Brazil has a long history in enhanced oil recovery (EOR) technology and is a leader in carbon capture and sequestration (CCS) initiatives. The country’s national oil company has more than 25 years experience in carbon dioxide (CO2) injection for EOR operations, which provides significant experience in the technology for CCS development and deployment. Brazil’s Energy and Carbon Storage Research Centre was opened in 2007 to promote and explore ways to make CCS commercially viable.
Lula is the first supergiant field in the ultra-deep waters southeast of Brazil and the most significant CCS project yet in Brazil. The pre-salt carbonate reservoir in the Santos Basin occurs just below a thick, 2000 m salt column that traps a light, 28-30° API oil and a high solution gas ratio (200-300 m3 / m3).
As in other carbonate reservoirs, the solution gas has some CO2 in its composition that varies from 8%-15%. This CO2 has made the Lula field a pioneer in deepwater CO2 EOR.
Lula is currently undergoing a phased development process that will be applied in each area of the field. This process includes extended well tests, production pilots and, ultimately, the development of systems for large-scale production. The pilots are important to calibrating simulation studies and selecting strategies to maximize recovery and profitability. The outcomes will help define systems for development in the Lula field and others in the Santos basin pre-salt blocks.
The Lula pilot
The Lula pilot project began in 2009 with the arrival of a floating, production, storage and offloading vessel. Early studies had already shown that the oil recovery factor could be greatly improved with secondary and tertiary recovery.
Water-alternating-gas (WAG) injection was chosen for Lula pilot project because of the abundant availability of seawater and produced gas, and reservoir conditions were particularly suited to miscible methods that mix gas and water.
The Lula pilot is currently producing from three wells with one gas injector. Injection at about 1.0 million m3/d was started in April 2011. In September, the facility began exporting some gas to shore and the injection wells began to inject mostly CO2 at rates of about 35 k m3/d. Pressure in all the wells is being monitored with downhole gauges, and gas injection is being observed with tracer monitoring.
In SPE 155665, the first results of injecting CO2 separated from associated gas in the pilot project suggests the strategy has the potential to be a successful one. They expect production and pressure data monitoring of the WAG installation from 2012 on will better determine feasibility and translate into EOR expansion at the field scale.
EOR and CCS
The deepwater EOR being explored in Brazil is the pointy end of a very long and successful industry history of CO2 EOR. The first patent for CO2 EOR was granted in 1952 and the Texas Railroad Commission reports the first three projects were initiated in Osage County, Oklahoma between 1958 and 1962.
Since the 1950s, the oil and gas industry has spent many billions of dollars on CO2 EOR technologies, commercial projects, and operational knowledge. Most of this activity has been in land-based oil and gas fields. These CO2 EOR projects have steadily increased over the years based on the growing availability of CO2 and technology advances.
The Oil & Gas Journal reported in their 2012 EOR survey that growth in CO2 flooding in the USA now produces more oil than steam injection (308,564 b/d vs. 300,762 b/d) and is 41% of output from all types of EOR. The total number of CO2 EOR projects in the USA increased to 120, which is 89% of the total 135 globally.
In past years, a handful of offshore EOR CO2 injection projects have also been conducted, as sources of CO2 were available. With a source, as with the Lula field, EOR technology is capable of being applied even in extreme deepwater applications. Petrobras may likely set the record as the first company to successfully combine CCS and CO2 EOR for large-scale, sustained oil production in deepwater.
CCS is a process that first captures or separates CO2 from industrial and energy-related sources such as power and chemical plants, steel mills and refineries. The CO2 is pipelined to a storage location and pumped into underground reservoirs via injection wells. There it is permanently isolated from the atmosphere and drinking water aquifers.
The gas can also be used to help extract hydrocarbons from the reservoirs through EOR methodologies. The EOR process of injecting CO2 into the reservoir is also an effective method of CCS and a potential new business for extending the producing life of depleted fields in such areas as the Gulf of Mexico and the North Sea.
Injecting CO2 improves production in a number of ways. Under miscible and near-miscible pressure and temperature conditions it mixes and dissolves with oil, thinning and expanding it so the oil can be pushed by flow from the injection well.
Injected under immiscible pressure and temperature conditions CO2 results in a lighter density for gas assisted gravity displacement (GAGD), and it helps push oil down to lower producing depths.
Over the last 25 years a small number of offshore saline aquifers and oil and gas reservoirs have successfully used many of the technologies developed through the last 58 years of land-based CO2 EOR experience. It is possible that CO2 EOR is a viable means to increase hydrocarbon output from many depleted offshore reservoirs that are marginally or no longer productive.
Most operators are not using this technique on their reservoirs because they do not have an economical supply of CO2. However, cost-effective supplies of CO2 for many of these offshore fields may become available as carbon capture from nearby electric power plants and other large, stationary sources of CO2 emissions becomes more common. Offshore projects may also become feasible as new CO2 pipeline projects are constructed, such as the one planned by Denbury between Mississippi and Texas to supply EOR projects with CO2 from both anthropogenic and natural sources.
In addition to two offshore projects where permanent storage of CO2 is the only objective (the Sleipner and Snøhvit CCS projects offshore Norway), there are about five EOR and enhanced gas recovery (EGR) projects around the world, from gas injection in the Bay St. Elaine oil field in the Louisiana marshlands, to the Dulang WAG project off Malaysia’s east coast in the South China Sea. A number of other projects are in the planning stages, including those offshore Brazil.
Challenges and solutions
Current challenges for offshore CO2 injection projects that are not faced in land operations include the investment’s higher development costs, existing offshore surface facility limitations (weight, space, power, etc.), the lack of sufficient and economical CO2 supplies, and fewer existing wells that are more widely spaced.
All these factors may contribute to uncertain EOR performance and require longer time periods for CO2 placement to displace oil and gas and achieve adequate sweep efficiency.
EOR is currently being considered for a number of offshore developments. The prognosis is better when successful secondary recovery methods have been employed through water and natural gas injection, which make CCS and CO2 EOR methods much more feasible and less costly to apply.
Some of the key challenges and solutions for offshore CO2 EOR and CCS projects include the use of CCS tanker ships and barges to ensure CO2 supplies and provide service facilities until construction of pipelines and expansion of permanent facilities is justified. Horizontal well designs may be needed to offset a lower well density and achieve a more uniform sweep and displacement.
The delivery of CO2 from land-based sources to offshore oil and gas fields has been successfully accomplished at several CO2 EOR projects using pipelines and barges. Another method is by ships with large refrigerated tanks. Tanker ships have successfully and safely transported CO2 for over twenty years. They are best suited for the small volumes needed for pilot CO2 injection testing. However, tanker ships that deliver LNG to ports with supplies of CO2 might carry it on their return voyages to economically supply EOR projects.
Outlook and growth potential
As the energy market is affected by declining oil and gas production, many industry observers believe CO2 EOR activity may increase proportionally. In this fashion, EOR may help offset the predicted decline in oil production over the next twenty years. Some believe that CO2 EOR may be a substantial portion of the growth in EOR. Key to this growth is a sustainable, economic supply of CO2 from CCS initiatives.
About Ron Sweatman
Chief Technical Professional – Halliburton’s Global Technical Solutions and Deepwater Team
Ron Sweatman has 42 years of experience in several well construction and production/injection technologies. Ron majored in Chemistry at Louisiana State University and in Petroleum Engineering at University of Louisiana, Lafayette. He has served on 20 industry committees, co-authored over 60 technical publications, received six industry awards, and invented 30 patented technologies. Ron has a broad range of oilfield-services experience, including assignments in laboratory testing, engineering design, field operations, regional management, and technical support groups. His deepwater experience started in 1978 working on the Baltimore Canyon well in 2,686 feet of water on the Atlantic Ocean Outer Continental Shelf and has continued in other offshore areas including the Gulf of Mexico, West Africa, and North Sea.