Constraints on Porosity Creation During Burial Diagenesis in Carbonate Reservoirs

摘要

Many authors have proposed that late burial dissolution has created significant volumes of porosity in carbonate reservoirs. We argue, however: (1) that this model is almost entirely unconstrained by quantitative evidence, (2) that mass-balance constraints indicate that the proposed causes of mesogenetic carbonate dissolution are vastly insufficient, and (3) that Occam's Razor can be employed to more simply explain our existing heritage of carbonate reservoir information in terms of rather minimal late porosity enhancement on a background of overwhelming porosity destruction during the course of progressive burial diagenesis. The model of mesogenetic porosity creation by carbonate dissolution should therefore not be used in the prediction of carbonate reservoir quality. We do not argue against the possibility of relatively small amounts (<1% overall) of porosity being formed by late-burial dissolution, which may occur along fracture surfaces and thus increase bulk permeability. Furthermore, plausible mechanisms of creating larger porosity volumes by burial dissolution in carbonates include anhydrite dissolution and thermal convection of water along deep fracture zones. The literature contains remarkably few case studies indicative of these processes, but examples do exist.