A process control system that automatically makes calls to plant operators lies at the heart of a major oil facility expansion in California.
Like many smaller independent oil companies, Orchard Petroleum relies heavily on outside help when it comes to major engineering and construction projects. The expansion of the company’s South Belridge field oil processing facilities in California, USA, is a case in point.
When Orchard first approached InterAct in 2007, it was simply for assistance in assessing several possible tank vendors. However, as the relationship between the two companies developed, so did InterAct’s scope of work: ultimately, the company provided engineering, project management and site supervision services for a large part of the expansion project.
Central to the project was the installation of six new tanks, the largest of which stores produced water before its reinjection into the reservoir. InterAct managed all this work, beginning with a detailed review of the tank designs and ending with the final inspection process. The company’s engineers also took care of the piping system that links the new tanks. Extensive use was made of 3D modelling during the design phase to optimise the layout and, as far as possible, to avoid on-site cutting and welding, both of which would have adversely affected the quality and the cost of the job.
As well as the new tanks, the project scope included upgrading the separation facilities and a simple gas scrubbing system, and providing a new flare, which was the first of its kind in the area. InterAct engineers undertook a rigorous evaluation process before selecting a sonic flare that exploits the Venturi effect to produce a smokeless flame without needing to force air into the gas flow.
Jeff Hall was InterAct’s lead on the Orchard project and worked closely with Orchard’s management and field staff. He says, “InterAct’s aim throughout this project was to provide strong, committed professionals who were comfortable with all aspects of the project: contract management; logistics; cost and schedule control; safety and quality management; and the permitting process. The last area is a particular strength of InterAct. Our specialists in this area dealt with all the relevant agencies to obtain the necessary building approvals and also secured the official backing for our unusual choice of flare.”
Process control
As the production stream at South Belridge contains up to 95% water, monitoring the fluid level in the 10,000-bbl water tank is essential to the smooth running of the new plant and, hence, maintaining maximum oil production. A constant balance needs to be struck between the water entering the tank and that leaving it for reinjection into the reservoir.
What appears to be a relatively simple process-control requirement is slightly more complicated because, although oil is produced continuously, the plant is supervised for only eight hours a day, five days a week. With this in mind, Hall personally devised a control system that makes calls to members of the operations team when problems occur and the site is unmanned.
The water tank control system consists of a top-mounted ultrasonic sensor that provides an output of between 4 and 20 mA, which corresponds to a difference in the fluid level in the tank of 9 m. This variable signal is sent to a programmable logic controller (PLC), which, as the site is not connected to the grid, is powered by a 24-V solar photovoltaic array. From there, the information is routed to a PC in the plant’s control room that constantly displays the condition of the tank. Users who know the password can access this information over the Internet at any time from remote locations.
The PLC is also programmed with various low and high alarm points. If one of these is reached, the system is configured so that the PC sends an SMS text message to nominated operators’ mobile phones. In the event that the level in the tank reaches a critical high point before anybody can reach the site, the system automatically shuts down selected wells producing the largest volume of water. Wireless links between the main PLC and the control panels (also solar powered) at two fuel manifolds activate solenoid valves to shut down the gas supply to the oil well pumps. Should the level in the tank reach a critical low point, the PLC reduces the flow of water out of the tank by reducing the running speed of up to six water reinjection pumps.
Hall says, “The system has proved so successful that we have subsequently added level indicators to the two three-phase oil– water separators and a sensor to monitor the site’s main generator. Again, the PLC generates text messages if alarm points are reached and, ultimately, reduces the production flow into the separators by cutting the supply of fuel gas to the oil well pumps. We are now incorporating the gas compressor and the oil tanks into the system. What started as a simple water tank control system has grown to encompass the whole facility, and multiple alarms trigger different text messages to the operators.”
The process control system at South Belridge epitomises the attention to detail that InterAct has brought to the project. Through its appetite for solving the numerous challenges that the project has presented, the company has ensured a facility that closely matches this highly efficient operator’s needs.