Beneficial Reuse of San Ardo Produced Water

Abstract

This DOE funded study was performed to evaluate the potential for treatment and beneficial reuse of produced water from the San Ardo oilfield in Monterey County, CA. The potential benefits of a successful full-scale implementation of this project include improvements in oil production efficiency and additional recoverable oil reserves as well as the addition of a new reclaimed water resource. The overall project was conducted in two Phases. Phase I identified and evaluated potential end uses for the treated produced water, established treated water quality objectives, reviewed regulations related to treatment, transport, storage and use of the treated produced water, and investigated various water treatment technology options. Phase II involved the construction and operation of a small-scale water treatment pilot facility to evaluate the process's performance on produced water from the San Ardo oilfield. Cost estimates for a potential full-scale facility were also developed. Potential end uses identified for the treated water include i) agricultural use near the oilfield, ii) use by Monterey County Water Resources Agency (MCWRA) for the Salinas Valley Water Project or Castroville Seawater Intrusion Project, iii) industrial or power plant use in King City, and iv) use for wetlands creation in the Salinas Basin. All of these uses were found to have major obstacles that prevent full-scale implementation. An additional option for potential reuse of the treated produced water was subsequently identified. That option involves using the treated produced water to recharge groundwater in the vicinity of the oil field. The recharge option may avoid the limitations that the other reuse options face. The water treatment pilot process utilized: i) warm precipitation softening to remove hardness and silica, ii) evaporative cooling to meet downstream temperature limitations and facilitate removal of ammonia, and iii) reverse osmosis (RO) for removal of dissolved salts, boron, and organics. Pilot study results indicate that produced water from the San Ardo oilfield can be treated to meet project water quality goals. Approximately 600 mg/l of caustic and 100 mg/l magnesium dosing were required to meet the hardness and silica goals in the warm softening unit. Approximately 30% of the ammonia was removed in the cooling tower; additional ammonia could be removed by ion exchange or other methods if necessary. A brackish water reverse osmosis membrane was effective in removing total dissolved solids and organics at all pH levels evaluated; however, the boron treatment objective was only achieved at a pH of 10.5 and above.