Print this pageNew Core Analysis Methods for Fractured Siliciclastic Reservoirs
LAUBACH, STEPHEN E.
In hydrocarbon reservoir rocks, gas and oil production may depend on attributes of natural fractures. Yet reliable information on such key fracture attributes as orientation and conductivity is sparse because few fractures intersect vertical wellbores. In quartzose rocks, quartz-lined microfractures (size: microns to millimeters) and textural relations among fractures and authigenic cement can be analyzed to estimate critical attributes of subsurface fracture populations. Key to microstructure characterization of such rocks is photomultiplier-based electron- beam-induced luminescence (scanned CL) imaging, which detects microfractures that are usually not visible using conventional CL or petrographic techniques. Because microfractures are widespread and small samples can be used to get accurate fracture data, scanned CL observations of rocks that do not contain large (i.e., visible to the unaided eye) fractures can be used to determine the timing of fracturing events relative to authigenesis, to infer orientations of large fractures, and -- in concert with new methods for classifying diagenetic histories -- to estimate the degree to which fracture networks have been filled with authigenic cements. Fracture orientation and quality assessments from several oil and gas plays will illustrate the application of this technology.