Delicate Reservoir Description And Residual Oil Distribution Research On The Second Member Of Yanchang Formation In Ansai Oilfield

Delicate reservoir description refers to precise geological studies and residual oil distribution research carried out after a oil field put into exploitation and production, with intense exploitation of oil reservoirs and increasing dynamic data of production. Generally, research content of delicate reservoir description includes analysis of precise depositional microfacies and reservoir heterogeneity, classification of flow units, research on spatial distribution of flow unit and changes of reservoir quality and dynamic development of oil and wate during injection and exploitation, explanation for water level, as well as three-dimensional geological modeling and reservoir simulation. The aim is to understand reservoir more accurately and figure out of residual oil distribution under the ground.At present, the Ansai Oilfield has entered the so-called three high-extraction stage of "high water-bearing, high degree of recovery, high oil production rate", after 10 year's development. The major problems in the study area include wells with high water-bearing, oil production with high liquid, difficulty of controlling water and making a stable oil production, serious reservoir heterogeneity, increasing formation pressure year after year, water injection profile moving downward but interface of oil and water elevating. Furthermore, it is hard to determine a reasonable production pressure and tough to make a comprehensive management, because of complex condition of seepage underground, highly dispersed distribution of residual oil, in addation to the above problems. Therefore, it is of practical and guiding significance in hydrocarbon exploitation and arrangement, sapping and adjusting potential hydrocarbon reserves further in the future, to construct a three-dimensional geological model for the reservoir, establish a data base of reservoir parameters in three-dimensional spatial distribution, research on numerical simulation of Chang 2 reservoir based upon the geological model, from the basic geological reservoir issues existed in the oilfield.Lithofacies and well log facies of typical wells are analyzed, horizontal distribution of depositional facies and its evolution is investigated, and isochronological stratigraphic framework of Chang 2 oil-bearing group of Yanchang formation in Pingqiao region of Ansai Oilfield, Ordos basin is constructed in this study, based on observation of lithofacies indicators from cores, high-resolution sequence stratigraphy and well log facies study, accompanied with sedimentology, geology and geophysical logging theory. The low critical boundary of lithology, physical quality and hydrocarbon-bearing property of the reservoir is determined, in the basis of secondary interpretation of logging curves and exploitation dynamic data. Inter-layer, intra-layer and horizontal heterogeneity of reservoir is studied, and relationship between sedimentary microfacies and reservoir properties is evaluated in this study.A rich geological knowledge base and a three-dimensional geological model for the Chang 2 reservoir is established under limited condation of depositional facies and geological characteristics, via geostatistics and stochastic simulation by using the Petrel geological model software, based on a combination of multi-disciplinary approaches, in considerating different geological reservoir variables. Numerical simulation and residual oil distribution is studied in this paper after outlined the geological model, which lays a robust foundation for hydrocarbon exploitation and development of Ansai Oil field in the future.