| M Oil Field is located in the West-South of Iran Basin, which was discovered in 1908 and has been developed since 1911. It is the first commercial oil field discovered and put into production in the Middle East Area. The Asmari Group, the main production layer, is a fracture-cave type carbonate reservoir. During nearly 100 years of development, a lot of historical events has occured such as the high-containing-H2S gas channeled from the lower part of Jurassic and large amounts of gas leaked out the ground. The distribution state caused by the above cases presents the upper gas cap, the lower fringe water, extremely low reservoir pressure (the pressure coefficient is only about 0.344), and serious reservoir heterogeneity. Piror to this study, the production in the oil field was basically closed. To continue to effective, sustainable and scale development of the century old field, it is necessary to perform comprehensively evaluation to the complex carbonate reservoir of Asmari Group once more and to provide the technical basis for the establishment of oil field development and other work.The paper mainly studies the carbonate reservoir of Asmari Group in M Oil Field on the basis of lots of outcrop observation, experimental analysis, data form mud logging, wireline logging and well testing. By the means of histogram and cross plot etc, the paper analyses the characters of sedimentary micro-facies and the reservoir development, identifies the effective reservoir and the fluid, defines the lower limit of effective reservoir. The paper also studies the distribution law of favorable reservoir, establishes the 3D geologicalmodel, and achieves abundant research results.(1) The previous researchers considered that the reservoir lithology of the Asmari Group was limestone in M Oil Field. But the paper verifies that the reservoir lithology is mainly dolomite, carbonatic dolomite, dolomitic carbonate and carbonate using lithology identification charts newly established.(2) The paper establishes the sedimentary model of Asmari Group in M Oil Field, identifies and divides three sedimentary mirco-facies(restricted platform, open-platform and evaporate platform), analyses the physical characteristics and the spatial distribution of different micro-facies, points out that the open-platform is the favorable facies belt, and provides geological basis for the follow-up reservoir study.(3) From macroscopic to microscopic, the paper further studies the types and properties of reservoir space in Asmari reservoir in different scales and different angles. Solution pore, cavities and fractures develop in research area. Thereinto Solution pore and cavities are the storage space of oil and gas, and the fracture is the migration pathway.4) Four types of pore throat are summarized in Asmari reservoir, which are the big, the middle, the small and the micro-pore throat. Corresponding to different porosity interval, the paper respectively analyses the pore throat distribution, establishes templates of pore throat distribution, and analyses the law of development of pore throat. All these studies can help to understand the reservoir.(5) The paper studies the heterogeneity and the reservoir connectivity of Asmari reservoir, referring to the geochemistry index and pressure change occured during production, which helps subsequent well placement and optimum perforation.(6)Using technical methods of processing fracture parameters based on conventional wrieline logging data, the paper analyses the relationship between the reservoir space distribution and the lithological combination. Solution pore and cavities develop as dolomitization enhance, and the fracture develops as dolimitization weaken. The identification templates of reservoir space type and the lithology are established.(7) With the relative permeability data, the crossplots between the porosity and the saturation, the oil occurrence characteristics and the mercury injection data, the cut off of Asmari Group reservoir in M Oil Field is defined. It provides a favorable basis for the further statistics of effective reservoir and reservoir evaluation.(8) The identification templates of dense layer, mudstone, water layer and oil-bearing layer are established by the lithology, the physical property and the oil-bearing property. The reliability of these templates is proved by production data.(9) The paper focus on the methods of fluid discrimination and fluid interface recognition in abnormal low pressure reservoir in Asmari Group.The law of fluid space distribution is defined, which is favor to solve the bottleneck that have plagued the drilling and developing technical staffs in a certain extent.(10) Utilizing Comprehensively in various technical indicators, the classification and identification standard of Asmari reservoir in M Oil Field is firstly established. According to these standards, the reservoir is divided into four categories. The distribution of four-type reservoirs is also studied. In virtue of the indexes such as daily capacity and period of stabilized production etc, the distribution of high productivity wells is studied, which can guide the well deployment and optimize the drilling track.Based on the results above,3D geological structure model and conventional property models are established. The reliability of these models is verified by drilling of horizontal well, the testing results and the production data. The Testing yield of horizontal well and all production indexes exceed the expected target. According to the success establishment and verification implementation of model, the technique idea and method for building geological model that is consistent with the underground actual objective law in the old oil field lack of seismic key data is formed. In addition a set of comprehensive evaluation process, method and technology system for similar complex reservoir is established. These will improve the overall efficiency of marginal oil fields which are at a standstill, in the late period of development and urgent need to restore the production. |
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