Revised results for geomechanical testing of MRIG-9 core for the potential SPR siting at the Richton Salt Dome. Page: 3 of 83

                                
SAND 2010-0658
Unlimited Release
Printed February 2010
Revised Results for Geomechanical
Testing of MRIG-9 Core for the Potential
SPR Siting at the Richton Salt Dome
Stephen J. Bauer and Scott T. Broome
Geomechanics Department
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0751
Abstract
This report is a revision of SAND2009-0852. SAND2009-0852 was revised because it was discovered that a gage
used in the original testing was mis-calibrated. Following the recalibration, all affected raw data were recalculated
and re-presented. Most revised data is similar to, but slightly different than, the original data. Following the data re-
analysis, none of the inferences or conclusions about the data or site relative to the SAND2009-0852 data have been
changed.
A laboratory testing program was developed to examine the mechanical behavior of salt from the Richton salt dome.
The resulting information is intended for use in design and evaluation of a proposed Strategic Petroleum Reserve
storage facility in that dome. Core obtained from the drill hole MRIG-9 was obtained from the Texas Bureau of
Economic Geology. Mechanical properties testing included: 1) acoustic velocity wave measurements; 2) indirect
tensile strength tests; 3) unconfined compressive strength tests; 4) ambient temperature quasi-static triaxial
compression tests to evaluate dilational stress states at confining pressures of 725, 1450, 2175, and 2900 psi; and 5)
confined triaxial creep experiments to evaluate the time-dependent behavior of the salt at axial stress differences of
4000 psi, 3500 psi, 3000 psi, 2175 psi and 2000 psi at 55  C and 4000 psi at 35  C, all at a constant confining
pressure of 4000 psi.
All comments, inferences, discussions of the Richton characterization and analysis are caveated by the small number
of tests. Additional core and testing from a deeper well located at the proposed site is planned. The Richton rock
salt is generally inhomogeneous as expressed by the density and velocity measurements with depth. In fact, we
treated the salt as two populations, one clean and relatively pure (> 98% halite), the other salt with abundant (at
times) anhydrite. The density has been related to the insoluble content. The limited mechanical testing completed
has allowed us to conclude that the dilatational criteria are distinct for the halite-rich and other salts, and that the
dilation criteria are pressure dependent. The indirect tensile strengths and unconfined compressive strengths
determined are consistently lower than other coastal domal salts. The steady-state-only creep model being
developed suggests that Richton salt is intermediate in creep resistance when compared to other domal and bedded
salts. The results of the study provide only limited information for structural modeling needed to evaluate the
integrity and safety of the proposed cavern field. This study should be augmented with more extensive testing.
This report documents a series of test methods, philosophies, and empirical relationships, etc., that are used to define
and extend our understanding of the mechanical behavior of the Richton salt. This understanding could be used in
conjunction with planned further studies or on its own for initial assessments.