This paper discusses the successful application of reverse osmosis membranes at the San Ardo Oil Field in California to desalinate produced water for beneficial re-use through surface discharge to the local groundwater.The field produces heavy oil via a recovery process called steam flooding, in which steam is injected into the formation to heat up the crude and decrease its viscosity, thereby allowing the normally tar-like substance to flow by gravity to producing wells. This process typically results in the production of ten or more barrels of water for every barrel of oil recovered. Historically, a portion of this water has been recycled and softened to provide water for steam generation, with the remainder going to local EPA class II injection wells for disposal. However, the injection zone capacity is limited, which has constrained full field development. In October 2007, a desalination facility was commissioned to allow a portion of the produced water to be treated and discharged to the shallow fresh water aquifer, thereby providing an alternate outlet for produced water, and allowing field development to progress.At the San Ardo site, the process is sized to treat 50,000 barrels of water per day, and consists of de-oiling followed by the OPUS™ technology, which consists of multiple treatment processes, including degasification, chemical and ion exchange softening, multi-media filtration, cartridge filtration, double-pass reverse osmosis, pH neutralization, and partial remineralization. The treated water is discharged to post-treatment constructed wetlands and aquifer recharge basins. This technology, portions of which were developed jointly and patented separately by Chevron U.S.A., Inc. and Veolia N.A. Water Systems, has proven to be a reliable and robust process for successfully treating produced water for surface discharge.This paper details the treatment process, water quality specifications, and challenges faced during the design and operation of the facility.

Controlled flow rate tests using mixtures of crude oil and water at different mass fractions were carried out in a flow loop at the University of Tulsa. A noninvasive acoustic method developed at the Los Alamos National Laboratory (LANL) was applied to calculate the mass and volume fractions of oil and water in the mixed two-phase flow by measuring the speed of sound through the composite fluid mixture along with the instantaneous temperature. The densities and sound speeds in each fluid component were obtained in advance for calibration at various temperatures, and the fitting coefficients were used in the final algorithm. In this paper, we present composition measurement results using the acoustic technique from LANL for different mixture ratios of crude oil and water and at varying flow rates and a comparison of the results from the acoustics-based method with those from Coriolis meters that measured individual mass flow rates prior to mixing. The mean difference between the two metering techniques was observed to be less than 1.4% by weight and is dependent on the total flow rates. A Monte Carlo analysis of the error due to calibration uncertainty has also been included.

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