intro - logging.ppt

Introduction to Well Logging

2 Intro to Well Logging Restored

Basic Well Logging Tools Lithology Tools

– Spontaneous Potential– Gamma Ray

Fluids Identification Tools– Resistivity

Laterolog Induction

Petrophysical Tools– Porosity

Neutron Density Sonic

Auxiliary Tools– Caliper


Caliper

The Caliper log is a continuos measure of the actual borehole diameter

Shows the condition of the well over the footage where other tools are being run (Washouts, bridges)

Caliper is also used to calculate the volume of cement needed behind the casing

Open hole log will give Volume of the wellbore


Spontaneous Potential - SP

Measures the electrical potential in the formation caused by the salinity difference between the drilling mud and the formation water

Generally an indicator of permeability Generally mimics the GR curve



SP:– Membrane Potential -

Em

– Liquid Junction Potential - Ej

“The SP cannot be recorded in holes with nonconductive muds”



If Rmf > Rw – Shales will have a low SP

and clean sandstones will have a higher SP.

If Rmf < Rw – Shales will have a high

SP and clean sandstones will have a lower SP.

If Rmf = Rw – Little SP will be

developed and the SP log will have very little character.



Shaliness indicator – SPshale = -10 mV – SPsand = -40 mV – SPlog = SP reading from

the log = -25 mV – The percentage of shale

will be : SPlog - SPshale / SPsand

- SPshale =

– 15/-30 = .5 or 50% shale Fresh and saltwater interface Correlation


SP Log Response

Shale

Imperviousnonshale

Imperviousnonshale

Reservoirbed

Reservoirbed

Shale

SP


SP LogGRC

0 150

SPCMV-160 40

ACAL6 16

ILDC0.2 200

SNC0.2 200

MLLCF0.2 200

RHOC1.95 2.95

CNLLC0.45 -0.15

DTus/f150 50

001) BONANZA 1

10700

10800

10900

SPLog


Gamma RayGamma Ray Tools detect the naturally occurring radiation within the rock

Radioactive elements tend to concentrate in clays and shales

Potassium (K)Uranium (U)Thorium (Th)


Gamma Ray In sedimentary formations,

the GR log reflects the clay or shale content

Clean formations, such as sandstones or limestones, usually have a very low level of radioactivity

In general, the lower the Gamma Ray reading, the cleaner the sand

Gamma Ray logs can be run in cased holes, but the data will be suppressed


Example GR LogGRC

0 150

SPCMV-160 40

ACAL 6 16

ILDC 0.2 200

SNC 0.2 200

MLLCF 0.2 200

RHOC 1.95 2.95

CNLLC 0.45 -0.15

DTus/f150 50

001) BONANZA 1

10700

10800

10900

GRLog


Resistivity Tools

Induction Tools– Run in nonconductive or low-conductivity muds– Dual Induction - DIL: Is the earlier version of induction

tool which read a Shallow (SFL) and deep measurement– Phasor Induction - DIT-E: Is an enhanced Induction tool

giving Shallow, Medium, and Deep measurements– Array Induction - AIT: Is the newer generation of

Induction tools giving 5 curves with set depths of investigation: 10” (shallow), 20”, 30”, 60”, 90”.

Laterolog Tools– Run in highly conductive muds (salt based)– HRLA


Resistivity

Resistivity of the salt water is low (highly conductive) Resistivity of the Oil is high

(Poor conductor)


Resistivity

Dry, nonmetallic minerals (rock matrix) have a very high resistivity


Resistivity

The resistivity of a rock is a measurement of the resistivity of the rock matrix as well as the resistivity of the fluid within the porous volume of the rock.


Induction


Borehole Effects

on Resistivity

Logs


Resistivity Profiles

Depth of Investigation:– Logging tools are designed to

measure resistivity at different depths radially from the wellbore to determine the resistivity of the flushed zone and the virgin zone.

– Flushed zone - is closest to the wellbore and has been invaded by drilling fluids (original fluids have been flushed out).

– Virgin zone - is farthest from the wellbore and has not been invaded by drilling fluids. Clients will want to use Virgin zone measurements


Invasion

Resistivity profile is the radial distribution of resisitivity resulting from the invasion of fluids having different conductivity than the formation fluids.

Resistivity Profiles can tell a client about permeability on a qualitative level.


Laterolog

Laterolog Principle: – Measuring the

voltage difference between two electrodes is the fundamental idea behind laterolog devices.


Example Log With ResistivityGRC 0 150

SPCMV-160 40

ACAL 6 16

ILDC 0.2 200

SNC 0.2 200

MLLCF 0.2 200

RHOC 1.95 2.95

CNLLC 0.45 -0.15

DTus/f150 50

001) BONANZA 1

10700

10800

10900

ResistivityLog


Porosity

Porosity Tools Density Neutron Sonic Magnetic

Resonance


Density 1 / Porosity

Density

Measuring the number of gamma rays and their energy levels at a given distance from the source, the electron density of the formation can be predicted


Bulk Density

Matrix Fluids

fmab 1


Porosity From Density Log

Porosity equation

The fluid density equation

xohxomff S1S

fma

bma


Bulk Density LogGRC 0 150

SPCMV-160 40

ACAL 6 16

ILDC 0.2 200

SNC 0.2 200

MLLCF 0.2 200

RHOC 1.95 2.95

CNLLC 0.45 -0.15

DTus/f150 50

001) BONANZA 1

10700

10800

10900

Bulk DensityLog


Example Solution Density Log GRC 0 150

SPCMV-160 40

ACAL 6 16

ILDC 0.2 200

SNC 0.2 200

MLLCF 0.2 200

RHOC 1.95 2.95

DPHISSdec0.45 -0.15

DTus/f150 50

001) BONANZA 1

10700

10800

10900

DPHI


Neutron

Neutron tools emit high energy neutrons from either a chemical source or a neutron generator device (minitron) and measure the response of these neutrons as they interact with the formation


Neutron

Hydrogen is the most effective element in the slowing down (elastic scattering) process of the Neutron


Density - Neutron

GAS EFFECT– In sedimentary rocks the

presence of gas causes low readings of porosity for the neutron tool and causes high values for the density tool

– This Crossover is called Gas Effect and is colored in red on the log

– The actual porosity is determined by crossplotting the Density porosity vs. the Neutron porosity in a chart book

*Sonic is not significantly affected by gas

This is why 2 different porosity tools are run at once


Example Compensated Neutron LogGRC 0 150

SPCMV-160 40

ACAL 6 16

ILDC 0.2 200

SNC 0.2 200

MLLCF 0.2 200

RHOC 1.95 2.95

CNLLC 0.45 -0.15

DTus/f150 50

001) BONANZA 1

10700

10800

10900

NeutronLog


Sonic Sonic Tools are based on

the measurement of the velocity and amplitudes of the sonic body waves in the Rocks

Applications:– Mechanical properties :

Rock strength, Earth stress

Rock Mechanical Properties

Rock failure mechanisms– Formation evaluation – Cement bond logging


Sonic - Formation Evaluation

The speed of sound depends

principally upon the rock

matrix material and the

porosity.

The measurement of

compressional and shear wave

slowness can help us estimate:

– Primary porosity

– Lithology

– Presence of natural gas

Gas Gas Effect in Effect in Sonic Sonic LogLog


Sonic Log

The response can be written as follows:

fmalog t1tt

maf

ma

tt

tt

log


Sonic LogGRC 0 150

SPCMV-160 40

ACAL 6 16

ILDC 0.2 200

SNC 0.2 200

MLLCF 0.2 200

RHOC 1.95 2.95

CNLLC 0.45 -0.15

DTus/f150 50

001) BONANZA 1

10700

10800

10900

SonicLog


Example Solution Sonic Log GRC 0 150

SPCMV-160 40

ACAL 6 16

ILDC 0.2 200

SNC 0.2 200

MLLCF 0.2 200

CNLLC 0.45 -0.15

RHOC 1.95 2.95

DTus/f150 50

SPHISSdec0.45 -0.15

001) BONANZA 1

10700

10800

10900

SPHI


tm

wnw

R

RaS

Formation Water Resistivity


Determining Rw

Directly– From measured water sample– This is the most accurate Rw reading

Indirectly– From openhole well logs

SP logs Pickett plots Rwa technique


Rw Using the Rwa Technique

tm

wa RR


Mechanical Properties from Logs

From sonic data the mechanical

properties of the rock can be

calculated giving a continuous stress

and mechanical properties profile, but

it needs to be calibrated with external,

data either from core test or DataFRAC

Dipole Sonic is an Array tool which

gives Mechanical Properties. Geoquest

will process the data and create a

FracHite log and Mechanical Properties.


Sonic - CBL Cement Bond

Logging

– Cement bond logs (CBL) are used to evaluate the quality of the cement that was put in place during the well completion process

– An Amplitude gives a quantitative reading and the VDL (Variable Density Log) shows the quality of the bond


CMR - Combinable Magnetic Resonance

CMR Gives information on:– Grain size and distribution– Permeability– Free-fluid porosity– Bound-fluid porosity

Helps client determine how much water will actually flow out of the formation, and how much is irreducible


CMR

T2 Distribution

MDT Perm plotted on topof CMR Perm


FMI

By wrapping the log we can envision the wellbore

Faults and fractures can be

traced on the log Thin laminations can

be seen in the images

intro - logging.ppt

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