Publications

[1] We used a two-dimensional coupled heat and fluid flow model to investigate large-scale, lateral heat and fluid transport on the eastern flank of the Juan de Fuca Ridge. Cool seawater in the natural system is inferred to enter basement where it is exposed close to the spreading center and flow laterally beneath thick sediments, causing seafloor heat flow to be depressed relative to that input at the base of the plate. The flow rate, and thus the properties of permeable basement (the flow layer), controls the efficiency of lateral heat transport, as quantified through numerical modeling. We simulated forced flow in this layer by pumping water through at a fixed rate and quantified relations between flow rate, thickness of the permeable basement, and the extent of suppression of seafloor heat flow. Free flow simulations, in which fluid flow was not forced, match heat flow constraints if nonhydrostatic initial conditions are used and flow layer permeabilities are set to the high end of observed values (10-11 to 10-9 m2). To match seafloor heat flow observations, the models required lateral specific discharge of 1.2 to 40 m/yr for flow layer thicknesses of 600 to 100 m, respectively. The models also replicate differences in fluid pressures in basement, and the local distribution of pressures above and below hydrostatic. Estimated lateral flow rates are 10× to 1000× greater than estimates based on radiocarbon ages of basement pore waters. Estimated lateral flow rates based on thermal and chemical constraints can be reconciled if diffusion from discrete flow zones into less permeable stagnant zones in the crust is considered. © 2003 by the American Geophysical Union.

The Big Hill salt dome, located in southeastern Texas, is home to one of four underground oil-storage facilities managed by the U. S. Department of Energy Strategic Petroleum Reserve (SPR) Program. Sandia National Laboratories, as the geotechnical advisor to the SPR, conducts site-characterization investigations and other longer-term geotechnical and engineering studies in support of the program. This report describes the conversion of two-dimensional geologic interpretations of the Big Hill site into three-dimensional geologic models. The new models include the geometry of the salt dome, the surrounding sedimentary units, mapped faults, and the 14 oil storage caverns at the site. This work provides a realistic and internally consistent geologic model of the Big Hill site that can be used in support of future work.

Existing paper-based site characterization models of salt domes at the four active U.S. Strategic Petroleum Reserve sites have been converted to digital format and visualized using modern computer software. The four sites are the Bayou Choctaw dome in Iberville Parish, Louisiana; the Big Hill dome in Jefferson County, Texas; the Bryan Mound dome in Brazoria County, Texas; and the West Hackberry dome in Cameron Parish, Louisiana. A new modeling algorithm has been developed to overcome limitations of many standard geological modeling software packages in order to deal with structurally overhanging salt margins that are typical of many salt domes. This algorithm, and the implementing computer program, make use of the existing interpretive modeling conducted manually using professional geological judgement and presented in two dimensions in the original site characterization reports as structure contour maps on the top of salt. The algorithm makes use of concepts of finite-element meshes of general engineering usage. Although the specific implementation of the algorithm described in this report and the resulting output files are tailored to the modeling and visualization software used to construct the figures contained herein, the algorithm itself is generic and other implementations and output formats are possible. The graphical visualizations of the salt domes at the four Strategic Petroleum Reserve sites are believed to be major improvements over the previously available two-dimensional representations of the domes via conventional geologic drawings (cross sections and contour maps). Additionally, the numerical mesh files produced by this modeling activity are available for import into and display by other software routines. The mesh data are not explicitly tabulated in this report; however an electronic version in simple ASCII format is included on a PC-based compact disk.