Conference Reflects Operators' Strong Interest In CO₂ Flooding

(Tech Connections Column, February 2005, American Oil and Gas Reporter)

With December came the 10th Annual CO2 Flooding Conference in Midland, TX. In its second year with an adjoining carbon management workshop, this conference has become the preeminent CO2 conference in the world. Theme sessions covered CO2 flood operations, unconventional CO2 floods, and conventional CO2 flood case histories. With “unconventional” being the buzzword for natural gas, it seems appropriate to focus on the unconventional CO2 flood session.

Unconventional applies to “near-miscible” operations being planned for Denbury Resources Inc.’s East Eucutta Unit in eastern Mississippi. The prior operator, Amerada Hess, performed both a “huff-n-puff” and small-scale pilot there in the early 1980s. Production is from Eutaw Sands at 5,000 feet. The pilot was termed near-miscible because limitations on bottom-hole pressures, in combination with oil properties associated with the 22-degree API gravity crude, precluded reaching minimum miscibility pressure. About 30 percent hydrocarbon pore volume of CO2 was injected in the single-pattern pilot.

In three years (January 1981-January 1984) incremental oil recovery was estimated at 17 percent of the original oil in place. CO2 utilization was 3.2 Mcf per incremental barrel of recovered oil. The bottom-line message is that near-miscible operations in the East Eucutta Unit performed well. Denbury estimates gross production will increase seven- to ninefold from 700 bbl/d levels in a full-scale project.

The CO2 will come from Denbury’s Jackson Dome CO2 field. Denbury began acquiring leases and rights of way in late summer for a pipeline to transport CO2 from there to eastern Mississippi. Completion of the pipeline, which will cost between $40 million and $50 million, is anticipated during 2006. There are sufficient CO2 reserves in Jackson Dome to support several CO2 floods in eastern Mississippi.

Unconventional has always applied to the Yates Field in West Texas. This giant field has had a long and colorful production history, and has produced more than 3.5 billion barrels of oil since its discovery in 1926. Production is from a highly fractured San Andres Carbonate. Reservoir differences exist in the east and west sides of the field. There is a long history of improved oil recovery since unitization in 1976: gas injection (1976-85), polymer-augmented waterflood in the west side (1981-88), CO2 injection in the east side (1985-91), double displacement process (1993-00), a steam injection pilot (1999-02), and now gravity drainage (2000 to present).

CO2, rather than nitrogen, is being injected in the gravity drainage process because it improves oil mobility compared to nitrogen. CO2 injection is concentrated within 50 feet of the gas/oil contact (COG) in the northwest portion of the field, where nitrogen content is high. Recycled CO2 as it occurs will be reinjected in the southeast area of the field.

CO2 injection at 42.5 million cubic feet a day through converted gassed-out horizontal producers began in March 2004. Oil production has increased nearly 1,200 bbl/d, occurring much sooner than model predictions. Future performance will ultimately answer the question of whether the production increase is coming from a true gravity drainage response, flush CO2 response with injection near the GOC, or movement of the GOC. There are plans to further increase CO2 injection.

Unconventional applies to a Lansing-Kansas City pilot flood in the Hall Gurney Field in Russell County, Ks., in that CO2 for the pilot is coming from a byproduct stream in an ethanol plant located a few miles away. The goal for this small, 10-acre pilot involving one CO2 injector, two producers and some containment water injection wells, is to establish whether sufficient oil can be mobilized to warrant CO2 flooding. A wide application of CO2 flooding in central Kansas will require significant CO2 pipeline investment. Much hinges on the technical results in this pilot.

CO2 injection began in December 2003, and 25 percent of the planned CO2 volume (290 MMcf) was injected through September 2004. Oil response–2.5 bbl/d–was evident in one producer within four months. Slow response in the second producer is attributed to the presence of an unanticipated permeability barrier between the injection well and the second producer.

Initial concerns about very rapid CO2 breakthrough with a known high-permeability streak in the upper portion of the flooded zone have been unfounded. Some CO2 production is occurring, but not at a level to warrant concern. Containment losses to the north are being considered in modeling.

Injection and field operations continue. Being a small pilot, volumes are small and modeling will be key to interpreting results. Those with a stake in CO2 flooding potential in Kansas are encouraged to attend the University of Kansas Tertiary Oil Recovery Project’s Oil Recovery Conference, April 6-7 in Wichita, Ks., to hear the latest update.