Lithofacies, Diagenesis and Reservoir Quality Evolution of Wolfbone Sandstone-Siltstone Successions in the Delaware Basin, West Texas

Abstract

The Wolfbone interval in the Delaware Basin is an important hydrocarbon play. Large volumes of tight oil have been produced from the Wolfbone turbidite sandstone in recent years. Reservoir quality, which is controlled by lithofacies and diagenetic modifications, is one of the critical aspects in understanding the basic elements of the Wolfbone play in the Delaware Basin. Although some sedimentological studies of the Wolfbone succession have been done, the diagenesis of these clay-rich sandstones–siltstones is poorly known. Based on cores, thin sections, Cathode Luminescence (CL), and scanning electron microscope (SEM) observations and X-ray powder diffraction (XRD) analysis, this presentation describes the composition, texture, pore systems, diagenetic minerals and interpret diagenetic history of the Third Bone Spring and Wolfcamp sandstone-siltstone reservoirs in the Delaware basin, and discusses the influence of these factors on porosity, with emphasis on the lithofacies within the Wolfbone Formation. Five types of lithofacies are described on the basis of microscopic observations, including diagenetic minerals, grain size, sorting, clay content, and pore systems. Then the typical diagenetic modifications in early stage and burial diagenesis of various lithofacies are summarized, and the reservoir-quality evolution pathways of various lithofacies are demonstrated by considering the variations of grain size, sorting, shape, and matrix content within various lithofacies. This study concludes that diagenesis of Wolfbone reservoirs comprises compaction, cementation and grain dissolution. Among the diagenetic minerals, carbonate and quartz form the major cements in clean sandstones, whereas the mixed-layer illite/smectite and illite are the dominant cements in clay-rich sandstones. The primary porosity is rare, and the secondary pores are of great importance for the Wolfbone reservoirs. The micro-pores are mainly associated with authigenic clay minerals. The reservoir quality of the Wolfbone play is controlled by the grain size, clay and cement content in various lithofacies. The best quality reservoir rocks are characterized by fine grain size, well sorting, and high percentages of detrital quartz and feldspars. This comprehensive study will reduce the risk of reservoir quality prediction and contribute to hydrocarbon exploration and development in the Wolfbone play.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017