Most sedimentary rock formations (tight or highly porous) have geochemical characteristics that can lead to significant reactive ion exchange processes in aqueous media in the presence of carbondioxide. While geomechanical properties such as rock stiffness, Poisson’s ratio and fracture geometry largely govern fluid flow characteristics in deep fractured formations, the effect of mineralization can lead to flow impedance in the presence of favorable geochemical and thermodynamic conditions. Shales which are prominent sedimentary rocks and seal more than two-thirds of oil and gas reservoirs have natural fractures that are unevenly distributed in the geosystem. Experimental works which employed the use of analytical techniques such ICP-OES, XRD, SEM/EDS and TOC techniques in investigating diagenetic and submicro-structural property of crushed shale caprock/CO2-brine system concluded that net precipitation reaction processes can affect the distribution of petrophysical nanopores in the seal rock. The results showed that geochemical precipitates can be formed such that fluid flow through open micro and macro fractures may be constrained. Simulation results reported by various researchers suggested that influx-induced mineral dissolution/precipitation reactions within shale caprocks can continuously close micro-fracture networks, while pressure and effective-stress transformation first rapidly expand the flow path then progressively constrict them. The extent of short term reactive transport is largely determined by available surface area.

Geochemical markers in diagenetic alterations of fracture conductivity of tight sedimentary rocks

249th National Meeting (2015)

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