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.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
21 September 2010
- Revised manuscript received:
30 December 2010
- Manuscript approved:
6 March 2011
- Version of record:
13 September 2011
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