EXPERIMENTALSTUDY ON TIGHT OIL RESERVOIR CHARACTERISTICS OF YANCHANG FORMATION IN ORDOS BASIN CHINA?

摘要

Continental tight sandstone oil reservoirs are widely developed in the Upper Triassic of the Ordos Basin. The study of the pore structure and petrophys-ical properties of the continental tight oil reservoir is the core content ofreservoir evaluation. In thispaper, taking Area A in the southwest of the Ordos Basin as an example, experimental methods such as closed coring technology, mercury intrusion testing, X-ray diffraction. thin sections, and scanning electron mi-croscopy are used to analyze the pore structure and petrophysical properties of tight oil reservoirs in the Chang 4+5 member of Yanchang Formation. The re-search results show that the lithology of the target layer is mainly feldspar sandstone, the interstitial materials are mainly chlorite and illite, and a small amount of chlorite film-coated particles are visible. The secondary pores are mainly dissolution second-arypores. According to the difference of soluble sub-stances, it can be subdivided into intragranular dis-solution pores (such as feldspar dissolution pores, rock debris dissolution pores) and intergranular pores(such as matrix and cement dissolution pores). The petrophysical property test results show that the porosity distribution range of the target layer is 1.94%-16%, with an average value of 12.0%; the permeability distribution range is0.0121 mD-10.841 mD, and the average value is 1.01 mD.When the po-rosity is greater than 10% or the permeability is greater than 0.1 mD, the petrophysical properties of the reservoir are significantly improved. The average pore throat radius has an obvious positive correlation with permeability, but it has a poor correlation with porosity. This shows that the throat channel mainly has an obvious control effect on the permeability. The mercury intrusion experiment was used to deter-mine the lower limit of the effective thickness of the reservoir, and the thickness of tight sandstone is pos-itively correlated with its effective thickness. The mercury removal efficiency has a positive correla-tion with porosity and permeability. The mercury re-moval process is equivalent to the oil and gas extrac-tion process. The higher the mercury removal effi-ciency, the higher the oil and gas recovery rate.Therefore, the relatively high porosity and high per-meability reservoirs have higher recovery rates.