Research On The Reservoir Characteristics Of The Lower Palaeozoic In Western Ordos Basin

Due to sound petroleum geology elements of the lower Palaeozoic in western Ordos Basin, many wells has been drilled since 1970s, but unfortunately, most of which has been proved to fail.For the stimulus of the success of Puguang gas fields, Jingbian gas field, A series of research program such as research on the Reservoir Characteristics of the lower Palaeozoicin western Ordos Basin et al, have been put forward.This paper discussed the evolution history of sediment and diagenesis, pore types, physical property,fluid property on the basis of the studied results of former geologists,detailed core observation, thin-sections observation, geochemical analysis, such as C, O isotope, fluid inclusion analysis, logging interpretation, and through statistical analysis of petrophysical data and logging data, finally pointed out the vertical distribution of favourable reservoir.Summary from research,on the studied areas,the dominated facies are restricted-marine platform, open-marine platform, platform-margin sand shoals, slope and basin facies. Zhangxia formation, Kelimoli formation and Zuozisan formation have developed large scale shoals. Dissolution, dolomitization, compaction, pressure solution and cementation played a crucial role in reservoir evalution.The reservoir rocks in Cambrian and Ordovician have undergone different diagenetic environments and yielded respective diagenetic evolution order.the prevalent pore types of Zhangxia formation and Sansanzi formation, Cambrian are intercrystal pore, intercrystal dissolved pore; the predominated pore types of dolostone formation in Zuozisan formation and Kelimoli formation, Ordovician are intercrystal pore, intercrystal dissolved pore, but the predominated pore types of limestone formation in Zuozisan formation and Kelimoli formation, Ordovician are dissolved enlarged interparticle,vugs, channels, structural fracture.Typeâ…¡reservoir in the outcrops of Ordovician in the western ordos basin account for 47 percent, type â…¢andâ…£reached 30 percent.typeâ…¤is 16 percent.similarly, there was no typeâ… reservoirs in the Ordovician outcrops in the western ordos basin. Typeâ…¡,â…¢+â…£andâ…¤reservoir accounted for the same propotions.According to the drilling data and log analysis, these sections of Kelimoli formation and Zuozisan formation on which dissolved enlarged interparticle,vugs, channels have developed well and on which the thickness of dolostone exceed 50 meters, are profitable reservoir intervals.During the process of drilling,many wells has occurred mud loss, well test of Tian1 well had obtained high productivity, E8 had also gained small amount gas.The grainstone reservoirs of Kelimo formation and the dolostone reservoirs of Zuozisan formation of the Tianhuan Depression in the western ordos basin are the optimum.prospecting well on these areas are in the hope of success. The favorable reservoir in Cambrian stratum is dolostone of Sansanzi formation. Middle-coarse crystallized dolomite, residual grain dolomite, fine crystallized dolomite and lime-dolomite are the reservoir rocks in this area,various reservoir spaces are developed. solution pore, vugs, fracture are the main reservoir spaces. Two reservoir rock bodies are developed in Sanshanzi dolomite.Because the upper reservoir had a better connectivity than the lower reservoir, The reservoir property of the upper reservoir rock body is better than its lower counterpart.the upper reservoir have something with crust of weathering which was formed by Huaiyuan movement, and The origin of lower reservoir concerns with the buried diagenesis. The profitable reservoirs of Sansanzi formation distributed on the southern of study areas.