Characteristics And Evaluation Factors Of Shale Oil Reservoir Of The Third Member Of Hetaoyuan Formation, Palaeogene In Biyang Depression

With the continuous decline in the worldwide production of conventional oil and gas,unconventional oil and gas resources have made a series of breakthroughs as alternativeresources, and shale oil has gradually become a hot area of oil exploration. The third memberof Hetaoyuan formation is the main source rock in Biyang Depression, and have broadprospects for shale oil exploration because of its stable distribution, large mono-layerthickness, and strong hydrocarbon potential. However, study of shale oil reservoirs isrelatively poor. A workable classification scheme of shale lithofacies hasn’t been made, theaccumulation mechanism of shale oil is not yet clear, neither is a systemic and effectiveevaluation criterion for shale oil reservoir established.In this paper, on the basis of core observation, thin section identification, scanningelectron microscopic analyses and a variety of laboratory datas, an intensive study of shalereservoir is conducted.According to organic carbon content and mineral constituent, the shale in the thirdmember of Hetaoyuan Formation in the study area is divided into six types, which areorganic-poor muddy siltstone, organic-poor silty shale, organic clayshale, organic-poormicritic calcareous shale, organic-rich sparry calcareous shale and organic dolomitic shale.Combined with log interpretation models, the distribution of shale lithofacies is determined.Seven kinds of reservoir spaces are also identified, including residual intergranular pore,intercrystal pore, secondary dissolved pore, organic pore, tectonic fracture, interlaminatedfracture and microfractures of different genesis. By comparing their genesis, size, distributionand validity, the dissolved pores, intercrystal pores between recrystallized calcite, interlayerfractures and tectonic fractures are considered best reservoir spaces.The occurrences of shale oil can be in adsorbed or free state. Liquid hydrocarbon mainlyadsorbs inside organic matters or at their surface. In mineral matrix (clay, quartz, feldspar,dolomite, calcite) pores, shale oil mainly occurs in free state, secondly in adsorbed state.While in fracture networks, free state is the major occurrence. The factors that affect the development of the shale reservoir consist of kerogen type andthermal maturity, abundance of organic matter, lithofacies and reservoir spaces association,thickness of organic-rich shale, preservation conditions, shale fracability and physicalproperty of crude oil. The importance of organic matter to the formation and evaluation ofshale oil reservoir is emphasized. That is, the content of organic matter determines the oilgeneration potential and reservoir capacity of shale, further controlling the reserves andproductivity of shale oil. A set of reservoir evaluation criteria are put forward by focusing onthe TOC content of source rock (threshold values2%and4%). Finally, based on sedimentarycycle division, integrating TOC content contour map, porosity contour map and lithofaciesdistribution map, the favorable areas are predicted.