Sustainable Reuse of Produced Water Treatment Waste in Drilling Operations

Abstract

In oil and gas explorations, produced water is generated from subsurface reservoirs along with crude oil and gas. The produced water gets separated from hydrocarbon in gas oil separating plant (GOSP). Proper treatment and reuse of the produced water is gaining attention across the globe. Zero liquid discharge (ZLD) produced water desalination technology generates low saline clean water from hypersaline produced water with recovery efficiency 80 to 90%. The minimal quantity of salt laden waste reject streams is generated from ZLD desalination plant. The waste water is extremely saline and not fit to reuse unless treated appropriately. Finding applications for waste water to reuse without additional treatment such as mineral recovery or drilling applications is preferred to achieve 100% circular economy. In our study, applicability of waste water for potential reuse in drilling applications is assessed in this study in order to circumvent waste discarding into the environment and promote sustainability. We have evaluated and confirmed the applicability of ZLD reject waste water as a makeup fluid for preparing water-based mud systems. The total dissolved salt of ZLD reject water is about 360000 ppm. The conventional water based mud chemicals have limitations in terms of salt tolerance. Therefore, it is important to study the conventional water based mud additives to ensure the compatibility in such high salinity conditions. Three basic water formulations with basic additives such as base to adjust pH, viscosifier to provide rheology and a fluid loss control additive to reduce filtration are prepared using 100 % regular fresh water, 100% ZLD reject waste water and 50:50 mixture of fresh water and ZLD reject waste water. Mud formulations were made with bentonite and xanthan gum as viscosifiers. After hot rolling the mud samples for 16 h, routine mud analysis were carried out such as rheological and filtration control tests. Initial screening was completed for choosing the viscosifier. Formulations prepared with Bentonite as a viscosifier failed to provide viscous and solids suspension properties for the muds formulated using 100% reject water and 50:50 mixture of fresh water and ZLD reject water. This is owing to the high salt intolerance of Bentonite. Formulation of 50:50 mixture of fresh water and reject waste water using Xanthan Gum as viscosifier lead to in satisfactory rheology and filtration control properties, however poor rheological and filtration control properties were observed for 100% reject water. Further testing was continued for additional screening by adding more mdu additives such as bridging materials, weighing materials and drill solids contaminants to the basic mud formulation having 50:50 mixture of fresh water and reject waste water. The muds were hot rolled at 212 °F and 500 psi and the test results 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 lab results prove that the waste water reject obtained from ZLD produced water desalination plant could be a potential alternate to fresh water currently used in mud preparation. The ZLD waste reject waste water was successfully used to formulate water-based mud to achieve 100% circular economy. This novel development paves the way to effectively recycle waste water for drilling applications to conserve fresh water and promote environmental sustainability in drilling operations.