Harmonic-Pulse Testing for Non-Darcy-Effects Identification

Gas reservoirs are generally subject to non-Darcy effects, especially in the near-wellbore zone. In fact, the assumption of Darcy flow regime is no longer valid because of inertial phenomena and/ or turbulence. These could significantly reduce the peak performance of a gas well. Therefore, characterization and monitoring of the non-Darcy effects is key for defining an optimal reservoir exploitation strategy. This is particularly true in the case of storage fields, where withdrawal- and injection-gas rates are typically very high (hundreds of thousands of m3/d) and determining and monitoring well performance is key to ensuring that deliverability meets demand and/or contract obligations. Pulse testing, which is dependent on a periodic variation of produced/injected rate, is an effective methodology to test a well during ongoing field operations without stopping production. Although pulse testing is very promising for monitoring well performance, it has never been exploited for this purpose. In this paper, the development of a method for pulse testing high-performing gas wells is presented and discussed. The pressure response to the imposed rates is analyzed in the frequency domain to evaluate reservoir and well properties. An analytical solution in the frequency domain taking into account wellbore storage effects was derived. The method was applied to test a real gas well of a storage reservoir under two different pressure conditions to assess the effect of turbulence on deliverability. Although the pulse-testing technique might not replace traditional well testing for determining reservoir properties, it can be successfully applied to monitor well performance as a function of reservoir pressure.