The Delaware Basin contains prolific unconventional reservoirs in the Wolfcamp and Bone Spring intervals dominated in many locations by sediment gravity flows. Core description and subsurface well log mapping identified calciclastic submarine fan complexes within the Wolfcamp C, Wolfcamp A, 3rd, 2nd, and 1st Bone Spring Limestones which alter the basin facies architecture and subsequent unconventional reservoir quality. The fan systems display radially distributive, predictable sedimentation patterns with fan axes containing carbonate dominated accumulations while fan fringe environments show a decrease in grain size and increase in the volume of siliciclastic mudstone, siltstone, and organic material, likely resulting from continued runout and evolution of mixed mineralogy sediment gravity flows.
Carbonate rocks most often display greater rebound hardness and calculated unconfined compressive strength which correlates strongly to sonic velocity rock strength and corresponding sonic velocity compared to siliciclastic mudstone to siltstone dominated units. Population of sonic velocity data through calibrated 3-dimensional geostatistical facies models using fan-generated trends highlight the interfingering of stronger non-reservoir carbonate facies and weaker reservoir quality mudstones and the lateral transitions moving throughout the fan complex. Fan axes house high volumes of carbonate with minimal segregated reservoir intervals. Medial fan environments display multiple potential reservoir intervals segregated by tight carbonate beds. Greater volumes of reservoir quality mudstone accumulate on the distal fringes of fans without significant interfingering carbonate baffles.
While fan systems do not comprise the entire basinal succession, these updated interpretations may increase predictability of both reservoir and non-reservoir units in certain locations. Correct stratigraphic characterization and geostatistical modeling may aid in locating sweet spots for reservoir quality, stacked well potential, and provide additional insight into geologic controls on well interference.
The Delaware Basin contains prolific unconventional reservoirs in the Wolfcamp and Bone Spring formations. These reservoirs differ from traditional black shale reservoirs representing quiescent anoxic to euxinic black shale deposition typically formed during greenhouse periods. Instead, these reservoirs form distal from carbonate platforms in deeper basinal settings with periods of episodic high energy deposition (Fig. 1a). These high energy events are represented by sediment gravity flows transporting sediments from the platform and slope to the deeper basin. The gravity flow deposits are interspersed with hemipelagic and pelagic sediments, adding an additional level of facies and subsequent reservoir heterogeneity in comparison to other major unconventional reservoir targets elsewhere.