Natural Gas Storage in a Southeastern Michigan Pinnacle Reef
F. W. Metzger and M. C. Rowan
Michigan Consolidated Gas Company
In 1992, Washington 10 Storage Corporation and Michigan Consolidated Gas Company, both affiliates of MCN Energy Group (soon to be DTE Energy), began planning for conversion of a Niagaran gas field to natural gas storage. The initial planning and design led to regulatory approval in 1994. Market conditions resulted in a delay in final design and construction until 1997. By that time rapid growth in Washington Township, Macomb County, 30 miles north of Detroit, caused the engineering team to re-evaluate the development plans.
The initial discovery well for Washington 10 was drilled in 1969 and production began later that year. By 1998 over 95% of the original 53 Bcf of gas had been produced from 23 wells scattered throughout the Village of Romeo and Washington Township. Initial storage plans included re-completing 17 original wells and drilling 13 new vertical wells. However, with the growth of the community and MichCon’s positive experience with drilling horizontal wells in central Michigan, this plan was deemed impractical and too costly. As a result, the Reservoir Engineering Department recommended drilling directional wells from four surface locations. This plan would maintain the 41.7 Bcf of working volume and 800 MMcf per day peak withdrawal requirements, while reducing the number of wells, limiting the amount of pipeline and the amount of surface acreage.
Fourteen horizontal wells were drilled over a 7-month period. The use of two drilling rigs reduced the project time by 3 months. Detailed pre-drill planning and review of multiple drilling scenarios allowed the project team to make rapid informed decisions during the drilling operations. On-site drilling supervision resulted in immediate decision-making and saved considerable costs. The depleted state of the reservoir required that the reservoir section of each well be drilled with air and foam. Initial plans were to drill the reservoir section with a downhole motor; however, experience on the initial well caused the drilling team to change to a combination fluid and air-foam system. Fluid was utilized until the desired angle was achieved or the fluid loss exceeded a maximum range, a lock assembly was then employed and an air and foam system was used to total depth. This method proved very successful, and all remaining wells were completed using this technique. Flexibility and teamwork resulted in a project that was completed on time and under budget.
Drilling directionally from multi-well pads provided the geologic challenge of identifying the flanks of very steep pinnacle reefs. Drilling at a high angle through alternating sequences of carbonate, salt and anhydrite before encountering reef rock made the determination of casing point at the top of the reef difficult. The anhydrite is considerably thinner at the flanks, and directional drilling does not provide optimal samples. Picking the casing point became a team effort by combining the expertise of geologists, engineers and drillers.Comparison of the pre-drill geologic maps with the post drill interpretation shows remarkable similarity. The added well control enhanced the definition of the flanks of the pinnacle reefs and the downhole logs proved that the reef top was picked with great consistency.
AAPG Search and Discovery Article #90900©2001 AAPG Eastern Section Meeting, Kalamazoo, Michigan