Page 14 - Offshore Well Construction
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CHAPTER 10
Formation Evaluation
Petroleum Extension-The University of Texas at Austin
INTRODUCTION
A wide variety of information is available from the well that can be used by the geologist and petrophysicist to refine
the geological and petrophysical models and to gain a better understanding of the reservoir, assess how large the
reservoir is, and how it will perform if placed on production.
Information can be obtained from the following sources:
• Data collected while drilling
• Penetration rate
• Cuttings analysis
• Mud losses/gains
• Shows of gas/oil/water
• Core analysis
• Lithology
• Presence of shows
• Porosity
• Permeability
• Special core analysis
• Log analysis (wireline and MWD/LWD)
• Electrical logs
• Acoustic logs
• Radioactivity logs
• Pressure measurements
• Special logs
• Productivity tests
• Formation tester
• Drill stem test
• Production test
Mud Logging
Data collected while drilling is usually incorporated as part of the mud logging service.
The mud log provides a record of the penetration rate, lithology (inferred from cuttings analysis), and cuttings description
on a depth basis together with general comments on the drilling parameters, mud type and properties, hydrocarbon
shows, logs run, cores cut, etc.
Coring
Cores provide more accurate information than cuttings. However, unless special circumstances dictate, it is usually
only cost effective to core the reservoir section of a well.
A core allows a detailed lithological description of the reservoir to be made. Additional tests can be performed in the laboratory
to establish the porosity and permeability of the rock, which can then be used to calibrate the response from logging tools.
Log Analysis
Logs can be obtained by running specialist tools on wireline or, as is becoming more common, by including a LWD
tool as part of the MWD tool string. Note that not all wireline logs are available as LWD logs.
A log is the recording of the physical properties of the formations drilled on a depth basis.
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