SPECIAL PETROPHYSICAL TOOLS: NMR AND IMAGE LOGS CORE...

Image Logs

SPECIAL PETROPHYSICAL TOOLS: NMR AND IMAGE

LOGS CORE

LEARNING OBJECTIVES

By the end of this lesson, you will be able to:

Identify the types of image logs and technology used

Identify the application of image logs for geological andpetrophysical data

Integrate the image data with core and other log data toreconstruct depositional models

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Special Petrophysical Tools: NMR and Image Logs Core

© PetroSkills, LLC., 2016. All rights reserved._____________________________________________________________________________________________

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FORMATION IMAGING TOOLS – APPLICATIONS

Structural dip

Paleocurrent direction

Thin bed analysis

Textural information (graded beds, bioturbation)

Fracture detection, analysis

Fault identification, characterization

Directional surveys, operational monitoring

In-situ stress estimation (breakout)

BOREHOLE IMAGES

Borehole images are electronic pictures of the rocks and fluids encountered in a wellbore.

Types are electrical, acoustic or video devices.

Images are oriented; they have vertical and lateral resolution.

Case studies show they are best used in conjunction with other wellbore data (logs, cuttings ,cores and production data).

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© PetroSkills, LLC., 2016. All rights reserved.

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ELECTRICAL BOREHOLE IMAGES

Based on dipmeter technology. The tools have microresitivity electrodes arranged around the wellbore that are pressed against the wall.

Trend from a few electrodes to an array of multiple pads.

Data acquisition: tools run in with pads closed; then 4,6 or 8 pads are pressed against the borehole wall.

Electrical current is forced into the rock and sensors measure the current interacting with the formation.

DIPMETERS

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FORMATION IMAGING TOOL MNEMONICS

SLB=Schlumberger HALS=Halliburton BA=Baker Atlas BPB=(now Weatherford)

Formation Imaging Tools –Resistivity Imaging Tools

Higher resolution than acoustic tools (1 cm)

Coverage of the borehole depends on hole size and tool type

Oil-based mud special problem (resistive muds)

Resistivity measurements are not calibrated

SPECIAL TOOLS

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ELECTRICAL IMAGES: DATA ACQUISITION

Raw data includes electrode readings, caliper and x-, y-, and z-axis accelerometer and magnetometer readings.

Borehole deviation and pad 1 tool orientation are determined form the magnetometers.

Sample rate is very high (120 samples per foot) resulting in large digital file size.

Areal coverage is a function of tool of width and number of pads. In general 40 to 80% of the borehole face is imaged.

Depth of investigation is small (less than an inch). Drilling mud must be conductive!

SPECIAL TOOLS – BOREHOLE IMAGING

Formation Imaging ToolsFormation Microscanner (Schlumberger)

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ACOUSTIC IMAGING TOOLS (TELEVIEWERS)

Tools are centralized in the well and a rotating transducer emits and records sound waves.

Acoustic amplitude and travel time are recorded and processed into images.

Tools must be in center of well so that reflections strike and return at correct reflection angle.

CBIL tool rotates at 6 revs/s and sample rate is 250 samples per rotation.

VR is 0.3in at logging speed of 1200ft/hr; can be run in oil based muds.

SPECIAL TOOLS – BOREHOLE IMAGING

Formation Imaging Tools –Acoustic Imaging Tools

Resolution lower than resistivity tools (3 cm)

360 coverage of the borehole.

Can be run in oil or water-based mud.

Provides a calibrated amplitude and travel time measurement.

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IMAGING: STATIC AND DYNAMIC NORMALIZATION

Static Normalization Color scale normalized over entire

processed interval.

Identical colors anywhere on imagerepresent same resistivity levels andreflect major changes in lithology / fluid composition.

Dynamic Normalization Colors determined using mean and

variance of a histogram of short(2-3 ft.) interval.

Colors can only be compared over short distances.

Small-scale features enhanced; not picked up on the static images.

Dynamic normalization enhances the contrast of the image, highlightingfine-scale sedimentary features such as cross-bedding or pebbles

IMAGE LOGS

Static vs. Dynamic Image Normalization

STATIC NORMALIZATION

DYNAMICNORMALIZATION

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STATIC VS. DYNAMIC IMAGE NORMALIZATION

STATIC VS. DYNAMIC IMAGE NORMALIZATION

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LWD IMAGES – RESISTIVITY – DISCRETE FRACTURE

APPLICATIONS: FRACTURE IDENTIFICATION

Open Fracture

An open fracture appears as a low resistivity feature that cuts or crosses through the bedding planes.

The fracture is considered ‘open’ and is filled with the low resistivity drilling mud creating the dark sinusoid on the image.

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TURNING RESISTIVITY CHANGES INTO DIP DATA

12 3

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567

81 2 3 4 5 6 7 8

APPLICATIONS: FRACTURE IDENTIFICATION

Healed Fractures Fracture filled with highly resistive material - calcite

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APPLICATIONS: STRUCTURAL INTERPRETATION

Structural Images can identify faults, folds, and

other structural features.

These features enable the geologist to understand the structural environment in great detail.

The example illustrates a fault plane intersecting the wellbore, with vertical displacement of the sediments.

Courtesy of Weatherford

APPLICATIONS: STRATIGRAPHIC INTERPRETATION

Stratigraphy Images can identify cross-

bedding, channels, ripples, and other stratigraphic features.

These features enable the geologist to understand the depositional environment, enabling description of reservoir geometry and production characteristics.

Cross-bedded sandstone

Soft sediment slump/collapse structure

Series of ripple small ripple beds


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APPLICATIONS: POROSITY / LITHOLOGY

Porosity / Lithology Images can help identify

lithology changes, and “see” certain types of secondary porosity, including vugs, casts, and micro-fractures.

Large vugs (individual pores) are clearly visible on the image

APPLICATIONS: THIN BED ANALYSIS

Thin-Bed Images can help identify and

quantify the amount of reservoir rock within thinly laminated sand-shale intervals.

Laminated sand-shale sequence

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APPLICATIONS: DEPTH AND ORIENTATION OF CORES

Core Depth / Orientation Log section intersects a high

angle strike-slip fault showing the NW-SE strike and evidence of the fault breccia and slip planes.

The photo is of a core splinter taken across the zone and confirms the image interpretation. Horizontal bedding can be seen on the face of the splinter and broken fractured breccia on the outside.

Breccia

Fault plane

BOREHOLE BREAKOUT

Breakout


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CALIBRATION OF BHI TO CORE: KEY STEPS

Ideally, any BHI should be calibrated to core.

Lithology, reservoir properties can be correlated to image attributes.

Sedimentological features visible on the cores identified on corresponding BHIs.

Calibrated image facies scheme extended to uncored intervals and, ultimately, to nearby wells.

Fracture properties (aperture, clay smearing), small scale diagenetic effects can be calibrated directly.

BHI TO CORE REALITIES

Image logs can replace cores to some extent.

Image logs are more continuous, faster and easier to acquire.

Core recovery is not optimal in unconsolidated sands.

Coring often induces hole problems and can jeopardize other well objectives.

Coring is more costly (x10), has greater risks.

Sidewall cores may be useful to confirm BHI analysis where continuous core not available

BUT, a continuous core is required for BHI calibration

AND, BHI does not give Φ, k, “m”, “n”, etc.

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DEP. ENVIRONMENT ANALYSIS WITH BHI

The knowledge of depositional environment in the subsurface enables better understanding of: Depositional history of a sedimentary basin

Spatial relationships of particular facies (e.g., source rocks, reservoirs and seals)

Geometry of reservoir bodies, essential for static reservoir modeling

Internal heterogeneities of reservoirs, and the associated variations in permeability anisotropy

Variations in reservoir properties (e.g., grain size, porosity, permeability and diagenesis)

BHI ENVIRONMENTAL RECONSTRUCTION

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INTEGRATED CORE – FMI LOG INTERPRETATION, ESTUARY DEPOSITS, MIDDLE EAST

Multiple stacked reservoir sandstones

Problem: Prediction of the size, shape and trend of the individual sand bodies to aid field

development

>700 ft of conventional core is available together with FMI log

Interpretation of FMI is complicated by the presence of multipleoil/water contacts

4700-5867.5 ft(4700-1788 m)

WAVE DOMINATED ESTUARY

Alluvial Valley

DeltaDistributary Channels

Coastal Plain

ShallowMarineShelf

Central Basin

L3L8

L7Bay

Mouth Bar

L5

L6

Delta Front

L4L2

Carb. Buildup

L1

Interpretation based on conventional cores

DIAGRAMMATIC RECONSTRUCTION OF DEPOSITIONAL ENVIRONMENTS

Coastal Plain

Central Basin

Delta Front

Delta Distributary Channels

Alluvial Valley

Carbonate Buildup

Shallow Marine Shelf

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Note discrepancy between CMD and MD. This is common and must be accounted for.

5620‘(1712.9m)

5619‘(1712.7m)

5618 '(1712.4m)

O/W Contact

LITHOFACIES 1: CROSS BEDDED ALLUVIAL VALLEY SANDS

High angle cross bedding in fluvial channel sands. Note FMI color change at O/W Contact (5625.2′; 1714.5m).

LITHOFACIES 1: CROSS BEDDED ALLUVIAL VALLEY SANDS

1713.6m

1713.9m

1714.2m

1714.5m

1714.8m

1715.1m

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No Core

The base of the channel at 5736.3′ (17.48m) is flat and rests on underlying shales. Overlying fluvial channel sands are cross bedded (moderate to high angle). Occasional intervals of low angle cross bedding occur in the sands (5725.5′; 1745m). The channel top is marked by a thin shale interval (yellow) that represents an episode of fine grained sediment deposition caused by avulsion of the channel complex.

LITHOFACIES 1: ALLUVIAL VALLEY, COMPLETE CHANNEL SEQUENCE

1744.9m

1746.5m

1748.1m

Distributary channel sands are cross bedded and contain scattered rip-up clasts of shale (5553′ – 5554′; 1692.5m – 1692.9m). A scour feature occurs within this channel (5555′ - 5556′; 1693.2m – 1693.5m).

LITHOFACIES 2: DELTA DISTRIBUTARY CHANNEL

1692.2m

1692.5m

1692.8m

1693.2m

1693.5m

1693.8m

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5046’(1438 m)

5175’(1577 m)

LITHOFACIES 2: DISTRIBUTARY CHANNEL

Rooted and burrowed shales of the swamp environment (5568.0′–5577.2′; 1697m–1699.9m) occur above laminated shales and low angle cross bedded sands of the estuary bay environment. The thin sand beds probably originated as distal crevasse splay deposits.

LITHOFACIES 3: POORLY DRAINED SWAMP ON ESTUARY BAY

1697.7m

1698.3m

1698.9m

1699.6m

1700m

1700.8m

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5578‘(1700.2m)

5579‘(1700.5m)

LITHOFACIES 3: POORLY DRAINED SWAMP ON ESTUARY BAY

This lithofacies is characterized by conformable cross bedding that represents the preservation of low angle bar forms by capping shales. Delta front sands contain scattered shale clasts.

LITHOFACIES 4: DELTA FRONT SANDS AND SHALES

1641.9m

1642.3m

1642.6m

1642.9m

1643.2m

1643.5m

1643.8m

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5390‘(1642.9m)

5391‘(1643m)

LITHOFACIES 4: DELTA FRONT SANDS AND SHALES

Laminated shales with sand-filled burrows. Burrow intensity increases upwards. The shale laminations dip at very low angles (<5 degrees). The basal shales grade downward into delta front deposits (contact at 5372.9′; 1637.7m) and drape over low angle bar forms reflecting the surface morphology of underlying delta front deposits.

LITHOFACIES 5: CENTRAL BASIN SHALES

1636.5m

1636.8m

1637.1m

1637.4m

1637.7m

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5371‘(1637.1m)

Alluvial Valley


Coastal Plain

ShallowM arineShelf

Central Basin

L3L8

L7Bay

M outh Bar

L5

L6

Delta Front

L4L2

Carb. Buildup

L1

LITHOFACIES 5: CENTRAL BASIN SHALES

Coarsening upwards sequence, consisting of shales that grade upwards into sands. The sands are burrowed. Some low angle cross bedding is preserved.

LITHOFACIES 6: BAY MOUTH BAR SANDS

1575.8m

1576.4m

1577.0m

1577.6m

1578.3m

1578.9m

1579.5m

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Extensively bioturbated, very fine grained sands. Few primary sedimentary structures exist due to burrowing. Burrow types indicate a shallow marine environment of deposition. Individual sands have variable thickness and coarsening upwards sequences are common.

5179‘(1578.6m)

Alluvial Valley


Coastal Plain

ShallowMarineShelf

Central Basin

L3L8

L7Bay

Mouth Bar

L5

L6

Delta Front

L4L2

Carb. Buildup

L1

Shale

Mixed shaleand sand

Dominantlysand withsome shale

Plain Light UV Light

GS/CU

LITHOFACIES 6: BAY MOUTH BAR SANDS

Intensely bioturbated intervals exhibit random FMI patterns.

LITHOFACIES 7: MARINE SHELF, BURROWED SHALES

1669.4m

1669.7m

1700m

1670.3m

1670.6m

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5479‘(1669m)

5480‘(1670.3)

Alluvial Valley


Coastal Plain

ShallowMarineShelf

Central Basin

L3L8

L7Bay

Mouth Bar

L5

L6

Delta Front

L4L2

Carb. Buildup

L1

LITHOFACIES 7: MARINE SHELF, BURROWED SHALES

Shallow shelf carbonate deposits (4841′ - 4846′) rest on burrowed shales of Lithofacies 7 (shelf mudstones). The carbonates lack obvious evidence of internal sedimentary structures.

No Core

Alluvial Valley


Coastal Plain

ShallowMarineShelf

Central Basin

L3L8

L7Bay

Mouth Bar

L5

L6

Delta Front

L4L2

Carb. Buildup

L1

LITHOFACIES 8: SHALLOW SHELF CARBONATES

1475.8m

1476.5m

1477.1m

1477.7m

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CROSS BEDDED SANDSTONE

1575.8m

1576.4m

1577m

1578.9m

1577.6m

1578.3m

1579.5m

CLASSIC DEPOSITIONAL SETTINGS

http://www.eos.ubc.ca/resources/slidesets/clastic/clastic.html

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LEARNING OBJECTIVES

identify the types of image logs and technology used

identify the application of image logs for geological and petrophysical data

integrate the image data with core and other log data to reconstruct depositional models

You are now able to:

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SPECIAL PETROPHYSICAL TOOLS: NMR AND IMAGE LOGS CORE...

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