Creation of pre-oil-charging porosity by migration of source-rock-derived corrosive fluids through carbonate reservoirs: one-dimensional reactive mass transport modelling

Abstract

Locally increased porosity of carbonate reservoir rocks may result from acidic fluids that migrated as a pre-oil phase through the reservoir. Here, hydrogeochemical modelling, which is based on the principles of chemical equilibrium thermodynamics, is performed to test such a hypothetical concept. Despite the generic nature of the model, the modelling results give basic and quantitative insights into the mechanisms of calcite dissolution in carbonate reservoirs induced by migrating acidic and corrosive aqueous fluids.The hydrogeochemical batch modelling considers pre-oil-phase aqueous fluids that form by kerogen maturation in siliciclastic source rocks underlying the carbonate reservoir rocks. Although saturated with respect to calcite, migration of such fluids through the carbonate reservoir triggers continuous calcite dissolution along their migration path following a decreasing pressure and temperature regime. One-dimensional reactive transport modelling reveals that thermodynamically controlled chemical re-equilibration among pre-oil-phase fluids, calcite and CO 2(g) is the driving force for continuous calcite dissolution along this migration path. This reflects the increasing solubility of calcite in the system 'pre-oil-phase fluids/calcite/CO 2(g) ' with decreasing pressure and temperature. In consequence, such fluids can preserve their calcite-corrosive character, if they are exposed to continuously decreasing pressure and temperature along their migration path through the reservoir. Supplementary material:The modelling input files to ensure retraceability of our modelling approach and its results are available at

Sol-Gel Processes in Micro-Environments of Black Shale: Learning from the Industrial Production of Nanometer-Sized TiO2 Polymorphs

“…However, during subsidence in a sedimentary basin, a variety of soluble organic compounds are released from the organic material which control different hydrogeochemical processes-as these compounds may change in pH. For example, during early diagenesis to the oil window, acidic and corrosive hydrogeochemical conditions develop due to the release of low molecular weight organic acids (e.g., acetic acid) or carbon dioxide and lead to dissolution of unstable minerals, which is compensated by the precipitation of solid solutions at equilibrium [28].…”