SPE Distinguished Lecturer Program

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SPE Distinguished Lecturer Program
Primary funding is provided by The SPE
Foundation through member donations and a
contribution from Offshore Europe The Society
is grateful to those companies that allow their
professionals to serve as lecturers Additional
support provided by AIME
Society of Petroleum Engineers Distinguished
Lecturer Program www.spe.org/dl
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Core Analysis A Guide to Maximising Added Value
Colin McPhee
Senergy (GB) Limited
Society of Petroleum Engineers Distinguished
Lecturer Program www.spe.org/dl
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Why core matters
Bob Harrison, JPT Technology Focus, August 2009

• Core.
• confirms lithology and mineralogy
• calibrates estimates of fundamental rock
  properties
• shows how fluids occupy and flow in pore space
• supplies mechanical properties for faster safer
  drilling and better completions
• Logs cannot characterize a reservoir if
  knowledge of the rock is absent
• a struggle to convince management that the
  project benefits from the knowledge gained

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Why core analysis matters - volumetrics
Oil initially in place OIP Gross rock
volume GRV Net to Gross
N/G Porosity ? Water saturation
Sw Formation volume factor Bo
Logs, welltests, CORE Logs, CORE Logs, CORE
PVT
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Why core analysis matters reserves

• Recovery factor depends on technical and economic
  factors
• Recovery factor is partly defined by formations
  relative permeability
• from CORE

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Core data do we get value?

• The ground truth for formation evaluation
• But.
• Lab
• variable lab data quality and method sensitivity
• poor lab reporting standards
• End user
• inadequate planning and inappropriate design
• Have undermined value from core analysis

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Core data do we get value?

• Review of gt 20,000 SCAL measurements
• 70 of legacy data is unfit for purpose
• 10,000,000 data redundancy cost
• Examples of unreported lab artifacts
• porosity, Sw, and capillary pressure
• Impact on hydrocarbons in place

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Example - Archie water saturation, Sw
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Porosity error excess brine

• Correct for excess brine in annulus between core
  and coreholder test sleeve
• Otherwise porosity too low

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Porosity errors - impact
Lab B -7 error in log ?
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Excess brine resistivity tests

• Ambient m and n
• core must be fully saturated
• excess brine on plug surface
• Formation factor (F)
• resistivity (R0) too low
• m too low
• Resistivity index (I)
• Rt unaffected
• n too high

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Correcting for excess brine

• Formation factor (F) tests at stress on tight sand

mean - 30 error in ambient m
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Correcting for excess brine

• Resistivity index (I) tests at ambient

15 error in ambient n
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Grain loss material balance
-

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Grain loss correction
-20 saturation unit error in Sw
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Impact of errors on OIP

• Uncertainty analysis
• North Sea reservoir
• 20 ? and 20 Sw
• 100 MMbbl OIP
• 20 error in input data
• Largest impact
• ?, m and n (core)

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Pc curve distortion

• Mercury injection capillary pressure (MICP)
• Pre-1994 tests on 50 80 ml plugs
• Now most tests on lt 10 ml chips/end trims
• Pc curve (Sw versus Pc) problems
• Use Hg-filled pore volume (gt 20,000 psi)
• clay destruction in small pores
• distorted Pc curves