A re-look at borehole images: What are we missing?

Abstract

Borehole Image (BHI) logs have been in the geoscientist’s tool kit for over 30 years. But despite being seen as a mostly mature technology, they are generally underutilized by geologists both for basic geological interpretations and reservoir characterization. This is surprising because BHI logs provide nearly the “ground truth” resolution of cores, and in certain aspects provide superior data. The most common applications focus on fracture characterization, stress field analysis, and structural interpretation. Much more information, however, can be gathered from a BHI data set. We review examples that highlight novel applications in structural analysis, sedimentologic and stratigraphic studies, and reservoir evaluation. A structural analysis of Ventura Avenue Field illustrates how BHI logs delineate a specific deformational style leading to a new interpretation of fault geometry. Image logs also reveal the heterogeneous character of a major fault and associated damage zone along a four-mile transect. This heterogeneity impacts the interpretation of fault seal and reservoir pressure compartments. BHI logs are most underutilized in sedimentologic and stratigraphic studies. The best interpretations are developed in conjunction with core calibration, but even in the absence of cores BHI logs enable the interpretation of sedimentary structures, diagenetic features, significant stratigraphic surfaces, and the stacking patterns of associated facies. These observations are critical for developing stratigraphic frameworks and depositional models. We illustrate with examples from both fine-grained sediments and coarser-grained clastic systems. Our final examples highlight reservoir characterization and productivity studies integrating core, image logs, and well test data. These integrated data sets can reveal the distribution of fluid saturation in the reservoir, mechanical stratigraphy related to fracturing, and fluid entry into the wells. BHI logs are not necessarily standalones in these applications, but are a critical element in the interpretation. BHI logs are commonly acquired for many wells, but the available data are often underutilized. Re-examining the role of image logs in both academic and industry evaluations has significant potential for more robust understanding of subsurface geology and improved integrated interpretations.

AAPG Datapages/Search and Discovery Article #90339 ©2019 AAPG Pacific Section Convention 2019, Long Beach, California, April 1-3, 2019