| Dongfang gas field is located in the north of central diapir zone of central depression in Yinggehai Basin, and it is a typical lithologic trap gas reservoir. In this study area, influenced by high temperature and high pressure, mud diapir invaded upwards intensively and frequently, a mass of thermal fluid containing carbon dioxide flowed into the first member of Huangliu Formation which is the target interval of middle-deep layers. Because the thermal fluid invaded unequally on the transverse and longitudinal direction, the degree of enrichment of carbon dioxide differentiated in different areas and formations, which led to different degree of transformation of reservoir’s property by the influence of thermal fluid. Affected by above factors and controlled by lithology, the physical property of formation presents a characteristic of strong heterogeneity, the correlation of porosity and permeability becomes worse. Besides, in the condition of high temperature and high pressure, rock-electro parameters are not easy to be tested, so it is a problem to build reservoir parameter models by a unified standard. On another side, because the size of partical is very fine, making the resistivity of gas zone generally low and the gas-water transition zone very long in some layers of the first member of Huangliu formation, the effect of using conventional identification charts to divide gas and water layers is bad, which causes a great difficulty in fluid property identification.In order to solve above problems, many parameters, including fluids’and cores’slowness travel time and resistivity in different temperature, pressure and saturation conditions, are measured in laboratory, and the variation law of some parameters just like compression and shear wave velocity and rock-electro parameters in different conditions is analyzed. Combined with physical propertiy analysis and mercury injection data, on the base of mastering general geology and four properties’relationship of this study area, the porosity-satuation model based on rock physical model and Archie equation and classified permeability model based on Fisher discriminant analysis are built. After the analysis of the logging response characteristics of gas and oil zone, combined with relevant mathematical theories, the fluid property identification work is performed respectively by fuzzy identification based on Fisher discriminant analysis and a model based on compression and shear wave velocity. Meanwhile, in order to realize the accurate calculation of gas reserves, on the base of the analysis of methane’s and carbon dioxide’s physical properties, the logging response characteristics of various gas layers in which the carbon dioxide is in high levels of volume ratio or not is analyzed, and a quantitative prediction model of carbon dioxide in gas zone is built by long and short spacing counting rate raw data of compensated neutron log.The well data is processed and interpreted in Dongfang gas field by these above methods. The average relative error of porosity calculation is lower than6%, which is in accordance with the standard of the National Mining Reserves Committee, and permeability and irreducible water saturation both have high degree of coincidence with core data. In the identification of gas or water layer, the accuracy of validation test is100%and the accuracy of non-sample layers interpretation is88.9%. In the quantitative prediction of carbon dioxide, two new wells are interpreted by above methods, the errors between logging interpretation values and the results obtained from MDT test are lower than10%in both wells. |
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