Chemical reactions in subsurface storage rocks - First results from reactive fluid flow experiments

Faults and fractures are important fluid pathways in subsurface energy reservoirs. Especially in geothermal energy production, hydrocarbon production, and energy storage in the deep subsurface, fractures can enhance reservoir quality and production- or storage potential. In subsurface reservoirs however, mineral precipitations often reduce available fracture apertures, and thus fracture porosity and permeability. The present study is performed on a homogeneous, massive marine Sandstone (Bentheimer Sandstone from Gildehaus Quarry, Lower Saxony, Germany, Lower Cretaceous) and a heterogeneous, laminated fluvial sandstones (grès vosgien from Cleebourg, Alsace, France, Lower Triassic). Hydrothermal flow-through experiments are performed at 420 °C and 30 MPa for 72 hours to compare resulting precipitated cement textures on fracture analog surfaces. The experiments reveal a heterogeneous development of syntaxial overgrowth cements. Homogeneous sandstone, composed of similar grain sizes and quartz grains, show a homogeneous formation of overgrowths. Heterogeneous sandstones, composed of laminae with different grain sizes and variable detrital grain compositions, show smaller overgrowths on finer grained laminae when compared to coarser grained laminae. The sedimentary texture might thus be an additional factor to consider when assessing mineral precipitations in fractures and their influence on subsurface fluid flow.