Reservoir Evaluation And Main Controlling Factor Analysis Of Mishrif Formation In BU Oilfield In The Middle East

BU oilfield is located in Missan oilfield group.Iraq.Due to the variety of genetic types and complex pore structure of marine carbonate reservoirs,the distribution of favorable reservoirs and oil and gas accumulation zones is not clear at present,which seriously affects the later development and production of the oilfield.In this paper,based on the data of core,physical properties,analysis and testing,conventional logging,logging interpretation and oil test conclusion,the Mishrif formation of BU oilfield is established as an open platform environment on the basis of the study of facies marks.The open subtidal and intra-platform reef beach deposits in the open platform are characterized by the development of open platform subtidal and intra-platform reef beach deposits.By establishing the plane distribution of single well facies,profile facies and sedimentary microfacies,it is concluded that the reservoir section in the study area has the characteristics of stable thickness and strong transverse comparability.and the reservoir has obvious lithologic zoning characteristics because of the vertical development of different strata without lithology.The analysis includes physical properties,lithologic characteristics,pore structure characteristics and reservoir space types.It is considered that only the pores of Mishrif formation in BU oilfield are the most developed,the fractures are not developed,and the interparticle dissolved pores and biological casting mold pores are the main reservoir spaces of carbonate reservoirs in the study area,especially the secondary intergranular dissolved pores have great influence on the reservoir seepage ability.Through the analysis of capillary pressure curve,the throat is mainly partial and fine,and the overall pore throat structure is mesoporous fine throat and low pore fine throat structure.A simple logging identification model is established to accurately identify the lithology of complex carbonate reservoirs in non-coring wells.Through the determination of the lower limit of the reservoir,the lithologic characteristics,sedimentary microfacies,porosity,permeability,reservoir spatial characteristics and productivity characteristics of the reservoir are established.the comprehensive influence evaluation method,six parameters restrict and influence each other,the carbonate reservoir in the study area is divided into three types,and the reservoir is evaluated from three angles of single well,section and plane.Then,in order to make the analysis results closer to the reality,the grey evaluation method is adopted,and five main influencing factors,namely,the ratio of grain beach to formation thickness,permeability,muddy content,porosity and oil saturation,are selected for grey cluster evaluation.By comparing the evaluation results with the ratio of grain beach thickness,the favorable reservoir distribution zone is clarified,and the reservoir is divided into three types according to the reservoir permeability on the plane.Finally,reservoir division is controlled from sedimentary facies.The distribution of effective reservoir controlled by Karst and the reservoir development controlled by Karst are analyzed in three aspects:cloth,rock type,physical properties and reservoir space characteristics,and the reservoir development is controlled by Karst.The results show that the reservoir of Mishrif formation in this area is a typical reservoir controlled by facies.Moreover,there are factors that control reservoir development jointly by Karst and sedimentary facies,and good sedimentary facies is the prerequisite for reservoir development.Generally speaking,through the research results.this paper establishes a geological model in accordance with the theoretical reality,and constructs a set of process,method and technical system for reservoir evaluation,which is not only helpful to clarify the direction of exploration and development in this area.Tap the potential of reservoir resources and realize the stable production and reservoir increase production of BU oilfield have important guiding and reference significance for the fine description of complex carbonate reservoirs and reservoir exploration and development under similar conditions in the surrounding areas.It plays a very important role in supporting the efficient development of reservoirs in this block,and provides favorable geological basis and new exploration and development ideas for better searching for oil and gas accumulation zones in BU oilfield and even Missan oilfield group.