A Calculation Method for the Time of Pressure Change of Tight Sandstone Gas Well to Reach Seepage Boundary

Abstract

Tight sandstone gas reservoirs have poor physical properties and percolation capacity, and it takes a long time for gas well pressure change to reach the seepage boundary, which results in large errors in gas well control dynamic reserves calculation and gas production capacity evaluation. Therefore, it is especially important to identify whether the gas well pressure change of tight sandstone reaches the seepage boundary and its exact time. In this paper, a typical single well in the Sulige gas field is taken as the research object. Based on the Blasingame theory for advanced production decline analysis, considering the variable production and pressure of gas well, the material balance pseudo-time is introduced. Through the dimensionless formula conversion, the calculation formula of the time when the pressure change reaches the seepage boundary is derived, and the time curves of different types of gas wells are established, as well as the main control factors affecting the time to reach the boundary of gas wells are analyzed. The result shows that the time to reach the seepage boundary in different types of gas wells in the Sulige gas field is different, which is 200–257 days in Type I gas wells, 446–497 days in Type II and 685–796 days in Type III. The time for gas well to reach the boundary is related to the reservoir porosity, permeability, comprehensive compression coefficient, single well control area, and fluid viscosity. Among which the change of the control area and permeability have a greater impact. The research result lays the foundation for accurately and reasonably evaluating the dynamic reserves and productivity of gas wells in tight sandstone gas reservoirs.KeywordsTight sandstoneGas wellSeepage boundaryPressure changeCalculation method