Daqing remains China’s top oil field, producing nearly 290 million bbl (40 million tons) per year of oil, defying predictions of serious decline after more than 50 years of production.
Those involved take pride in the fact production has remained steady since the target was reduced 20% in 2004. “We want that to continue,” said He Liu, in charge of production engineering and enhanced oil recovery (EOR) research at the Research Institute of Petroleum Exploration and Development (RIPED), which is part of Petrochina.
Liu’s career has been tied to maintaining the field’s output. Before moving to RIPED, he was the deputy general engineer at the Daqing oil field. He worked for 28 years there as part of a team whose responsibilities included managing the ever-evolving polymer-enhanced waterflooding system that is credited with 25% of the field’s output.
Extending the life of the field will require another generation of EOR methods to postpone the natural decline of the reservoir as older zones are produced, Liu said. The push provided by water plus polymer adds to the amount of oil recovered, but there is a limit to how much of the oil is likely to be produced before the well reaches the point when the fraction of oil in the produced water is too low to justify further production.
RIPED is working on improved chemical combinations to extend Daqing’s life past that point, and new methods that will allow it to efficiently identify and flood the many layers that have been missed, which tend to be thin and less permeable. Liu said that without improved EOR methods the benefit of polymer flooding would likely decline to 5% to 7% of the reservoir’s total output.
China’s domestic production depends on maximizing production from older fields. Daqing has been a center for developing these methods.
“The polymer-flooding technology has been implemented for a long time. It is very much their own,” said Hui Pu, a research engineer at the University of North Dakota Energy & Environmental Research Center who has written about Chinese chemical EOR methods along with employees of PetroChina working at Daqing. “They have a lot of experience in all types of reservoirs.”
Nearly every sort of enhanced recovery method has been tried at Daqing. The list includes polymers; polymers plus various combinations of alkali and surfactants; colloidal dispersion gel; and carbon dioxide flooding. Even biological methods are being considered.
“They have tried everything available in EOR,” said James Sheng, an associate professor at Texas Tech University, who worked at RIPED early in his career, before working as a reservoir engineer at several international oil and service companies.
Researchers in China are looking for ways to get at what is left in the complex formation. Liu calls it “redevelopment.”
One of Liu’s major interests is developing a system for efficiently putting zones into production that have been missed. The device, called the Integrated Bridge Eccentricity Packer with Steel Cable measuring and adjustment technology (IBEPC), is used to precisely manage flooding in zones that other tests have indicated failed to produce using waterflooding, often because they were bypassed because they are less permeable. The device combines injection control devices to precisely control the fluid flow and chemical mix.
Improved chemicals are also a priority in Daqing, with expanding use of chemical combinations—primarily alkaline- surfactant-polymer (ASP). This combines the ability of polymer to increase the viscosity of water to near that of oil, and the ability of surfactants and alkali to reduce interfacial tension and free oil adhering to reservoir rock.
Making it work on a large scale will require improvements that reduce ASP’s cost and side effects. Strong alkali can lead to scale deposits and broken sucker rods, plus increased pump maintenance and failures. It can also cause oil and water emulsions, making it difficult to separate out the oil. Finding a combination that is as effective, without strong alkali, is one of the difficult challenges Chinese EOR researchers are working on, Pu said.
Sheng is updating a paper delivered in 2013 surveying ASP test results worldwide. The initial paper covering projects six tests at Daqing, making it the most active test site in the global survey. Information on more recent ASP projects six tests at Daiqing, making it the most active test site in the global survey. Information on more recent ASP projects in Daqing shows the scale of later ASP flooding tests is much larger.
What has been learned in Daqing is being applied in other parts of China. RIPED is working on chemicals that can tolerate conditions in reservoirs elsewhere in the country with higher temperatures and salinity levels than Daqing, which is a hospitable environment for polymers, Liu said. RIPED is also looking for ways to deliver production- enhancing chemicals more effectively, and match what is used to reservoir conditions.
“There are some new-generation techniques such as horizontal wells, separated-zone injection, intelligent completion, and integrated reservoir and production management systems and so on,” Liu said.
“Each year we derive new data from downhole to analyze production performance so we can make adjustments to the production strategy,” he said. Looking ahead, “there are many, many new techniques.”
Driven by Need
Daqing is the largest field in China based on reserves and production, according to the US Energy Information Administration (EIA), at a time when demand for oil is more than twice what the country can produce. It has also long been a symbol of China’s drive to become a world economic power.
The field has its own oil company, PetroChina’s Daqing Oilfield Company; a museum; and a legendary oilman, Wang Jinxi, known as the Iron Man. The story of how he and his crew overcame the elements and rudimentary drilling equipment to drill the discovery well was used in the past to exhort workers to demonstrate “the spirit of diligence, loyalty, bravery, and tenacity.”
Daqing was discovered in 1959, first oil was delivered to a refinery the next year, and waterflooding began 5 years later as China pushed to accelerate development of the field to demonstrate that Chinese workers could build a domestic oil industry.
By 1976 Daqing, which encompasses three large reservoirs, hit its peak level of 1 million B/D (50 million tons a year). That level was maintained until 2004, when the target was lowered by 20%.
The drive to maintain Daqing production led PetroChina to begin working on polymer flooding more than 30 years ago. It began large-scale use of it in the mid-1990s. China stuck with its program to use chemicals to improve waterflooding on a large scale at a time when interest in chemical EOR had waned in other countries because prices were low and oil was plentiful.
China’s national oil industry was focused on the government mandate to produce all the oil available in its fields. “Because production levels were based on what the state wanted, they did it even though at that time prices were low or prices were high,” Sheng said.
In the past decade, there has been a strong economic need for Daqing’s output. China’s domestic oil output is rising—it totaled 4.42 million B/D in 2012, up 1.6% from the previous year according to the EIA—but demand rose 4.3% to 10.3 million B/D in 2012, a shortfall of 5.88 million B/D.
While Daqing’s 36 billion bbl of original oil in place make it among the world’s largest fields, maintaining its production has tested the energy and ingenuity of those running it because there is little gas pressure or natural water drive pushing the oil out of the ground.
Waterflooding was started early on. Without it, Daqing’s production would have been minimal. Water injection should push ultimate recoveries from 40% to as high as 45%, Pu said. Adding polymer is likely to get recovery past 50%, and going to ASP holds the promise of a 60%-plus ultimate rate of recovery of the oil, he said.
Polymer has its limits. Sheng, who recently wrote a book on the subject, Modern Chemical Enhanced Oil Recovery: Theory and Practice, said polymer can add 5% to 10% to what waterflooding could ultimately produce, and ASP could add 20% to 30%. ASP is an option when a polymer waterflood reaches its economic limit, with a water cut of about 98% in Daqing.
The six Daqing ASP tests, reported in a 2013 paper by Sheng, resulted in incremental recoveries of about 20% and significant reductions in the water cut, and led to expanded testing. “They are using ASP on a large scale now,” Sheng said. There are ASP applications with more than 100 injection wells, compared to an average of 5 injectors in early tests. Mass use will depend on the cost and reduced operating issues. “There are two sides to everything,” he said.
Since strong alkali is blamed for costly maintenance issues, PetroChina is seeking a substitute—a weak alkali that limits side effects without reducing EOR performance— or a breakthrough technology that allows a combination of surfactant and polymer to be as effective as ASP, Pu said.
Another method tried in the field has been carbon dioxide injection. Liu said they have had “some success” with CO2, which is used to free oil adhering to reservoir rock and to reduce the viscosity of heavier crude.
“For 5 years we have had CO2 flooding,” he said. There is CO2 available in Daqing because “You must separate natural gas from CO2,” which produce together around Daqing and are separated during processing, Liu said. Reinjection answers the question: “After separation, where does it (CO2) go?”
Well by Well
PetroChina has intensively managed the huge field with the meticulous attention to detail that traditional Chinese farmers apply to their small plots.
Polymer flooding has been credited with 25% of the production at Daqing, but there is a significant human element required to match specific chemicals to the location. “They need experts with a range of expertise to make it all work together efficiently,” Sheng said.
Daqing’s complexity rewards attention to detail. It is a thick sandstone reservoir with large variations in rock properties from layer to layer, as well as barriers, such as fractures, leaving many pockets of oil.
In one area researchers studied the properties of 36 oil-bearing layers, with permeability ranging from 15 mD to 710 mD. The goal of that test was to target the water injection so that it flooded hard-to-penetrate layers which had been missed, despite drilling more closely spaced wells and reducing the number of producing wells per injection well. One paper described a pattern where there were two wells injecting water for every three producing wells.
Injection programs are adjusted on a well-by-well basis. The polymer concentration and type of polymer is chosen based on the reservoir to be flooded. The molecular weight of the polymer and the concentration of the polymer solution are adjusted to fit the injection interval, Pu said.
PetroChina is looking for the right polymers to match with lower-permeability layers. Core testing to see which molecular weight of polymer can flow through rocks from different locations in a conventional reservoir found that samples with the same measured permeability may not be able to accommodate the same-sized polymer molecules. One paper (SPE 14595) said that testing “suggests that the pore structures of the oil layers in different areas are not the same.”
A 2006 paper coauthored by Liu, said there is a clear need for EOR after polymer flooding. “During the thick-layer polymer flooding period in Daqing oil field,” the paper said, “the recovery rate can only reach 52% approximately, and nearly half of the geological reserves will remain underground, so conducting new after-polymer enhanced oil recovery technology is demanded.”
SPE 100855: Commercial Success of Polymer Flooding Application in Daqing Oilfield—Lessons Learned by Wang Yupu and Liu He, Daqing Oilfield Co.
SPE 165358: A Comprehensive Review of Alkaline-Surfactant-Polymer (ASP) Flooding by James J. Sheng, SPE, Texas Tech University
SPE 89175: Advances in Polymer Flooding and Alkaline/Surfactant/Polymer Processes as Developed and Applied in the People’s Republic of China by H.L. Chang, SPE, Intratech Inc., and Z.Q. Zhang, PetroChina
SPE 118746: An Update and Perspective on Field-Scale Chemical Floods in Daqing Oilfield, China by Hui Pu, SPE, Department of Chemical and Petroleum Engineering, University of Wyoming, and Qinglong Xu, Exploration and Development Research Institute of Daqing Oilfield Co.
SPE 109546: Study of Polymer Flooding in Class III Reservoir and Pilot Test by Hui Pu, SPE, University of Wyoming, and Daiyin Yin, Key Laboratory of Enhanced Oil Recovery of Ministry of Education, Daqing Petroleum Institute
SPE 164595: The Polymer Flooding Technique Applied at High Water Cut Stage in Daqing Oilfield by Wang Yuming and Pang Yanming, Daqing Oilfield Company, et al.
Stephen Rassenfoss is the Emerging Technology Senior Editor for the Journal of Petroleum Technology.