Gas-water two-phase productivity prediction model of multistage fractured horizontal wells in anisotropic tight sandstone gas reservoirs

Abstract

Tight sandstone gas reservoirs have the characteristics of poor physical properties of the reservoir， complex pore throat structure， strong anisotropy， and extensive coverage of initial water saturation， which lead to the complex flow mechanism of fluids in reservoirs and bring significant challenges to the accurate prediction and evaluation of gas well productivity. Therefore， based on the theory of gas-water two-phase non-Darcy flow， this study comprehensively considers the complex productivity factors， such as reservoir anisotropy， different degrees of stress sensitivity between reservoir matrix and fracture， two-phase starting pressure gradient， high-speed non-Darcy flow effect， gas slippage effect， finite conductivity of fracture， and inter-fracture interference. A new gas-water two-phase productivity prediction model for multistage fractured horizontal wells in anisotropic tight sandstone gas reservoirs is established by using coordinate transformation， perturbation ellipse theory， equivalent development rectangle theory， equivalent well diameter principle， pressure superposition principle， and hydropower similarity principle. Field examples verify the accuracy and practicability of the model. The gas-water two-phase productivity prediction curve is drawn， and the influence of sensitive parameters on productivity is evaluated. The results show that the open flow capacity of a fractured gas well increases with the increase in slippage effect， fracture conductivity， fracture half-length， fracture number， and the angles between the wellbore of the horizontal well and the main permeability of the formation. The open flow capacity of the fractured horizontal well decreases with the increase in reservoir anisotropy， reservoir stress sensitivity， fracture stress sensitivity， two-phase starting pressure gradient， and water-gas volume ratio. Water has an inhibitory effect on the flow of gas， and greater displacement pressure difference indicates a more significant inhibitory effect， so it is necessary to take waterproof and water control measures in advance. The research results further narrow the gap between the productivity prediction results of tight sandstone gas reservoirs and the actual production of the field， which is helpful for parameter evaluation， dynamic prediction， productivity evaluation， and exploration and development decision-making of tight sandstone gas reservoirs.

Keywords

• tight sandstone gas reservoir
• multistage fractured horizontal well
• anisotropy
• gas-water two-phase
• productivity prediction