Impacts of Water Saturation on Gas-Bearing Property and Recovery Ratio of Marine Shale

Water occurrence characteristics and water saturation are crucial for evaluating the gas-bearing property of marine shale formations and the development law of gas wells. In this work, the impacts of water saturation on the gas-bearing property and recovery ratio of marine shale are studied using 2D NMR technology and an improved adsorption gas/free gas calculation model. The results demonstrate that the main factors of shale water saturation are capillary water and free water. Water saturation and shale's capacity to saturate methane are negatively correlated. Bound water effectively inhibits the readsorption of free gas and encourages the desorption of adsorbed gas. Capillary water blocks the gas seepage channel, which lowers the reservoir's gas phase permeability. Free water saturation can be used as a marker to gauge the marine shale's ability to saturate methane. Bound water disrupts the methane adsorption-desorption equilibrium; the recovery of adsorbed gas is therefore greater than that of free gas with high water saturation. Immersion after hydraulic fracturing helps the fracturing fluid fully enter the reservoir matrix and replace the adsorbed gas, improving the recovery rate of gas wells. This study provides a solid foundation for the calculation of geological reserves and assessment of development impacts.