Derivation, simplification and application of the pseudo-pressure elastic one-phase method for gas wells

Abstract

For the new gas well with a closed boundary， the pressure drawdown curve testing was carried out after it operated at a stable production rate. Theoretically， the pressure drawdown curve can be divided into an unsteady state stage， a transit state stage （also called the late unsteady state stage）， and a pseudo-steady state stage according to its pressure dynamics. The unsteady state stage refers to the outer edge radius of the pressure drawdown distribution of the gas well not reaching the boundary. The transit state stage refers to the range from the unsteady state stage to the pseudo-steady state stage. At this stage， the elastic two-phase method used in China can be employed to determine the initial gas in place controlled by a gas well. This method has been listed four times in the national oil and gas industry standard. For the unsteady state stage， according to the differential formula of the plane radial flow based on Darcy’s law， this paper derived the elastic one-phase method of pseudo-pressure by using the pseudo-pressure function proposed by Al-Hussainy. This method could be used to evaluate the effective permeability of gas reservoirs and the total skin factor of wells. In addition， the elastic one-phase method expressed by the one power of pressure and pressure that was squared was obtained by simplifying the research results of Wattenbanger on the properties of the pseudo-pressure function. The practical application showed that the evaluation results with the three methods were consistent.

Keywords

• gas well
• elastic one-phase method
• pseudo-pressure
• one power of pressure
• pressure squared
• effective permeability
• total skin factor