Geochemical and Economic Evaluation of Brine Exchange as a Means of Produced Water Management

Abstract

The extraction of crude oil generates large amounts of wastewater, also referred to as brine or produced water. This water is often high in salinity, heavy metals, and other toxic compounds. Its constituents make conventional treatment difficult and expensive, so a common practice is to inject this water deep underground for long-term storage. While convenient, deep well injection of produced water has been linked to environmental concerns, such as increased water stress and induced seismic activity. Alternative methods to produced water management are critical to alleviating concerns associated with current produced water disposal practices. Produced water brine exchange is one such alternative method that involves exchanging produced water between reservoirs to create a salinity gradient. A lower salinity brine is injected into a high salinity reservoir for use in Low Salinity Waterflooding (LSWF)—a practice that can lead to increased oil recovery. The high salinity brine is injected into the low salinity reservoir for long-term disposal, maintaining reservoir pressure.This study evaluates brine exchange between the Arbuckle formation (~20,000 mg/L TDS) and Lansing-Kansas City (LKC) formation (~150,000 mg/L TDS). To ensure geochemical compatibility between the injected brine, the in-situ brine, and reservoir rock and to evaluate the economic potential of brine exchange, a series of mixing experiments, geochemical modeling, and economic analysis were conducted. Bulk mixing and coreflooding experiments were conducted to evaluate brine-solid compatibility under both non-transport limited conditions and transport dominated conditions experienced in real-world environments. Experimental results were supplemented with geochemical modeling using PHREEQC with three sets of thermodynamic databases (PHREEQC, PITZER, and MINTEQ) to aid with compatibility analysis. Additionally, a techno-economic assessment was conducted to gauge economic viability of potential brine exchange projects. Results from the mixing experiments showed the risk of calcium carbonate scale formation is present in brine-brine-rock systems with low salinities (high ratio of Arbuckle:LKC brines) but only to a minor degree. None of the three databases used for geochemical modeling could accurately capture all trends in aqueous cation concentrations due to inherent limitations in each approach. Further study to identify discrepancies between model approaches and experimental results is warranted. Lastly, simulation modeling revealed that the economic viability of conducting brine exchange is highly correlated with the distance between wells and the energy cost of brine transportation. Conditions needed for economically viable operations have been identified, and the boundary between viable and unviable conditions have been found to be resilient to changes to material costs. The results gathered identify scenarios where brine exchange could be feasible and the key parameters needed to assess the risk of geochemical incompatibility.