. the salinity, formation factors(a,m,n), type of shale, etc.






Petrophysics Process • Steps in petrophysical analysis : 1. V clay 2. Clay point 3. Lithology 4. Porosity 5. Water resistivity 6. Water saturation • Cross-plot logs that mostly used for guidance :

1. Density - Neutron 2. G Ray - Rwa

Petrophysics Process • Steps in petrophysical analysis : 1. V clay 2. Clay point 3. Lithology 4. Porosity 5. Water resistivity 6. Water saturation • Cross-plot logs that mostly used for guidance :

1. Density - Neutron 2. G Ray - Rwa

V Clay V Clay

Clay Point Clay Point

Porosity Porosity

Water Resistivity Water Resistivity

Water Saturation Water Saturation

Lithology Lithology





V clay Determination

• In most cases, this can be done by using GR as clay indicator :

Cross-plot Gamma-ray vs. Rwa

V clay Determination

• In most cases, this can be done by using GR as clay indicator :

Cross-plot Gamma-ray vs. Rwa

V Clay V Clay


Porosity Porosity




Lithology Lithology





Clay point

• Clay density in dry and wet must be defined for input in matrix correction

• This can be done by using cross-plot, most user use Density-Neutron as shown below :

Clay point

• Clay density in dry and wet must be defined for input in matrix correction

• This can be done by using cross-plot, most user use Density-Neutron as shown below :

V Clay V Clay


Porosity Porosity



𝑅ℎ𝑜𝑏 = 𝑅ℎ𝑜𝑓. 𝑃ℎ𝑖𝑡 + 1 − 𝑃ℎ𝑖𝑡 . 𝑹𝒉𝒐𝒅𝒓𝒚𝒄𝒍𝒂𝒚


Lithology Lithology





Lithology

• Lithology volume calculation :

VCL_CPX + VSND_CPX + VSILT_CPX + PHIE_CPX = 1.0

Lithology

• Lithology volume calculation :

VCL_CPX + VSND_CPX + VSILT_CPX + PHIE_CPX = 1.0

V Clay V Clay


Porosity Porosity




Lithology Lithology





Porosity With SSS(silt sand shale) Model, porosity is computed as follow : PHIE = (RHOB - Vclay * ( RHOBcl - RHOMA) - RHOMA) / (RHOF - RHOMA) RhoBcl : from clay point determination Rhof : assume 1 G/CC Rhoma : as its lithology ( sandstone = 2.65 G/CC )

Porosity With SSS(silt sand shale) Model, porosity is computed as follow : PHIE = (RHOB - Vclay * ( RHOBcl - RHOMA) - RHOMA) / (RHOF - RHOMA) RhoBcl : from clay point determination Rhof : assume 1 G/CC Rhoma : as its lithology ( sandstone = 2.65 G/CC )

V Clay V Clay


Porosity Porosity




Lithology Lithology





Water Resistivity Rw is proportional with salinity given by client With salinity 4000 PPM , Rw is about 0.643

Water Resistivity Rw is proportional with salinity given by client With salinity 4000 PPM , Rw is about 0.643

V Clay V Clay


Porosity Porosity




Lithology Lithology





Water Saturation Sw computed using Indonesian equation : Assume Rt=ILD Rcl = ILD at adjacent Shale Rw, a=1, m=2, n=2 are input from client

Water Saturation Sw computed using Indonesian equation : Assume Rt=ILD Rcl = ILD at adjacent Shale Rw, a=1, m=2, n=2 are input from client

V Clay V Clay


Porosity Porosity




Lithology Lithology





Result

Result

V Clay V Clay



Sw Sw Porosity Porosity Lithology Lithology

Porosity Porosity



Lithology Lithology

Pay Summary

Hydrocarbon volume report :

Pay Summary

Hydrocarbon volume report :

Data Preparation Data Preparation



Cross Plot Cross Plot


Net Reservoir Net Pay

Vclay Cutoff PHIE Cutoff SWE Cutoff

Zone 5 40.0% 10.0% 65.0%

RESERVOIR PAY PAY AVE PAY AVE PAY AVE

WELL

NAME FORMATION FROM TO INTERVAL INTERVAL VCL PHIE SWE

FT FT FT FT % % %

Mywell-26 Zone 5

[Rumput Laut] 3662.0 3764.5 86.0 21.0 13.219 22.409 54.381

TOTAL 86.0 21.0 13.219 22.409 54.381

Pay Summary

Pay Summary

Data Preparation Data Preparation



Cross Plot Cross Plot


Net Pay

Gross Pay

Gross Pay

Thank You

Thank You

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