The Study On The Characteristics Of Carbonate Reservoir In Ordovician Of The Tuofutai Area, Xinjiang

The fracture-cave carbonate reservoir of Tahe oilfield is different from the fractured carbonate reservoir and reef-pore reservoir, and even more different from the conventional porous sandstone. It is a kind of complex geological body, which has undergone multi-stage tectonic disruption and paleo-weathering karstification, with strong heterogeneity on both vertical and horizontal direction. This paper synthetic studied the characteristics of carbonate reservoir in Ordovician of the Tuofutai Area, Xinjiang and analyzed its control factors based on previous data, the observation and description of cores, cores laboratory analysis combined with stratigraphy, petrology, karstgeology, reservoir geology and petroleum development geology.By using the seismic, geologic and logging data, this paper tries to through a deep study on the characteristics of carbonate reservoir and has obtained the following achievements.The fracture-cave carbonate reservoir of Tahe oilfield is mainly controlled by paleokarst, structure and rifting, with Caledonian and Hercynian karstification dominantly developed. It is held that the sedimentary facies in Ordovician of the Tuofutai Area include open platform facies, basin among platforms facies, the edge of the platform facies, mixed depositions of continental shelf facies. the Middle Ordovician Yijianfang Formation mainly was open platform environment with intraplatform point reef sub-facies developed in Yijianfang formation.Because it is covered very thick Sangtamu formation, the karstification mainly was the middle Caledonian karst and the karstification types mainly was supergene karstification controlled by iyngenesis karstification and parallel unconformity surface which controlled by the sea level change. The reservoir-rock types in these formations are sparite grained limestone, sparite (micrite) calcarenite, microspar calcarenite-biolclastic limestone, microspar biolclastic-calcarenite limestone, contain biolclastic (calcarenite) calcipulverite. During the long evolutionary history the Ordovician carbonate were reworked under different diagenetic environments, i.e. normal littoral-neritic and shallow-deep burial diagenetic environment.The porosity through four evolutionary stages, namely construction and destruction of primary porosity stage, fracturecavity of construction stage, construction of fracturecavity stage, Buried modification and filling fracture stage.The Ordovician reservoirs was controlled by fault, and The upper reservoirs of Yijianfang Formation divided into four fracturecavity zones (TP8 wellblock, TP7 wellblock, TP12 wellblock, TP10 wellblock). Fracture and karsts along the preexisting faults where structural deformation was very strong was the ideal site of reservoir. The middle Caledonian karstification play an very important role in development of reservoir. Distributiong and development of dissolution-pore reservoir was controlled by the sedimentary facies.