Diagenesis And Controlling Factors Of Palaeogene Mid-deep Reservoir In Baxian Depression

Baxian Depression is one of the main oil and gas Jizhong Depression, but also one of the key areas of Huabei Oilfield exploration. At present, Baxian Depression has nearly 70% of the remaining hydrocarbon resources are not found, so it has great significance to study mid-deep strata reservoir of Baxian Depression for its exploration and development.This paper aims to study Shahejie Formation of palaeogene mid-deep reservoir in the Baxian Depression of Central Hebei Province, Es3 and Es4 are the target formation, the depth is more than 3000 m, the area of Cha-gao-mao and Wen’an slope as the main research area. Based on a lot of research about the sedimentary characteristics of Shahejie Formation and a large number of relevant documents, using sedimentary petrology, reservoir geology theory and diagenesis theory as a guide, according to lots of slice analysis, combining with X-ray diffraction analysis, vitrinite reflectance, carbon and oxygen isotope, fluid inclusion, cathodoluminescence, scanning electron, core properties, reservoir pressure and other geochemical data. This paper studied Es3 and Es4 characteristics of reservoir rock, pore structure and diagenesis, discussed the main types, characteristics and effects on reservoir properties. Establish reservoir formation and evolution models on this basis, and analyze the factors affecting the reservoir control. This paper has made the following main knowledge and achievements:(1) Baxian Depression Es3 and Es4 has high feldspar and lithic component, with an average content of 20%~40%. Low compositional maturity of reservoir sandstones laid a favorable foundation material for late dissolution laid a favorable foundation material. Wen’an slope and the area of Cha-gao-mao regardless of Es3 and Es4, reservoir sandstones are in lithic feldspathic sandstone and feldspathic sandstone.(2) Dissolution developed well at Es3 and Es4 of Baxian Depression lead to secondary porosity development is more than the primary porosity, both the rate of contribution to the total surface porosity of 73% and 58%. Comparing the reservoir of Es3 and Es4, the total surface porosity of Es3 over Es4 which is deeper, but Es4 had more primary porosity than Es3, while micro crack is relatively developed, abnormal development of the high-pressure make primary porosity preserve.(3) The constitution of cements is more monotonous in the third member of Shahejie Formation(Es3) and the fourth member of Shahejie Formation(Es4) in Baxian Depression. Carbonate minerals(calcite, dolomite, pyrite, siderite) is the highest content, nearly 90%. Besides, authigenic quartz and kaolinite followed and a very small amount of chlorite and other authigenic minerals do not actually have impact on the reservoir.(4) Calcite cement of Es3 and Es4 is formed mainly in A period of middle diagenetic which is analyzed by the alcite cement, oxygen isotope test and previous inclusion data from the Microprobe Laboratory of University of Regina, Canada. Based on the research of Vitrinite reflectance, the maximum peak temperature pyrolysis, analyses of X-ray diffraction(XRD), electron scan microscope(ESM), and measurement of homogeneous temperature for inclusions, the author divided the reservoir diagenetic stages of the study area into several stage including Syngenetic stage, the early to late period of early diagenetic stage(A~B stage) and the early to late period of middle diagenetic stage(A~B stage), not including the late diagenetic stage.(5) The controlling factors of mid-deep strata reservoir of Baxian Depression include deposition, diagenesis, formation pressure and hydrocarbon emplacement and so on. Deposition factor is congenital factors to the development of reservoir and indirectly controls reservoir properties. Diagenesis factor has great impact on reservoir and decides the acquired factors and dissolution is the main ideal to the good reservoir. Primary porosity preservation can be saved well in deep because of the developmental abnormalities hypertension.(6) By analyzing the test data, logging data and comprehensive research of existed core drilling(wall core) testing data and combining with clastic grade of reservoir porosity and permeability classification criteria, author established classificated(grading) standards of Baxian Depression Es3 and Es4.