Carbonate Reservoir Services Guide

1
Dr Andy Horbury Sedimentologist (
andy_at_cambridgecarbonates.co.uk ) Francis
Witkowski MSc. I.A. Geologist (
francis_at_cambridgecarbonates.co.uk )
Alt., Contact- neil.pickard_at_telia.com
pete_at_CaCO3.demon.co.uk Jogarland_at_cambridgecarbon
ates.co.uk http//www.cambridgecarbonates.com
2
Introduction

• Data capture
• Pore masks (porosity maps)
• Various types of graphical output
• Measures of accuracy
• Case histories
• Future development

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Data Capture at Different Scales

• Using various types of equipment
• Data capture at many scales
• SEM
• Standard/CL petrography
• Cuttings
• Whole T-section scan
• Scanned core/hand specimen/MRI
• Outcrop images/image logs

4
CL and IA Equipment

• Technosyn 8200 Mk.2
• 3CCD digital video camera

• Nikon Optiphot microscope
• Dell IPP v.4 I.A. software

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SEM Scale

• SEM images to obtain the finest pore sizes
• Yield pore maps to quantify smallest pores

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Standard Petrographic Data

• Digital images (e.g. 4x obj, 10x obj, 25x obj)
• Minimum of 10 F.o.V captured in PPL CL

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Cuttings Data

• T-S scan with sampled chips outlined (red)

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Core or Hand Specimen Scale

• Core/hand specimens yield larger pore sizes

Scanned Core
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Outcrop Scale

• Digitized large format images

• Vuggy macroporosity development at this location
• Pore mask reveals 17.01 macroporosity

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Characterization of Dual Porosity

• Adjacent outcrop area to previous slide
• Improved understanding of micropore to reservoir
  scale pore systems

4.7 fracture porosity measured from digital
picture of outcrop

• surface
• weathering

20cm
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Pore Map (Outcrop Image)

• 4.7 fracture porosity from digital outcrop mask

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Combine Different Scales of Data

• Porosity extracted from 3 separate scales
• Core, thin-section microscope (10x obj)

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Graphical Output

• Pore Size Distribution (PSD)
• Based on pore areas (not pore throat apertures)
• Pore Frequency
• Pseudo-capillary curves (Pcap)
• PSD comparison plots
• Pore Roundness (R)
• Combined PSD and Roundness plots

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Standard Graphs

• PSD, pore frequency pseudo cap curve

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Pseudo-capillary Curves

• Below is a diagrammatic representation
• Less Ø Higher entry pressure (at lower right)
• Lower intergranular Ø steeper curves

Adapted from Lucia (1999)
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Pseudo-capillary Curves

• First pass indicators of permeability
• Generated from image pore mask data
• Proxies for true Sw-capillary pressure curves
• Easy sample comparison within data-sets

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PSD Comparisons at a Glance

• Break out families of pore size distributions
  (PSD)
• Proportion of micro, meso and macro porosity

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Pore Size Distribution Matrix
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Roundness (R) Classification

• Scale independent (similar to specific surface)
• A ratio of pore area to pore perimeter
• Improves on g value of Anselmetti et.al.(1998)

• pores in black

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Pore Area v Roundness

• Roundness (R) of 1 perfectly equant
• Elongate (fracture-like) pores (R) gt 9

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Pore Area vs. Gamma
pores above are in black
circular pores plot close to 1
After Anselmetti et.al. 1998
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Accuracy, Repeatability and Anisotropy

• IA porosity within 5 of plug ø values
• IA repeatability significant correlation
• Accurate assessments of anisotropy
• Accurate assessments of heterogeneity

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Plug - IA Porosity Comparison

• Establishes the accuracy of IA porosity
• No plug values discarded (even doubtful ones)

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Image Analysis - Repeatability

• Quality control check
• Establishes the accuracy of IA technique
• Highly significant correlation (R2 0.9087)

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Anisotropy

• Core faces cut at 90 degrees
• May show distinct pore maps/PSDs
• Shows variation in pore systems

• IA Porosity 12.8

• IA Porosity 1.76

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Measures of Heterogeneity

• Standard deviation reveals heterogeneity
• A guide to porosity influence on permeability
• Zero homogeneous 1 totally heterogeneous

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Porosity Type Differentiation

• We provide 2 types of pore classification
  (Lucia's and a pore area based one)
• Largest pore size and its ECD (equivalent
  circular diameter)
• 2 heterogeneity indices (S.D. And simple
  heterogeneity index)

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Case Histories

• Using non-standard data
• Ground-truthing petrophysical data
• Characterizing flow units
• Dual porosity reservoirs
• Pore area v roundness (R)
• Understanding Sw in certain carbonates
• Well test failure analysis
• Well cuttings analysis
• Quantitative CL screening

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Use of Non-standard Data

• Using photos from old reports
• Even broken thin-sections
• Maximizes available data for quantification
• Allows for remote working access

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Use of Non-standard Data (cont.)

• Remove periodic noise to improve images
• Enables better segmentation
• Improves count accuracy

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Use of Non-standard Data (cont.)

• Remove cracks from t-section pore areas
• Even broken section can be segmented
• Maximizes available data

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Ground-truthing petrophysical data

• NB- some samples have overestimated plug
  porosities (dark blue)
• Close inspection of plugs and their t-sections
  did not reveal significant ø
• Accurate plug test error is typically 2.5 for
  plug ø of 20, i.e. 0.5 ø units (Thomas Pugh,
  1989)
• Is Your plug data reliable?

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Characterization of Flow Units

• Each flow unit shows different porosity fabrics
• Porosity fabrics generate unique Pcap curves

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Dual Porosity Reservoirs

• T-S has both matrix fracture porosity
• Only IA allows characterization of matrix
• Small to medium pores in the matrix a few large
  bitumen-filled fractures

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Understanding Sw

• Differentiate macro and microporosity
• microporosity often determines Sw
• May cause re-evaluation of recovery factors

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Well Test Failure Analysis

• Determine reliability of old well test data
• Using available old core
• Porosity variation linked to patchy cementation
• T-section image analysis showed 7.6 - 8.8 Ø

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Well Test Failure Analysis

• Porosity size distribution (PSD) matches highly
  productive fields nearby
• As does the pseudo capillary curve
• Suggests re-evaluation of poor test results and
  re-testing at well site

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Well Cuttings Analysis

• T-S scan i.d. cuttings for detailed I.A.
• Higher mag. images used to generate data

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Deriving Porosity Data

• 10x objective CL-PL pairs (minimum of 10)
• Yield dolomitisation porosity information

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Deriving Porosity Data

• 10 calibrated porosity maps generated
• Each F.o.V 0.95 mm x 1.4 mm

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Data from Cuttings CL/PL images

• 4.76 porosity, 2.48 S.D., skew 0.157
• Compare 3M and Lucia (1999) Ø classes

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Data from Cuttings CL/PL images

• 2.29 microporosity, 2.46 mesoporosity

2.46
2.29
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Data from Cuttings CL/PL images

• Pseudo cap curve based on 10 CL/PL pairs

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Quantitative CL Screening

• Dolomitised ooid grainstone oomouldic pores

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What Next ?

• Speed analysis via software automation
• Extend Rock Properties Database
• Further statistical comparison of samples
• Improved permeability prediction
• through reference to Rock Properties Database

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Contact

• http//www.cambridgecarbonates.com
• 44 (0)121 705 8472
• andy_at_cambridgecarbonates.co.uk
• 44 (0)7788 581 252 (mob)
• francis_at_cambridgecarbonates.co.uk
• 44 (0)7881 788 019 (mob)
• neil.pickard_at_telia.com
• 46 733 130495 (mob)
• jogarland_at_cambridgecarbonates.co.uk
• 44 (0)7887 781 867
• pete_at_CaCO3.demon.co.uk
• 44 (0)7887 781 865 (mob)