A NEW UNSTEADY PRODUCTIVITY PREDICTION METHOD OF FRACTURING HORIZONTAL WELLS IN LOW-PERMEABILITY GAS RESERVOIRS

摘要

This study derived a new gas plane radial unsteady seepage formula, which is adaptable to even when the start-up pressure gradient introduced, which is unprecedented. In previous similar models, the scholars used unstable seepage formulas were derived under the traditional instantaneous point sink model where the planar radial flow is unsteady; but this formula would work is based on the assumption that the outer boundary conditions for the formation is infinite. However, this formula does not work when introducing the start-up pressure gradient. To solve this problem, we changed the boundary conditions, that is, outside the boundary condition is infinite formation changed to the circular constant pressure boundary. On this basis, the start-up pressure gradient is introduced into the unsteady seepage flow equation, which is adaptable to the reservoir environment. In the derivation, gas wells are not seen as a point sink. When r_w→0, the gas plane radial unsteady flow formula of instantaneous point sinks in circular formation is obtained, with taken the introduction of the start-up pressure gradient into consideration. Based on the new formula to deduce a new unsteady productivity prediction model. Furthermore, the high-speed non-Darcy effects and the stress sensitivity effect are added to the model.