These are the wells specified in the development plans, for production of the hydrocarbon
to the surface. They may be oil production wells or gas production wells. The spacing of
these wells will be selected based on reservoir properties and economics. A common
spacing for oil reservoirs for onshore operations has been the 40 acre spacing. 1 mile =
5,280 ft. and 1 mile2 is equal to 640 acres of area. 1 acre = 43,560 ft2.
Consider the 1 mile2 area. If that 1 mile2 is divided into quarters, each quarter = 160
acres. If those quarters are further divided into quarters, the result will be 16 square area
of acres each (16 times 40 acres = 640 acres).
A 40 acre spacing for the drilling of development wells implies that one well will be
drilled in each 40 acres. The result will be 16 wells per 1 mile2. Each well, therefore, will
be ¼ mile or 1,320 ft from its offset wells and will have 4 offsets (north, south, east and
west). In the ideal production plan, over a reasonable lifetime of production, each well is
expected to drain a rock cylinder 660 ft in radius and of thickness equal to the
hydrocarbon reservoir rock thickness.
