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Gas Threshold Pressure Tests in Deep Boreholes for Determining Two-Phase Flow Properties of the Host Rock at the Proposed L/ILW Repository, Switzerland

Published online by Cambridge University Press:  10 February 2011

Rainer Senger ,
Paul Marschall  and
Jean-Marc Lavanchy
Rainer Senger
Affiliation:
Intera Inc., 9111 Research Blvd., Austin, Texas, 78758, USA, [email protected]
Paul Marschall
Affiliation:
Nationale Genossenschaft für die Lagerung radioaktiver Abfälle (NAGRA), Hardstrasse 73, 5430 Wettingen, Switzerland, [email protected]
Jean-Marc Lavanchy
Affiliation:
Colenco Power Engineering Ltd., Mellingerstr. 207, 5404 Baden, Switzerland, [email protected]
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Abstract

Safety assessment of potential gas release from the L/ILW requires information on two-phase flow behavior of the host rock. To determine the relevant formation properties for gas flow through the host rock, a combination of hydrotest and gas-injection sequences were designed and subsequently implemented in the Nagra field testing program at Wellenberg. The results of the design caculations indicate that the gas threshold pressure can be estimated from a gas injection test followed by a shut-in test using the log-log diagnostic plot of the gas injection sequence and the Homer plot of the recovery sequence. For a composite well-aquifer model, the gas threshold pressure of the outer zone, when estimated from the gas injection sequence, is increased, because water is displaced from the inner zone into the outer zone as gas is injected into the inner zone. This results in the overestimation the gas threshold pressure of the outer zone, and in turn, of the air-entry pressures in the corresponding capillary pressure models. The pressure response during the gas injection sequence in a composite well-aquifer model can be drastically different for different relative permeability models. For a Brooks-Corey model, the pressure indicates a distinct increase when gas flow starts into the outer zone. For a Grant model, the pressures can actually decrease during a constant-rate gas injection sequence. A decrease in interval pressure during gas injection was observed in two different field tests in the Palfris Formation at Wellenberg. In borehole WLB-SB4as, the gas injection test in interval VM16 was analyzed with the inverse code ITOUGH2 to determine the two-phase flow parameters for two different conceptual models. The simulations indicated that the particular pressure response, characterized by a sudden decrease during gas injection, could not be reproduced with a Brooks-Corey relative permeability model. However, assuming a Grant model, a sudden pressure decrease during the gas injection sequence could be simulated. The results indicate the importance in determining the hydraulic properties and the well-aquifer model from a combined analysis of hydro- and gas injection tests, in order to accurately determine the two-phase flow parameters.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 506: Symposium – Scientific Basis for Nuclear Waste Management XXI , 1997 , 829
Copyright
Copyright © Materials Research Society 1998

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References

REFERENCES

CROISE, J. and SENGER, R. K., 1996, GTS-TPF: Analysis of extended gas threshold pressure tests at the Grimsel Test Site for determination of field-scale two-phase flow parameters in the FRI zone, Nagra Internal Report NIB 9641, Wettingen, Switzerland.Google Scholar
DAVIES, P.B., 1991, Evaluation of the role of threshold pressure in controlling flow of waste-generated gas into bedded salt at the Waste Isolation Pilot Plant (WIPP), SAND 90-3246, Sandia National Laboratories, Albuquerque, NM, USA.Google Scholar
ENACHESCU, C., LAVANCHY, J.M., SENGER, R.K, TAUZIN, E., and WOZNIEWICS, J., 1996, WLB: Testing SB4a/s Interval Report Tests VM12, VM13, VM14, VM15 & VMI6, Nagra Internal Report NIB 95-15G, Nagra, Wettingen.Google Scholar
EUGSTER, S., and FINSTERLE, S., 1995, GTS-TPF: Design calculations for an extended gas threshold pressure test at Grimsel Test Site, Nagra Internal Report NIB 95-74, Wettingen, Switzerland.Google Scholar
, FINSTERLE, 1993, ITOUGH2 User‘s Guide, Version 2.2, LBL-35454, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.Google Scholar
HORNER, D. R., 1951, Pressure buildup in wells, Proc. Third World Pet. Congr., The Hague, Leiden, Sec. II, p. 503–523.Google Scholar
MARSCHALL, P., CROISE, J., FISCHER, U., SENGER, R., WYSS, E., 1997, Gas flow through water-saturated shear zones: field- and laboratory experiments and their interpretation (this issue).Google Scholar
PRUESS, K., 1987, TOUGH user‘s guide, LBL-20700, Lawrence Berkeley National Laboratories, Berkeley, CA, USA.Google Scholar
PRUESS, K., 1991, TOUGH2-A general-purpose numerical simulator for multiphase fluid and heat flow, LBL- 29400, Lawrence Berkeley National Laboratories, Berkeley, CA, USA.Google Scholar
SENGER, R.S., MARSHALL, P., JOHNS, R., and LAVANCHY, J.M., 1987, Results of design calculations for gas threshold pressure tests: Nagra Internal Report, Wettingen, Switzerland.Google Scholar