Identifier

etd-05302013-141118

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

Geothermal energy is a renewable energy source that can contribute to the U.S. energy mix. As such, new technologies are being explored for lower temperature systems which would open new areas for exploration in Louisiana. Unlike concepts proposed in the early 1980s, in which heat would have been extracted at the land surface from produced overpressured waters, methods currently being proposed would involve engineered down-hole heat exchangers with zero-mass-fluid withdrawal. A re-examination has been made of the controls on the composition of formation waters in south central and offshore Louisiana in the context of providing insight into water-rock reactions that might be expected as a result of lowering reservoir temperatures and mixing native formation waters associated with in situ heat extraction. An evaluation was made of produced waters from several fields in the south-central coastal area of Louisiana, the Weeks Island field, the Bullwinkle offshore field, and a proprietary offshore field called Bellatrix. Thermodynamic analysis suggests that the chemical composition of these waters is being buffered in part by the mineral assemblage albite, illite, smectite, chalcedony, calcite, dolomite, and barite. The waters are highly undersaturated with respect to gypsum, anhydrite, and halite. Thus it should be possible to predict reactions in the subsurface which could occur as a result of removing heat and lowering temperature. Data from Weeks Island, Bullwinkle, and Bellatrix establish the existence of significant spatial variations in formation water compositions within individual reservoir sands or fault blocks. Of most significance, in terms of the potential for precipitation of mineral cements or scale, are the inverse relations of the concentrations of dissolved barium and sulfate and of dissolved calcium and alkalinity. Mixing of waters within these sands could cause the precipitation of barite and/or calcite within a down-hole heat exchanger and/or conventional production tubing.

Date

2013

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Hanor, Jeffrey

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