Successful Treatment and Reuse of Flowback Guar Frac-Fluid in Ordos Basin and Associated Cost Savings to Operators

Abstract

Ordos basin is known for its tight sandstone formations and fracturing has been the most effective approach to improve production[1,2]. With increasing stimulation activities, water consumption, and associated water cost, flowback fluid volume also increased dramatically. Successfully treat the flowback fluid and the reuse of the treated fluid in making new frac fluid are keys to improve stimulation economics and protect the environment. However, treatment and reuse of commonly used guar frac fluid system remains a significant challenge to operators and service companies. To successfully treat and reuse flowback fluid in Ordos basin, two major obstacles have to be overcome: First, in the fracturing process, the local common practice is to add the entire designed amount of gel breaker at the end of propant pumping job, to avoid sand plugging and sanding out. This incorrect, but common practice results in incomplete breaking of gel of the frac fluid, which inevitably flows back leading to greatly increased difficulties in flowback fluid treatment. Secondly, organic boron crosslinking agent is widely used as crosslinking agent in the guar fluid system in this area. As boron compounds are extremely difficult to be removed during flowback fluid treatment, proven treatment methods alone cannot make the treated water reusable in making new frac fluids. Technology and processes were developed to manage four key factors that affect the performance of guar frac fluid configured with treated flowback fluid: a) Metal ions, b) Bacteria, c) Breaking agent, d) Crosslinker. Mobile units developed in association with treatment processes and agents also help avoid secondary pollution from the transportation of fresh and flowback fluid. In 2017 and first quarter of 2018, more than 15,000 cubic meters of flowback fluid have been successfully treated and reused. One third of the treated water was guar frac fluid and was reused in making new frac fluid, reducing the need for fresh water significantly. Fracturing service company conducted tests on the treated water and found that the performance of the fluid configured with the treated water completely satisfy the requirements of the SY/T6376-2008 "General Technical Requirements for Fracture Fluid" and SY/T 5523-2016 "Oilfield Water Analysis Method" standard. Frac fluid configured with the treated water was successfully applied to the stimulation jobs of horizontal wells, resulting in double savings to the operators: purchase of fresh water and transportation of flowback fluid (to treatment centers) and fresh water, also avoided secondary environmental impacts such road safety hazard and fluid seepage. With the treatment and reuse of flowback fluid, savings up to 8% of total frac costs per well were observed which could lead to 100+ million RMB within 2018 alone. Most importantly, the technology can effectively relieve environmental pressure and reduce the need of fresh water which is a scarce in this area.