Overpressure retardation of organic acid generation and clastic reservoirs dissolution in central Huanghua Depression

Abstract

There exist overpressures in the Paleogene of the central Huanghua Depression, Bohai Bay Basin, and the hydrocarbons of deep zones are dominantly accumulated in secondary pores of the overpressure formations. The diagenetic physical simulating experiments were done at different temperatures and under 25 Mpa and 55 Mpa, respectively to study the relationships between the overpressures and the organic acid generation in mudstones and the dissolution of reservoirs. The residual total organic acid contents in the samples under 25 MPa are lower than those under 55 MPa at the same temperatures, whereas the generated total organic acids contents under 25 MPa are higher than those under 55 MPa, suggesting that pressure retards the organic acid generating. The porosity data from the different pressure settings also supports the results. The main secondary porosity zone of Well GS48 with overpressures is 580 m deeper than that of Well QN2 with no overpressure; overpressures retard the organic acids generation and result in the delay of reservoirs dissolution. The hydrocarbon exploration in deep basins should be focused on the over-pressured formations. Key words: overpressure, organic acid, diagenesis, secondary pore, diagenetic physical simulation, Huanghua Depression