A new fuel for enhanced oil recovery projects
Solar power in enhanced oil-recovery projects holds high promise, increasing oil reserves while freeing up valuable natural gas supplies
Thermal enhanced oil-recovery (EOR) is an increasingly important tool in oil production worldwide. Since the 1960s, thermal recovery has been the primary method for heavy-oil production in California and now plays a significant role in tight formations and older reservoirs, elsewhere.
Steam generated at the surface is injected and heats the formation, reducing crude viscosity and making oil extraction easier. Decades ago, steam generators mainly burned oil; more recently, most have switched to natural gas. Today, solar heat can provide the lowest cost source of steam, cheaper even than gas.
In sunny locations, solar heating methods can supply up to 80% of annual steam requirements, reducing gas usage without affecting oil output. Solar steam generation would free large amounts of gas for other uses, including power generation, desalination and industrial projects, and even for export. This is an especially important development for oil producing regions suffering from growing gas shortages, such as Oman and the United Arab Emirates, where demand is high and rising.
Heating up with solar EOR
Solar steam generation is simple: curved mirrors track the sun and focus sunlight onto steel pipes carrying water. The concentrated sunlight heats the water in the pipes, creating high-pressure steam that feeds directly into existing steam-distribution systems. Gas-fired and solar steam generators can deliver steam continuously.
Using constant-rate injection, solar steam generation can replace about 25% of annual fuel use. Another option is variable-rate injection, a method already proved in oilfield operations, which can provide up to 80% of annual steam requirements from solar power.
A recent study published by Petroleum Development Oman (PDO) looked into the effects of variable-rate solar steam injection and concluded: "Oil recovery from solar-generated steam injection and that from constant-rate steam-injection are essentially the same, both for the fractured reservoir and the non-fractured reservoir. From a subsurface oil-recovery point of view, solar-generated steam provides a viable alternative to constant-rate steam injection."
Hybrid operation with some gas-fired steam generation can compensate for seasonal variations in sunshine and reduce thermal cycling of wells and equipment. Existing steamflood projects can be retrofitted with solar generation to reduce gas demand, meaning new oilfields can be developed without sourcing and producing new gas supplies.
The secondary effects of reducing gas usage for EOR can be profound in regions where gas supplies are overcommitted. In Oman, for example, steamfloods deliver more than 1m barrels a day of steam, consuming around 0.5bn cubic feet a day of gas. Together, the three largest steamflood projects consume almost twice as much gas as annual imports from Qatar through the Dolphin pipeline. If solar steam generation replaced just 35% of gas-fired steam in Oman, the sultanate's demand for imported gas would be eliminated.
The majors are already evaluating solar EOR technologies. Shell and PDO are planning a solar-thermal pilot project in Oman; and Chevron has announced a solar-steam project at its Coalinga oilfield in California.
In late February, GlassPoint commissioned its first commercial solar EOR project in Kern County, California for Berry Petroleum, the state's largest independent oil producer. The project, which took less than two months to build, is, at present, the only commercial solar EOR project in the world. While smaller than a fully deployed solar steam-generation development, the Kern County project showcases the new technology and the system's advantages.
Concentrating solar collectors are old news – commercial-scale projects existed 100 years ago and utility-scale solar-power projects have been in operation for more than 30 years. These systems use large amounts of land, require significant labour for cleaning and maintenance, and can be installed only in low-humidity, low-dust environments and with very high levels of sunshine.
Oilfields pose much greater difficulties for solar generation than power-generation sites, however, and existing solar technologies are not best suited to upstream operations. EOR projects are based on geology and the oil resource, not on air cleanliness. Oilfields have limited staff on the ground, are often in very dusty, dirty locations and demand large amounts of thermal energy from a small amount of space.
But a new type of solar steam-generator has been designed specifically to meet the operational requirements of the oilfield. GlassPoint's collector system is completely enclosed in a durable, sealed glasshouse structure, which supports and protects lightweight, curved solar mirrors. The reflectors are isolated from the environment, assuring long-term durability in any environmental conditions. The innovative lightweight mirrors weigh a tenth of traditional solar mirrors and are shielded from wind, dew, rain, dust, sand and humidity. Fully automatic washing equipment for the generator system also reduces operating costs.
Taken together, these cost benefits, for the first time, make solar steam-generation cheaper than steam produced by burning natural gas. Using sunlight as the fuel for thermal EOR leads to more stable and predictable production costs, improving profits while freeing up a valuable gas resource.
Minimising risk, maximising profit
California's oilfields rely heavily on thermal-recovery technology – more than 40% of the state's oil output is produced using steam-injection EOR techniques. Steam accounts for about 70% of per-barrel production costs and an evolving regulatory environment is adding further to the cost of generating steam.
Solar EOR offers compelling financial benefits. By reducing the need for natural gas, solar steam generation reduces the largest and most variable part of thermal-recovery production costs. In California, GlassPoint systems deliver steam for less than $3.50/m British thermal units, a fixed cost unaffected by fluctuating fuel prices or changing emissions regulations.
With low-cost, fixed-priced steam, operators can optimise recovery strategies to produce more oil over the field's lifetime. Wells will produce for longer, extending the life of the reservoir and increasing proved reserves.
*Rod MacGregor is chief executive officer of GlassPoint Solar. www.glasspoint.com