Hydraulic Fracturing and Organic Compounds - Uses, Disposal and Challenges

Abstract

Abstract Hydraulic fracturing has allowed oil and natural gas producers in the U.S. to effectively tap reservoirs that would otherwise be unfeasible to produce. In recent years, the natural gas industry has experienced a boost in production through the increased use of hydraulic fracturing in shale and tight sand formations. Despite its production advantages, the hydraulic fracturing process is not without its concerns. Hydraulic fracturing utilizes large quantities of water which, together with a number of chemical additives known as the ‘fracturing fluid’, are injected into underground formations. After being injected, between 5 and 60 percent of this fluid mixture flows back to the surface as produced water carrying with it any remaining chemical additives and naturally occurring material from the formation. Due to the complicated cycling of water and organic compounds during hydraulic fracturing and produced water treatment, the ability to independently identify and quantify chemicals associated with fracturing activities at different stages of the shale gas water lifecycle remains challenging. The ability to identify and quantify organics may be relevant both for maximizing efficiency during fracturing and water treatment, and for environmental management. Continued analyses of both the ‘hydraulic fracturing fluid’ and the produced water have shown that not all organic compounds that were injected into the well return to the surface. This suggests that adsorption/desorption and/or chemical transformation processes are taking place within the formation. Determination whether organic compounds detected in produced waters are synthetic or naturally-derived from the reservoir is complicated by the number of compounds that exist both naturally in the formation, and are injected with the hydraulic fracturing fluid. Depending on the fracturing job, roughly 4 – 10 different synthetic organic compounds are added to the hydraulic fracturing fluid at one time. A survey of 1000 API registered wells hydraulically fractured in Western Pennsylvania and West Virginia showed roughly 150 different organic compounds used as ingredients in the fracturing fluids. This makes identification and analysis of these compounds in produced waters difficult. Further complications for evaluating organics in the shale gas water life cycle stem from the use of recycled produced waters. Analysis of samples from produced water treatment facilities showed the presence of organic compounds in the inlet and effluent of the treatment facility. The effluent of many treatment plants is reused bringing with it the organic compounds that are still present to the next hydraulic fracture job. This paper looks into the different organic compounds used in the hydraulic fracturing process, their possible life-cycle after the process, the difficulties encountered when analyzing for these compounds, and possible challenges with site planning and environmental decision-making.