Pioneer Natural Resources

About: Pioneer Natural Resources is a based out in . It is known for research contribution in the topics: Oil shale & Fracture (geology). The organization has 187 authors who have published 161 publications receiving 1656 citations.

Postrift sequence stratigraphy, paleogeography, and fill history of the deep-water Santos Basin, offshore southeast Brazil

Abstract: Events that influenced the Santos Basin were different from the Campos Basin to the north (where the bulk of the petroleum reserves in Brazil have been discovered) and resulted in a very different stratigraphy. Because of these differences, the Campos Basin stratigraphic model is poorly suited to the Santos Basin (cf. Cobbold et al., 2001).We divide the postrift stratigraphy of the deep-water Santos Basin into 11 major sequences, each representing an average duration of approximately 11 m.y. and encompassing the middle–Late Cretaceous and Tertiary. The complex fill history of the Santos Basin was strongly influenced by the uplift of the Serra do Mar coastal mountain ranges in the Late Cretaceous and the subsequent organization of the coast-parallel Paraiba do Sul drainage system. The ancestral Paraiba do Sul tended to focus clastic influx into the northern and central Santos Basin during the Late Cretaceous and Paleogene. Focused clastic influx forced massive shelf progradation and deep-water turbidite sedimentation despite globally high-standing sea level. The southern Santos Basin, at the same time, was relatively starved of clastic influx, and drowned shelf conditions prevailed.These depositional patterns persisted until the Oligocene, when the Paraiba do Sul was captured and diverted into the Campos Basin to the north into which it currently empties. After the capture and diversion of the Paraiba do Sul, the north-central Santos Shelf was starved and drowned, and the shelf edge backstepped more than 50 km (30 mi). The southern Santos Basin, in contrast, was buried by a thick sequence of mud-prone upper Oligocene and Neogene sediments that had a great impact on source rock maturity.

Natural fractures in the Spraberry Formation, Midland basin, Texas: The effects of mechanical stratigraphy on fracture variability and reservoir behavior

Abstract: Horizontal cores from sandstone-siltstone reservoirs in the Spraberry Formation (Midland basin, west Texas) have documented two systems of dramatically different yet dynamically compatible natural fractures, in reservoirs separated vertically by only 145 ft (44 m). Each system is capable of producing a different degree of the northeast-trending permeability anisotropy recognized in Spraberry reservoirs. One fracture system consists of two vertical fracture sets with an apparent conjugate geometry (striking north-northeast and east-northeast). The other system consists of evenly spaced, northeast-striking vertical fractures, nearly bisecting the acute angle of the first system. Although lithologically similar, differences in quartz-overgrowth and clay content in the layers resulted in a yield strength of the lower bed that is only half of that of the upper layer, producing different fracture systems in the two reservoirs despite their proximity. Such differences in the mechanical properties, due to variations in diagenetic and depositional histories of the strata, are probably widespread within the formation. They have the potential to cause significant vertical and lateral variation in the Spraberry fracture system across the basin. Low present-day in-situ stresses in the reservoirs allow the fractures to open, to become more conductive, and even to propagate, under very low injection pressures.