Stratigraphic Characteristics And Comprehensive Evaluation Of Reservoirs In Missan Oilfield

The marine carbonate reservoir in Missan oilfields is of characteritics of complex genetic types and reservoir interspaces types.And differential distribution of oil-water relation is due to strong heterogeneity of reservoirs. The problem is not clear to the distributed regularity of high quality reservoirs and hydrocarbon enrichment areas. These severely restrict the oilfield development and production during the later process. For all this, the paper focuses on the late Cretaceous carbonate reservoir of Mishrif group. Through the following research work, like the fine strata classification and correlation, the study of sedimentary geological characteristic and the evaluation in detail of the reservoir interspaces types and pore structure characteristics, In the meanwhile, according to fuzzy clustering algorithms and Well Logging Curve Unit, the lithology of the complex carbonate reservoir could be identified precisely and fracture could be depicted accurately. Finally, the fine characterization and comprehensive evaluations of the carbonate reservoirs could be achieved.This paper is based on the plentiful information of drilling, core, analysis of laboratory and logging data. The classification system of marker bed is set up to limite the boundary of formation. And the isochronal stratigraphic framework of Mishrif group layers are established in consideration of the variation characteristics about flooding surface, depositional base-level cycle and the trend of formation thickness, aiming to reveal the formation distribution disciplinarian. Based on the study of facies indicators, it is considered that the Mishrif Reservoir develops carbonate platform depositional system under the background of shallow water, and the sedimentary system could divide into four phase and six subfacies, like shelf, platform shoal,open platform,intertidal and supra tidal zone. And it is clear that the palaeo stratum presents the vertical sedimentary sequence evolution of prograding in the early stage and retrograding in the late. Then a carbonate sedimentation model about carbonate platform to open sea shelf on the background of shallow water is established. The Mishrif Reservoir space is mainly pore-fissure composite type, and secondary dissolution pores and fractures are the main components, especially the increasingly growing cracks greatly impact the reservoir percolation capacity. According to the capillary pressure curve analysis of the core sample, the reservoir presents smaller slanting degrees. The pore structure has characteristic of low-medium porosity and fine throat. Research is carried out about four characters of reservoir and the reservoir parameters model is set up. By using conventional histogram and cross plot, rock-electricity relation of the complex Mishrif carbonate reservoir is found. Firstly the rock type distributed approximately into micritic limestone, limestone and reef limestone.Then by using cross plot of preferably curve like DEN, GR, RD, AC, quantitative lithology identification standards is found.And the high-precision recognition of complex carbonate reservoir lithology is also achieved by means of fuzzy clustering algorithm.The consistent rate reaches up to 97.73%.With defining the absolute value of dual lateral resistivity logs, horizontal fractures and diagonal fractures could be primarily recognized combining sonic, density and neutron porosity. Furthermore, Well Logging Curve Unit is used in calculating the range, mathematical expectation and variance. It appears that there is a strong positive correlation between the fracture development probability and variance. Through this method, flowing ability and dip occurrence of the fracture could be quantitative expressed, and the developed area of facture could be effectively predicted. It is provided a reliable geologic evidence for finding high quality reservoirs, directing exploitation and adjusting scheme.