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Provenance and pore system analysis of carbonate mass transport deposits in the Permian Basin: Insight into Wolfcamp unconventional reservoirs

Mitsdarffer, McKensie
Mass Transport Deposits (MTD's) make up a significant portion of basinal sedimentation and can serve as a reservoir unit, flow unit barriers, or paleo-topographic highs that may control overlying reservoir distribution. These deposits have been increasingly studied to determine their mechanism of transport, the resulting depositional geometry, and reservoir architecture. While these aspects are important, most studies lack the meter and sub-meter scale detail that is vital when considering reservoir compartmentalization often observed in these types of deposits.
The Wolfcamp Formation is a major oil and gas play in the Permian Basin, located in west Texas and southeast New Mexico, with an estimated 20 billion barrels of oil equivalent (BBOE) of recoverable reserves. The Formation is characterized as a mixed carbonate/siliciclastic system deposited mostly due to highstand shedding with non-calcareous and calcareous mudstones interbedded with carbonate sediment gravity flows. The carbonate sediment gravity flows consist of fusulinid and crinoidal packstones, grainstones and intraclast wackestones, and carbonate conglomerates and breccias, deposited by a variety of mass transport mechanisms and resulting in variability in the vertical and lateral distribution of the reservoir units.
This study will build upon recent sedimentological work done on 4 cores in the southern New Mexico portion of the Basin and focuses on the variability and provenance of grain types within various MTD's, the probable geometric variability dependent on the mass transport type, and the resulting porosity and permeability that may be contributed by the individual allochems. In addition to core and thin section analysis, SEM and digital image analysis is utilized to constrain the pore system architecture of the different types of MTD's. A proxy for permeability from facies type and sonic log response is developed by comparing the pore system architecture from ion milled samples under SEM. A comprehensive study of the allochems, and their possible contribution to overall reservoir porosity and permeability provides insight into the internal variability of each facies, allowing for a better understanding of the reservoir architecture and compartmentalization in these and similar types of unconventional carbonate reservoirs.