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Core Inspection Why? Cores offer the best idea of the formation next to the reservoir. They also help correlate the open hole logs, giving valuable guidance on pay identification, formation strength, permeability, fluid type, bed tilt, reworking, etc. 8/25/2015 1 George E. King Engineering GEKEngineering.com

Core Inspection

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Page 1: Core Inspection

Core Inspection

• Why? Cores offer the best idea of the formation next to the reservoir.

• They also help correlate the open hole logs, giving valuable guidance on pay identification, formation strength, permeability, fluid type, bed tilt, reworking, etc.

8/25/2015 1 George E. King Engineering

GEKEngineering.com

Page 2: Core Inspection

Pay Zone and Cores

• BHP – 4990 psi

• Perm – 200 – 700 md

• Porosity – 26%

• Oil – 36 API

• Cloud Pt – 70 F

What does the formation really look like?

Where are the permeability streaks, barriers, lithology changes, permeability variance and weak zones?

From which zones is the produced fluid likely to flow?

What core is missing?

What does the log really tell you?

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Page 3: Core Inspection

H145

H150

H160

TOPS.TOPS

GR

GAPI0 150

AO90

OHMM0.2 200

2950

2975

3000

DE

PT

HM

ET

RE

S

RHO8

G/C31.95 2.95

HTNP

V/V0.45 -0.15

Log Responses – Pay Zone Identification

Take your logs along and correlate them with the logs. Get a Geologist’s comments as well to help understand the rock.

Correlating the log with the core makes the log “come alive” if you can visually identify the types of rock that correspond to the log readings and understand how each rock type will eventually influence completion or production.

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Page 4: Core Inspection

Pay Zone Variance – What would oil stains in some of the core indicate?

• BHP – 5000 psi

• Perm – Clean sand 100 – 1000 md mixed with claystone

• Porosity – 25%

• Oil – 36 API

• Cloud Pt – 68 F

And: Bed tilt to well deviation? Mineralogy changes and barriers? Kh and Kv differences? Soft or reactive zones? Reworking? Minerals like salts, anhydrite, calcite? Natural fractures?

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Page 5: Core Inspection

Mineralogy of Sands

CALCULATED WHOLE ROCK COMPOSITION RELATIVE CLAY ABUNDANCE

(Weight %) Normalized to 100%

Dolomite / Total Mixed-Layer

Quartz Plagioclase K-Feldspar Calcite Fe-Dolomite Siderite Pyrite Clay Illite Kaolinite Chlorite Illite/Smectite *

Core

Core 1 88.77 2.10 2.13 0.27 0.00 0.25 1.08 5.40 49.63 18.47 20.40 11.50

Core 2 88.9 2.4 2.1 0.0 0.1 0.3 0.8 5.4 48.1 17.6 18.8 15.5

Core 3 85.2 3.4 2.4 0.0 0.0 1.2 0.5 7.4 42.7 19.8 20.7 16.8

Core 5 -145 81.6 4.5 2.2 0.0 0.0 2.5 0.5 8.7 46.3 18.0 20.3 15.5

Core 5-150 86.3 3.3 2.1 0.0 0.0 0.8 1.2 6.3 41.3 26.3 20.9 11.5

Cores with similar mineralogy may have sharply different permeabilities. The difference is in depositional energy, reworking, tectonic forces that create fractures, water flow that creates cementation and/or mineral growths in the pores, etc.

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Page 6: Core Inspection

SEM Photos are needed in high clay wells – Just a gross mineralogy analysis may be very misleading

SEMs (scanning electron microscope) photos are needed to determine clay location and type. Clay are most problematic when they occupy the pores (authogenic), rather than just emdedded in the matrix (detridal). The form of the clay may also be very important – clays have a million times more surface area than the rock in authogenic form and can be very reactive to specific liquids.

The kaolinite on the left is in a weathered form, and reactivity may range from highly reactive to near totally inert.

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Page 7: Core Inspection

SEM Photomicrographs – Near Unconsolidated Sands

The strength of the rock depends on the extent and stability of the cementation between the grains.

Cementation types include: calcite, quartz overgrowth, clay, heavy oil, cohesion by oil phase and some precipitated minerals.

The level of cementation can be significantly affected by presence (or absence) of pore water, mineral forming reactions, reworking, arching of upper formations (overburden presence or absence), pressure development, etc.

Core testing is very helpful in understanding the rock, but care is

needed to get representative samples.

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Page 8: Core Inspection

Lessons from core

• Take the log – see what the rock looks like for the various log readings.

• See how the core changes: the location of the barriers, channels, fractures and mineralogy variance.

• What is missing from the recovered core? Why?

• Oil stains, bedding planes, tilt, mineral streaks, layered and laminated core….

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