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

Abstract

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 gaswell pressure-drawdown (DD) and-buildup (BU) tests. Overall, the developed simulator is an accurate and strong tool for design and analysis of transient gaswell 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 gaswell 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 gaswell 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.

Transient Nonisothermal Fully Coupled Wellbore/Reservoir Model for Gas-Well Testing, Part 1: Modelling

“…4 through 7 all suggest the presence of a variable wellbore-storage coefficient and temperature effects on the behaviour of transient pressure tests. These behaviours will be analyzed thoroughly in Part 2 of this research study (Bahonar et al 2010). …”

“…Comparisons of these results and some unusual thermal effects on the transient well tests are described in Part 2 of this research study (Bahonar et al 2010). …”

“…For instance, the dual-porosity behaviour may be seen for the well testing of nonisothermal conventional homogeneous gas reservoirs. Another interesting case that results from neglecting nonisothermal effects in the interpretation of data with well-testing software, but for a conventional heterogeneous gas reservoir, will be presented in Part 2 of this study (Bahonar et al 2010). The reason that using the well-testing software for well-testing design, analysis, and interpretation of nonisothermal gas reservoirs may lead to improper test design and/or wrong interpretation resides in the assumptions used in the software.…”

“…Applications of this simulator to analyzing gas-well testing problems, in addition to several important observations, are extensively studied in Part 2 of this research work (Bahonar et al 2010).…”