Research On The Reservoir Characteristics Of The Palaeozoic In Southwest Ordos Basin

With the continuous development of oil and gas exploration degree, more and moreattention was paid to Southwest Ordos Basin. Though oil and gas was detected in thePalaeozoic oil and gas exploration, the natural gas distribution characteristics is not clear. Theexploration degree is still low. It is significant and urgent to strengthen the research on thePalaeozoic reservoir in Southwest Ordos Basin.Based on previous studies, combined with field outcrop geological survey, sectionobservation and measurement, core observation, geochemical analysis, exploratory well dataand experimental analysis, this paper conducted a systematical evaluation and research on thereservoir characteristics of the Palaeozoic in southwest Ordos Basin. From the aspect ofreservoir rock characteristics, physical characteristics, pore structure characteristics anddiagenesis, it pointed out the reservoir characteristics of the Palaeozoic in southwest OrdosBasin, predicted the distribution of effective reservoir, provided a reliable geological basis forfurther exploration and development in this area.After research, a conclusion was obtained that the reservoir in this area contains thelower Palaeozoic Majiagou formation dolomite reservoir and the upper Palaeozoic Shanxi-Shihezi formation clastic rock reservoir.According to physical property analysis and rock thin section observation, the majorporosity of Majiagou formation carbonate reservoir is2-6%, and the permeability is0.01-0.1×10－3μm2, which means that it is the reservoir of middle-low porosity and lowpermeability. The prevalent pore type is dissolution pore and intergranular pore in the nextplace. Shanxi formation reservoir is the especially low porosity and low permeabilityreservoir with the porosity of1-3%, permeability of0.01-1×10－3μm2. And the porosity ismainly between1-3%, permeability is0.01-1×10－3μm2for Shihezi formation. It is also thereservoir of low porosity and low permeability. Residual intergranular pore, intergranulardissolution pore, intercrystal pore and microfracture pore are the main reservoir space types.Dissolution and metasomatism are the main diagenesis of Majiagou formation, which hasdistinctly improved the reservoir physical property. The diagenesis of Upper Palaeozoic Shanxi-Shihezi formation includes compaction, cementation and dissolution. Among them,compaction and cementation are the main reasons of destroying the porosity and permeability,while the dissolution plays good effects for physical property of reservoir.The effective reservoir of Majiagou formation in the study area includes Ma5dolomitereservoir and Ma4limestone, dolomite reservoir, and distributes in Chang3Well region.Shanxi formation effective reservoir distributes in the east of Jingchuan and north of Lingtaiarea. Since the reservoir thickness is very small, it is poor reservoir. The reservoir of Shiheziformation is He8section with the effective reservoir distributing in Lingtai and Changwuregion in the eastern of study area.