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Well Logging

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Practical definition of a log

Log is an indirect measurement of formation

properties exposed by the wellbore acquired

by lowering a device or a combination of

devices in the well bore.

Oldest and most used methods that depends

on the geophysical properties of rocks.

Good when surface outcrops are not available.

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Seismic can be used to determine the

subsurface structure but a direct sample ofthe rock is needed to be sure of the lithology.

The most practical way is to drill a well and

record all the useful information possible froma core.

Continuous core recovery is far too expensive

and is not done except when great detail isneeded.

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Objectives

To give an insight in the basic well logging

methods used to derive petrophysical

properties for hydrocarbon exploration

Well logs provide continuous, in situ

measurements of parameters related to

porosity, lithology, presence of

hydrocarbons, and other related rockproperties of interest

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Well Logging History The first electrical log was introduced in 1927 in France.

The first commercial electrical resistivity tool in 1929 was

used in Venezuela, USA and Indonesia.

SP was run along with resistivity first time in 1931

Schlumberger developed the first continuous recording in

1931

GR and Neutron logs was started in 1941

Microresistivity array dipmeter and lateralog were first

time introduced in 1950s

The first induction tool was used in 1956 followed by

Formation tester in 1957, Fomation Density in 1960s,

Electromagnetic tool in 1978 and most of Imaging logs

were developed in 1980s

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Well in Pechelbronn - France Surface Recording Instrument

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Purpose of Well Logging

Are there any hydrocarbons? Oil? Gas?

Where are the hydrocarbons?

How much of the hydrocarbons is

contained in the formation?

How producible are the hydrocarbons?

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Uses of Well Logging

Detect presence of hydrocarbons - Gas, oil or water

Estimation of total reserves

Estimation of productive zones

Zone correlation

Isopach mapping

Defining physical rock properties:

Lithology

Porosity

Pore geometry

Permeability

Determination of depth and thickness of zones

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Correlation with seismic data

Structural and sedimentological studies

Formation boundaries and stratigraphiccorrelation

Quantitative fluid saturation

Reservoir modelling Reservoir monitoring

Uses of Well Logging

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1. Rock type

The basic concentration during the

interpretation of well logs is the rock type

or Lithology. It could be either, Sandstone

Limestone

Shale (unconventional)

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2. Fluids

a. What are the fluid type

Water

Oil

Gas

b. Saturation

Water saturated, oil saturated, gas saturated

c. Pressure

Fluid pressure

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ROCK PROPERTIES

Porosity

Permeability

Lithology / Mineralogy

Density Velocity

Pore Fluids (Water, Gas, Oil) / Pore Fluid Ratio

Thickness and Depth of the Formation Fracture

Temperature

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Types of Logs

Lithological logs Porosity logs Fluid indicator logs

Gamma ray Sonic Resistivity

SP Neutron Induction

Litho-density Density

Neutron-density

Calliper logs for bore-hole properties

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Wireline Logging Logging while Drilling