Water-blocking damage and its solution in low permeability gas reservoirs

The gas reservoirs of Upper Paleozoic strata in the Ordos Basin are characterized by low permeability with minute pores and microscopic throats, which results in severe water-blocking damage in the lithologically heterogeneous formations (with an average damage level up to 83.6%). The analysis of drill core suggests that the degree of water-blocking damage is inversely correlated with permeability: the greater the permeability, the lower the level of damage. The correlation between damage and porosity is difficult to define, although a generally inverse relationship exists. Water-blocking damage is also inversely related to the amount of primary pore water, but it is positively proportional to the saturation level of fetter water. The study of 17 core samples using reversed drainage test indicates that water flow is associated with the porosity and permeability of the reservoir rock, draining pressure, and draining time. Improving the flow of formation water can reduce the damage of water blocking.