The Study On Fractured-vuggy Reservoir Of Ordovician Condensate Gas Reservoir In Block9of Tahe Oilfield And Xidaliya Area

By studying the cores and thin sections of the strata of relating well ofOrdovician condensate gas reservoir in block9of Tahe oilfield and Xidaliya Area,according to the shape, size, the causes and the classification principles of reservoirand permeable space, the Ordovician reservoir and permeable space can be dividedinto karstification porosity, karstification fractured-vug, karstification cave, weatheredfracture and structural fracture. Based on the classification, the type of Ordovicianreservoir can be divided into the reservoir of karstification porosity, the reservoir ofkarstification fractured-vug, the reservoir of karstification cave and the reservoir offracture. And reservoirs of karstification porosity and karstification cave are generallydeveloped; but the reservoir of karstification fractured-vug is more developed; and thereservoir of fracture is most developed. But for the contribution rate, the reservoir ofkarst cave in the region is the largest, and the reservoir of fractured-vug is larger, andeservoirs of fracture and dissolution porosity are small. The characteristics amongthese types of reservoir are different, which are as follow. The reservoir ofkarstification porosity mainly developed in the Yijian formation of the MiddleOrdovician, and the reservoir of karstification fractured-vug mainly developed in theYijianfang formation and the Lianglitage formation of the Upper Ordovician, and thereservoir of karstification cave mainly developed in the Yingshan formation of theMiddle-Lowwer Ordovician, and the reservoir of fracture mainly developed in theYingshan formation and the Yijianfang formation. After the study on the cores andthin sections of the strata of relating well, the results show that the diagenesis of the Ordovician reservoir are complex and diverse, including cementation, micritization,recrystallization, silicification, pressure solution, dissolution and karstification andfracturing. The type of the mechanism of Ordovician reservoir space in the study areacan be divided into contemporary corrosion, Caledonian Paleo-Karstification, earlyHercynian karstification, and fracturing. And the Caledonian karstification mainlydeveloped small corrosion holes or irregular solution porosity; and the earlyHercynian karstification developed three karst cycles under the unconformity, whichcan produce the reservoir of cave; however, fracturing can develop a large number ofcracks, which can form the reservoir of fracture and also can be used as the infiltrationchannel of dissolution fluid. After studying the development and distribution of theOrdovician reservoir in the study area, it can be learned that the reservoir ofkarstification porosity mainly developed in the upper of the Yijian formation, and thereservoir of karstification fractured-vug mainly is controlled by the unconformity; andthe reservoir of karstification cave mainly developed in the three karst cycles whichare developed by the early Hercynian; and the reservoir of fracture mainly developedin the Yingshan formation and the Yijianfang formation. The Ordovician reservoirs inthe region mainly are controlled by lithology, fractures, karstification, and tectonicposition of the rock, which affect each other and commonly control the developmentand the distribution of the reservoirs. Based on the study above, the Ordovician karstreservoir developing zone can be divided into three types. And zone III is generallyfavorable developing areas; and zone II is more favorable developing areas; zone I isthe most favorable developing areas.