Economic Evaluation of Treating Oilfield Produced Water for Potable Use

Abstract

Abstract Conventional opinion has often viewed produced water as a byproduct from oil production. Disposal of this water is an expense every treatment facility must contend with as long as their wells continue to produce. This issue can become a serious logistical or environmental problem for fields with limited disposal capacity or that generate produced water with poor water quality. Instead of discarding the water as waste, advances in membrane water treatment technology can allow economical treatment of water for potable consumption. Placing this water to productive use may not completely eliminate daily wastewater disposal. However, it will drastically reduce the disposal volume, possibly freeing up other resources. This concept shifts the paradigm for produced water, transforming its image from what seemingly is a costly waste to possibly a valued commodity. This paper will present a conceptual design for a 50,000 BPD integrated membrane filtration plant capable of handling typical oilfield produced water. Included will be an evaluation of capital and operating & maintenance costs. A discussion on the marketing potential for this water as a new potable or irrigation water source will also be presented by comparing its economics against conventional surface water or seawater desalination treatment. 1.0 Introduction Treatment of oilfield produced-water typically involves the removal of hydrocarbons, ammonia, hydrogen sulfide, and perhaps silica before injection into wastewater disposal wells. Should limited disposal capacity require disposal into nearby waterways or watersheds, the produced water must be further treated to remove salinity, boron, dissolved organics, and certain heavy metals. This report describes how current chemical precipitation and advance membrane technologies can enhance conventional oilfield water treatment plants to provide an economical answer for removing all of the above constituents. The goal of the proposed plant is to produce high quality water that can meet drinking water standards. The produced water can then be sold for irrigation or potable consumption or safely discharged into local rivers and streams for disposal. 2.0 Design Overview The conceptual design focuses on the removal of hydrocarbon, ammonia, hydrogen sulfide, hardness, silica, boron, and salinity from the produced water. The design basis assumes that most free oil in the produced water has been removed by conventional processes, such as wash tanks, dissolved gas floatation, and walnut shell filtration. The following is a list of conceptual treatment processes and the constituent(s), which these processes will remove:Warm Lime Softening (WLS) - Carbonate Hardness and SilicaMembrane Bioreactor (MBR) - Emulsified Oil & Grease, Ammonia, Soluble Organics, Settleable / Suspended solidsReverse Osmosis (RO) - Salinity and Boron A block flow diagram of the above processes is presented in Figure 2.1.