Reservoir Characteristics And Oil - Bearing Controlling Factors Of Jurassic Cold Alpine Group In Central

Sichuan Jurassic Lianggaoshan Formation is one of the main oil layer of Sichuan Basin, and the escalation of its oil shows promient exploration prospect and potential. Exploitation is difficult due to the low porosity, low permeability and heterogeneity of the reservoir. In well-extensive area such as Well Xian9, Gong17and Dacheng5, reservoir sandstone which are called white sandstone has such characteristics as high porosity or high permeability without oil trace. Therefore, it is necessary to make research on the characteristics of the Lianggaoshan formation of the Jurassic reservoir and find out factors controlling the Jurassic Lianggaoshan tight sandstone reservoir.In this paper, on the basis of previous studies, with the application of petroleum geology, geochemistry, reservoir geology, logging geology and other theories and methods serving as analyzation of Lianggaoshan formation is done using casting thin sections, scanning election microscope, mercury injection and other advanced testing means.Based on core observation, by combining logging data, analyzation of the formation oli controlling factor is done, and such are the conclusions gained.The hydrocarbon source rocks of Lianggaoshan tight sandstone reservoir are mainly-black shale. In the longitudinal direction, containing coarse sand and fine sand, the cumulative thickness from20to70m. And in the transverse direction, the hydrocarbon source rocks thicken to east. The study of the content of organic carbon in hydrocarbon source rocks find that the content of organic carbon change from0.13%to3.45%, the average is1.46%. Confirm that the abundance of organic matter is high, indicating there is good hydrocarbon source rock in the eastern part of the Sichuan basin. The main types of organic matter the sapropelic type source rock and the humic sapropelic source rock. The average of Ro is1.16%which is means that the hydrocarbon source rock is in the mature stage, and have good hydrocarbon generation potential.The main type of rock in Jurassic Lianggaoshan of middle Sichuan basin is relatively simple:primarily lithic quarts sandstone and quzriz sandstone. The grain size of sandstone ranges from silt to fine sand. The type of reservoir space consists of intragranular dissolved pore, intergrannular dissolved pore, tectonic microfracture and dissolution fissure etc with little original pore space. The sandstone reservoir has such characteristics as:high displacement pressure, high median pressure, high undersaturation volume of mercury, short radius of pore and throat and inefficiency in mercury withdrawal procedure. Distribution of porosity between1%-3%accounted for67.3%, porosity of more than3%accounted for only12.4%of total porosity; permeability below O.1mD accounted for74.9%,proving the poor physical conditions of sandstone.In macroscopic, the distribution of oil in Lianggaoshan Formation is generally affected by the distribution of source rock while in microcosm, the characteristic is controlled by mudstone-sandstone transition, formation characteristic and fractures. Only when the source rock and the reserve rock are in direct contact and the condition of the reserve rock is good can oil and gas accumulative in the formation. Fractures in the formation boost the condition of the rock while providing the fluid with transmission passages. The sweet points in the Lianggaoshan Formation lie where there are pure sand body with thick layer of source rock in the beach-dam microfacies.