Mechanism of generating abnormal overpressure and its influences on super low permeability reservoirs for upper Es4 member in Chexi depression

Key words:  Chexi depression  abnormal overpressure  super low permeability reservoirs  reservoir properties  geological parameters

Abstract:

By means of analyzing sedimentary microfacies, structure features, diagenesis, porosity and permeability and geochemical testing data, the mechanisms of generating abnormal overpressure and its influences on super low permeability reservoir of upper Es_4member in Chexi depression were discussed detailedly. The results show that the principal mechanism of generating abnormal overpressure is disequilibrium compaction, and the secondary is mineral diagenesis. The formation temperature increasing and diagenesis deepening with depth are inhibited by abnormal overpressure. In the abnormal overpressure section, secondary porosity is relatively well preserved, which is a favourable condition for oil and gas exploration and development. In argillaceous sandstone based super low permeability reservoir, it is not a linear relationship between oil and gas production capacity and formation pressure coefficient, as a higher capacity corresponds to the pressure coefficient of 1.2-1.3. This phenomenon results from single sand body thickness (sand mud ratio), physical parameters, oil saturation and pressure sensitivity and so on.