SHELL WESTERN ENLARGING CO2 FLOOD IN WASSON FIELD

Shell Western E&P Inc. has begun work to expand its carbon dioxide flood in Wasson field's Denver Unit, Yoakum and Gaines counties, Tex., to include the western portion of the unit as well as the eastern.

Shell expects the expansion, which will cost about $100 million, to boost recovery to about 60% of original oil in place and extend field life by at least another 25 years (OGJ, Feb. 12, Newsletter).

The Denver Unit CO2 flood is the world's largest in terms of enhanced production.

The planned expansion includes, among several other things, an increase in the unit's CO2 recovery plant inlet capacity to 290 MMcfd from 180 MMcfd.

Shell also plans to switch to a hybrid water-alternating-gas (WAG) injection process in the unit's eastern portion, which has been undergoing continuous CO2 injection since 1984.

WHAT'S PLANNED

There currently are 800 producing wells, 204 CO2 injection wells, and 176 water injection wells in the unit, developed on an inverted nine spot injection pattern.

The water injection wells, all in the western portion of the unit, will be converted to CO2 injection. No drilling is planned.

Peak oil production is expected to be about 50,000 b/ d in 1994.

The unit covers 28,758 acres.

The existing CO2 flood involves the eastern two-thirds of the unit.

Lee Blanton, manager of Shell's western production division, said the expansion is a result of success of the original flood.

"During the past 4 years, careful surveillance has led us to recommend a significant flood modification that will further increase the amount of recoverable oil," he said.

"We will convert to a new process we call the hybrid WAG, which combines the best features of two commonly used CO2 injection methods."

HYBRID WAG

Shell's hybrid WAG involves injecting CO2 continuously for a number of years, then following with the WAG process.

The eastern portion of the Denver Unit, which has undergone the continuous flood for 6 years, will be converted to the WAG process. After a number of years of continuOUS CO2 flood in the western portion, it also will be converted to WAG.

All sections of the unit will return to a continuous flood after a period of hybrid WAG flooding.

The Denver Unit CO2 recovery plant expansion involves two major aspects: replacing and expanding hydrogen sulfide treating capacity by installing the Shell SulFerox Process and debottlenecking and modifying the existing plant.

The major engineering and construction contract for the plant has been awarded to Pritchard Corp., Kansas City. Shell expects plant construction to begin this summer with completion of the expansion project scheduled for early 1992.

Most of the CO2 used in the Denver Unit moves to West Texas through the 500 mile Cortez Pipeline from McElmo Dome field in Southwest Colorado.