EFFECT OF GUAR GUM ON THE MOBILITY OF BARIUM IN DISPOSAL WELLS OF THE ARBUCKLE FORMATION

Flowback and produced water (wastewater) from unconventional gas wells in Oklahoma are injected into deep disposal wells of the Arbuckle formation. Total dissolved solids includes heavy metal ions (e.g., Ba and Sr) whose concentrations are in many cases hundreds of time above the US drinking water standards. This poses a huge environmental risk as wastewater disposed into deep wells might leak to shallow groundwater systems due to well integrity flaws or presence of natural fractures.

This work focuses on the effect of viscosifiers on the mobility of heavy metals, specifically we focus on the effect of guar gum on the mobility of Ba²⁺. Guar gum is used to increase the viscosity of the fracturing fluid to help suspend proppant (a granular material used to hold induced fractures open after treatment), and Ba²⁺ is one of the most common/abundant heavy metal detected in wastewaters. Although the effect of organic polymers on the mobility of oxidizing reagents in shallow aquifers has been studied before, this is the first work aiming to reveal the transport mechanism of heavy metals under the presence of polymers through Arbuckle dolomite rocks.

Batch and core-flooding experiments were conducted using powdered dolomite (212-300 and 500-512µm grain size) and dolomite plugs (2.54 cm diameter and 5-12 cm length) prepared from Arbuckle outcrop in Missouri. The porosity and permeability of the plugs were 4-15% and 1-15mD. We conducted eight batch experiments to study the sorption of Ba²⁺ on the surface of powdered dolomite under the presence of guar gum. Core-flooding experiments were conducted at a confining pressure of 4000 psi and room temperature at three flow rates (0.01, 0.05 and 0.1 ml/min). The concentration of Ba²⁺ and guar gum in the core-flooding experiments were 100 and 50 mg/l, respectively. Our results indicate that guar gum decrease the sorption of Ba²⁺ on the surface of dolomite through chelation-like interactions between guar gum and Ba²⁺, however the mobility of Ba²⁺ through dolomite plugs does not increase as one might expect. Guar gum readily clogged the pore space of the dolomite plug. This was reflected by a reduction in the hydraulic conductivity of the dolomite plug and the accumulation of Ba²⁺ within the plug. Reducing the flow rate of the fluid containing guar gum resulted in higher clogging levels of the plug.