Sustainability in Drilling Operations Using Zero Liquid Discharge Wastewater

Abstract

Produced water is generated from subsurface reservoirs during oil and gas extraction. Zero liquid discharge (ZLD) produced water desalination technology generates clean low salinity water from hypersaline produced water with 80 to 90% recovery efficiency. The minimal volumes of salt laden reject streams discharged from ZLD desalination plant could be recycled for mineral recovery or drilling applications to achieve 100% circular economy. Such applicability of wastewater streams for potential reuse in drilling applications is evaluated in this study in order to avoid waste disposal into the environment and promote sustainability. We have tested and demonstrated the applicability of ZLD reject water as a makeup fluid for preparing water-based mud systems. The total dissolved salt of ZLD reject water is around 360000 ppm. The conventional water-based mud additives have limitations in terms of salt tolerance. Therefore, it is essential to study the conventional water-based mud additives to ensure the compatibility in such high saline environment. Three basic water formulations with viscosifier, fluid loss control and pH controlling additive are prepared using 100 % regular fresh water, 100% ZLD reject water and 50:50 mixture of fresh water and ZLD reject water. Mud formulations were made with bentonite and xanthan gum as viscosifiers. The mud samples have been subjected to routine mud analysis such as hot rolling, rheological and filtration control tests. Initial screening was done for choosing the viscosifier. Formulations made with Bentonite as a viscosifier failed to provide viscosity and solids suspension property for the muds formulated using 100% reject water and 50:50 mixture of fresh water and ZLD reject water. This is due to the high salt intolerance of Bentonite. Formulation of 50:50 mixture of fresh water and reject water using Xanthan Gum as viscosifier resulted in acceptable properties such as rheology and filtration control, whereas poor rheological and filtration control properties are observed for 100% reject water. Further testing was conducted by adding more additives such as bridging materials, weighting materials and drill solids contaminants to the basic mud formulation having 50:50 mixture of fresh water and reject water. The results for the mud that was hot rolled at 212 °F and 500 psi showed acceptable rheological and filtration control properties. Excellent mud suspension property has been observed with no solids settling or separation even after 24 h. These interesting laboratory results demonstrate that the waste reject water obtained from ZLD produced water desalination plant could be an alternate to fresh water currently used in mud preparation. The ZLD waste reject water was successfully used to formulate water-based mud to achieve 100% circular economy. This novel development paves the way to effectively recycle wastewater for drilling applications to conserve fresh water and promote environmental sustainability in drilling operations.