ABSTRACT

The Upper Jurassic Smackover Formation is being intensely investigated as a reservoir for lithium-rich brines (Fig. 1). Reservoir quality, controlled by lithofacies and diagenesis, is important for understanding deliverability of the brines. Production of lithium-rich brines is not dependent on trapping mechanisms but rather can be considered to occur as continuous reservoirs. However, even in continuous reservoirs, reservoir heterogeneity must be defined and considered. In the upper Smackover, coated-grainstone belt in northeast Texas (Fig. 2), dolomitized peloidal/oncoid/ooid grainstones (Fig. 3A) contain the highest reservoir quality and are the dominant lithofacies for high flow rates for brine production. Within the upper part of the coated-grainstone sections, beds of evaporites (anhydrite) and dissolution-collapse breccias may form vertical permeability barriers. These evaporite beds are interpreted to have been deposited behind an ooid-dominated strandplain, in saline ponds on sabkhas (Fig. 2). The evaporites occur as anhydrite-bearing beds (Fig. 3B) several feet thick or as dissolution-collapse breccias (Fig. 3C) created by evaporite dissolution. The anhydrites are generally crudely bedded but sometimes nodular, indicating salina deposition. Other evaporite zones are mixtures of small anhydrite nodules, peloids, and coated grains. The evaporite-related collapse breccias contain lithoclasts of ooid grainstones within a dolomudstone matrix indicating proximity between evaporitic and shoaling depositional settings. The evaporite-dominated zones and some of the dissolution-collapse breccias are tight and will form vertical barriers to flow; however, there is insufficient well (i.e., wireline) data to define their lateral extent.