Characteristics of Lacustrine Shale Reservoir and Its Effect on Methane Adsorption Capacity in Fuxin Basin

摘要

The Lower Cretaceous Shahai and Jiufotang Formation in Fuxin Basin, located northwest of Liaoning Province, with stable planar distribution contains abundant shale gas reserves, which are key horizons in the exploration breakthrough of the Mesozoic continental shale gas in northeastern China. FuYe-1 (FY-1) well was recently drilled, and it is an important shale gas parameter well in the Fuxin Basin area. A total of 60 shale samples were collected from Shahai and Jiufotang Formation of FuYe-1 well and DY-1 well in this work. A series of experiments including organic matter vitrinite reflectance, X-ray Diffraction (XRD) analysis, total carbonate content (TOC) measurement, scanning electron microscopy, low-temperature nitrogen adsorption, and methane isothermal adsorption were conducted through the samples. The final results revealed that in FuYe-1 well, the shale of the Lower Cretaceous Shahai and Jiufotang Formations has a maturity of 0.46-1.68% (average of 0.92%), which is at the immature-high maturity stage. The kerogens are mostly of types II-III. The mineral components are dominated by clay minerals and quartz, with an average of 21.39% and 30.89%, respectively. The main controlling factors of the methane adsorption capacity are the TOC content, the total clay content, and the shale pore structure. Langmuir's volume (V-L) of the shale ranges between 0.17 and 1.98m(3)/t (with an average of 1.21 m(3)/t). The methane adsorption capacity is positively correlated with the content of the total clay minerals and quartz, but varies in different clay minerals. The specific surface area of the shale and the total pore volume were calculated by BET and BJH, the macropore ratio of which is negatively correlated with the methane adsorption capacity, whereas the specific surface area and the total pore volume of the mesopores and micropores ratio are positively correlated with the methane adsorption capacity, indicating that the content of the micropores and mesopores is the major contributor to the specific surface area of shale.