Controlling factors for oil production in continental shales: A case study of Cretaceous Qingshankou Formation in Songliao Basin

Continental shale oil is widely distributed in the Cretaceous Qingshankou Formation of the Songliao Basin in Northeast China. In the Qijia-Gulong sag and the Changling sag in the Songliao Basin, breakthroughs of shale oil exploration and development have been made in the first and second members of the Qingshankou Formation, and several wells represented by Well GYYP1 have achieved high and stable shale oil production. However, some horizontal wells in shale oil development pilot test (Well groups A and D) were characterized by low shale oil production, high flowback rate and rapid production decline. Therefore, controlling factors of the shale oil production were investigated. The results show that shale oil enrichment area and optimal sweet spots are fundamental for high shale oil production, improving horizontal length and drilling ratio of sweet spots is a technical guarantee for enhancing shale oil production of single well, and artificial fracture network (incl. scale, complexity, and coupling with pre-existing geological bodies) created by fracturing is a direct factor for controlling the shale oil production. For subsequent exploration and development of the shale oil, the heterogeneity of sweet spot distribution should be carefully considered, the shale oil enrichment areas and optimal sweet spots also need be optimized, and the wellbore trajectory control and fine geological modeling techniques should be figured out. Moreover, the fracturing techniques suitable for the shale with high clay mineral content and weak brittleness should be developed, and the personalized and differentiated staged fracturing also needs to be performed, to effectively enhance single-well shale oil production and estimated ultimate recovery.