Abstract: Integrated Techniques for Quantifying Fractures: Monterey Formation, Offshore California, USA

SCHWALBACH, JON R., and DALTON F. LOCKMAN, Exxon Company, USA, Thousand Oaks, California

Fractures are the critical element controlling production from Monterey Formation reservoirs of the offshore Santa Barbara Channel, California. The fractures provide important storage volume in the subsurface and the permeability required for fluids to move into the well bore. Our efforts focus on understanding the distribution of fractures in the reservoir, mapping the fractures that intersect the borehole, and quantifying the fracture void space.

Numerous techniques are integrated to evaluate the fractures in the cherts, dolomites, porcelanites, and shales of the Monterey Formation. Approximately 4000 feet of core has been collected and described using a visual technique designed to quantify fracture properties. The visual description has been calibrated with laboratory-based measurements of cores using CT-scans, confocal microscopy, and mercury injection capillary pressure techniques. Extensive observations and data collection at outcrops have been integrated to build a conceptual geologic model. We make extensive use of borehole image logs, carefully calibrated to the cores, to evaluate fractures over the complete reservoir interval in most wells. Fracture orientation determined from image logs is often superior to orientations measured from cores, and the data are obtained much more quickly. We also use borehole images to predict fracture porosity throughout the logged interval, but have found sources of uncertainty related to borehole environmental conditions during logging, interpreter variability, and resolution limits for evaluating small-aperture fractures. The key element for applying the borehole image data quantitatively is having sufficient core material, from a variety of reservoir facies, to conduct a robust calibration.

AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California