Speaker: Bill Ambrose, Research Scientist with the Texas Bureau of Economic Geology
Subject: “Canyon and Cisco Groups in the Eastern Shelf of the Permian Basin from Outcrop to Subsurface”
Abstract: Coastal-plain, incised-valley, shelf, and shelf-edge depositional facies in the Missourian Canyon Group and Virgilian-Wolfcampian Cisco Group are well-documented in outcrops near Mineral Wells, Cisco, Graham, and Jacksboro Texas (Brown et al., 2009). A recent study by Hentz et al. (2017) links coastal-plain, incised-valley, and shallow-marine systems in these outcrops into slope and basin-floor systems in the subsurface in a ~12,000 mi2 (~31,000 km2) area across the southern Eastern Shelf of the Permian Basin. This study is a southwestward extension of a previous regional study of the Eastern Shelf of the Permian Basin by Brown et al. (1990).
The Canyon Group (base Palo Pinto Limestone to top Home Creek Limestone) consists of an aggradational carbonate bank succession with locally prominent reef facies that also accumulated during early Cisco sedimentation. The bank/reef interval, largely equivalent in age to the Horseshoe reef complex, is as much as 1,540 ft (~470 m) thick in northeastern Coke County and forms an irregular shelf margin. Reef buildups are aligned at the margin but also occur in local pinnacles in the platform interior. Canyon basin-floor facies are equivalent to the lower part of the Cline shale (“Wolfcamp D”) and consist mainly of dark, organic-rich (˃2% TOC) mudrocks.
The overlying Cisco section consists of a cyclic series of thirteen mudrock, limestone, and sandstone facies (top of the Home Creek to top Coleman Junction Limestone), correlated from outcrop, that collectively form a progradational succession extending from the eastern edge (Bunger Limestone) to the central part of the study area (Coleman Junction Limestone). The top of the Home Creek Limestone coincides with a regional down-lap surface for the progradational Virgilian lower Cisco shelf strata. Progressive upward decrease in height of shelf-margin clinoforms indicates that accommodation decreased during deposition of the upper Cisco Group.
The Pennsylvanian–Permian (Virgilian–Wolfcampian) boundary is at the top of the Cline Shale in the basin and slope provinces, and it occurs just above the Crystal Falls Limestone in the shelf area. Thickness of the Wolfcampian section is regionally consistent at the shelf (~700 to 850 ft [~210 to 260 m]), expands basinward to as much as 3,500 ft (~1,070 m) thick into a “foredeep” area of high accommodation and high sediment influx associated with slope sedimentation. However, it is thinner basinward (<500 ft [<152 m]). Slope facies closest to Virgilian and lower Wolfcampian shelf margins are dominantly siliciclastic mudrocks and sandstone turbidite deposits in channel-levee complexes. The same facies of the upper Wolfcampian section are dominated by calcareous mudrocks and allochthonous carbonates as superimposed debris-flow deposits. The Wolfcampian (upper Cisco) basin system to the west comprises (1) primarily siliciclastic strata occurring as unconfined, thin turbidites and hemipelagic mudrocks in the lower part of the Wolfcampian succession and (2) carbonate debris-flow deposits and turbidites in the upper part. In contrast, the Virgilian (lower Cisco) basin succession constitutes organic-rich mudrocks of the upper Cline Shale.
Depositional cycles of the Virgilian and Wolfcampian (Cisco) shelf are dominantly transgressive limestones interstratified with highstand fluvial-deltaic and lowstand incised-valley-fill sandstones and mudrocks. Alternating thickened transgressive shelf-edge limestone systems and lowstand shelf-edge deltaic systems were deposited along the margin of the deepening basin. Shelf-edge systems of the thirteen depositional cycles trend north-northeastward and subregionally coincide as stacked, composite successions and record periods of prolonged shelf-edge stability.
Wolfcamp strata comprising distal slope and basin-floor sandstone facies in the basinal eastern part of the study area have produced about 500 MMbbl (million barrels) of oil and 2.3 Tcf (trillion cubic feet) of natural gas. Cumulative production from Canyon shelf and reef carbonate deposits and fluvial-deltaic sandstones, primarily in the western part of the study area, totals about 430 MMbbl and 1.8 Tcf. Production totals from incised-valley-fill and deltaic sandstones and shelf and proximal slope carbonates of the Cisco Group, also in the western part of the study area, lag considerably behind those of the other two plays, with about 55 MMbbl and 230 Bcf (billion cubic feet) cumulative production.
Bio: William A. Ambrose is a Senior Research Scientist at the Bureau of Economic Geology. He received a Master of Arts degree in geological sciences in 1983 from the University of Texas at Austin. Since joining the Bureau of Economic Geology in 1987, he has worked on a variety of projects at the Bureau, including characterization of the Woodbine Group in the East Texas Basin, Pennsylvanian reservoirs in the Eastern Shelf of the Permian Basin, Frio fluvial and deltaic reservoirs in South Texas, tight-gas reservoirs in the Cleveland Formation in the Texas Panhandle, co-production of gas and hot brine from Oligocene reservoirs in the Texas Gulf Coast, evaluation of coalbed methane reservoirs in Rocky Mountain basins, and reservoir characterization and basin analysis studies in Venezuela and Mexico. He is currently the principal investigator of the Bureau’s STARR (State of Texas Advanced Oil and Gas Resource Recovery) program, past president of the Energy Minerals Division (EMD) of AAPG, chair of the EMD Coal Committee, and vice chair of the AAPG Astrogeology Committee.