Performance Aspects of Water Quality in Disposal Wells

Abstract

Abstract Water quality is one of the most significant variables that influence the injectivity in matrix disposal wells. Permeability reduction through water/rock interaction or pore throat blocking are two common mechanisms of injectivity loss. This paper investigates the relative contribution of fluid/water compatibilities, water/rock interactions and all of the other water borne contaminants on formation damage. A series of systematic experiments were conducted to determine the most significant parameters contribution to potential formation damage mechanisms, their contribution to the cumulative damage, and possible treatment designs to restore core permeability. The proposed analytical workflow included a comprehensive characterization of potential injection water (both liquid and solids) utilizing advanced analytical techniques to characterize water quality in terms of salinity and solid organic and inorganic contamination such as ICP and XRD. In addition, coreflooding experiments were performed to quantify the impact of oil content, dissolved and suspended solids, and particle sizes on the injectivity loss as a function of time core plugs. Treatments to remove or bypass the damage to regain permeability were also investigated. Experimental results uncovered the water parameters that contribute to formation damage such as water salinity, oil-in-water content, and suspended solids. The average particle size of the suspended particles was in the order of 10 microns. Coreflooding results indicate that the water severely damaged cores up to 42%, with permeability to air below 30 md. The water composition, along with the high total suspended solids played an important role in the damage observed in the lab experiments. Total suspended solids and scaling tendency of the water accounted for over 60% of the damage, with oil content for the remainder. Based on the analysis of the relative contribution of the various damage mechanisms, for low permeability (25 – 50 mD), the following water quality requirements would be recommended to best manage the loss of injectivity: oil in water content less than 100 ppm, total suspended solids less than 50 mg/L with an average particle solids size less than 5 microns. In this paper, a systematic analytical workflow is investigated that provides methodology of screening water quality for injection purposes. The methodology can be adapted to different water sources for enhanced injectivity and disposal.