Well Logging Summary

8/12/2019 Well Logging Summary

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WELL LOGGING

is a continuous record of measurement madeWell login bore hole respond to variation in some physicalproperties of rocks through which the bore hole is drilled.

the study of rock properties and theirIsPetrophysicsinteractions with fluids (gases, liquid hydrocarbons, and

aqueous solutions). Study occurred on core samples.

is the process of usingformation evaluationbore hole measurements to evaluate the characteristicsof subsurface formation

Types of well

1) Vertical

Drilled to aspecific target

Measured Depth = True Vertical depth


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2)Deviated

usually from a platform or

from land to near offshore

Measured depth has to be converted to true

vertical depth

3) Horizontal Drilled to maximize production or minimize problems

such as coning.

Types of boreholes

According to Casing operation

Cased holes

Wireline has developed instruments that can takeformation measurements without interference from the

casing and cement


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the equipment needed for wireline logging consists of thefollowing:-

Up-hole instruments:- (Logging Unit and Rig)

A logging unit :- and an instrument for takingmeasurements. For land rigs, the unit is mounted on a

truck

The unit has a winch and an electrical wireline cable

Down- hole instruments:- (Sondes and cables)The Downhole logging instrument :- called a sonde, is

attached to the end of the cable. The unit also includesequipment to power the sonde and to make a permanent

record of the logSonde normally consists of two main parts:

Sensor: It is an electronically complicated part used forpicking the required property

Cartridge: Surrounding the sensor in the modern tools

and do three functions: * Powering the sensor to be

ON/OFF . * Processing the acquired data (First step of

processing). * Data transmission along cables to the up-

hole instruments.

Open holes

Open hole logs to determine:

Thickness (h) : measured by tool depth-

Porosity (F) : measured by porosity/density tools--Saturation (Sw) : computed from a combination of

porosity, density/lithology & resistivity tool.

According to conductivity of the borehole

Conductive (water base drilling mud)


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Non-conductive boreholes (oil base mud, air drilled orcased holes)

(Radius of investigation) : TheDepth of investigation

distance away from the bore hole that a logging toolcan measure .

: the minimum thicknessVertical resolution

formation that can be distinguished by a tool under

operating conditions).

Depth of investigation and vertical resolution of the

log can vary from millimeters to a few meters.

Ways to check your logs

Calibrations-

-Repeat sections

-Trends and Marker bedsOffset well comparison-


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Resistivities:

Rt - Resistivity of the formation in the virgin zone, ohm-

m

Rxo - Resistivity of the flushed zone, ohm-m

Rm - Resistivity of the mud, ohm-m

Rmc - Resistivity of the mudcake, ohm-m

Rw - Resistivity of 100% formation water, ohm-m

Rmf - Resistivity of 100% mud filtrate , ohm-m

Saturations:

Sxo -Mud filtrate saturation in the flushed zone, %

Sw - Water saturation in the virgin zone, fraction of pore

volume in, %

Diameters:

dh - Diameter of the hole, m

di - Diameter of the flushed zone, m

Dri - Diameter of the flushed and transition zonestogether, m

Thicknesses:

h -Height of the bed being logged , m

hmc - Thickness of the mudcake, m

Well logging tools

. Mechanical tools Caliper log Lithology tools Spontaneous potential log

Gamma Ray log

Resistivity tools MSFL LLS LLD

Porosity tools Density log & LDT Neutron log &

APS Neutron- Density Combination Sonic log


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a-Caliper

A caliper log is a well logging tool that provides a continuous

measurement of the size and shape of a borehole along its depth

The measurements that are recorded can be an important indicator

of cave ins or shale swelling in the borehole.

Indicator of good permeability and porosity zones (reservoir rock)

due to development of mudcake in association with gamma ray log.


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Sp logSP log was

one of the earliest electric logs used in oil industry

SP log is

used to identify impermeable zones such as shale, and

permeable zones such as sand, as well as several otheruses

The SP logis a record of DC voltage differences between the

naturally occurring potential of a movable electrode in

the well bore and the potential of the fixed electrode

located at the surface


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It measured

in millivolts

Electric

currents arising primarily from electrochemical factors

within the bore hole create the SP log response.

Theseelectro chemical factors are brought about by differences

in salinities between mud filtrate (Rmf) and theformation water resistivity (Rw), within permeable bed

Because a

conductive fluid is needed in the bore hole for the SP logto operate, it can't be used in non-conductive (oil based)drilling muds

SP log isused to-detect permeable bed

-detect boundaries of permeable beds

-determine formation water resistivity RW

determine the volume of shale in permeable beds


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GrGamma ray

logs measure natural radioactivity in formations and sand

stones and carbonates have low concentration ofradioactive material. And give low gamma ray readings.

As shale content increase, the gamma ray log responseincrease because of the concentration of radioactive

material in shale.Units :API &PPM.

May beused in calculation of volume of shale

IGR= (GRlog-GRmin)/(GRmax-Grmin)


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Resistivity

Resistivity logs

are electric logs which are used toDetermine HC versus water bearing zones

Because the

rocks matrix or grains are non-conductive the ability ofthe rock to transit a current is almost entirely a function

of water in the bores

Hydrocarbons,like the rocks matrix, are non-conductive;therefore, as the hydrocarbon saturation of the boresincrease, the rock's resistivity also increases.

Unit is "ohm.m"

A geologist, by

knowing a formation's water resistivity (RW), itsporosity (PHI), and a value for cementation exponent

(m), can determine a formation water saturation (SW)from the Archie equation


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Two basics types of logs which are used to measure the formation

resistivity are;

- Induction log

- Electrode log


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Sonic

The sonic log is a porosity log that measures

interval transit time (t) of a compressional sound

wave traveling through one foot of formation.

The sonic log device consists of one or more sound

transmitters and two or more receivers.

Interval transit time (t) in microseconds per footis

the reciprocal of the velocity of a compressional

sound wave in feet per second.


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When time increase the saturation of fluids in rock

increase.

The interval transit time is dependent up on both

lithology and porosity. There for, a formation's

matrix velocity must be known to derive sonic

porosity either by chart or by formula

Phisonic = ((t)log-(t)ma) / ((t)f -(t) ma).


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Neutron

Neutron log is a porosity log that Measures the

hydrogen ions concentration in a formation

Unit MeV or eV "million electron volt"

In clean formations where the porosity is filled

with water or oil, the neutron log measures the

liquid-filled porosity.

Neutrons are created from a chemical source in

the neutron logging tool. The chemical source

may be a mixture ofamericium and beryllium

which will continuously emit neutrons. The

neutrons collide with nuclei of formation's

material result in losing some of its energy.

Because the hydrogen atom is almost equal in

mass to the neutron, maximum energy loss occurs

when neutron collide with hydrogen atom. So, the

maximum amount of energy loss is a function ofhydrogen concentration because hydrogen in a

porous formation, so the energy loss can be

related to the formation's porosity.


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Density

Bulk density increase whit decrease prosity& Porous

rock density increases with increasing water saturation

(compared to dry rock)

The formation density log is a porosity log that measures

electron density of formation.

It can assist the geologist to :1. identify the evaporate minerals

2.Detect gas bearing zone

3.Determine HC density

4.Evaluate shaly-sand reservoir and complex lithology.


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The density logging device consists of a medium energy

gamma ray source that emits gamma rays into a formation.

The gamma ray source is either Cobalt-60 or Cesium-137.

Gamma ray collides with electrons in the formation the

collisions result in a loss of energy from the gamma ray

particle.

Scattered gamma rays - which reach the detector located a

fixed distance from the gamma ray source - are counted as

an indicator of formation density.

The of Compton scattering collisions is a direct function of

the of electrons in a formation (electron density).

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Well Logging Summary