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Controls on Wolfcampian and Leonardian Slope Morphology and Implications for Basinal Sedimentation Patterns and Stratigraphy, Delaware Basin, Southeast New Mexico and West Texas


Few studies have assessed carbonate slope morphology and associated slope to basinal facies architecture to characterize potential conventional and unconventional reservoir distribution. This study integrates well logs, 2D and 3D seismic, core, and outcrop exposures of Lower to Middle Permian (Wolfcampian through Leonardian) strata in the Delaware Basin in Southeast New Mexico and West Texas to assess the linked depositional processes and stratigraphic architectures from platform to slope to basin. Detailed mapping (using >10,000 logs over approximately 15,500 km2 creating depth constrained pseudo-seismic visualization) reveal a high degree of variability in slope profiles rimming the basin. The 3rd, 2nd and 1st Bone Spring margins all exhibit irregular plan-view geometries, progradation to aggradation (P/A) ratios ranging from < 1:1-25:1, and slope gradients ranging from 2-30°.

Data indicate variability in shelf margin profiles is related to several factors which also strongly influenced basinal sedimentation patterns: 1) Locations of underlying shelf margins influenced deposition and resulting geometries of overlying slopes. Zones with the highest sedimentation rates and rapid progradation in the 3rd, 2nd, and 1st Bone Spring compensationally migrated from the west to northwest to north, respectively, in response to filling accommodation offsetting promontories in relict platform margins. These zones mark dominant sediment input pathways to the basin during each stratigraphic sequence. 2) Low gradient (2-5°) slopes typically have P/A ratios between 10:1-25:1 and promote consistent downdip transport of sediment to the basin, evident from laterally continuous and mappable well log signatures. Higher gradient (15-25°) slopes with P/A ratios <1:1 likely created laterally variable sediment pathways that resulted in more complex basinal sedimentation patterns, observed in chaotic and discontinuous well log response. 3) Mapped major deep-seated faults focused sediment dispersal which created zones with high P/A ratios (>15) and created anomalous progradational noses reaching 15-25 km into the basin. Some faults also channeled sediment gravity flows at point sources creating basin floor carbonate fan complexes in the Wolfcamp through 1st Bone Spring Formations with thicknesses reaching 400m and proximal axis-to-distal fringe lengths up to 100km. 4) Antecedent topography in underlying toe-of-slope to proximal basin floor deposits created anomalous thickness trends, altered sediment transport pathways, and channeled coarser grained carbonate sediment gravity flows into mud-rich basinal settings in all observed units.

Findings suggests detailed analyses of slopes is necessary to constrain controls on basinal sedimentation. This work may provide analogs for assessment of unconventional targets distal from current conventional carbonate slope reservoirs.