Strength and Stability Analyses of Retaining Structure Models for the Fracturing Fluid Characterization Facility

Abstract

Millions of dollars are spent annually on hydraulic fracturing for oil and gas well stimulation. Various researchers have proposed models to optimize the stimulation treatment, with limited success due to a lack of understanding of the behavior of critical parameters in the models, especially the fracturing fluids. Thus, the Gas Research Institute and the U.S. Department of Energy are sponsoring a project at the University of Oklahoma to investigate fracturing fluids in a large physical fracture model, the Fracturing Fluid Characterization Facility (FFCF). This simulator was initially expected to consist of a parallel plate simulator as large as 16 ft high by 100 ft long, with an internal pressure as high as 1200 psi, to determine critical fluid parameters under full-scale operating conditions. A smaller and more economical version of the simulator (7 ft high by 9 1/3 ft long) has since been built and moved to its own facility. As the reaction forces of the originally intended structure were tremendous (over 275,000,000 lbf for a full-scale simulator), structural analyses were essential. Thus, static strength and stability (buckling) analyses were performed on various full-scale models and on the smaller final version of the pressure retaining structure for the FFCF simulator. An interior segment of each structural model consisting of the pressure chamber and the reaction beam/ plate/tie rod assemblies was modeled in detail and analyzed by the finite element method using the industry standard code MSC/NASTRAN together with the MSC/XL pre- and postprocessor. In addition to the linear analyses for all models, a material nonlinear analysis was run for Model 1. General buckling analyses by the finite element method were performed on square plates and on retaining structure plates with various boundary conditions to determine the influence of these conditions on the critical buckling loads. Finally, the full final model was analyzed for buckling proving the stability of the design.