Transient Non-isothermal Fully Coupled Wellbore/ Reservoir Model for Gas Well Testing, Part II: Applications

M. Bahonar, J. Azaiez and Z. Chen

After the development of a numerical fully-implicit non-isothermal wellbore/reservoir simulator in Part I of this study (Bahonar et al. 2010b), this simulator is implemented for a close and detailed study of gas well pressure drawdown and buildup tests. Overall, the developed simulator is an accurate and strong tool for design and analysis of transient gas well testing, particularly for high temperature and high pressure (HTHP) gas reservoirs.

Several numerical results will be presented. This includes the demonstrating of the behavior of the wellbore fluid pressure, temperature, density, and velocity and an overall heat transfer coefficient during drawdown or shut-in tests for non-isothermal reservoirs and conceptual comparisons with the isothermal counterparts. Thermal effects on the behavior of derivative plots and the sandface flow rate of deep non-isothermal 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 back-flow from the wellbore to the reservoir, and other thermal effects during the gas well tests are also presented.

Hundreds of million dollars are spent every year on the well testing in 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.