Effect of low-velocity non-Darcy flow on well production performance in shale and tight oil reservoirs

Abstract

There are many core flooding studies showing that the liquid-measured permeability is lower than the Klinkenberg-corrected gas permeability. The flow velocity in a low pressure gradient regime is lower than what is estimated from Darcy’s law. This phenomenon is considered as low-velocity non-Darcy flow in the literature. Besides, many researchers believe that there is a threshold pressure gradient (TPG) that needs to be overcome before the fluid flow can occur. The related results in the literature are critically reviewed in this paper. By analyzing the flow mechanism, considering boundary effect, and presenting counter examples, we conclude that the low-velocity non-Darcy flow regime consists of a nonlinear flow part and a linear flow part. The nonlinear flow part starts from the zero pressure gradient instead of TPG. Based on this observation, a non-Darcy model is introduced and the corresponding correlation parameters are derived by fitting the available experimental data. This model is used to estimate the well performance of a vertical well and a multi-fractured horizontal well. For a vertical well, the production rate of non-Darcy flow is much smaller than that of Darcy flow, and the ultimate oil recovery of non-Darcy flow is approximately 48% of the Darcy flow. The production rate of a multi-fractured horizontal well if non-Darcy flow is considered is smaller in the beginning but greater than the corresponding Darcy flow rate after about some time (in our example model, 2700days). The ultimate recovery factor of non-Darcy flow is 80% of Darcy flow, which indicates that multi-fractured wells are less affected by the low-velocity non-Darcy phenomenon compared with the vertical wells. Multi-fractured horizontal wells exhibit a significant advantage in developing shale and tight reservoirs, and low velocity non-Darcy flow plays a significant impact on the well production performance in tight and shale reservoirs.