log types

Log Types

• A general explanation of log types, their uses and potential problem areas.

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48/6-2 True Vertical Depth Sub Sea

8/25/2015 1 George E. King Engineering

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Cased Hole – Fluid Composition

Capacitance, Fluid Di-elect. Fluid type - hydrocarbon vs. water.

Fluid Resistivity Fluid type - hydrocarbon vs. salt water.

Pulsed Neutron Capture 3-phase ID in well, req. homogeneous formation

Gradiomanometers Fluid type - oil and water, looses resolution in high deviation,

limited in high rate and high oil cut.

Fluid Density Fluid type- oil vs. water, better in high GLR.

Temperature Fluid entry (zones/leaks) rate/temp limits.

Noise Leak/zone entry. Channel flow behind pipe, depending on

rate.

Fluid Level Survey Fluid level only, confused by foams, froths and emulsions.

Spinners Total flow rates and entry/exit points. Deviated wells are a

challenge.

Radioactive Tracer Tool Total flow rates and entry/exit points. Not useful in deviated

wells.

Oxygen Activation Velocity of water phase. Holdup and leak detection. 8/25/2015 2 George E. King Engineering

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Cased Hole – Casing/Cement Inspection

Caliper Log Accuracy depends on number of

fingers, speed, tool type. Casing Inspection

Eddy Current Inner wall investigation. Shows some

smaller flaws, measures ID Casing Inspection

Flux Leakage Casing body inspection. Id of inner /

outer wall, and body casing

problems, not in OBM

Casing Inspection

Ultrasonic Casing body inspection. Affected by

fluids, used in thicker wall pipe

(>0.2”)

Casing Inspection

Electromagnetic Phase Shift Casing body inspection. ID and wall

thickness, averaging tool may

miss small defects

Casing Inspection

Conventional Acoustic Cement presence. Averaged data, not

really useful for most problem

identification

Cement Evaluation

Segmented Acoustic Channels, Bond. 360o, channels and

voids, bond under right

conditions.

Cement Evaluation

Ultrasonic Casing and Cement bond. 360o,

channels, voids, bond, pipe

conditions w/ right application.

Cement Evaluation


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Cased Hole – Correlation/Evaluation

Gamma Ray Lithology and correlation

Inexpensive. No porosity.

Correlation

Neutron log – single detector Lithology and correlation

Inexpensive. No porosity.

Correlation

Neutron log – dual detector Porosity. RA source needed,

accuracy less than OH log.

Formation

Evaluation

Acoustic Porosity. Limited in cased wells,

requires good bonds for accuracy

Formation

Evaluation

Pulsed Neutron Capture

PNC

Water saturation. Does not work in

low or changing salinity, or low

porosity

Formation

Evaluation

Pulsed Neutron

Spectrometry PNS C/O

Water saturation. Does not work

well in low porosity

Formation

Evaluation

Cased Hole Resistivity Water Saturation. Salinity

dependent, stationary reading,

relative deep reading

Formation

Evaluation 8/25/2015 4

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Locating a Tubing Leak

• High resolution temp tool shows leak by friction heating (high rate leak)

• PLT w/RST waterflow logging tool. Intro trace chemical into the annulus and read with tool.

• Pony tail (frayed nylon rope) on a WL cutter tool (moderate rate leak)

• Run and set a plug going down the well and pressure test above plug until leak is located

• Run downhole camera – inject liquid into annulus & watch for entry into tbg.

• Plug tubing at bottom and fill tbg w/ water. Displace with gas and locate top of liquid. If gas N/A, then use a pump down dart.


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Problem or Information Needed

Rec. Logging Tools

Procedure/Level of Detail

Detection of Crossflow or Underground Blow out

Temperature Survey

Difference in slope of temperature gradient – will detect flow rates down to 25 BPD if liquid and temperatures of fluids are different. Figures on temperature vs. flow distance help estimate water flow in the annulus.

Noise Log

Best performance of noise logs is with gas flow. Gas flow to about 10 actual ft3/D (Note – not standard ft3/day). At very low gas flow rates (q<400 actual ft3/D), gas flow can be estimated from millivolts of noise between the 200-Hz and 600-Hz frequencies: q = 0.35 (N200 – N600). Where q is the actual gas flow in ft3 and N = noise log cut at that frequency.

Oxygen Activation Survey

Open hole or channels behind single string. Accuracy is sharply reduced for investigating channels behind two strings (use temp or noise tools).

Detection of Crossflow


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Rec. Logging Tools

Procedure / Level of Detail

Location of Cement Top

Temperature Survey

OK if run within 12 to 24 hrs of cement job. Little temperature variation with the formation may make cement top difficult to see.

CBL (cement bond log)

Best results after 3 days or when cement has developed 70%+ of the compressive strength. These tools may be too large for slim hole wells.

Gravel-pack logging (GR)

Tool response depends on density difference between cement and annular fluid.

Location of Cement Top


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Rec. Logging Tools


Evaluation of Cement Placement

Open hole caliper

Accuracy depends on caliper and hole roughness and washouts. Caliper tools with more than 4 arms are needed for hole volume measurement accuracy.

Sweeps with markers after running casing

Sweeps give decent estimates of hole volume, but sweeps may not reach all of the annular space in uncentralized cased holes. Useful for swept hole % analysis.

Temperature Survey

OK if run within 12 to 24 hrs of cement job. Little temperature variation with the formation may make cement top difficult to see.

Gravel Pack Log

Good if fluid density difference greater than 0.3 gm/cc (0.13 lb/bbl). Could run before and after cement for background data.

CBL – both regular and segmented

Semi-quantitative contact measurement of pipe/cement and cement/formation. Affected by casing pressure and tool calibration.

Evaluation of Cement Placement and Bond


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Problem or Information

Needed

Rec. Logging Tools


Detection of casing wear from drilling

E-line calipers

Multi-arm calipers generally good, but slick line calipers may rotate and “over-report” the bad spots.

EM – eddy current tool that measures wall thickness

Highly accurate if the hole is filled with a non conductive fluid.

Acoustic wall thickness

tool

Qualitative indicators of wear (thickness numbers are not very accurate)

Casing Inspection


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Needed

Rec. Logging Tools

Level of Detail

Detect casing collapse

EM – eddy current wall thickness survey

Investigation is to 8 to 10” radius. Investigation ability falls off after the first string encountered. Qualitative investigation. Splits are more difficult to see.

Gravel-pack (GR – density)

Depth of investigation depends on source strength – may range from 4” to 16”. Splits are more difficult to see.

Determination of External Casing Corrosion


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Needed

Rec. Logging Tools


Annular Flow

Temperature Survey

Useful where the well has active annular flow. Can spot flows on the order of 1 bpd (after 24 hrs) if temperature of formation at measurement and source of water is sufficiently different. Two surveys, 12 hrs apart is usually adequate to spot presence of a channel.

OA - oxygen activation

Accurate, but don’t swap out muds. Migration of fluids in pipe may be seen as “channel”.

Noise logging

Accuracy depends on channel variations to accelerate flow and change sound.

Flow Behind Pipe


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Needed

Rec. Logging Tools


Determine annular flow in injector

RA Tracer Survey - inject slug of I-131 in brine.

Track from surface to annulus until slug is completely pumped away. Track any flow that goes behind pipe and moves up.

OA- oxygen activation survey

Not as reliable as the chemical tracer, due to fluctuations in the injection rate.

Temperature survey

Three temperature surveys are needed: one before annular injection (base line), one during and one 4 to 6 hours after injection (decay).

Borax Log

Pumping borax/water solution down tbg into the liner, allowing mix to invade perfs & any channels in casing/formation annuli. Initial pass, before borate injection, is w/ Pulsed Neutron log (no Borax), followed by passes at 20bbls, 40bbls, and 60bbls as borax mix pumped. Borax affects neutron capture, leaving a characteristic signature. Overlays of the Sigma/CNL counts reveal the zones of borax penetration, and identifies channels taking fluid.

Determination of Flow Behind Pipe for Injector


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Rec. Logging Tools


Certification for annular disposal

Radioactive Tracer Survey with RA isotope in brine, pumped into annulus while logging with a GR tool in tubing.

Can distinguish entry points and limited detail on up or down movement of the inject slug.

Oxygen activation survey

Not as accurate as RA logging. Fluctuations in rate create problems.

Temperature survey

Can determine channels and entry points. Needs 3 runs – before, during and after.

Borax Log


Location of Annular Leak


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Needed

Rec. Logging Tools


Location of leak to annulus or crossflow behind pipe

Temperature survey

Relatively accurate at rates of at 1 bpd or more. Need minimum of 2 runs, before and during injection. A third run may help define a qualitative level of leak rate. Run at 1oF/in sensitivity. Will not see small gas leak rates through liquid.

Noise log

Best for gas leak detection. Run static log and then again during flow or negative test. Upward gas movement (percolation) at actual 10 ft3/D or more should be detectable.

Oxygen activation log

Can detect flows of 20 to 40 bpd in the annulus of a single string well if the leak is directly opposite the tool. Resolution drops to >200 bpd when two strings are present

Borax Log


Location of Source of Annular Leak


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Quick View - Openhole Logging

• Principally a formation evaluation service – Performed before setting casing or liner

– Several tools can be run simultaneously

• Two distinct types of application for openhole CT deployed logging: – In highly deviated and horizontal wellbores

• toolstring can no longer be lowered into well by gravity

– Special applications in vertical wellbores


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Openhole Logging Tools –Quick View

– Gamma ray • lithology identification and correlation

– Dual induction • measures formation resistivity

– Litho density • measures porosity and identifies lithology

– Compensated neutron • measures porosity and identifies lithology

• locates gas and fluid contacts

– Borehole seismic • recovers seismic data


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Openhole Logging Tools - Quick View

– Sonic measurement • measures acoustic velocity for porosity

• identifies lithology

– Stratigraphic • identifies bed orientation, fracture location, hole direction and

geometry

– Rock sampling • provides side wall cores

– Fluid sampling • retrieves fluid samples under reservoir conditions

• estimates permeability


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SP

• One of the oldest and simplest logs

• Measures voltage between formations and the fluid in the wellbore. Potential differences arise due to the difference s between salinity of the formation and the wellbore fluids.

• SP is used for qualitative permeability, reservoir quality evaluation, Rw calculations and zone shaliness estimation.

• Check Rmf value and correct for formation temperature to determine if SP deflections really are a valid indicator of permeability.


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Gamma Ray Tool (Basically a Geiger Counter)

• Uses a scintillation crystal and a photomultiplier tube to measure naturally occurring and artificially induced gamma-ray radiation.

• The gamma-ray radiation is a signature of the formations in a well – very useful in depth control. Used in open hole or pipe

• Also used to spot changes in radiation (NORM scale) and radioactive tracers.

• GR is sensitive to logging speed and factors/statistics that govern radioactive decay.

• Used as one measurement of shaliness, correlation tool for stacked beds and in shales, seal/barrier location, id of organic rich zones, gross and net reservoir thicknesses.


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No porosity logs


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Capacitance Tool

• Measures the fluids capacitance – uses the wellbore fluid as the fluid between plates of a capacitor.

– Determine water entry points

– Identify static fluid interfaces

– Assists production logs


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Resistivity

• Measures resistance difference between formation and wellbore fluids to various depths in the formation.

• The shallowest measurements are indicative of severely invaded zone and the deepest measurements are most reflective of actual formation fluids.


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Resistivity (continued)

• Generally the rock matrix is not conductive, so the resistance of the fluids in the pore space are reflective of invasion.

• Used to establish qualitative permeability, correlate markers, and determine water and hydrocarbon bearing zones.


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ML - Microlog

• A special resistivity tool that measures the resistivity of the mud cake on one curve and the resistivity of the fluids in the formation, but near the wellbore, on a different curve.

• Separation between the curves is an indication of permeability since mud cake builds on permeable zones.

• Tight zones usually show high resistivity readings.


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Density Tool

• Measures electron density of the formation. A Co60 or Cs137 source bombards the formation with gamma-rays. A higher degree of Compton scattering on return is associated with higher density formations.

• Used for porosity estimation, density measurement, lithology determination, indication of gas bearing zones (effect of free gas on density shows a higher porosity / lower density reading than when the formation is wet).


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Density Tool (continued)

• Readout is displayed as bulk density (g/cc) and density porosity (%).

• The porosity reported is a derivation based on departure from an assumed matrix density.

• The pad readouts are very sensitive to hole roughness. Check hole for roughness as part of log Q/C. Tool reads high porosity / low density when pad does not contact the formation. Density variances also cause log readout problems.


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Sonic

• A sonic log measures the interval travel time (delta t) of compression sound waves moving through one foot of a formation (milliseconds/ft). If matrix velocity is known, porosity can be calculated since sound waves travel slower in porous media (travel slower in less dense materials such as fluids).

• Sonic logs are used for porosity determination, pressure determination in shale, as a correlation log, and a gas detector.


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Neutron Tools

• Source emits neutrons into the formation. Neutrons interact with hydrogen nuclei resulting in an energy loss that is converted to neutron porosity. All hydrogen bearing materials (water, oil, gas) contain hydrogen, but the formation usually does not.

• Amount of hydrogen affects reading, so gas filled porosity creates a lower porosity than oil or water filled porosity.


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Neutron Tools (continued)

• The porosity is calculated based on an assumed matrix density. Variances in density and fluid type alter reading accuracy.

• Used for lithology when compared with other logs (density, PE and GR). Also a measure of shaliness. Useful to spot gas (dry vs. wet). Correlation log, porosity evaluation, qualitative measurement of of reservoir depletion (gas pressure affects readings).


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Compensated Neutron

• Radioactive neutron source bombards the formation with high energy neutrons. The high energy neutrons are slowed and captured by atoms of the formation. The low energy neutrons are reflected back to the tool and counted. The amount of neutrons returning is inversely proportional to the porosity of the formation.


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Compensated Neutron

– Locate gas-liquid and evaluate

– Locate hydrocarbon bearing zone

– Determine lithology

– Structural analysis


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Pulsed Neutron Decay

• A neutron source – measures interactions with the elements in the formation.

– Basis of carbon-oxygen logs

– Monitors fluid contacts

– Can be run through casing


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PE – Photoelectric Log

• A direct measurement of values present in formations. Under ideal conditions the PE can be read off the log and compared to tables to determine the mineralogy.

• Bad hole conditions, heavy muds, thick mud cake, barium from drilling fluid additives and multiple formation types (stacked pays) can confuse the PE.


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Caliper (Open Hole)

• Measures the roughness or the rugosity of the borehole wall.

• One to four arm calipers are available. Multi arm calipers give an impression of the shape of the wellbore.

• Used for roughness measurement, gauging washouts, hole “gauge”, diameters for hole volume calculations, establishing mud cake thickness (qualitative permeability), identification of sloughing formations (washouts).


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Multi-sensor caliper (cased hole)

• Multi-arm feeler – gauges the shape and smoothness of the casing id.

– Corrosion and pit detection

– Pipe collapse and deformation

– Pipe wear


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Collar Locator

• A simple magnetic field that measures a disturbance of thicker (or thinner) metal mass moving through the field.

– Typical use is collar location

– Can see profiles

– Locates packers and hangers

– Locates tubing crossovers

– Can see some corrosion problems

– Can see some perforations


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Cement Bond Tool

• Transmitter-receiver tool measures the signal received back from a segment. Helps assess cement presence and bond to the formation and the pipe.


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Temperature Tool

• A recording of the wellbore temperature. – Identify fluid entry or exit

– Gas channeling

– Tubular leaks

– Hydraulic frac height

– Cement top

– Fluid levels

– Differential temperature curve


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Down Hole Static Temperature Varies with

Depth - Effect of the Geothermal Gradient

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Temperature, F

De

pth

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"cellar effect - temperature normally cools from surface

temperature to about 100 ft below surface, then temperature

begins to increase with increasing depth. Watch for

anomolies.

This response is about 2.1oF per 100

ft


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Temperature log – Saaman Well – Trinidad. Leak at packer using annular injection after base line at same rate.


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Gradiomanometer

• Measures the differential pressure of a 24” column of fluid – calculates the fluid density.

– Determine gas or liquid entry points

– Identify static fluid interfaces

– Determine exact depth of fluid density change

– Assist production logs


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Flow meter

• Measures fluids moving past the tool. Moving fluids turn the spinner

– To determine fluid entry or exit points

– Evaluate perforations

– Evaluate cross-flow occurrence

– Helps evaluate completion design


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Tension Measurement Device

• A component of the tool string that records the tension during logging in various parts of the wellbore. Helps spot increased drag and break free points (tool jumps) that may signal poor logging tool records.

• Used for quality control on logs, as an indicator of depleted zones (fluid loss sticking), dog-legs, location of sticking (above or below tool when compared with a surface record).


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Logging Behind Casing

• Key Elements:

– Understand the condition of the casing

– Understand the connection of casing to the formation – cement bond.

– Inclination, diameter, geometry


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Information Sought Logging Tools Used

Casing Condition USIT, Multi-arm Calipers, Sonic Calipers, Downhole TV

Cement Condition Cement Bond Logs (sonic)

Saturation Resistivity Tools (CH), C/O Logs, Reservior Saturation Tools, DSS

Lithology Gamma Ray, Density, Neutron, Sonic

Porosity Resistivity Tools (CH), Porosity (CH), CNL, Dipole Shear Sonic

Formation Strength Dipole Shear Sonic,

Oil Resistivity, Casing Wall Coring Tools,

Gas Neutron and Sonic Tools

By-passed Pay Resistivity, O/C Logs,

Pressure Casing Wall Coring Tools

Partial List of Information Sought and Cased Hole Logging Tools


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Channel Detection Behind Pipe

• Channel logging, with borax solution injection, is accomplished by pumping the solution down the tubing into the liner, allowing the mix to infiltrate the perforations and any channels in the casing formation annuli.

• The initial pass, before borate injection, is made with a thru-tubing Pulsed Neutron logging (or memory neutron) base pass (no Borax), followed by subsequent passes at 20bbls, 40bbls, and 60bbls as the borax solution is pumped away.

• The borax affects neutron capture, leaving a characteristic signature. Overlays of the Sigma/CNL counts reveal the zones of borax penetration, and identify the channels taking fluid.


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Alaska CTD well with good cement isolation over a shale zone


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Comparison of a memory CNL and PNL method. A channel is apparent in the pre and post squeeze logging tracks.

In some cases, the borax logging technique is sufficiently robust to complement or replace temperature logging when looking for behind the pipe channels. (SPE 25383 for Borax logging)

The technique has not been used widely outside Alaska, due to the problems in making the “Borax Brew” and keeping it hot to avoid precipitation of the Borax at colder temperatures (<100degf).

The Borax needs to be mixed at a near critical saturation in order to give the best result. Typically this is 7lb/bbl Borax Pent hydrate and 7lb/bbl NaCl.

Gamma Ray

GAPI0 100

TVD Depth

FEET8950 8850

9500

9600

9700

9800

9900

10000

10100

10200

DEPTHFEET

Po

st-

Sq

ue

eze

Pe

rfo

ratio

ns

MCNL Seawater Near Counts

0 10000

MCNL Borax Near Cts

0 9200

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-Sq

ue

eze

Pe

rfo

ratio

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MCNL Seawater Near Counts

0 10000

MCNL Borax Near Cts

0 8500

RST Seawater Form. Sigma

CU35 0

RST Borax Form. Sigma

CU35 0

Post-SqueezeMemory CNL

Pre-SqueezeMemory CNL

Pre-SqueezeCoil/E-line RST

Horizontal Well C-35A

Channel Detection using Memory CNL

Source- Alaska PE manual 8/25/2015 51

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fluid level survey fluid

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