Abstract

The Bone Spring play and associated Avalon sub-play represent a succession of calcareous, siliceous, and carbonaceous sediment gravity-flow deposits associated with significant production of oil, condensate, and dry gas in the Delaware Basin. Correlation of the upper Bone Spring and upper Avalon systems to the outcropping Cutoff Formation slope system and Lower San Andres composite sequence (PCS9, 2—4 m.y.) in the Guadalupe Mountains region allows us to investigate how: 1) slope and basinal accumulation patterns are linked to deposit types, 2) accumulation patterns vary in space and time, and 3) migration of the active sediment factory (shelf system) control sediment transport and accumulation in slope and basinal environments.

Regional mapping of the Cutoff–upper Bone Spring–upper Avalon interval reveals the multivariate evolution of a deep-water system associated with a drowned carbonate platform margin (large-scale inflection) characterized by (1) an increase in the rate of sediment supply to the drowned platform, (2) a transition along the relict platform from styles of sediment transport dominated by turbidity currents and hemipelagic settling to styles dominated by mass-transport events, and (3) a landward shift in the locus of deposition downdip of the relict shelf margin. PCS9 strata associated with hemipelagite and turbidite systems demonstrate basinward-stepping geometries along shallow slope gradients downdip of the relict shelf margin, and aggradational geometries along steep slopes. Strata associated with carbonate–rich mass-transport deposits accumulate near the relict shelf margin on both shallow and steep slopes.

The proposed stratigraphic framework combined with a calibration of Cutoff-Avalon rock-types to wireline-log signatures allow for the construction of field-scale facies maps in the northern Delaware Basin (Eddy County, New Mexico). In this area, the lower part of the studied interval (L7 – G3 HFS) records an alternating pattern of siliceous mudstone and carbonate sediment gravity flow accumulation. This unit becomes increasingly rich in siliceous mudstone in the basinward direction as carbonate deposits become thinner and more difficult to correlate between wells. Siliceous mudstones comprising this interval are often organic-rich and represent an important component of “Avalon shale” reservoirs. The central part of the studied interval (lower G4 HFS) records widespread accumulation of sandstone turbidite systems along the slope and basin floor which are equivalent to “Avalon sandstone” reservoirs. The uppermost part of the interval (upper G4 HFS) is equivalent to the “upper Cutoff” of Amerman et al. (2011) and records the widespread accumulation of carbonate-rich sediment gravity flow deposits across the basin. Correlation of these units to the equivalent lower San Andres shelf system (PCS9 of Kerans and Fitchen, 1995) reveals that organic-rich deposits accumulated mainly during major backstepping of the shelf system at the nexus of a global-scale, 2^nd order transgression. Sandstone rich deposits accumulated during intermittent high-frequency scale lowstand and platform exposure events during the earliest stage of PCS9 and later in the high-stand. Shelf-to-basin sequence stratigraphic models shown in this study can be used during exploration to help predict the spatial and temporal distribution of reservoir-prone strata in the Delaware Basin, or other basins with analogous systems, when data is sparse.