Transient Nonisothermal Fully Coupled Wellbore/Reservoir Model for Gas-Well Testing, Part 2: Applications

Abstract

Summary After the development of a numerical fully implicit nonisothermal wellbore/reservoir simulator in Part 1 of this study (Bahonar et al. 2010), this simulator is implemented for a close and detailed study of gas-well pressure-drawdown (DD) and -buildup (BU) tests. Overall, the developed simulator is an accurate and strong tool for design and analysis of transient gas-well testing, particularly for high- pressure/high-temperature (HP/HT) gas reservoirs. Several numerical results will be presented. This includes demonstration of the behaviour of the wellbore-fluid pressure, temperature, density, and velocity and an overall heat-transfer coefficient during DD or shut-in tests for nonisothermal reservoirs and conceptual comparisons with the isothermal counterparts. Thermal effects on the behaviour of derivative plots and the sandface-flow rate of deep nonisothermal gas reservoirs will be studied. A significant effect of neglecting the heat capacity of tubular and cement materials on the wellhead-temperature simulation, and thus transient well tests, will be demonstrated. A sample case to show that neglecting the thermal effects in the gas-well tests of composite reservoirs leads to unreliable results in well-testing analysis will be presented. Several other numerical experiments, including the presence of a variable wellbore-storage coefficient, gas backflow from the wellbore to the reservoir, and other thermal effects during the gas-well tests, are also presented. Hundreds of millions of dollars are spent every year on well testing around the world (Hawkes et al. 2001). A proper design and truthful interpretation of these tests can be achieved by a reliable coupled wellbore/reservoir simulator, which in turn can save a large portion of the required costs.