Transmission, Distribution, & Refining
Geomechanical Analysis of Pressure Limits for Thin-Bedded Salt Caverns

DE-FC26-03NT41813

Goal:
Develop a fundamental understanding of the geologic and geomechanical properties of thin-bedded salt formations for safe and effective use for natural gas storage.

Background:
Bedded salt formations are found in several areas throughout the United States and Canada. They are useful for storing natural gas, especially near major markets. However, cavern development and operation in thin-bedded salt presents additional challenges over conventional salt dome storage due to the heterogeneous geomechanical properties of these formations. This project used numeric analytical tools to characterize these formations to improve geotechnical design and operating guidelines for thin-bedded salt caverns.

Performer: Terralog Technologies

Location:
Arcadia, California 91006

Project Impact:
Thick domal salt formations provide excellent conditions for large storage caverns in Texas and Louisiana. The Midwest and Northeast Regions of the United States, with much higher population density and greater market demands for storage capacity, are underlain by thinner bedded salt formations that present technical challenges for cavern development. This project investigated the long-term geotechnical integrity of bedded salt caverns and developed improved design and operating guidelines for the range of geologic conditions that are typical in the Michigan, Permian, and Appalachian basins. These results can improve industries’ ability to develop stable caverns and enhance storage capacity in these important markets.

Results:
The geologic and pressure conditions, and critical design factors that may lead to fracture in heterogeneous materials, differential deformation and bedding plane slip, and propagation of damage around single and multiple caverns are summarized. Improved design recommendations for single and multiple cavern configurations in various bedded salt environments are provided based on numerical modeling of cavern pressure, operating conditions, cavern height/diameter ratio, overburden stiffness and roof thickness. A step by step methodology for operators to assess these critical cavern design parameters for thin bedded salt formations is presented. The basic process involves estimating the current rock strength and formation stress values with the best available data, calculating induced stresses due to cavern creation and pressure cycling, and then comparing the induced stresses to the estimated limiting strength and stress values. The specific steps taken for a given project will depend on the available data and the desired solution accuracy, but can be summarized as follows: evaluate the geologic setting, including detailed stratigraphy, lithology, and number and type of interbeds; determine the mechanical properties of the salt and non-salt interbed materials; determine the in situ stresses and fracture pressures for individual formations; evaluate fracture pressure variations after cavern development; evaluate stresses induced by pressure cycling with geomechanical modeling; compare stresses induced by pressure cycling with estimated in situ stresses and formation fracture pressures; and, evaluate bedding plane slip and potential impact on cavern integrity.

Current Status and Remaining Tasks: 
A final project report is listed below under "Additional Information".

Project Start Date: May 30, 2003
Project End Date: May 30, 2005

DOE Contribution: $207,707
Performer Contribution: $184,193

Contact Information:
NETL - Gary Sames (412-386-5067 or gary.sames@netl.doe.gov
Terralog Technologies - Mike S. Bruno (626-305-8460 or msbruno@terralog.com)

Additional Information:
Final Report - August, 2005 - “Geomechanical Analysis and Design Considerations for Thin-Bedded Salt Caverns” [PDF-8454KB] , June 1, 2003 to May 30, 2005. Principal Author - Michael S. Bruno.