RIASSUNTO
The Chevron San Ardo Oil Field case study is a success story for produced water reuse. The case study provides a potential window into the future. As existing oil fields mature, water cut increases, and as world-wide water demand grows, beneficial reuse may present an increasingly attractive option for produced water management.
Instead of injecting produced water into Class II disposal wells (a common management practice for onshore oil fields), Chevron cleans up brackish produced water by an innovative, multi-step treatment process involving oil/water separation, chemical treatment and reverse osmosis to remove oil, solids, and salts. A portion of the treated water is used as cooling tower water. The remaining water undergoes further conditioning steps that include ammonia removal, pH adjustment, ion balancing, and a treatment wetland polishing step to create water suitable to recharge a shallow aquifer that is used in the area for crop irrigation. Up to 50,000 barrels of brackish produced water per day (BWPD) is transformed into 6.4 acre-ft per day of freshwater for agricultural reuse, which is enough to irrigate about 800 acres of farmland per year.
This innovative solution was the result of more than a decade of research on steam flood operations, oil/water separation equipment, reverse osmosis membranes, and treatment wetlands. A diverse team of Chevron technical experts collaborated to design, permit, build and operate the produced water treatment system. Scaling up a pilot treatment system into a full-scale operation was not a simple engineering task. Start-ups for new one-of-a-kind water treatment facilities typically have operational surprises. This treatment system was no exception. Controllers, piping and treatment chemistry needed to be adjusted to work correctly. Today the full-scale produced water treatment system effectively converts brackish produced water into high quality irrigation water, a potential model for other oil fields with nearby farming communities.