The Study On Ordovician Karst Reservoir Analysis Of Characteristics And Rich Accumulation Zone Of Oil And Gas In Block9of Tahe Oilfield And Xidaliya Area

In this paper, through the study areas’ core and thin section analysis of Tahe9blocks-Xidaliya, Ordovician, according to the principle of space shape, size and origin,the core space in study areas can be classified as dissolution-pore type、dissolution-cavity type、karst-cavity type、weathering-fracture type、tectoclase type.In the basic of above, there are four reservoir types: beach face dissolution-porereservoir、 karst-fractured-cavity reservoir、 karst-cavity reservoir and tectoclasereservoir. According to the analysis of the study areas’ drilling section reservoir’sdevelopment distribution, it reveals that karst-fractured-cavity reservoir is mostdeveloped, and the next is tectoclase reservoir, the karst-cavity reservoir is also welldeveloped, while, beach face dissolution-pore reservoir is less developed. The beachface dissolution-pore reservoir is mainly developed in Yijianfang formation, MiddleOrdovician, the karst-fractured-cavity reservoir is mainly developed in Yijianfangformation, Middle Ordovician and Lianglitage formation, Upper Ordovician, thecavity reservoir is mainly developed in Yingshan formation, Middle and LowerOrdovician and Yijianfang formation, Middle Ordovician, and partially developed inLianglitage formation. The tectoclase reservoir is mainly developed in Yingshanformation, Middle and Lower Ordovician and Yijianfang formation. The study of thisareas’ 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. With the combination of reservoir’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 fracture-cavity reservoir in the long direction is mainly distributed under theuncomformable surface of top Lianglitage formation, in plane the platform edgebeach facies is this reservoir’s developed distribution zone; The karst-fractured-cavityreservoir is mainly result from the atmospheric water’s denudation in the lateCaledonian-early Hercynian and local parts is the result of the hydrothermal activityin the late Hercynian, some parts is a upgrading result of former two efforts;formation lithology、 surface of unconformity、 karst palaeogeomorphology andfaulting are still controlling this reservoir’s development and distribution; The cavityreservoir in the part of north-western are major developed and distributed in the rangeof150～250m of crust of weathering, early Hercynian and controlled bypalaeogeomorphology; karst-cavity reservoir in the part of south-eastern are mainlydeveloped in the deep level under the crust of weathering, early Hercynian with300mand controlled by fracture. With the study of reservoir’s development controllingfactor in study areas, it turns out that the reservoir is mainly controlled by formationlithology、palaeostructure、fossil fracture、palaeogeomorphology and karstification,etc, this efforts are interacted and collaboratively controlled the reservoir’sdevelopment and distribution. Based on the comprehensive research of the reservoirin study areas, three zones can be divided from reservoir’s developing level:Ⅰ-optimum reservoir’s developing zone;Ⅱ-favorable reservoir’s developing zone;Ⅲ-moderate favorable reservoir’s developing zone. With the existing and preexistingdata of the development and distribution feature of reservoir、the controlling factor offluid distribution、seismic reservoir predicting、and exploitation and production, it ispointed that the rich accumulation zone of oil and gas in Ordovician has two optimumreservoir’s developing zone and four favorable reservoir’s developing zone.