Abstract

High resolution sequence stratigraphy determined from 451 well gamma ray logs coupled to X-ray fluorescence (XRF) and spectral gamma ray logging of five cores of the Northern Delaware Basin reveal a systematic interplay between slope to basin sediment gravity flows and pelagic deposition. The eight members of the Bone Spring Formation correspond to third order parasequence sets (PSS) which overlie the basal Wolfcampian Unconformity and are bounded at the top by the Leonardian Unconformity. These two unconformities represent second order sequence boundaries reflecting tectonic and eustatic influences upon the basin. That the global eustatic influence is an important control upon the deposition is the remarkable correlation between the third order PSS and the global sea level curve. Moreover, the composition of these PSS is influenced by basin physiography and subaqueous erosion which reflects a reciprocal sedimentation model and bathymetric compensational stacking patterns.

Sediment inorganic and organic provenance together with the syndepositional pale-oxidation state of the waters are provided by compositional and paleoenvioronmental XRF proxies. The Cr, Co, and Ni proxies suggest transported organic matter during lowstands while the U proxy enrichment implies an in situ pelagic organic matter source during high-stands. These together with other proxies clearly associate siliciclastic terrigenous, detrital concentrations with lowstands in sea level and carbonate-rich intervals with highstands in sea level. In addition, anoxic proxies such as Mn and Fe suggest that though anoxic conditions generally increase with increasing paleobathymetric depth, they also alternate with changes in cyclical water depths. During lowstands, the anoxic zone may have expanded vertically with increased Delaware Basin restriction owing to possible curtailment to closure of the Hovie Channel to the Panthalassia Ocean.

Coupling paleoenvironmental proxies with compositional proxies reveal internal heterogeneities within the individual Bone Spring members that make the case for spatially varying source rock, reservoir rock, and potentially self-sourced reservoir quality. Oil and gas exploration and production can use these geo-chemical indicators to reduce risk in horizontal well placement (i.e. drilling lateral in zones with higher anoxic proxy concentrations coupled to elevated TOC) and cutting down completion costs (i.e. placing frack stages within zones of high Si and low clay, Al and K concentrations as these zones will offer the best conditions for successful completion). The high resolution sequence analysis of the Bone Spring Formation begins to unveil the complicated sedimentary and chemical process-responses of the Delaware Basin during an important time in the Permian, as well as provide practical insight into optimization of its oil and gas exploration.