Fresh water generation from aquifer-pressured carbon storage: Feasibility of treating saline formation waters

Abstract

Abstract Brines up to 85,000 ppm total dissolved solids produced during Carbon Capture and Storage (CCS) operations in saline formations may be used as the feedstock for desalination and water treatment technologies via reverse osmosis (RO). The aquifer pressure resulting from the injection of carbon dioxide can provide all or part of the inlet pressure for the desalination system. Residual brine from such a process could be reinjected into the formation at net volume reduction, such that the volume of fresh water extracted is comparable to the volume of CO 2 injected into the formation. Such a process could provide additional CO 2 storage capacity in the aquifer, reduce operational risks (e.g., fracturing, seismicity, leaking) by relieving overpressure in the formation, and provide a source of low-cost fresh water to offset costs or operational water needs equal to about half the water usage of a typical coal ICGG power plant. We call the combined processes of brine removal, treatment, and pressure management active reservoir management. We have examined a range of saline formation water compositions propose a general categorization for the feasibility of the process based total dissolved solids (TDS): • 10,000–40,000 mg/L TDS: Standard RO with ≥50% recovery • 40,000–85,000 mg/L TDS: Standard RO with ≥10% recovery; higher recovery possible using 1500 psi RO membranes and/or multi-stage incremental desalination likely including NF (nanofiltration) • 85,000–300,000 mg/L TDS: Multi-stage process using process design that may differ significantly from seawater systems • >300,000 mg/L TDS brines: Not likely to be treatable Brines in the 10,000–85,000 mg/L TDS range appear to be abundant (geographically and with depth) and could be targeted in planning CCS operations. Costs for desalination of fluids from saline aquifers are in the range of $400–1000/acre foot of permeate when storage aquifer pressures exceed 1200 psi. This is about half of conventional seawater desalination costs of $1000–1400/acre foot. Costs increase by 30 to 50% when pressure must be added at the surface. The primary reason for the cost reduction in pressurized aquifers relative to seawater is the lack of need for energy to drive the high-pressure pumps. An additional cost savings has to do with less pre-treatment than is customary for ocean waters full of biological activity and their degradation products. An innovative parallel low-recovery approach is proposed that would be particularly effective for saline formation waters in the 40,000–85,000 mg/L TDS range.