Impact of non-Darcy flow on vertical well productivity in low-permeability gas reservoirs

The obvious non-Darcy seepage effects of gas percolation,such as stress sensitive effect,start-up pressure gradient and slippage effect are due to the low porosity,low permeability and high water cut in low-permeability gas reservoirs.Therefore,based on the Forchheimer binomial flow equation,a new pseudo-pressure function is introduced and a new improved vertical well productivity equation considering the comprehensive influences of stress sensitive effect,start-up pressure gradient and slippage effect is deduced.The above-mentioned effects are studied based on the real data from a low-permeability gas reservoir.The results indicate that the impact of stress sensitive effect on the productivity is much stronger than that of start-up pressure gradient and slippage effect.Specifically,stress sensitivity effect can result in a significant decrease of gas well deliverability with a maximum rate of 49.46%,while start-up pressure gradient can also lead to a decrease of deliverability with 3.09% and slippage effect can increase the deliverability with 2.58% on average.