Sweet spots evaluation and exploration of lacustrine shale oil of the 2 member of Paleogene Kongdian Formation in Cangdong sag, Dagang Oilfield, China

Based on the systematic data of 565m cores, thin section, X-ray diffraction, rock pyrolysis, CT scanning, nuclear magnetic resonance and oil testing of Paleogene Kong 2 Member in Cangdong sag, Huanghua depression, the macro and micro components, sedimentary structure characteristics of the Kong 2 Member, and evaluation standard and method of shale oil sweet spot are studied, and then the best shale sections for horizontal wells are determined. According to the dominant rock type, rhythmic structure and logging curve characteristics, four types of shale fabric structure models are established, namely, thin-layered dolomitic shale, lamellar mixed shale, lamellar felsic shale, and bedded dolomitic shale, and the Kong 2 sub-member is divided into four parasequences PS1 to PS4. The shale oil classification criteria based on five parameters, free hydrocarbon content S1, shale rhythmic structure, clay content, TOC and porosity, are established. The evaluation by using the weighted five parameters shows that PS2 is both geological and engineering sweet spot of shale oil, with developed laminar structure, large size and good connectivity of pores and throats, high contents of TOC (2%–6%) and movable hydrocarbon, S1 of over 4 mg/g, clay content of less than 20%, and porosity of more than 4%. PS3 and PS1 are geological and engineering sweet spot of shale oil respectively. PS3 shale has a S1 value higher than 6 mg/g and a clay content of 20%–30%; PS1 shale has a porosity higher than 6% and clay content of less than 20%; PS4 shale has low TOC content and poor oil-bearing property. Two shale oil sweet spots, PS2 and PS3, are selected. Several vertical and horizontal wells drilled in the two sweet spots have achieved high oil production. Among them, Well 1701H has produced stably for 623 days, with cumulative production of over 10000 tons, showing a good exploration prospect of lacustrine shale oil in Kong 2 Member.