Shale Oil Reservoir Structure Characteristics of the Second Member of Kongdian Formation in Cangdong Sag, Bohai Bay Basin

In order to further clarify the dominant reservoir lithology of lacustrine shale strata, focus on sweet spots, improve the drilling encounter rate of sweet spots in the horizontal section, and increase the shale oil production of horizontal wells, this paper comprehensively uses the 494.29 m core of Well G108-8 in the second member of Kongdong Sag, more than 3 000 sub-sections, scanning electron microscopy, nuclear magnetic resonance, mercury intrusion and whole-rock X-ray analysis data to systematically analyze the carbonate rock, sandstone and shale pore types, structures, and heterogeneity. The results show that feldspar, quartz and organic matter have a constructive role in the development of reservoirs. Calcite, clay and analcite minerals are unfavorable factors for the development of reservoir space. Although dolomitization has improved carbon to a certain extent, dolomite-like microcrystalline, micrite nano-scale intercrystalline pore storage and poor seepage conditions, the dominant reservoir lithology of shale oil mainly includes feldspar lithic sandstone, laminar type shale and fractured dolomite. Laminar shale has various types of reservoir space, and the residual intergranular pores and dissolution pores in the laminae rich in felsic minerals have good connectivity. Artificial fractures form complex fracture network structure with the matrix pores and fractures, and has the ability to stabilize production, which is the main production layer of shale oil in the second member of the hole. The newly implemented horizontal well focuses the drilling box to the 8-10 m thick layered felsic shale interval, wells GY5-3-1L and GY5-1-9H produced more than 1.0×10⁴ t of oil per well in the first year, and the cost per barrel of oil dropped to US ＄65, realizing the profitable development of lacustrine shale oil.