Quality difference analysis of source rocks in the Fengcheng Formation, Hashan area, Junggar Basin

Shale oil in the Permian Fengcheng Formation of the Hashan area shows promising momentum, with breakthroughs achieved in multiple wells. Previous research indicates that the Fengcheng Formation in the Hashan area is mainly composed of four lithofacies: terrigenous clastic lithofacies, dolomitic mixed lithofacies, volcanic clastic-bearing mixed lithofacies, and alkaline mineral-bearing mixed lithofacies, within which various types of source rocks have developed. ObjectiveTo further evaluate the quality of these source rocks and the factors controlling it, Methodsthis study investigates the sedimentary background and conducts a lithofacies-based evaluation. The aim is to identify lithofacies containing high-quality source rocks and to analyze the controlling factors of source rock quality, thereby clarifying the further exploration directions. ResultsThe results show that, among the mudstones in the Fengcheng Formation of the Hashan area, the volcanic clastic-bearing mixed lithofacies has the highest total organic matter content, whereas the dolomitic mixed lithofacies has the greatest hydrocarbon generation potential. The kerogen of the mudstones in the Fengcheng Formation of the Hashan area is mainly Type Ⅰ-Ⅱ. The mudstone maturity in the western section of Hashan area ranges from 0.79% to 0.97% Ro, while in the middle section, Ro is mainly between 1.2% and 1.37%. ConclusionThe source rock quality in the Fengcheng Formation of the Hashan area is mainly controlled by sedimentary environment, hydrocarbon-generating parent material, maturity, alkaline minerals, and volcanic activity. Organic matter in dolomitic mixed lithofacies and alkaline mineral-bearing mixed lithofacies is more enriched in deep-water, reducing, medium-to-high salinity, and arid environments. In contrast, organic matter in terrigenous clastic lithofacies and volcanic clastic-bearing mixed lithofacies is more enriched in relatively shallow-water, oxygen-poor, low-salinity, and arid-semi-arid environments. Green algae (dunaliella-like) developed in high-salinity areas of the sedimentary center exhibit higher oil and gas conversion rates, enabling dolomitic mixed-lithofacies mudstones to have high hydrocarbon generation potential even with low organic matter abundance. Increased maturity and alkaline minerals reduce the measured TOC (total organic carbon) content and hydrocarbon generation potential, while an appropriate amount of volcanic clastics provides favorable conditions for the organic matter enrichment.