Matrix acid stimulations with hydrochloric acid have been instrumental in maximizing the production of crude oil from the Bonnie Glen D-3A Pool since 1951. This type of acid treatment has been the main source of reservoir stimulation for this pool. However, changing reservoir conditions have necessitated significant acid additive and procedural modifications.
This paper discusses:
the changing reservoir conditions;
the modifications to the acid and stimulation procedures
the results of acid treatments after the changes were made; and
the ongoing acid stimulation monitoring program in Bonnie Glen.
Texaco Canada Resources operates 75% of the Bonnie Glen D-3A Pool located 40 km south and 25 km west of Edmonton, Alberta (Figure 1). The pool vas discovered by Texaco in December, 1951. The oil zone is under primary depletion and recovery of 85 × 108m3, or 6BZ of the 125 × 108m3 original oil in place is expected. To date approximately 80 × 108m3, or 95Z of the estimated recoverable oil reserves, have been produced.
The Bonnie Glen D-3A Pool originally had a 91 m oil zone overlain by a 123 m gas cap. As the oil was produced the gas/oi1 contact moved down and the oil/water contact moved up. At present, the remaining oil zone Is only 3 m thick as indicated in Figure 2. The original reservoir pressure was 17 100 kPag as compared to the current pressure of 8 700 kPag.
This significant decreases in net pay and reservoir pressure necessitated major revisions to operational and workover strategies at Bonnie Glen. Matrix stimulation with hydrochloric acid continues to be an integral part of the workover strategy; however, changes to the acid additives and acidizing procedures were required to maintain its effectiveness. A comprehensive monitoring program is maintained to identify Bdditional changes vhich may become necessary as reservoir conditions continue to change.
The Bonnie Glen D-3A Pool is contained in an Upper Devonian Ledue reef in the Acheson-Homeglen- Rimbey Ledue reef trend (Figure 3). The reef is a dolomitized carbonate structure. It has good to excellent pinpoint, Intercrystalline and vuggy porosity. Reef porosity is generally in the range of 9 to 14 percent. The average horizontal and vertical permeabilities are 2000 md and 20 md, respectively. The reef is approximately 11.3 km long and 3.2 km wide, running in a north-south direction (Figure 4). Underlying the Bonnie len D-3A Pool is the Cooking Lake aquifer.
Due to the reservoir rock characteristics in the Bonnie Glen Leduc reef, matrix stimulation with hydrochloric acid has proven to be the most effective form of reservoir stimulation.
Dolomite is easily dissolved in hydrochloricacid and responds readily to one of two methods of stimulation; matrix or fracture acidizing fracture acidizing is the preferred method of stimulation in carbonates with very low permeability. During fracture treatments, a high fluid injection pressure is maintained to create fractures along which the stimulation fluid can travel. [2 ]