Analysis of Salt and Casing Fracture Mechanisms During Cavern Integrity Testing for SPR Salt Caverns

摘要

This report presents computational analyses to evaluate the risk of Cavern Certification Testing on casing damage and salt fracturing. This deliverable is performed in support of the U.S. Strategic Petroleum Reserve. Several models have been built utilizing either a 1-cavern or 19-cavern, 30-degree wedge of symmetry as has been used on previous West Hackberry and Big Hill analyses. Various stages of complexity have been added to each model: mesh generation for both 1-cavern and 19-cavern fields; the inclusion of the small-diameter well going from the surface to the top of the caverns; and the addition of steel casing and cement liners to the well surfaces. A stratigraphy based on the Bayou Choctaw site has been chosen for modeling, and the caverns are modeled as equivalent cylinders to simplify the calculations. Salt dilation, as defined by two separate dilation criteria, has been generated during simulated work over routines and cavern integrity tests, but only for the models that include the steel casing and cement liners. The addition of these features generates the tensile and shear stress conditions in the model necessary to cause stress states that exceed dilation criteria. These predictions have been made using the power law creep model. The results show that the salt can be damaged during high pressure change conditions in the wells and caverns.