Effect of the non-Darcy flow boundary in low permeability reservoirs

Non‐Darcy flow is an important characteristic of gas well and its accurate description will increase accuracy of productivity evaluation and prediction. In this article, we study the influence of non‐Darcy flow boundary on production prediction. Based on flow theory in porous media, we discuss the models of non‐Darcy flow boundary with different Reynolds numbers, and propose the criteria judging non‐Darcy flow: non‐Darcy critical permeability (kc), non‐Darcy critical flowing pressure (pc), non‐Darcy critical rate (qgc). Then, non‐Darcy skin‐depended factors are derived with different Reynolds number, which reflect the influence of true skin on non‐Darcy flow. Finally, we study the influence of these factors on productivity prediction and well testing. The results show that non‐Darcy flow boundary may be nearby wellbore radius in low permeability reservoirs, whose influence could be considered as a negative skin which will decrease non‐Darcy flow. And, compared with the open flow capacity of convenient binomial deliverability equation and Darcy equation, the open flow capacity of the equation that considers the influence of non‐Darcy flow boundary is just between that of the two equations, which will verify the influence of the non‐Darcy flow boundary. What's more, the non‐Darcy boundary influences the open flow capacity significantly. And, non‐Darcy skin‐depended factor will become larger with the increase of skin. Finally, when the designed rates of well testing should be larger than the critical rates, the points of test will be on a perfectly straight line or else the points will not. The research of this article will increase the accuracy of productivity evaluation and prediction in low permeability reservoirs. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1822–1831, 2015