Abstract

Coalesced collapsed-paleocave systems are characterized by strong spatial complexity that reflects the distribution of paleocave facies and associated pore networks. Recognizing how cave systems form and evolve with burial into the deeper subsurface is essential in identifying and understanding the distribution of paleocave facies and their pore networks.

Six basic cave facies are recognized in a paleocave system and are classified by rock fabrics and structures: (1) undisturbed strata (undisturbed host rock), (2) disturbed strata (disturbed host rock), (3) highly disturbed strata (collapsed roof and wall rock), (4) coarse chaotic breccia (collapsed-breccia cavern fill), (5) fine chaotic breccia (transported-breccia cavern fill), and (6) sediment fill (cave-sediment cavern fill). Pore networks associated with paleocave reservoirs can consist of cavernous pores, interclast pores, crackle and mosaic breccia fractures, and less commonly matrix pores. Each paleocave facies has a different combination of pore types. The paleocave facies classification can be used to describe the complex geology expressed in coalesced collapsed-paleocave systems and can be used to understand and predict pore-type distribution and magnitude of reservoir quality.