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Nos. 02-8B58and 05-7466). 1.The collected data included axial and lateral strain, axial and confinement stresses, time and temperature. Periodically, axial stress was adjusted to account for specimen strain in order to maintain a constant differential stress. Frequency of the stress correction was dependent on the rate of deformation; two or more corrections in a 24 hour period were typical. Data were automatically recorded with a printer, manually receded from the print-out to punched cards and reduced by means of a computer. A preponderance of the data (see Section 4.1) was collected in the transient creep regime. In some tests specimen rupture occurred, while in others an accelerating creep rate brought the specimen in contact with the pressure vessel wall. Also, a considerable amount of data was collected during stress application to creep stress level. It is the purpose of this report to present all of the data obtained in a concise manner such that use can be made of these results by Dr. Wawersik in his more comprehensive experimental program. For that matter, the contents have been divided into sections which present summaries of the collective results. The experimental data have been fit with equations which describe transient creep. All of the data is presented in plots in the Appendices. Considerable attention was also given to specimen characterizationand measurements after deformation. 10* The prefix UT denotes untested specimen. The saffix (A) or (B) differentiates between specimens recored from the same depth. ** Approximated, DC'DT temporary malfunction.

Fifteen triaxial compression creep tests were performed on clean and argillaceous salt from the Waste Isolation Pilot Plant (WIPP). The temperatures in the tests were either 25°C or 100°C while the stress difference ranged from 3.5 MPa to 21.0 MPa. In ali tests, the confining pressure was 15 MPa. Test duration ranged from 23 to 613 days with an average duration of 300 days. The results of the creep tests supplemented earlier testing and were used to estimate two parameters in the Modified Munson-Dawson constitutive law for the creep behavior of salt. The two parameters determined from each test were the steady-state strain rate and the transient strain limit. These estimates we_e combined with parameter estimates deTLerminedfrom previous testing to study the dependence of both transient and steady-state creep deformation on stress difference. The exponents on stress difference determined in this study were found to be consistent with revised estimates of the exponents reported by other investigator,;. • This report was preparedby RFJSPECInc. underContract No. 05-7502 with SandiaNational Laboratories.

This report documents research performed to develop a new stress-based criterion for predicting the onset of damage in salt formations surrounding natural gas storage caverns. Laboratory tests were conducted to investigate the effects of shear stress, mean stress, pore pressure, temperature, and Lode angle on the strength and creep characteristics of salt. The laboratory test data were used in the development of the new criterion. The laboratory results indicate that the strength of salt strongly depends on the mean stress and Lode angle. The strength of the salt does not appear to be sensitive to temperature. Pore pressure effects were not readily apparent until a significant level of damage was induced and the permeability was increased to allow penetration of the liquid permeant.Utilizing the new criterion, numerical simulations were used to estimate the minimum allowable gas pressure for hypothetical storage caverns located in a bedded salt formation. The simulations performed illustrate the influence that cavern roof span, depth, roof salt thickness, shale thickness, and shale stiffness have on the allowable operating pressure range. Interestingly, comparison of predictions using the new criterion with that of a commonly used criterion indicate that lower minimum gas pressures may be allowed for caverns at shallow depths. However, as cavern depth is increased, less conservative estimates for minimum gas pressure were determined by the new criterion.ii EXECUTIVE SUMMARYThe main objective of the research discussed in this report is to improve the predictive technology used to evaluate the structural stability of natural gas storage caverns in bedded salt deposits. The structural stability of caverns in bedded salt depends on many interrelated factors, including local hydrology, local geology and rock properties, cavern operating conditions, cavern depth, cavern geometry, and cavern location with respect to other caverns. Cavern design entails avoidance of conditions known to be adverse for cavern stability. For caverns sited in salt deposits, integrity of the salt is crucial for long-term cavern stability. Rock salt is a viscoplastic material that is difficult to fail under moderate levels of confining pressure, which is one of the reasons salt is a favored storage medium. To maintain the integrity of a host salt formation, cavern design philosophy involves circumventing states of stress that cause the salt to dilate. Dilation manifests as a volumetric expansion resulting from microfracturing of the material. Therefore, structural stability is maintained by avoiding or limiting microfracturing in the salt.