Characteristics of the Cretaceous continental shale oil reservoirs in Luanping Basin

Shale oil was first discovered in Well Luantan 1 in the Cretaceous of Luanping Basin, filling the gap in the discovery of Mesozoic oil and gas in the Yanshan structural belt. Based on analysis and laboratory data such as cores, thin sections under microscope, logging data, mud logging data and X-ray diffraction, a study is performed on the characteristics of shale oil reservoirs in the Cretaceous Xiguayuan Formation in Luanping Basin. The shale oil reservoirs of Xiguayuan Formation in the study area mainly include six rock types: shale, siltstone, dolomite, mixed fine-grained felsic rock, carbonate-type mixed fine-grained rock and clay-type mixed fine-grained rock. The reservoir space is dominated by pores and fractures. The fractures include tectonic fracture, abnormally high pressure fracture and interlayer fracture. The pores are dominated by intercrystalline pores and dissolved pores. The average porosity of the shale oil reservoir is 1.6%, and the average permeability is 0.265 mD, indicating the dominant development of low porosity and ultra-low permeability reservoir. According to the lithology combination and logging display, two sets of shale oil reservoirs were identified vertically. The lower shale oil reservoirs are volcanic-lacustrine deposits, mainly containing shale, siltstone, dolomite, mixed fine-grained felsic rock and carbonate-type mixed fine-grained rock. The reservoir space is predominated by pores. The hydrocarbon resource is mainly shown as yellow-green light oil, and natural gas is produced. The upper shale oil reservoir is consisted of normal lacustrine deposits, and the rock types are presented as shale, siltstone, carbonate-type mixed fine-grained rock, and clay-type mixed fine-grained rock and mixed fine-grained felsic rock. The reservoir space is dominated by fractures, and black heavy oil and gas are precipitated. The analysis suggests that sedimentary environment, diagenesis, tectonic background and total organic carbon are the main controlling factors for the development of shale oil reservoirs in the Xiguayuan Formation. © 2020, Editorial Office of ACTA PETROLEI SINICA. All right reserved.