Abstract:

A horizontal well is one of the most effective methods for developing low-permeability gas reservoirs which are characterized by the effects of start-up pressure gradient and turbulent flow under high-speed non-Darcy flow.A seepage flow model was established and solved for horizontal gas wells.It involves well-bore structure parameters,turbulent gas flow under high-speed non-Darcy flow in near-wellbore area and start-up pressure gradient.A binomial deliverability equation for horizontal gas wells was derived.Based on strict theoretical derivation and calculation,deliverability of horizontal and vertical wells was compared to understand the influences of start-up pressure gradient and non-Darcy flow on the deliverability of horizontal gas wells.The results indicate that the start-up pressure gradient is in negative linear relationship with the deliverability,the non-Darcy flow decreases the deliverability of horizontal gas wells and its influence on horizontal gas wells is smaller than that on vertical gas wells.

Key words: start-up pressure gradient, binomial deliverability equation, non-Darcy flow, horizontal gas well, formation with nonlinear seepage flow features