Basic Logging Introduction Overview

Introduction to Basic Logging1.1- Introduction to Basic Logging

Introduction to Basic Logging

Introduction to Basic Logging


Contents

1- Overview2- Classical Reservoirs3- The Logging Process4- Fundamentals of Log Interpretations

- Porosity- water Saturation- Permeability- The Invasion process

5- Vertical Resolution


OverviewWhat you should know

•Basic hydrocarbon geologyWhat you will learn

•What logging means•Different measurements we make•Understanding of log analysis•And how we use them•Simple log analysis

Tools you need

•Calculator or Excel•Ruler and pencil


Contents





Classical Reservoirs

Anticline Pinch-out

Angular UnconformityFault TrapSalt Dome


GASGAS

OILOIL

WATERWATER

ShaleSandstone

Drilling Rigs

Salt

ShaleSandstone

Salt

ShaleSandstone

GasOilWater

sandstonesandstonepinch outpinch out

Mudstone

Oil and Gas Wells


Contents





The LoggingProcess


Cased hole logging

CasingCement

Perforation & Production logging

Early

life o

f a w

ell

Open hole logging


Why we log ?• Lithology (reservoir rock?)• Resistivity (HC,water,both?)• Porosity (how much HC?)• What type of HC

• Formation mech. properties• Permeability / cap pressure• Shape of the structure• Geological information• Geothermal• Unconventional applications


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Cond

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Tool-1Tool-2Tool-3Tool-4

What does logging mean?



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Tool string is moving at a certain logging speed, and data are recorded at certain intervals called sampling rate.

MovingUp



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MovingUp


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MovingUp



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7016And we get a group of wiggly lines called a “log”

And we get a group of wiggly lines called a “log”


MovingUp


First well logs recorded in 1927


Modern logs have more measurements but the principle is the same

Gamma Ray (GR)

0 (GAPI) 150

SP (SP)

0 (MV) 200

FXND

50 (PU) 0

1:220 Ft Pad

-180 180

Rt from HALS

RX18

1 1000

1 1000

Rt from AITH

1 (OHMM) 1000

Mud Resistivity from HALS

1 1000

Mud Resistivity from AITH

1 (OHMM) 1000

AHTPR

5.007.75

12.0118.6228.8544.7269.81

107.43166.51258.08400.00

90 0 90

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Gamma Ray (GR)

0 (GAPI) 150

SP (SP)

0 (MV) 200

FXND

50 (PU) 0

1:220 Ft Pad

-180 180

Rt from HALS

RX18

1 1000

1 1000

Rt from AITH

1 (OHMM) 1000


1 1000


1 (OHMM) 1000

AHTPR

5.007.75

12.0118.6228.8544.7269.81

107.43166.51258.08400.00

90 0 90

1700

Gamma Ray (GR)

0 (GAPI) 150

SP (SP)

0 (MV) 200

FXND

50 (PU) 0

1:220 Ft Pad

-180 180

Rt from HALS

RX18

1 1000

1 1000

Rt from AITH

1 (OHMM) 1000


1 1000


1 (OHMM) 1000

AHTPR

5.007.75

12.0118.6228.8544.7269.81

107.43166.51258.08400.00

90 0 90

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1600

Some times a large group of log curves are grouped and color coded into an “Image”.More on this later

Shading is often added to make the log curves easier to read.


The Early Years—1912–1927

1912: Conrad conceives the idea for electrical measurements

1919: Marcel joins his brother–first work in Normandy

1921: Office opens in Paris, rue Saint–Dominique

1927: First electrical downhole log in Pechelbronn, France


Logging Truck


Maxis (MCM) acquisition system

Winch man

Wireline Engineer Acquisition Equipment

Wireline cable todownhole toolsCable drum

Unit EngineClient (“Witness”)


Logging Tools


Standard Logging String (Triple Combo)

Formation Gamma RayNeutron PorosityDensity (Porosity)Caliper (hole size)Pad Resistivity (good v.resolution)Resistivity (good depth investigation)Spontaneous PotentialMud Resistivity


Open Hole Measurements :

• Wireline Logging.• LWD (Logging While Drilling)• Logging on Drill Pipe (TLC)

Open Hole Measurements :

• Wireline Logging.• LWD (Logging While Drilling)• Logging on Drill Pipe (TLC)


Multiwell Plots


Contents





Fundamentals of Quantitative Log Interpretation

Log Interpretation is the process by which logging measurements are translated into the desired petrophysical parameters (porosity, hydrocarbon saturation, permeability, producibility, lithology etc)

Objective of a Well

H= Constant . φ . (1−Sw ) . h . Α

whereH = initial oil in place

φ = effective porosity (How do we measure Porosity? )

Sw = initial water saturation (how do you get Sw ? )

h = productive interval

A = drainage area


Porosity - Definition


A rock can be made up of small grains or large grains but have the same porosityPorosity depends on grain packing, not the grain size

Porosity (Continued)


Primary (Original) Porosity

Developed at deposition

Typified byIntergranular sandstonesIntercrystalline, oolitic carbonates

Usually more uniform than induced porosity


Secondary (Induced) Porosity

Developed by geologic process occurring after deposition

Typified by Fracture development in some shales and carbonates Vugs and solution cavities in limestones and dolomites


Pore-Space Classification

Total porosity, φt =

Effective porosity, φe =

VolumeBulkSpacePoreTotal

VolumeBulkSpacePorectedInterconne


Comparison of Total and Effective Porosities

Very clean sandstones : φt = φe

Poorly to moderately well -cemented intergranular materials: φt ≈ φe

Highly cemented materials and most carbonates: φe< φt


SaturationThe saturation of a formation represents the amount of a given fluid present in the

pore space.

The porosity logs react to the pore space.The resistivity logs react to the fluids in the pore space.The combination of the two measurements gives the saturation

Matrix

water

oil

Sw = S w irr + Sw "free"

So = S oresidual + So"free"


Saturation Definitions – how do we obtain Sw?

HydrocarbonWater

Matrix

Φ.SwΦ. (1-Sw)

(1- Φ)

Φ. Sw = amount of water per unit volume

Φ. (1-Sw) =amount of hydrocarbon per unit volume


Archie’s EquationArchie’s Equation

n

t

mw

wR

RaS =Water saturation, fraction

wSResistivity of formation water, Ω-mwR

Resistivity of uninvaded formation, Ω-m

tRPorosity, fraction

Empirical constant (usually near unity) a

Saturation exponent (also usually near 2)

n Cementation exponent (usually near 2)

m


PermeabilityPermeability is a measure of the ease with which fluids can flow through a formation.

Note: To be permeable, a rock must have some interconnected pores, capillaries, or fractures. Hence, there exists some rough relationship between porosity and permeability. Greater permeability, in general, corresponds to greater porosity, but this is not an absolute rule.

Shale and some sands have high porosity but the grains are small that the paths available for the movement of fluid are quite restricted and tortuous; thus their permeabilities may be very low.

Limestone may be composed of a dense rock broken by a few small fractures of great extent. The porosity can be low but the permeability of a fracture can be enormous.


The Invasion process


Invasion


InvasionInvasion


Contents





Volume of measurement

Sampling rateDepth of investigationVertical resolution


Volume of measurement – vertical resolutionSpike response function

90% of response

FWHM(Full Width at Half Maximum)

Good vertical resolution Poor vertical resolution

FWHM used for statistical measurements, 90% point used for instantaneous measurements


Volume of measurementvertical resolution+ sampling rate

Coarse sampling rate

Fine sampling rate


Good VR

Poor VR

Real Signature

Enhanced VROf poor VR measurement


SP

GR

GR has better vertical resolution compared with SP

Basic Logging Introduction Overview

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