Abstract

Produced water accounts for greater than 80 percent by volume of the residual material generated in the production of natural gas. Thus, cost-effective, and environmentally acceptable disposal of these waters is critical to the continued economic production of natural gas. This paper describes a Gas Research Institute (GRI) sponsored pilot-scale (500 bbls/day, 15 gpm) produced water field experiment performed in a natural gas field in the Rocky Mountains. The pilot system consisted of treatment for deoiling, dissolved organic removal, and partial demineralization. Based on the results of the pilot system, the overall treatment process achieved the effluent water quality requirements for surface water discharge. The overall treatment system cost is approximately $0.25/bbl of water treated. This cost included the treatment system capital cost, and operating and maintenance costs.

Introduction

Natural gas is an important energy source in the United States accounting for approximately 22 percent of the aggregate energy consumption in 1990. Natural gas consumption should continue to increase well into the twenty-first century as concerns with air quality impacts associated with fossil fuel combustion assumes a greater role in energy selection decisions. To ensure that the potential of natural gas is fully developed, it will be necessary for the natural gas production industry to focus increased attention on the control of potential environmental impacts resulting from the exploration and production of natural gas. Because produced water accounts for more than 80 percent by volume of the wastes associated with natural gas production, a continuing effort is required by the industry to develop costeffective and environmentally acceptable produced water management strategies.

To Provide leadership in this effort, GRI has been evaluating the potential for reducing produced water treatment and disposal costs for the natural gas industry. Two products of this evaluation are the reports entitled A Regional Assessment of Produced Water Treatment and Disposal Practices and Research Needs and GRI-ProwCalcTM, a produced water treatment engineering-economic cost model. Results from the report and GRI-ProWCalcTM, along with consultations with GRI member companies, indicate that there is an opportunity to reduce produced water treatment and disposal costs in the High Plains region of the United States. Therefore, GRI co-funded a produced water treatment field experiment in Lysite, Wyoming.

The GRI produced water treatment field experiment described in this paper was designed to contribute to the success of this industry effort. Realizing that injection of produced water is the dominant disposal methodology, this GRI produced water field experiment contributes to the goal of reducing the cost of produced water management in two ways by:

  1. developing effective partial demineralization technologies to reduce the volume of brine that must be injected, and

  2. developing an effective treatment system for deoiling, dissolved organic removal, and partial demineralization.

A treatment system would have to partially demineralize produced water before surface water discharge under a National Pollutant Discharge Elimination System (NPDES) permit to meet water quality standards for beneficial reuse. Thus, the permit levels become the treatment goals. The actual produced water treated in this field experiment was characterized before and after each individual treatment process. Treatment to remove oil and grease (O&G) and dissolved organics, both to achieve permit requirements and to protect various treatment processes, were incorporated into the overall produced water treatment system.

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