Unlocking the Sustainable Synergy of Geothermal Energy with ZLD Produced Water Desalination

Abstract The conventional thermal based ZLD technologies used for produced water desalination are energy intensive. This study aims to leverage the geothermal energy from abandoned wells to enhance the temperature of pretreated high-salinity produced water and achieve an optimized Zero Liquid Discharge (ZLD) system to significantly lower carbon foot-print associated with produced water desalination. The proposed approach utilizes the closed-loop geothermal heat extracted from the abandoned well to pre-heat the produced water before it enters the evaporation-based thermal desalination unit such as Dynamic Vapor Recovery. A semi-analytical model, comprising a wellbore heat flow model coupled with a formation heat conduction model, is employed to rapidly determine the thermal energy output potential from the closed-loop geothermal system. The study evaluates the feasibility of increasing the temperature geothermally from 25°C to reach the desired output temperature of 80-85°C by the continuous once through circulation of produced water through an abandoned well. Sensitivity analysis is conducted to study the influence of various parameters, including reservoir characteristics, well parameters, and operational conditions, to identify the optimal scenarios that can result in near zero carbon foot-print ZLD solutions for produced water desalination. The results of sensitivity analysis indicate that casing size, well depth, flow rate, and reservoir temperature are the most critical parameters affecting the achievable output temperature for the integrated ZLD system. The tubing size was the least influential parameter within the value range (2.5-4.5 inch) studied. It was found that well depths above 10,000 ft and circulation flow rates below 10,000 BPD can reach the desired temperature geothermally with a thermal energy gain of 4.0 Mwth. The reservoir temperatures above 300°F and casing sizes greater than 8.0-8.5 inch are determined to be optimal to provide the sufficient geothermal heat needed for raising the temperature of the pretreated feed produced water into ZLD desalination system without the consumption of any additional heat. Based on these interesting results, it can be concluded that the proposed approach can minimize energy consumption and reduce operational costs, thereby making the geothermal energy integration with produced water desalination both viable and sustainable. In summary, the findings demonstrated the feasibility of leveraging abandoned well geothermal energy to enhance the temperature of high-salinity produced water and significantly lower the energy requirements of ZLD produced water desalination processes to generate fresh water. These favorable outcomes align very well with UN Sustainability Development Goals 6 and 13 focusing on "clean water", and "climate action", respectively. The utilization of semi-analytical approach for optimizing the integration of geothermal energy with ZLD technology is a novel contribution to the existing knowledge. This cost-effective synergistic solution can facilitate the broader adoption of sustainable geothermal energy for the desalination of high-salinity produced water, which eventually enhances the environmental and economic viability of ZLD desalination processes to promote both circular water/carbon economies in upstream operations.