Quantitative Assessment of Shale Gas Preservation in the Longmaxi Formation: Insights from Shale Fluid Properties
Guanxiong Ren, Wenbo Guo, Yuan Lu
Abstract
The shale gas content of the Longmaxi Formation exhibits significant spatial variation in different structural parts of the Sangzhi area in Hubei Province, reflecting differences in preservation conditions. To quantitatively evaluate these conditions, this study integrates analyses of structural features, fault distribution, formation water chemistry, and shale gas composition from four wells. Results show that preservation is primarily controlled by the F1 and F3 faults. Wells distant from these faults (SY3 and SY5) display weak connectivity with surface water, feature CaCl2-type formation water with high salinity and diagnostic ion coefficients, and contain hydrocarbon gases derived from organic pyrolysis. These characteristics lead to high gas content and favorable preservation conditions. In contrast, wells adjacent to faults (SY1 and SY6) exhibit strong connectivity with the surface, NaHCO3-type water of low salinity, high N2 and CO2} contents of atmospheric origin, and low gas content, indicating poor preservation. These findings demonstrate that shale gas preservation in the Longmaxi Formation is jointly controlled by structural settings, water--rock interactions, and nonhydrocarbon gas sources, providing a quantitative framework for assessing preservation conditions in shale gas exploration.