SUITABILITY OF BRACKISH WATER FOR USE IN HYDRAULIC FRACTURING: HYDROGEOCHEMISTRY OF DOCKUM GROUP GROUNDWATER, MIDLAND BASIN, TEXAS
Potentiometric surface maps indicate that groundwater generally flows southward and eastward across the basin, possibly as a result of basin uplift and eastward tilting in the past 5–10 m.y. Transmissivities range 2–990 m2/day (geometric mean = 42 m2/day) indicating that water yield from the unit is mixed, but generally productive. Geochemical results suggest two dominant water types of meteoric origin: 1) a high salinity (up to 70 g/L) Na-SO4- to Na-Cl-type water found mainly in the center and western parts of the basin; and 2) a lower salinity (< 7.5 g/L) mixed ion water, with larger proportions of Ca and Mg, found on the southern and eastern basin margins.
Both slick water (low viscosity fluid with a friction reducer) and cross-linked gel (high viscosity fluid containing a gelling agent) fluids are used for hydraulic fracturing in the basin. The feasibility of utilizing brackish groundwater for hydraulic fracturing, particularly with cross-linked gels, is limited by a variety of chemical conditions including high concentrations of alkaline earth metals (AEM), SO4, and DOC. Despite having lower salinity, the water in the downgradient southern and eastern margins of the basin is most likely to exceed acceptable limits for AEM and/or SO4. Generally, the majority of the water in the basin is suitable for use with slick water hydraulic fracturing. Findings from this research provide important baseline data on potential use of brackish groundwaters in the oil and gas industry.