Abstract
A large scale miscible water-alternating-gas (WAG) project was implemented in the Prudhoe Bay field in 1987. Many of the original patterns are no longer receiving miscible injectant (MI) due to pattern maturity and diminishing EOR response. The EOR project is being revived in the gravity-dominated eastern part of the Prudhoe Bay Field waterflood area, Flow Station 2 (FS2), by using horizontal sidetracks to place MI at various locations within existing conventional WAG patterns which have a significant remaining EOR target.
The sidetracks are completed at the toe and then perforated sequentially along the length of the horizontal wellbore to allow up to 7 independent points of miscible gas injection. Distributing the injection points enables MI to contact additional pore volume not contacted by the original WAG injector due to gravity segregation of the MI as it moves away from the injection wellbore.
Typical WAG benefits in this area range between 0.5 to 2 MMSTB. MIST injectors (MI Sidetracks) are recovering an additional 1.5 to 4.8 MMSTB in patterns that have already been WAG flooded. Typical MIST patterns accumulate 3 to 4 times the EOR reserves of conventional vertical well WAG patterns.
This paper will explain the reservoir characteristics that contribute to such large incremental recoveries. It will also cover well design and operational issues. Based upon the success of the initial MIST program, several additional MIST patterns have been drilled, and more are possible.
