Devonian Antrim shale gas, the Michigan basin's dominant hydrocarbon play in terms of number of wells drilled for several years, shows every sign of continuing at a busy pace.
About 3,560 Antrim completions now yield 350 MMcfd, more than 60% of Michigan's gas production. Antrim averaged about 23 MMcfd statewide during 1985-86, Michigan Geological Survey figures show.
The outlook is for Antrim production to climb in the next 2-3 years to 500-600 MMcfd, about 1% of U.S. gas output.
These delivery numbers, slow decline rates, and expected producing life of 2030 years has snagged pipelines' attention. The growing production overtaxed local gathering facilities last fall, and the play recently got its first interstate outlet.
Completion and production technology advances are improving well performance and trimming costs. Several hundred wells a year are likely to be drilled during the next few years. Production increases are coming from new wells, deepenings, and workovers.
Numerous pipeline/gathering projects are planned in the area to handle the growing Antrim volumes.
HOW IT HAS GROWN
The play, centered in Otsego County and becoming well developed in four neighboring counties, is expanding to the east, south, and southwest in Michigan's Lower Peninsula.
Antrim work amounted to only about 10 completions/year in Michigan in the early 1980s. Completions doubled for several years in a row in the late 1980s with the combined effects of improved drilling, completion, and stimulation techniques, reservoir characterization, and extensive research.
Some operators say the technologies have evolved to the point that Antrim drilling is viable in many areas without the Sec. 29 federal tax credit for gas produced and sold from Devonian shales. The credit expired at yearend 1992 but helped draw large amounts of investment capital to the play.
Three Michigan Antrim reservoirs ranked among Petroleum Information Corp.'s top 12 fields in the U.S. in terms of 1993 well completions reported by yearend 1993. They are Montmorency County-Antrim field with 225 wells reported completed during the year, Otsego County-Antrim field with 132 wells, and Antrim County-Antrim field with 122 completions. Crawford County-Antrim field ranked 42nd in the U.S. with 50 completions reported during the year.
EXTENDING THE PLAY
Antrim underlies most of Michigan's lower peninsula, and success at extending it far beyond the core area of Otsego and adjoining counties has been limited.
However, PI noted that: successful 1993 completions, extended the play 12 miles, eastward into lightly drilled. Alcona County and more, than 30 miles southwestward into Manistee County Expansion occurred within Antrim, Otsego, Montmorency, Crawford, and Oscoda counties.
Eight operators have applied for drilling permits, been issued permits, or drilled holes in attempts to open Alcona and Alpena counties to Antrim shale development. They have drilled 12 Antrim tests in Alcona County and one by mid-May 1994 in Alpena County, says Michigan Oil Gas News, Mt. Pleasant.
Antrim production is also starting in far flung Manistee, Iosco, and Livingston counties. Amoco Production Co. is reentering several existing wells to drill short radius horizontal penetrations in Antrim in Kalkaska County, between Manistee and the core Antrim producing area.
GEOLOGY, PRODUCTION
Costs range as high as $250,000-280,000 including 5 1/2 in. casing, beam jacks to pump off water, disposal wells, and gathering lines. Wells generally tap Antrim at 1,200-1,806 ft, but the range has been 600-2,200 ft depending on position in the basin.
Authors with Advanced Resources International Inc. and Gas Research Institute note that current production is from the Norwood and Lachine members that correspond to the Lower Antrim's two lower black shales. The Lower Antrim's Upper Black member is an attractive secondary target.
A consistent Antrim gas in place estimate is 16 bcf/sq mile, but estimates for some areas have ranged to slightly more than double that figure.
Recoveries of 400 MMcf-1 bcf/well or more are thought likely.
A majority of the wells were drilled on 40- and 80-acre spacing, but newer wells are on 160 acres. The effective per-well drainage area is uncertain.
The Antrim's reservoir and production characteristics are similar to those of coalbed methane reservoirs.
Gas production gradually increases as water is pumped from the fracture system, allowing gas to desorb from the reservoir matrix. Some operators use progressive cavity pumps to unload water early and switch later to beam pumps. Gas production decline curves are widely 10%/year or less.
Antrim gas averages 5-6% carbon dioxide content. Fiberglass tubing, is used in some areas to resist corrosion, and plastic flow lines are common.
DRILLING PROGRAMS
Here is a rundown of a few multiwell Antrim drilling alliances:
Mercury Exploration Co., Fort Worth, and Enron Gas Services Group, Houston, set up Michigan Gas Partners LP in late 1993 to acquire and develop the Antrim.
Enron Gas Services is to provide funding for development using Mercury's operations technology. The partnership last Nov. 1 acquired producing properties in Otsego and Antrim counties. It plans to develop those and other Mercury owned properties with total net reserves estimated at 33 bcf.
Nomeco Oil & Gas Co., Jackson, Mich., and Mercury last year started a program to evaluate Antrim potential on about 80,000 acres in 15 townships in Alcona and Iosco counties.
The companies said 300 or more wells might be drilled on the acreage starting this year, depending on results of exploration, and appraisal drilling. The 300 or more wells might involve outlay of more than $100 million for wells, pipelines, and other facilities.
Other operators of Antrim wells include Wolverine Environmental Production Inc., Grand Rapids, Mich.; Ward Lake Drilling, Oilfield Investments Ltd., and Force Antrim Development Co., all of Gaylord; Shell Western E&P Inc.; Terra Energy Ltd., Savoy Oil & Gas Inc., and Antrim Gas Inc., all of Traverse City, Mich.; Trendwell Oil Corp., Greenville, Mich.; and Muskecon Development Co., Mt. Pleasant.
GAS TRANSPORTATION
A flurry of applications to the state for intrastate pipeline expansions and CO, removal plants resulted in late 1993 after Antrim deliveries began to overwhelm intrastate facilities.
The applications generally call for construction of 10-70 miles each of 8-24 in. pipe.
Meanwhile, Wilderness Energy Services, a partnership comprised of Mercury and Dominion Reserves, Mercury's primary drilling partner in the play, became the first operator to connect with an interstate pipeline, Great Lakes Gas Transmission Co., last Dec. 7.
The hookup allows backhauling of gas to an interconnection with Northern Natural Gas Co.'s system at Carlton, Wis., serving Minnesota and Wisconsin. It also allows forward hauling to ANR Pipeline Co.'s U.S. system at Farwell, Mich., and to St. Clair, Mich., where a group that includes Enron is developing the Grands Lacs gas marketing center to serve eastern Canadian and most U.S. gas consuming areas.
The long reserve life and deliverability spread over many wells spells reliability for industrial end-users. One potential market is a cogeneration plant planned for construction at Ludington near the Lake Michigan shore in Mason County.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.