Summary
The Delaware Basin, a western sub-basin of the Permian Basin, is located in west Texas and southeast New Mexico. The industry's focus on oil assets has influenced the resurgence in horizontal drilling activity in the basin targeting the tight sands and organic shales of the Bone Spring and Wolfcamp formations. The Wolfcamp formation consists of a multiple billion barrel oil equivalent resource. This paper will examine the Wolfcamp pay distribution, corresponding optimal landing zones, and elucidate the thermal maturity corundum that exists across the basin.
The remaining Total Organic Carbon (TOC) content of shale source rocks plays a key role in the characterization and development of self-sourced unconventional plays. Resource in-place calculation and landing target selection for horizontal wells commonly rely on TOC in the Delaware Basin. The underlying assumption is that the permeability of shales is insufficient to allow for the migration of hydrocarbon generated during the thermal maturation process. Subsequently, remaining TOC is a good proxy for original hydrocarbon in place (OHIP).
The Wolfcamp can be differentiated into 5 stratigraphic pay zones distributed across the basin. A review of the basin stratigraphy and architecture will demonstrate this followed by a discussion leveraging core data showing 1) the middle and lower Wolfcamp reservoirs (Wolfcamp C & D) where TOC and OHIP are colocated and 2) log-based techniques used to characterize these reservoirs. We also discuss the upper Wolfcamp reservoir (Wolfcamp A) where the hydrocarbon generated during the thermal maturation process has migrated, at least at a local scale. Production logs verify TOC-based pay calculations can lead to suboptimal landing zone placement in the upper Wolfcamp. Thus, an alternative OHIP-based characterization is the preferred pay and subsequent landing zone identification. This petrophysics workflow can provide insight in qualifying pay in hybrid lithologic systems.
The Delaware Basin can be divided into two GOR thermal regimes; low GOR to the east and high GOR to the west. Multiple hypotheses may explain this segregation; chromatographic migration, basin inversion, heat flow fluctuation, etc. This paper will explore these alternatives to thermal maturity and demonstrate the potential for fluid flow in low permeability systems not only at a local scale, but more regionally.
