The Role of Seal and Source Rocks in Fluid-rock Interactions and their Reservoir Effects within the Carbonate Deep Burial Realm

Discoveries of deep high-quality carbonate reservoirs challenged the general understanding on the evolution of porosity decreasing with depth. New mechanisms of pore generation and preservation in the deep realm require to be proposed. Dolostones in the Feixianguan and Dengying Formations experienced maximum depths in excess of 8000 m, but still retained high porosity. Petrographic observation and homogenization temperatures help to identify products of deep fluid-rock interactions, visual and experimental porosity were used to quantify reservoir effects, the distribution of products finally being plotted to unravel the mechanisms. Th data reveal that thermochemical sulfate reduction (TSR), burial dissolution and quartz cementation are typical deep fluid-rock interactions. The SO42- of residual porewater sourced from the evaporative dolomitizing fluid was supplied for TSR in the hydrocarbon column, the TSR-inducing calcite cements were homogeneously dispersed in the hydrocarbon column. Quartz cementation was caused by the increasing acidity and Si-rich residual porewater in the oil column. Burial dissolution is forced by organic acid and limited in oil-water contact. This study suggests that seal and source rocks not only play important roles in hydrocarbon accumulation, but also have a general control on the deep fluid-rock interactions and porosity evolution in the deep burial realm.