A Numerical Wellbore Model for Analyzing Transient Pressure Fluctuation for Gas Wells during Emergency Shut-In

Summary In the emergency shut-in operation of ultradeep high-yield gas wells, the high-pressure, high-speed gas flow channel is rapidly cut off, causing the kinetic energy of the gas to quickly convert into pressure potential energy, resulting in severe fluctuations in wellhead pressure. Therefore, in practical engineering, how to effectively suppress the excessively high transient pressure peaks of the gas while achieving a rapid shut-in has become a pressing technical challenge. With this study, we innovatively establish a transient flow model incorporating dynamic variations in gas compressibility factor and gas friction resistance based on gas/solid coupling theory. To simplify the model and maintain computational efficiency, we assume that the bottomhole pressure and wellbore temperature remain constant during the short shut-in period. Through the application of an explicit finite difference algorithm, we successfully obtain numerical solutions for pressure wave propagation characteristics under complex boundary conditions. To validate this model’s reliability, we designed and constructed a high-pressure gas transient pressure test system for experimental wells in Oilfield Co. A. Experimental results demonstrate that the model calculations exhibit a peak pressure fluctuation amplitude error of merely 9.4%, with a pressure fluctuation periodicity error of merely 5.3%. Through massive parametric sensitivity analyses based on the Well X case study, our research revealed the governing mechanisms of bottomhole pressure, gas production rate, and valve closure time on wellhead pressure fluctuations during the shut-in process, while also establishing an emergency optimal shut-in time guidance map for ultradeep gas wells. This study not only holds significant engineering significance in ensuring the safety of ultradeep gas well tubing but also provides theoretical support for pressure analysis and safety assurance in energy transmission systems, particularly in high-pressure pipeline systems.