Diagenetic effects of high thermal overpressure in the Yinggehai basin, offshore South China Sea

摘要

There are unique temperature-pressure characteristics in the Yinggehai basin, so its reservoir diagenesis has some unusual processes and traits. Through comparing two types of overpressure systems (selfsource type and conduction type) that have been confirmed by study of cores and logs, this paper illustrates the impacts of high geothermal gradients and overpressure as the conditions for water-rock reactions on diagenesis.The process of diagenesis and its effects on reservoirs are also discussed. The results show that: [1] high geothermal gradients result in the easy dissolution of some minerals, thus resulting in the decreases of sandstone porosity, and creation of secondary porosity; [2] self-source overpressure can prevent parts of the original porosity from compacting, which sometimes results in high porosity in deep reservoirs; [3] fluids expulsion causes lots of cracks which effectively increase reservoir permeability, and hot fluid from depth can accelerate the process of diagenesis in overlying strata.