Lawrence Berkeley National Laboratory, Report LBNL-39620
Design and analysis of a well test
for determining two-phase hydraulic properties
Stefan Finsterle and Karsten Pruess
Lawrence Berkeley National Laboratory, Earth Sciences Division
University of California, Berkeley, CA 94720
Abstract.
This paper describes the design and analysis of a well test for determining hydraulic
properties of a low permeability, low porosity formation that potentially contains a small
amount of free methane. Estimation of gas-related parameters in such formations is difficult
using standard pumping tests because (i) pressures and flow rates may fluctuate as a
consequence of gas exsolution during the test, (ii) data may not allow discriminating among
alternative conceptual models, making the parameter estimates ambiguous, and (iii) the key
parameters of interest are highly correlated. In this study we adopt an inverse modeling
perspective to examine a test sequence that can be appended to a standard hydraulic testing
program. The design calculations show that a series of water and gas injections can
significantly reduce parameter correlations, thus decreasing estimation uncertainty.
Moreover, the extended test sequence enhances the possibility of identifying the model
describing relative permeabilities and capillary pressures. A prerequisite for a successful
inversion is that data of high accuracy are collected under controlled test conditions. We
discuss the assumptions and limitations of the procedure, and propose some
recommendations for testing. Finally, we analyze pressure and gas flow data from a well test
performed by the Swiss National Cooperative for the Disposal of Radioactive Waste (Nagra)
that partially followed the proposed test sequence.
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