The origin and source of heavy oil and its control on oil and gas accumulation

Abstract

ABSTRACT A large amount of heavy oil have been found in the eastern section of Dinan uplift, Junggar basin. Previous studies on heavy oil mainly focused on the origin and source, and few studies have been conducted on the influence of heavy oil on reservoir physical properties and the control of oil and gas enrichment. Based on this, through the analysis of oil and gas geochemical characteristics and the comparison of reservoir physical properties before and after oil washing, the genesis of heavy oil in this area and the control effect of heavy oil on oil and gas accumulation are systematically studied. The results show that: (1) The carbon isotope of crude oil in this area is lower than −30‰, Pr/Ph is less than 2, C28 and C29 sterane content is high, which is a typical Permian source rock product. (2) Due to the incompleteness of saturated hydrocarbon chromatogram, low maturity of heavy oil isassociated with bacterial decomposition gas, which indicates that the heavy oil is formed by biodegradation of early products of Permian source rock. (3) Heavy oil fills the pores and fractures of the reservoir and occupies a large number of pores and throats, which affects the physical properties and pore structure. After the heavy oil was dissolved, the average increase in sample porosity and permeability is 3.79% and 0.435 × 10−3μm2. (4) The heavy oil formed in the high part of the structure has a certain plugging effect on the reservoir, which leads to the high mature oil and gas in the deep part of the depression did not migrate to the high part of the structure to form an oil reservoir. Therefore, the next step of the exploration for products in the high maturity stage of the depression should be extended to the depression slope area.