Control on Formation Water Properties at a Site in Southern Iberia Parish, Louisiana: Implications for the in Situ Extraction of Geothermal Energy

Marielle Ausburn and Jeffrey Hanor
[email protected]

There has been renewed interest in the feasibility of extraction of geothermal energy from deep sands in the Louisiana Gulf Coast. 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 explored at LSU involve engineered downhole heat exchangers. Our research focuses on what water-rock reactions could occur as reservoir temperatures are lowered during heat extraction and as native reservoir waters are made to circulate through a heat exchanger. The first phase of this study has involved characterizing formation water and sediment properties in a deep, 23,000-ft borehole in southern Iberia Parish, a potential resource area. Data available include formation water salinities calculated from SP and dual-conductivity techniques, temperatures and pressures from log header information, XRD and whole-rock chemical analyses, and chemical analyses of nearby produced waters. Top of overpressure occurs at a depth of 13,800 feet. Most of the overpressured section is in a Lower Miocene marine shelf facies. The corrected in situ temperature in the deepest well-developed sand encountered is 337°F at 21,900 feet. Salinities increase with depth, with considerable scatter, to maximum values of 200 g/L at the top of overpressure. There then is a progressive decrease in salinity to much less than seawater salinities (35 g/L) below this depth. There is a good correlation between the decrease in salinity with an increase in the proportion of illite in mixed layer I/S, presumably reflecting dewatering during the smectite-illite transition. Future work will include characterizing the chemical composition and reactivity of overpressured formation waters in Iberia Parish.

AAPG Search and Discovery Article #90167©2013 GCAGS and GCSSEPM 63^rd Annual Convention, New Orleans, Louisiana, October 6-8, 2013