黄骅坳陷中区超压对有机酸生成和溶解作用的抑制

渤海湾盆地黄骅坳陷中区古近系具有超压特征,深层油气主要分布在超压地层的次生孔隙中.为了研究超压与泥岩有机酸生成及储集层溶蚀作用的关系,进行了不同温度、压力条件下泥岩有机酸生成的成岩物理模拟实验.结果表明,当模拟温度相同时,在25MPa压力条件下泥岩的剩余总有机酸含量要比55MPa压力条件下的低,而25MPa压力条件下的有机酸生成量却比55MPa压力条件下的要高,这说明压力对有机酸的生成具有抑制作用.孔隙度的实测数据也支持了这一结论,超压发育的港深48井储集层的主要次生孔隙发育带埋深比超压不发育的歧南2井下移了580m,超压抑制了有机酸的生成,并由此导致了储集层溶蚀作用的延迟.因此,深层油气勘探应集中于超压地层中.图2参23

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

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 overpressured formations. The diagenetic physical simulating experiments were done at different temperatures and under 25MPa and 55MPa respectively to study the relationships between overpressure 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 under the 25 MPa are higher than those under 55 MPa, suggesting that pressure retards the organic acid generating. The porosity data from different pressure settings also supports the results. The main secondary porosity zone of Well GS48 with overpressure is 580m 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.