Sedimentary Facies Characteristics And Reservoir Evaluation. Tabamiao Taiyuan Formation

Tabamiao Block is located in the north of Ordos Basin with an exploration area of7200Km~2, and it's gas reserves is 671.608 billion cubic metres. Taiyuan Formation is one ofthe important oil reservoirs, but less study has been done there in the block and manydisputed questions exist about sedimentary facies' characteristic and reservoir evaluation ofthe second section of Taiyuan Formation especially in recent years. With the developing ofthe farther studies in Tabamiao Block, it has been a prominent obstacle to the next work for along time. To clarify the characteristic of sedimentary facies carefully and evaluate reserviors of thesecond section of Taiyuan Formation reasonably, A way of solving these questions has beenfound: With the guide of high-resolution sequence stratigraphy theory, sedimentary facies ofTaiyuan Formation would be analysed in this paper using core and log data, based on thesequence division and lithofacies analysis when tectonism and deposition backgroud in thelarger area be known well. This method follows a path from point (well) to line (crosssection), to surface (map), to area (field) finally in order to find the spacial relations amongsedimentary microfacies and to give reason of the next work in exploration and exploitation. In this paper, high-resolution sequence stratigraphy theory has been used to analysisshort stacking patterns of basal-level cycle and divided Tabamiao strata into 3 sequenes: S1,S2 and S3. 400 metres core of 11 wells has been observed carefully and described delicately.It is considered that Taiyuan Formation is composed of shore and delta environment and itcan be divided 8 subfacies and 16 microfacies after lithofacies and log facies is identified.Compining sedimentary parameters' distribution, sandbodies' plane distributing laws areachieved and sedimentary modes are set up. According production data analysis, cutoff ofefficiency reservoir is confirmed, and that is ф>6%,K>0.15md. Then efficiency layers insingle well are identified, and Vk,Sk and Nk are used to analysis reservoir planeheterogeneity. It is considered that distributary channels and submarine distributary channelsare major pay reservoir, and mouth bars and barrier bars are secondary pay reservoir. And tidechannels are not considered that they have good gas production ability. Gray Theory is usedin the paper to classify reservoir different categories by its quality by way of electing 1 majorgene and 7 secondary genes. The result of reservoir evaluation is that S2 cycle and S3 cycleare better reservoirs and have more potential.