Formation Mechanism And Distribution Prediction Of Tight Oil In Zhahaquan Area,Southwest Qaidam Basin

The Zhahaquan area is a new area of tight oil exploration in Southwest Qaidam Basin, in order to master the formation mechanism of tight oil and favorable regional distribution, based on core observation, flake analysis, scanning electron microscopy, rock pyrolysis, inclusions temperature, X-all rock diffraction, etc. Based on the theories of sedimentary petrology and petroleum geology, using conventional logging and imaging logging as the means, systematically studied sedimentary and reservoir characteristics, diagenesis, reservoir properties and main controlling factors, coupling relationship of the history of reservoir tightness and hydrocarbon accumulation, the formation mechanism and accumulation pattern of tight oil, the main controlling factors of dense oil distribution, the spatial relationship between conventional reservoir and tight reservoir, the favorable area forcasting of the Shangganchaigou Formation(Ni) and the exploration and development management style.When Shangganchaigou Formation deposited, the Zhahaquan area is a gentle slope zone, shore shallow lake-half-deep lake development and accompanied by deep lake deposition, gravity flow sand body and beach bar sand body development, the reservoir property is good and the scale is large, is a favorable reservoir. But there is a difference between the lower formationg (N11) and the upper formationg (Ni2). The lower formationg (N11) is characterized by deep water body and strong reducibility during the deposition period, meaning while accepting the sedimentary material imported from Tumulike and Dongchai Mountain, gravity flow sand body developmented. When the upper formation(N12) deposited, the water becoming shsllow and the reducibility weakening, mainly accept the Tumulike source of imported sediment material, beach bar sand body developmented. The types of sedimentary petrology are feldspathic lithic sandstones, lithic feldspar sandstones. Cement mainly is calcite, a small amount of zeolite and anhydrite, heterogeneous are mainly clay and clay. The compositional maturity, structural maturity, sorting, grinding roundness and clastic composition of the lower formationg(Ni') of the rock are worse than those of the upper formation(Ni2). The porosity of the lower section (Ni1) and the upper section (Ni2) are 5.8%and 11.5%, respectively; the permeability is 0.43mD and 2.55mD respectively; the reservoir type is typical dense reservoir and low permeability reservoir respectively; the reservoir space is mainly composed of primary intergranular pores, and secondary pores are dissolved hole, the pore structure is of type III, In the lower section (Ni1), the reservoirs are mainly of grade III. while the upper section (Ni2) of the low permeability reservoirs are group II.The diagenesis of the Shangganchaigou Formation(Ni) is stronger, the lower (Ni1) and the upper (Nr) reach the diagenetic stage B and A respectively. The deposition and the deposition component are important external factors for the densification of reservoirs. Strong compaction, carbonate rock, anhydrite cementation and other diagenesis is an important external cause of reservoir densification.The study of porosity evolution history of reservoir shows that the reservoir has been dense during the Shangyoushashan Formation Period (N22). According to the history of burial-thermal evolution and homogenization temperature of inclusions, the time of the tight oil of the lower Shangganchaigou Formation(N11) in Zhahaquan Area accumulation on a large scale is from Shizigou-Formation(N22). First the reservior densed and then the oil and gas filled, gathered into a reservoir. Comparison of oil source shows that the lower Shangganchaigou Formation(N11) is a self-generated, self-storage reservoir, the upper Shangganchaigou Formation(N12) is conventional lithologic reservoirs, the oil is mainly from the upper Xiaganchaigou Formation (E32)Through the statistical analysis, the upper limit porosity of the tight reservoir is 10%, and the permeability is 1mD. According the empirical statistic method, etc. determines the lower physical property is 3.5% porosity and 0.05 mD permeability for Oil and gas injected into the tight reservoir. The moving power for the oil and gas in the reservoir is the remaining source reservior pressure, the vertical accumulation is the main source, forming a source-wide aggregation mode.This thesis reveals that the distribution of tight oil is controlled by depositional environment, source rock and reservoir distribution, source-reservoir relationship and so on, predicting the favorable exploration and development area.