I apologize, as I apparently overlooked a portion of your post.
You don't need the whole section. I was assuming from the question that the whole "section" meant the whole "unit" since unit and section boundaries commonly overlap.
You're correct that, in general some states do specify a minimum acreage amount to allow pooling. I thought this topic was restricted to Oklahoma, which does not have any such minimum requirement.
I'm not familiar with any lease that sets a minimum size for leased acreage. Maximum sizes, I'm certainly familiar with. It is also common to provide that the a minimum amount of the leased acreage is included in a unit. But I don't see why a lessor would want a minimum unit size. Ideally, the lessor would want the unit to be one acre, and that it be made entirely of their one acre, right?
As for Oklahoma regulations, there are none that I'm aware of that proscribe a minimum acreage size to form a unit. The regulations deal with spacing, allowables, reporting, etc. Pooling and unitization are dealt with by statute.
I would be shocked if an Operator in Oklahoma or virtually any other state can drill a well with only five acres assigned to a well.
Yes, you can technically do this by drilling a non-unit well on a lease basis. To prevent drainage, most states including Oklahoma have spacing rules that prevent a well being located within a certain distance from neighboring property lines. Oklahoma's minimum offset distance is 330 feet from the neighboring property line, so you could technically drill a well in a 330' x 330' square, which would equal exactly 2.5 acres in a square if you were so inclined to form a unit that small. If the offsetting owners were displeased, they would be free to drill their own wells 330' from the property line and 600' from the now-existing well producing on the 2.5 acres.
If you were in the dead center of a large tract with no wells, you could form a 1 acre unit. But obviously, no one would do that, they would drill the well on a lease basis or form a voluntary unit.