Husky operates seven mature vertical hydrocarbon miscible floods in the Rainbow Field.
Up to June 1993, eleven horizontal wells have been drilled, one horizontal well re-entered for extension and one vertical well re-entered to drill a lateral. Even though these wells were all drilled into mature miscible floods, the variation of reservoir characteristics, the horizontal well location and exploitation strategy made each well unique in terms of drilling, completion, workover and production performance.
This paper describes the evolution and improvements in horizontal well applications made in redeveloping these mature reservoirs. Advancements are described in several areas as follows:
Drilling:
the use of pilot holes;
entering the reef laterally;
overcoming damage, loss of circulation, and high torque and drag; and
extending the existing horizontal hole.
Completions and workovers:
selective testing and stimulation of different zones along the horizontal hole using multiple open hole packers and sliding sleeves, or straddle packers on tubulars.
Production strategy and reservoir optimization of EOR performance:
controlled rate to approximtely twice vertical well rates;
controlled vertical movement of the oil bank;
interference tests with vertical wells;
use of bottom hole chokes; and
use of circulation strings for combating asphaltene deposition.
The potential applications of horizontal wells in miscible floods have been mentioned in previous papers(1–3). However, Husky's well 16-29-108-08W6M was the first field application(4). Later, other companies have also used horizontal wells in miscible floods(5).
Husky has redeveloped six pools (Figure 1) since March 26, 1989, to improve the recovery of oil sandwiched between solvent and water zones in vertical hydrocarbon miscible floods, by drilling eleven new horizontal wells, one horizontal extension and one vertical well re-entry. The abbreviated well names on Table 1 will be used throughout the remainder of this paper. There have been significant differences in the drilling, completion and production techniques and problems encountered on these horizontal wells. Each well has outperformed its vertical offsets in the same pool in terms of oil production rates (Figure 2) and GOR (Figure 3), which is unique for such a large well program. The vertical well rates and GOR's are averages of all vertical wells producing the reservoir behaves as a typical pool with water drive. Because reservoir pressure has been largely maintained, the dominant depletion mechanism is water influx.
Following development of the northern part of the pool on a 32 ha (80 acre) spacing pattern, about a dozen vertical wells were drilled on 16 ha (40 acre) spacing, either as infill wells or as pool edge (step-out) wells. In five wells which are truly infill wells, the initial (first-year) oil rate was lower than the initial oil rate for the four surrounding original vertical wells; except for the well in Lsd. 11-3-5-32WIM, the total daily fluid was also less than it was in the surrounding original vertical wells (Table 2).
