In-depth gel shows promise in Daqing IOR pilot

July 11, 2005
A field pilot, started in 1999, of an in-depth colloidal dispersion gel (CDG) in the Daqing oil field had favorable economics and increased oil recovery from the pilot area.

A field pilot, started in 1999, of an in-depth colloidal dispersion gel (CDG) in the Daqing oil field had favorable economics and increased oil recovery from the pilot area. This success has led to subsequent expanded pilots in Daqing and plans for pilots in other waterfloods in China.

Injection of CDG into an appropriate reservoir can increase oil recovery by improving vertical sweep efficiency of the injected fluid.


Daqing is the largest oil field in China and produces more than 900,000 bo/d from multiple sands and reservoirs. A unit of PetroChina Co. Ltd. operates the field, which is in China’s northern Heilongjiang province.

First commercial oil from the field flowed in 1959, and starting in 1976 Daqing maintained a relatively stable 1 million bo/d production plateau until the recent onset of a production decline.

To arrest the declining production, Daqing has started implementing polymer injection as well as investigating other technologies for improving oil recovery.

CDG technology

CDG technology evolved from a need to improve the sweep efficiency of polymer flooding in heterogeous formations. Both polymer and water have poor sweep efficiency in heterogeous formations.

CDGs are a mix of a polyacrylamide with a crosslinker at relatively low 200-1,200 mg/l. polymer concentrations. The CDGs provide a resistance to flow in a porous media by forming colloids or microgels in the viscous polymer solution.

This resistance to flow in the most permeable rock forces subsequent injected fluid into less permeable rock, resulting in a better sweep of the reservoir and higher oil recovery.

Tiorco Inc. developed CDG technology in the early 1980s and implemented the first field project in 1985. The company started discussions with Chinese oil companies in the late 1980s on the use of CDG technology for improving volumetric sweep efficiency in waterfloods.

By the mid-1990s, Tiorco had conducted more than 40 CDG field projects in the US that resulted in economic incremental oil recovery. These results and the need for Daqing engineers to improve sweep efficiency in their water and polymer floods motivated them to initiate a CDG lab study in late 1997.

Daqing lab studies

The cooperative Tiorco and Daqing Petroleum Administrative Bureau lab study started in 1997 to investigate the use of in-depth CDG technology at Daqing. The study included a training program to ensure consistent laboratory methods and techniques, testing conducted in both laboratories, and computer simulation.

In the study, screening tests first evaluated the best polymer and formulations for Daqing. This was followed by core experiments to determine an optimum CDG formulation. Results showed that CDG can increase oil recovery more than straight polymer flooding and is a viable improved oil recovery process for the Daqing oil field.

In Daqing, reservoir heterogeneity combined with its viscous crude causes the injected fluid to bypass some oil, thus limiting oil recovery.

Polymer flooding for mobility control in Daqing reservoirs has been ongoing for several years. Daqing manufactures its own polymer and annually injects the most polymer in the world.

Uncrosslinked polymer for mobility control is effective in increasing oil recovery at Daqing, but straight polymer injection cannot overcome high reservoir heterogeneity, even at high polymer concentrations.

The laboratory core tests demonstrated that the enhanced properties of CDG relative to uncrosslinked polymer improve oil recovery in heterogeneous rock. A computer simulation confirmed these core flooding results and translated them to a field pilot scale.

The studies showed that CDG injection was similar to polymer injection but increased resistance to water flow by a factor of five or more.

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Core floods showed that CDG injection compared with straight polymer injection could recover about 9% more original oil in place (OOIP), and computer simulation calculated a 10% increase in OOIP (Fig. 1).

Daqing CDG field pilot

Based on the encouraging laboratory studies, Daqing started its first large-scale CDG pilot test in May 1999. The pilot test covered a 0.75 sq km (185 acre) area and contained a double five-spot well pattern of 6 injection wells and 12 producers (Fig. 2). The wells have about a 250-m spacing.

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The pilot was in the northern part of the Saertu area. The treated sandstone reservoir is a fluvial deltaic sedimentary sand of the Lamadian river system. The sand was deposited at a steep gradient in swiftly flowing water and has much fragmented material. The reservoirs, therefore, have large blocks of sandstone rocks with thick layers and high effective permeabilities.

Fig. 3 shows the components of the injection system.

The CDG injection system included an injection manifold (top) , high-pressure CDG injection pumps (below), and CDG crosslinker pumps (2nd below). The pilot involved the injection of three chemical slugs during the period May 1999 to June 2003 (Fig. 3).
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To June 2003, the pilot test injected three chemical slugs. These consisted of a 0.179-pore volume (PV) slug of CDG, followed by a 0.155-PV slug of 600 mg/l. polymer solution, and then a 0.196-PV slug of CDG. After June 2003, water has been injected in the pilot.

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The pilot test indicates that the CDG had adjusted the reservoir permeability between injectors and producers so that volumetric sweep was improved. It demonstrated that CDG:

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• Can be injected before, during, or after a polymer flood to effectively control water production and maintain a high oil production rate.

• Has a higher incremental oil recovery with better economics than straight polymer flooding.

• Has wide applications in heterogeneous reservoirs for improving waterflood efficiency and oil recovery.

• Can reduce produced-water treatment costs as compared with polymer flooding due to lower polymer production in producing wells.

For the pilot, the engineers designed the CDG injection based on the laboratory studies. The pilot used polymer produced at the Daqing polymer plant and Tiorco manufactured crosslinker.

The assessment of improved oil recovery has to rely on the two central producers because two other polymer injection projects influenced the production of the 10 outside oil producers.

The initial estimate from the central wells was that the CDG would increase incremental oil recovery by 9% of OOIP. The actual incremental oil recovery from the pilot was greater. Also all 12 producing wells showed a significant decline in the water cut.

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In seven producers, the water-cut declined by more than 10%. Incremental oil recovery to June 2003 reached 13.08% OOIP and has continued to increase (Fig. 4).

Incremental oil production in the central area peaked at more than 1,000 bo/d and water cut decreased by 12%.

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Central producer B1-7-P124 had the best incremental response with the current incremental oil recovery of 10.5% OOIP (Fig. 5). One estimated is that when the water cut from this well reaches 98%, the incremental recovery compared to a waterflood will increase by 12% OOIP.

The engineers over designed the CDG pilot to learn the maximum improved oil recovery potential of CDG technology. Future expansions will have more economically optimized designs.

Although the pilot had more CDG injected than needed to maximize the rate of return, the internal rates of return for the pilot and central areas are 60.8% and 75.5%, respectively.

Future expansions

The favorable economics and improved oil recovery of the Daqing pilot has led to additional CDG pilots and expansion in the Daqing field. Subsequent pilots also have shown excellent results.

Other producing reservoirs in China have similar waterflood sweep problems, and therefore China has initiated gel and laboratory studies at the Shengli, Karamay, and Dagang fields.

The Shengli field in China’s eastern Shandong Province covers about 170,000 sq km and has a cumulative production in excess of 800 million tons of crude oil and 53 billion cu m of gas. The field is China’s second largest in terms of oil and gas produced.

The encouraging results of the Shengli CDG laboratory studies have led the Shengli field to initiate plans to start a CDG pilot before yearend 2005.

The Karamay and Dagang fields are starting CDG laboratory studies in 2005.

The author

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James C. Mack is president of Tiorco Inc. His responsibilities include managing an oil field service business, developing international markets, designing chemical IOR projects, researching new techniques, training personnel, and transferring technology. He previously worked in sales and engineering for Betz Chemical Oil Recovery, Stearns-Roger Inc., and ARCO. Mack has a BS in chemical engineering from the University of Wisconsin and an MBA from Colorado State University. He is a member of SPE and a registered professional engineer in Colorado.