Solar thermal enhanced oil recovery (abbreviated solar EOR) is a form of thermal enhanced oil recovery (EOR), a technique applied by oil producers to extract more oil from maturing oil fields. Solar EOR uses solar thermal arrays to concentrate the sun's energy to heat water and generate steam. The steam is injected into an oil reservoir to reduce the viscosity, or thin, heavy crude thus facilitating its flow to the surface. Thermal recovery processes, also known as steam injection, have traditionally burned natural gas to produce steam. Solar EOR is proving to be a viable alternative to gas-fired steam production for the oil industry. Solar EOR can generate the same quality steam as natural gas, reaching temperatures up to 750 °F (399 °C) and 2,500 PSI. While typical fuel-fired steamflood operations inject steam into the ground at a constant rate, research conducted by leading oil producers shows that variable rate steam injection has no negative impact on production levels. In effect, solar EOR could supply up to 80 percent of a field's annual steam requirements, by injecting solar-generated steam during the sunny hours, and a reduced amount of gas-fired steam at night or in less sunny weather or climates. This method of integrating solar EOR will displace larger amounts of gas consumption without affecting oil output.
Technology While there are many types of solar-to-steam technologies, often referred to as solar thermal or concentrated solar power, only two are currently deployed for solar EOR.
Central tower Originally designed for generating electricity, central tower, or power tower technology, uses a field of large tracking mirrors, called heliostats, to concentrate the sunlight on a boiler filled with water that rests on a central tower. The sun's energy is reflected on the boiler to produce steam, which is used to turn a traditional turbine to create electricity. For EOR, the process ends at steam production. High-temperature steam made from demineralized water in the tower receiver passes through a heat exchanger, generating steam of lower temperature from high-contamination oilfield feedwater at lower temperatures. The steam is fed into distribution headers which lead to injection wells, which convey steam into the oil-bearing formation.
Enclosed trough
The enclosed trough architecture encapsulates the solar thermal system within a greenhouse-like glasshouse. The glasshouse creates a protected environment to withstand the elements that can negatively impact reliability and efficiency of the solar thermal system. Lightweight curved solar-reflecting mirrors are suspended within the glasshouse structure. A single-axis tracking system positions the mirrors to track the sun and focus its light onto a network of stationary steel pipes, also suspended from the glasshouse structure. Steam is generated directly, using oil field-quality water, as water flows from the inlet throughout the length of the pipes, without heat exchangers or intermediate working fluids. The steam produced is then fed directly to the field's existing steam distribution network, where the steam is continuously injected deep into the oil reservoir. Sheltering the mirrors from the wind allows them to achieve higher temperature rates and prevents dust from building up as a result from exposure to humidity. GlassPoint Solar, the company that created the Enclosed Trough method, states its technology can produce heat for EOR for about $5 per million British thermal units in sunny regions, compared to between $10 and $12 for other conventional solar thermal technologies.
Recent projects
21Z in McKittrick, California
GlassPoint Solar partnered with Berry Petroleum, California's largest independent oil producer, to deploy the world's first commercial solar EOR project. Commissioned in February 2011, the project is located on a 100-year-old McKittrick Oil Field in McKittrick, California. Coined the Kern County 21Z Solar Project, the system spans roughly one acre and will produce approximately one million Btus per hour of solar heat, replacing natural gas used for steam generation. The solar EOR project was constructed in less than six weeks and is the first installation of GlassPoint's enclosed trough technology in an oil field.
Coalinga in Coalinga, California In October 2011, Chevron Corp. and BrightSource Energy revealed a 29-megawatt solar- to-steam facility at the Coalinga Oil Field in Fresno County, California. The Coalinga solar EOR project spans 100 acres and consists of 3,822 mirror systems, or heliostats, each with two 10-foot (3-meter) by 7-foot mirrors mounted on a 6-foot steel pole focusing light on a 327-foot solar tower. BrightSource was contracted to provide the technology, engineering and production and construction services, and Chevron Technology Ventures will manage operations of the project. The facility began construction in 2009. It was reported that Chevron spent more than its $28 million on the contract, and BrightSource has lost at least $40 million on the project and disclosed it will lose much more.
Petroleum Development Oman
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