Physical simulation on gas percolation in tight sandstones

Capillary pressure was tested on 40 matrix cores (in situ permeability: 0.002×10−3–100 ×10−3 μm2) in the Sulige gas field and the pore structure features of different type sands were described finely. Based on the research on the pore structure features, gas percolation experiments were designed under the conditions of homogeneous cores with different permeability, heterogeneous cores and different water saturation, to research the gas percolation laws in tight sand. Nanometer pore throats and microscopic capillary pore throats are the main flow channels for gas in tight sand. Percolation resistance of gas or gas-water in tight sand is far greater than that in conventional sand or medium-high permeability sand. Depletion experiments show that gas percolation resistance is bigger when permeability of dry sandstone is lower than 0.1×10−3 μm2 or permeability of water sand is lower than 1×10−3 μm2, so the starting pressure gradient exists. Water saturation has great effect on gas percolation in sandstones. When water saturation is higher, producing reserves are lower. The starting pressure gradient, calculated by monitoring the pressure values of all test points in depletion experiments of long cores, would be scientific and helpful for forecasting the oil drain radius and evaluating producing reserves.