Influencing factors and thermodynamic-kinetic mechanism of feldspar dissolution in deep-buried sandstone in Bozhong Depression
摘要
The deep layer has become an important replacement field for oil and gas exploration, but the formation mechanism of effective reservoirs is unknown, and the distribution of dessert reservoirs is difficult to predict, which seriously affects the discovery of deep resources. In this paper, the reservoir of the first and second members of the Shahejie Formation in the Caofeidian 6-4S area of the Bozhong Depression is taken as an example. Through the comprehensive means such as well-seismic calibration, denudation recovery, source-sink quantitative coupling, basin simulation, microscopic observation, X-ray diffraction, inclusion and thermodynamic analysis, the reservoir formation mechanism of dissolution pores and the favorable area distribution of thermodynamic prediction of dissolution reaction in the study area are carried out. The results show that the dissolution pores are the dominant type, accounting for more than 80% of the total pores. The dissolution reaction between soluble minerals such as feldspar accumulated in the near source and acidic fluids such as organic acids formed in the adjacent strata is the main mechanism for the development of dissolution pores. The organic matter in the adjacent strata is controlled by temperature and pressure during the burial evolution process to form organic acids, and migrates to the adjacent reservoirs for selective dissolution under the action of pressure and other driving forces. The characteristics of thermodynamic parameters (ΔG, which can determine whether feldspar is dissolved) and kinetic parameters (R, indicating the degree of feldspar dissolution) of feldspar dissolution reaction show that the thermodynamic parameters of feldspar dissolution are positively correlated with temperature, and the kinetic parameters are correlated with the concentration of organic acid discharge. The results of thermodynamic and kinetic parameters are coupled with provenance-sedimentary facies-diagenetic facies, and it is predicted that the plane area of Type I favorable area is 50 km2, and the plane area of Type II favorable area is 62.4 km2. This method provides theoretical reference and method guidance for the prediction of favorable reservoir distribution of deep clastic rocks, and has a good application prospect.