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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
DOI: 10.1306/0726171609317002
Integrating borehole image logs with core: A method to enhance subsurface
fracture
characterization


F. Fernández-Ibáñez,1 J. M. DeGraff,2 and F. Ibrayev3
1ExxonMobil Upstream Research Company, 22777 Springwoods Village Parkway, Spring, Texas 77389; fermin.fernandez.ibanez@exxonmobil.com
2ExxonMobil Upstream Research Company, 22777 Springwoods Village Parkway, Spring, Texas 77389; jmdegraf@mtu.edu
3North Caspian Operating Company, Chagala District, 01 Smagulov Street, 060002 Atyrau, Kazakhstan; farkhat.ibrayev@ncoc.kz
ABSTRACT
Image logs provide critical data for characterizing fractured reservoirs. However, the nature of such logs, coupled with borehole-modified stresses, creates challenges that may lead to erroneous fracture
interpretations. We developed a methodology to integrate image logs, core, and geomechanical models to obtain high-confidence,
fracture
data sets derived from image logs. The methodology starts with a detailed comparison of overlapping image logs and core, first to properly shift them into alignment (core-to-log shift) and second to determine which features interpreted as fractures on image logs (picks) can be validated as fractures in core. Then we derive guidelines for interpreting image logs without core control to reduce the likelihood of false
fracture
picks. Geomechanical modeling is used to assist with quality control and interpretation of image logs where drilling-induced tensile fractures occur. We use a fractured carbonate reservoir to demonstrate the application of this methodology. Comparison of image log
fracture
picks with core led to an average rejection rate of greater than 50% of fractures picked on the image logs. These high rejection rates are mostly caused by overinterpretation of discontinuous sinusoids and misidentification of sedimentary features and induced fractures. We derived rules for interpreting high-quality fractures: (1) only sinusoids with continuity greater than 50% should be interpreted and (2) sinusoids with dip angles less than 55° should be excluded from the interpretation. Application of this methodology has provided much higher quality
fracture
orientation and frequency data than that resulting from interpretation of borehole images alone. The improved
fracture
data set provides a more reliable basis for testing hypotheses and deriving models of
fracture
distribution.
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