Tight gas production model considering TPG as a function of pore pressure, permeability and water saturation
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ORIGINAL PAPER
Tight gas production model considering TPG as a function of pore pressure, permeability and water saturation Atif Zafar1,2 · Yu‑Liang Su1 · Lei Li1 · Jin‑Gang Fu1 · Asif Mehmood1 · Wei‑Ping Ouyang3 · Mian Zhang3 Received: 28 January 2019 © The Author(s) 2020
Abstract Threshold pressure gradient has great importance in efficient tight gas field development as well as for research and laboratory experiments. This experimental study is carried out to investigate the threshold pressure gradient in detail. Experiments are carried out with and without back pressure so that the effect of pore pressure on threshold pressure gradient may be observed. The trend of increasing or decreasing the threshold pressure gradient is totally opposite in the cases of considering and not considering the pore pressure. The results demonstrate that the pore pressure of tight gas reservoirs has great influence on threshold pressure gradient. The effects of other parameters like permeability and water saturation, in the presence of pore pressure, on threshold pressure gradient are also examined which show that the threshold pressure gradient increases with either a decrease in permeability or an increase in water saturation. Two new correlations of threshold pressure gradient on the basis of pore pressure and permeability, and pore pressure and water saturation, are also introduced. Based on these equations, new models for tight gas production are proposed. The gas slip correction factor is also considered during derivation of this proposed tight gas production models. Inflow performance relationship curves based on these proposed models show that production rates and absolute open flow potential are always be overestimated while ignoring the threshold pressure gradients. Keywords Inflow performance relationship · Pore pressure · Threshold pressure gradient · Tight gas field development · Tight gas sand reservoir
1 Introduction There is an increase in the development of tight sandstone reservoirs for the last couple of decades. Due to this increasing demand, understanding the flow mechanism of such reservoirs has achieved a great interest. Particularly, the Edited by Yan-Hua Sun * Yu‑Liang Su [email protected] Atif Zafar [email protected] 1
School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, Shandong, China
2
Department of Petroleum Technology, University of Karachi, University Road, Karachi 75270, Pakistan
3
Changqing Downhole Technology Company, Chuangqing Drilling Engineering Co., Ltd, CNPC, Xi’an 710018, Shaanxi, China
threshold pressure gradient (TPG) is an important parameter of a tight gas reservoir (Civan 2017). TPG is the pressure gradient that allows the fluid to become movable against the viscous forces. These viscous forces are found between solid and gas and are one of the main reasons for deviation of gas flow from Darcy or linear flow (Liu 2019; Liu et al. 2019; Yan et al. 1990). As shown in Fig. 1, the ideal Darcy flow has a linear relationsh
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