--> The Hydrocarbon Generation Ability of Organic Matter in Tight Sandstone of the Permian Lucaogou Formation in Jimusaer Sag, Junggar Basin and Its Significance for Tight-Oil Reservoirs

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The Hydrocarbon Generation Ability of Organic Matter in Tight Sandstone of the Permian Lucaogou Formation in Jimusaer Sag, Junggar Basin and Its Significance for Tight-Oil Reservoirs

Abstract

Unconventional resource plays have become increasingly important components of the global hydrocarbon endowment. Tight oil exploration of the Permian Lucaogou Formation in Jimusaer Sag, Junggar Basin has made an important breakthrough. The Lucaogou Formation comprises fine-graded sedimentary rocks with the characteristics of single thin layers and frequently alternating beds. The tight sandstone in upper and lower sweet spot are interbedded with mudstones, which makes up a good interbedded relationships of spatial configuration. In contrast to most known tight sandstone oil reservoirs, both mudstone and tight interlayer reservoir rock (particularly siltstone in the tight interlayer reservoir rock) have good hydrocarbon potential. Experimental analysis shows that the total organic carbon (TOC) of a high proportion of tight sandstone samples handled by extraction is greater than 1%. The kerogen type is mainly Type II1 and Type I; the thermal evolution degree is suitable; and the value of vitrinite reflectance (Ro) distribution is between 0.7% and 1.0%. The microscopic observation indicates exinite organic maceral are clearly mixed with the grains of the tight sandstones. These conditions imply possible contribution to oil generation. The entire Lucaogou Formation formed in a low-energy environment. A certain amount of clay minerals exists in the tight sandstone, which may have adsorbed organic matter in the sedimentation process. The hydrocarbon generation quantity of the tight sandstone interlayer reservoir rocks is estimated by the simulation of hydrocarbon generation. The quantity of hydrocarbon generation of the siltstone reservoir was found to account for approximately 40% of the reserves. Part of the accumulation of tight oil likely originates from hydrocarbon generation in mudstones interbedded with the tight sandstone reservoir through a short primary migration distance; the remaining accumulation is through self-generation and self-accumulation in the tight sandstone. Part of this process differs from traditional tight sandstone oil generation, and similar to that in a shale oil reservoir.