Cost Effective Treatment of Produced Water Using Co-Produced Energy Sources

Abstract

Abstract Produced water (PW) treatment is a daunting significant challenge that continues to have negative impacts on the oil and gas industry, especially, small oil producers. The total dissolved solids (TDS) in produced water from most oil fields can be higher than 250,000ppm (parts per million) in concentration and may also contain a significant percentage of dissolved organic carbons. Many small oil producing companies operate at the edge of profitability; the current cost of treating a barrel of produced water can exceed $2.50 if the operator has to pay for hauling and disposal. This can make it uneconomical to operate mature producing wells which tend towards high watercuts. As part of a RPSEA (Research Partnership to Secure Energy for America) research project, a Humidification-Dehumidification (HDH) Unit (figure 3) has been built tested and optimized to treat PW using co-produced heat and active solar energy. This has very low electricity consumption and has been tested to process PW at a cost less than $0.50 per barrel if co-produced, or latent heat sources are used. The HDH Unit effectively treats produced water with varying degrees of inorganic dissolved solids concentration and yields fresh water with TDS in the neighborhood of 400ppm when optimized for maximum throughput which is suitable for most oil field activities, irrigation, and could satisfy other basic human needs of water. The existing 80ft3 HDH Unit can process about 50 barrels of PW per day with high total dissolve solids concentration, and reducing this waste stream into concentrated waste and fresh water. Each pass of PW through the system has approximately 19% efficiency with some variations due to changes in seasonal humidity and temperature. The process works using simple thermodynamic principles. Air (at atmospheric pressure) has the capacity to tremendously increase water vapor saturation pressure to about 50Kpa when the temperature is about 180°F. Consequently, the efficiency of the unit is primarily contingent on ambient temperature and relative humidity. The system uses the high solar radiations prevalent in the Southwest United States to heat PW to about 180°F which is then pumped into an 80ft3 stainless steel that has evaporation and condensation compartments; air is then pumped into the Unit through the opposite direction (to the water) for the humidification of the air at elevated temperature. The heated and humidified air is then cooled to or below dew point to produce fresh water.