40 acre spacing is established for all wells in Michigan according to R 324.301 of the Administrative Rules of Part 615 of the Natural Resources and Environmental Protection Act, P.A. 451 1994, as amended .  Exceptions to these rules have been ordered by the Supervisor of Wells for some formations.  The following are general exceptions affecting large areas of the State.  Exceptions for individual drilling units are not listed here.

Antrim Spacing

Supervisor of Wells Order 10-12-87allows for multiple drain holes for Antrim wells north of Town 20 N. ( most of the northern lower Michigan counties).   Supervisor of Wells Order (A) 3-3-95extended this to 34 more counties (42 total) so that all the counties in the Lower Peninsula are covered except for Monroe County.   Supervisor of Wells Order
(A) 14-9-94changed the spacing in the Administrative Rules to allow the creation of Uniform Spacing Plans(USPs) within 22 counties with an average spacing of no less than 80 acres per well in each USP.  In March of 1999 Supervisor of Wells Order (A) 20-12-98amended Supervisor of Wells Order (A) 14-9-94 to allow more than two lateral drain holes per well.  In July of 2002 an amendment to Supervisor of Wells Order (A) 10-12-87was issued to include the Sunbury, Bedford, and Ellsworth shales (but not the Berea sandstone), and a similar amendment to Supervisor of Wells Order (A) 14-9-94, was made to include the Sunbury, Ellsworth, and Bedford shales (but not the Berea sandstone).  Order (A) 24-8-05 allows twinning of Antrim wells (two wells near one another) in the lower three tiers of Otsego and Montmorency counties.

Map of  Antrim spacing  

Niagaran Spacing

Special Order 1-73set 80 acre spacing for the Niagaran formation and deeper in many northern lower Michigan counties and some of the southern counties.  This order also includes all counties in the Upper Peninsula.  This was amended (Special Order 1-73, amended), to add six townships in Calhoun county (Cause No. 12-6-75), and finally,
Special Order (A) 2-81set 40 acre spacing for Oakland county.

Map of Niagaran spacing

Trenton-Black River Formation Spacing

Two large areas of south central Lower Michigan are spaced for the development of the Trenton & Black River Formations.  The Albion-Scipio Field is the larger of the two fields and includes parts of Calhoun, Jackson, and Hillsdale Counties.  Currently, the Albion-Scipio Field is spaced on 20 acre stand-up drilling units by Order No. 9-7-84.  The smaller Stoney Point Field in Jackson and Hillsdale Counties is spaced on 40 acre units by Order No. 4-4-84, as amended by 4-10-88, and (A) 12-3-85.  Within the Stoney Point Field, a North Stoney Point Unit, Order No. (A) 1-1-90, and a South Stoney Point Unit, Order No. (A) 26-9-91, have been established. 
Map of Trenton-Black River spacing.  Map of Stoney Point Unitized Areas.

Glenwood and below Spacing

Special Order 1-73  and its amendmentstemming from Cause No. 12-6-75, set spacing for the Niagaran formation and deeper (which includes the Glenwood) at 80 acres for the Upper Peninsula and many counties in Lower Michigan.   Later, Special Order 1-86set spacing for the Glenwood and deeper in most of these counties and some others also at 640 acres.  A few areas not covered by this order are still under the original 80 acre spacing.

Map of Glenwood spacing