Isochronal Well-testing of Gas Well in Low-Permeability Reservoirs and Productivity Formula of One-point Method

For low-permeability gas reservoirs,characterized by low porosity,low permeability,and high water saturation,gas must avoid start-up pressure drawdown before it can flow.So,an influence of start-up pressure gradient needs to be considered when analyzing isochronal well-testing and employing productivity formula of one-point method.In this study,the relationship between loss value of additional pressure and open well time is established,and a reasonable method to process isochronal well-testing data is also proposed.Meanwhile,based on the productivity formula of which the start-up pressure influence is considered,the one-point method formula suitable for low-permeability gas well is derived.The derivation shows that(1) the number of empirical parameter changes from one to two;and(2) all parameters are related to start-up pressure gradient when com pared to conventional one-point method formula.Finally,the method is proved to be feasible through case study.