Abstract:

At present, we cannot use the conventional gas reservoir productivity evaluation equation to accurately predict the abnormal high pressure and low permeability gas reservoir capacity. Based on this fact, we considered the actual seepage of abnormal high pressure and low permeability gas reservoirs and established a new physical model to regionalize the seepage zone of gas reservoir. By the novel pseudo pressure function and the principle of superposition, and on the basis of considering the critical radius of gas flow, high-speed non-Darcy flow of gas, pulse effect, reservoir permeability stress sensitivity and starting pressure gradient effect, a new abnormally high pressure and low permeability gas reservoir productivity equation was deduced, and the validity of equation by actual test date was tested. The results showed that the relative error between the calculation results of the conventional productivity equation and the actual capacity test results without considering the influence of seepage area and multi factors could be as high as 21.5 %. The relative error between the capacity calculation results of the new equation and the actual capacity test was less than 5 %, and with the decrease of the bottom hole flow pressure, the high velocity non-Darcy flow effect, the starting pressure gradient effect and the permeability stress sensitivity effect could lead to the serious decrease of the gas well production. However, the critical radius of gas low velocity and the effects of pulse on gas well productivity were small.

Key words: abnormally high-pressure and low permeability gas reservoir, stress sensitivity, pulsation effect, high-speed non-Darcy flow, pressure gradient, productivity equation