Interactions Between Rocks and Fluids in a Mature Field of Song Hong Basin, Vietnam: Implication for Carbon Storage

ligocene rocks and fluids of A-1X well were conducted for source rock and fluid characterization and implying the suitable geological sites for CO2 storage from high-salinity water in sandstone reservoirs based on Rock-Eval pyrolysis, vitrinite reflectance measurement, bitumen extraction, hydrocarbon fractionation, gas chromatography, stable carbon isotope, formation water and X-Ray Diffraction analyses. Shale source rocks reveal fairly good potential of hydrocarbon generation. Compositions of gas sample in gas-related zones 1010-1110m are mainly composed of CH4, following C2+, N2, and a little content of CO2 and no noticeable of H2S. Carbon isotopes of oil and gas samples reveal the organic matters mainly derived from sapropelic and little humic sources, entering the mature stage to oil window phases. The formation water is classified as Calcium-Chloride type that contain high concentrations of total dissolved solid, salinity, and K+, Na+ and Cl- cations. This formation water is associated with deep source, and close system that are effective conditions for a large pool with good sealing capacity and not impacted by dissolution of the salt rock around. Most sandstones comprise very high visual porosities including high quartz, plagioclase and calcite minerals that are favorable conditions for subsurface pore space and CO2 injection in over saturated fluids. The popular presence of brittle minerals in the upper part of strongly fractured basement indicates this could be a good sandstone reservoir. The finding is identification of suitable candidate for storing CO2 in the saline aquifer under the active petroleum system with current oil and gas accumulations.