Shale dominant lithofacies and shale oil enrichment model of Lower Permian Fengcheng Formation in Hashan area, Junggar Basin

Abstract

Compared with the Mahu Sag in the Junggar Basin, the adjacent Hashan area has undergone multi-stage napping and complicated oil-gas formation and evolution process, making its shale oil exploration facing many challenges, such as unclear dominant lithofacies and enrichment law. In order to optimize the dominant lithofacies of the Lower Permian Fengcheng Formation shale in Hashan area and summarize the enrichment model of shale oil, by taking more than 200 samples from 8 exploration wells in the area, including Hashan 5 and Hashen X1 wells, and using methods such as core and ordinary thin section observation, a systematic classification of shale lithofacies types was carried out based on the study of sedimentary environment and facies. A comprehensive evaluation of reservoir physical properties and oil content was conducted based on lithofacies by combining experimental methods such as XRD, scanning electron microscopy, low-temperature nitrogen adsorption, and pyrolysis. The enrichment law of the Fengcheng Formation shale oil in Hashan area was preliminarily revealed based on the correlation analysis of shale mineral composition, organic matter abundance and oil content. The results show that the Fengcheng Formation shale in Hashan area can be divided into four lithofacies types: terrigenous clastic, dolomitic diamict, alkaline mineral diamict and volcanic clastic diamict. The (argillaceous) siltstone in terrigenous clastic lithofacies, the dolomitic sandstone in dolomitic diamict lithofacies, and the volcanic clastic diamict lithofacies have good physical properties and oil content, which are good shale oil reservoirs. The shale oil enrichment patterns can be divided into three types: in the terrigenous clastic lithofacies of the outer delta front, the shale oil enrichment patterns are mainly migrated from adjacent strata. In the shallow- semi-deep lake section, the dolomitic mixed-deposit lithofacies are mainly the shale oil enrichment model of the same layer fracture migration and adjacent layer migration, while the volcaniclastic mixed-deposit lithofacies are mainly the self-generated and self-stored matrix shale oil enrichment model.

Keywords

• shale oil
• lithofacies
• enrichment model
• fengcheng formation
• hashan area
• junggar basin