Geochemical Feasibility of Brine Exchange Between Arbuckle and Lansing-Kansas City Formations as a Produced Water Management Alternative

Abstract

The State of Kansas is facing increasing demands on limited available drinking water sources. Reclaiming and reusing wastewaters for water applications able to utilize lower quality water sources could help to extend and conserve existing drinking water sources. Oil production in Kansas generates over one billion barrels of produced water each year, which must be properly managed in compliance with environmental regulations. Successful reclamation of this wastewater for industrial and other uses could reduce freshwater requirements in the oil industry and provide a new water source for other water needs of the state. Produced waters from Kansas oil fields are usually very salty with a median total dissolved solids (TDS) concentration of 90,000 mg/l. However, there are a few oil formations in the Central Kansas Uplift area that have less salty water with a TDS of 40,000 mg/l or lower. Exchange of formation brine, where the highly salty brine from one formation is injected into the lower salinity formation, along with extraction of the lower salinity formation water to balance formation pressure, has been proposed as a way of managing produced water for potential reuse applications. This study was conducted to further investigate the feasibility of brine exchange as a produced water management practice from a geochemical and environmental standpoint. A geochemical software program (PHREEQC) was utilized, along with both the PHREEQC and Pitzer databases, to predict precipitation reactions that might occur during the brine exchange. These predictions were compared to laboratory results to determine the limits and degree of accuracy of the model. Adverse reactions such as precipitation of solids in the formation during the exchange could block the pore spaces and reduce the conductivity of the formation. This study established that mixing Lansing Kanas City formation brine with Arbuckle formation brine (from the Wellington wellfield in Kansas) could potentially cause calcium carbonate scale formation, and that cutting down the bicarbonate content is essential to prevent scaling. Also, using both the Pitzer and PHREEQC databases, PHREEQC accurately predicted the amount of carbonate scale formed at well oversaturated conditions, i.e., having a saturation index (SI) 2, within the range of ionic strength investigated, i.e., 1 M to 3.65 M. However, the model is likely to overestimate the amount of scale formation at close to saturation conditions, for SIs between -0.5 and 2, for the mineral phases barite, celestite, gypsum, and anhydrite. For SIs in this range, both databases are likely to predict similar SIs for the sulfate minerals; but for the carbonate mineral phases, the predicted SIs from the Pitzer database are higher. This is due to the higher predicted activity for the carbonate ion, as the Pitzer database does not consider ion pairing or complexation, and more specifically the formation of NaHCO3+. pH predictions from both databases closely agree with the each other but failed to accurately predict measured pH values in lab experiments. This is most likely due to interference with pH measurement due to the high sodium ion concentration.