Genesis And Mode Of Fractured-Vuggy System In Carbonate Rocks, Tahe Oilfield, China

Tarim basin is one of promising exploration area in china, and Tahe oil field (Located at the Akekule uplift in the Tarim Basin, Xingjiang, China) is one of favorable exploration block in Tarim Basin. Factual survey shows Tahe oilfield is carbonate karst reservoir, the reservoir spaces are mainly caves, pores, and fractures that resulted from karstification and structural deformation over several geologic periods. Complexity and inhomogeneity of reservoir becomes a baffle of exploration and development in Tahe oilfield.Fracture surveys were conducted across the North part of Tarim Basin in order to investigate the development and geometries of Karstification in Tahe oil field. Through five times field work , a mount of firsthand data be collected and multi-analytical approaches were applied for getting chemical, structural and the genesis of fissure, fracture and cavies in Ordovician carbonate rocks. Analytical results have high resemblance with Tahe oil field. We integrate the comprehensive study, such as Geology, Structure, Topography, Climate and hydrology for getting the characteristics of cavies. The characteristics from microcosmic to macrocosm, ground surface to underground and modern karst to paleokarst are also being considered for getting forming conditions, development characteristics , genesis and mode of fractured-vuggy system.Firstly, karst reservoirs are controlled by fracture system. Fracture and derived fracture are prophase passway of karstification, enlarge the contact area between water and carbonate rocks, also increase the contact area of between surface water and ground water. Fracture and derived fracture improve carbontes rocks permeability, enhances the karstification, accelerate the solution speed. Fractured region is beneficial area for fracturing and karst development. Between Fracture strike and direction of karstificaiton have great extent of consistency. Beading form reflection is typical shape of large cavies or fracture in seismic profile. Distribution of beading form reflection also has a large extent of consistency with the strike of fractures. Furthermore, huge cave system is located at the junction of several fractures/fault developed area.Secondly, Karst slope is the most favorable and preservation area for karstification. When seeking the karst reservoir, the gentle slope or upper residual hill is the most advantage area for exploration target. Karst highland and Karst basin is the next favorable target for karst reservoir. Fracture/ derived fracture and topography of Karst are two domain factors for controlling the karstification. The study shows topography of Karst is the main controlling factor for karstification during early hercynian. Fracture/ derived fracture are the domain controlling factor for karstification during middle Caledonian and early hercynian.Thirdly, three kind mode of fractured-vuggy system were built by field survey in the North part of Tarim Basin. There are paleo-subterranean river fractured-vuggy system, hall type fractured-vuggy system and bedding fractured-vuggy system. The study of heavy (thick) layer collapse karst shows thick breccia in collapse karst is multicycle formed. Giant cave system is forming on the base of original cave and continuous collapsing of burden.At last, we discussed the favorable distribution of karst region in Tahe oil field from three different way of fluid input. Study shows the wedge out of SANGTAMU formation is the advantage area for karstificaiton, and its corrosion fluid input by multivariate way to fractured-vuggy system.