The Study On Ordovician Karst Reservoir Analysis Of The Yi Jian Fang Formation In Tuofutai Area Of Tahe Oil Fileld

In this paper, by studying the core and thin section analysis of Tuofutai area, Yijian fang formation, according to the principle of space shape, size and origin, I thinkthe core space in study areas can be classified as4reservoir types: dissolution-poretype、dissolution-cavity type、karst-cavity type、tectoclase type. In the basic of above,there are four reservoir types: beach face dissolution-pore reservoir、karst-fractured-cavity reservoir、 karst-cavity reservoir and tectoclase reservoir.According to the analysis of the study areas’ drilling section reservoir’s developmentdistribution, it reveals that karst-fractured-cavity reservoir is most developed, and thenext beach face dissolution-pore reservoir and the karst-cavity reservoir is welldeveloped, while, tectoclase reservoir is less developed. After the study on the coresand thin sections of the strata of relating well, the results show that the diagenesis ofthe Yi jian fang formation reservoir are complex and diverse, including cementation,micritization, recrystallization, silicification, pressure solution, dolomitization,dissolution and karstification and fracturing. Combining core observation, thin sectionidentification and cathode ray analysis, consider there are5times of Stage developedfracture diagenesis and fracture in Yi jian fang formation, incould diagenesis stagecrack, the middle Caledonian, early Hercynian, the late Hercynian Himalayan periodin turn. and the early hercynian，tectonic fractures is the most developed. In terms ofone plane， the structural fractures is closely to the development of failt. The study ofthis areas’ Ordovician formation mechanism of accumulation space shows that theformation mechanism of accumulation space includes atmospheric water’s denudationon syndiagenetic stage、atmospheric water’s denudation in the middle Caledonian、atmospheric water’s denudation in the late Caledonian-early Hercynian、hydrothermalactivity in the late Hercynian and hydrothermal denudation. The atmospheric water’sdenudation on syndiagenetic stage depend on the third-order sequence HST highfrequency sequence interface, developmental dissolved pore,incoulding thentergranular dissolved pore、 intragranular dissolved pore and mould pore.Theatmospheric water’s denudation in the middle Caledonian mainly following themiddle Caledonian uncomformity surfaces developed a few irregular dissolution-cavity.The atmospheric water’s denudation in the late Caledonian-earlyHercynian as a major dissolution in the area,dissolution mainly guided by the fractureof atmospheric water, developed a lot of dissolution-cavity. The hydrothermal activityin the late Hercynian and hydrothermal denudation control by fracture,with thedevelopment of hydrothermal minerals in dissolution-cavity. With the combination ofreservoir’s well point control、formation mechanism and controlling factor ofreservoir、seismic cross section interpretation result, pointed out the beach facedissolution-pore reservoir’s major developed member is upper Yijianfang formationlongitudinally, in plane this reservoir’s development controlled by beach distribution;The karst-fractured-cavity reservoir is mainly result from the atmospheric water’sdenudation in the late Caledonian-early Hercynian and local parts is the result of thehydrothermal activity in the late Hercynian, some parts is a upgrading result of formertwo efforts; those reservoir controlled by fracture. Based on the comprehensiveresearch of the reservoir in study areas, three zones can be divided from reservoir’sdeveloping level: Ⅰ-optimum reservoir’s developing zone; Ⅱ-favorable reservoir’sdeveloping zone; Ⅲ-moderate favorable reservoir’s developing zone.