Chevron is using a sophisticated water treatment system to clean up produced wastewater at a Southern California oil field and using that recycled water to boost recovery from a previously idled portion of the field – demonstrating along the way that what’s good for the environment can also be good for a company’s bottom line.
The Optimized Pretreatment and Unique Separation (OPUS) system was installed at the San Ardo oil field by water treatment company Veolia a decade ago and the company continues to oversee it today. The installation is the first of its kind to use the OPUS system as part of a produced water desalination facility and the cleaned up water is either used in steam flooding operations or safely disposed of on the surface.
San Ardo is one of the most prolific fields in California. It was initially discovered in the late 1940s and has been producing for decades. State data shows that it was pumping 21,400 barrels of oil per day in 2015, earning it the designation of being California’s eighth producing oil field. Output has actually been ticking upward annually since the OPUS system was put into place, with state data showing oil output in 2015 was nearly double production of 11,400 b/d recorded in 2008.
To counter natural production declines, the aging field has been using steam flooding since the 1960s to soften the remaining oil and coax it out of the ground. During this process, large volumes of water rise to the surface that must later be treated and disposed of. In fact, for every barrel of oil produced in 2015, state data show about 15 barrels of water rose to the surface as well – or an average of 328,000 b/d of water per day.
A case study by Veolia says, “Historically, a portion of this water had been recycled and softened to provide water for steam generation, with the (rest) going to local EPA class II injection wells for disposal. However, the injection zone capacity is limited and that had constrained full field development.”
That’s where to OPUS system comes in to make up the difference and ease water constraints. OPUS cleans up about 50,000 bb/d of water that using a multiple-treatment process that takes out contaminants and removes 92% of total dissolved solids.
With the treated water clean enough for reuse, the limited capacity of the injection wells becomes is less of a limiting factor in operations. The recycled water that is not used to generate steam is clean enough to meet California’s strict effluent discharge requirements and can be released through shallow wetlands into aquifer recharge basins that replenish water resources.
Veolia says the project goal was to reduce the total dissolved solids (TDS) of the feed water to less than 6,500 parts per million (pps), and the boron to less than 0.64 ppm for discharge, while achieving 75% water recovery across the treatment system and minimizing the volume of produced water. “For steam generation, the project goal was to reduce the feed water hardness to less than 2 ppm total hardness as CaCO3,” the case study said.
The system’s daily operations are overseen by Veolia, and Veolia staff also provides onsite and offsite technical and engineering support to troubleshoot issues as they arise. In short, they are responsible for ensuring that optimal function is maintained at the site.
The team displayed noteworthy ingenuity in 2005 and 2008 when a shortage of hydrochloric acid arose after powerful hurricanes pummeled the US Gulf Coast. OPUS uses hydrochloric acid in the regeneration process of the water softeners that are a part of the system. To get around this issue ad keep operations rolling, Veolia staff came up with a different concentration that lowered the field’s reliance on hydrochloric acid.
Indeed, the OPUS system is demonstrating one of the ways that producers can use technology and ingenuity to make their operations more environmentally responsible. To read the full case study on Veolia’s San Ardo project, click here. https://www.veolianorthamerica.com/en/case-studies/san-ardo-refinery