2025 GCAGS Journal, Vol. 14
TITLE
Evaporite Zones and Associated Dissolution-Collapse Breccias in the Upper Jurassic Smackover Formation in Northeastern Texas: Are They a Concern for Heterogeneity?
AUTHOR(S)
Robert G. Loucks
ABSTRACT
The Upper Jurassic Smackover Formation in northeastern Texas is being intensely investigated as a reservoir for lithium-rich brines. Reservoir quality, controlled by lithofacies and diagenesis, is important for understanding lithium-brine deliverability. Production of lithium-rich brines is not dependent on trapping mechanisms, as the brines occur in continuous reservoirs. However, even in continuous reservoirs, reservoir heterogeneity must be defined and evaluated to understand controls on production. In the upper Smackover coated-grain grainstone belt in northeastern Texas, dolomitized peloidal/oncoid/ooid grainstones contain the highest reservoir quality, being the dominant lithofacies for high flow rates in brine production. Within the upper part of the coated-grain grainstone sections, beds of evaporites (anhydrite) and evaporite dissolution-collapse breccias may form vertical permeability barriers. These evaporite beds were deposited in saline ponds and within sabkha sediments landward of ooid-dominated strandplain deposits. The evaporites, where preserved, occur as anhydrite-bearing beds several feet thick. Where the evaporites were dissolved, the evaporite zones occur as dissolution-collapse breccias. The anhydrites are crudely bedded but sometimes nodular, indicating dominant salina deposition with some precipitation within sabkha sediments. Other evaporite zones are mixtures of small anhydrite nodules, peloids, and coated grains. The evaporite-related collapse breccias contain early cemented breccia clasts of ooid grainstones within a dolomudstone matrix. The evaporite-dominated zones and some dissolution-collapse breccias are tight and form vertical barriers to flow; however, well control is insufficient for defining their lateral extent.
PAGE(S)
23-35
DOI
https://doi.org/10.62371/UIGM3300
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