Coupled Geochemical and Nano-Petrophysical Study of the Spraberry-Wolfcamp Trend; West Texas, U.S.A.
Quintero, Ryan P.
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With the rise in interest of unconventional plays, efforts have moved to understand these formations across 12 orders of magnitude through nm-km scale. Recent work by others has shown the importance of the nanometer range due to the fact this is the predominant pore size within shales. In attempt to understand nanopore structure and production behavior within a shale unconventional reservoir, a number of complementary experimental methods must be employed. This research involves the use of wettability droplet analysis for micron scale assessment of wetting properties and Mercury Intrusion Capillary Pressure (MICP) analysis for pore structure characterization within the Spraberry and Wolfcamp Formations of the Permian Basin in west Texas. In conjunction with pyrolysis and X-ray diffraction data from two wells, total organic carbon (TOC), thermal maturation, and mineralogy are considered for the development of the pore system. The Spraberry Formation was found to contain a larger porosity, higher permeability, and lower tortuosity than the Wolfcamp. The two formations also showed different pore size distributions, with the Spraberry containing more intra- and inter-pores (10-100 nm) while the Wolfcamp containing more organic sized pores (predominantly at 5-10 nm). Mineralogy differences between these shales showed no strong relationship with pore sizes distribution nor maturation. Values of S1 (volatile hydrocarbon content) from pyrolysis analyses showed the strongest relationship with pore sizes. As S1 values increased, the higher porosity increased; this rise in porosity is seen predominantly within organic pore sizes. Production data from the Rogers #3804 and Wright #44 are compared to Jarvie’s oil generation crossover line (S1 vs. TOC). This crossover line accurately predicts the historical trend of these two wells.