Dear FO,
Since we are both Texas, let’s talk about Texas.
If you own no surface and 1/2 of the minerals and the other 1/2 is leased (or any percentage, really), the operator can horizontally drill under your lands and produce the minerals. However, every tract on a horizontal well is a drillsite tract and you are able to get into the well as a co-tenant.
The more common scenario with a 1/2 MI not leased is to horizontally drill under the tract and buffer out the take points (frac zones or stages) to keep out of Rule 37 implications. For example, you have a 10 acre tract between two other tracts. 1/2 minerals is leased, which gives the operator the right to drill under the tract, they buffer out the 10 ac tract and drain you. Your recourse is MIPA or drill your own well.
If no interests under our 10 acre tract is leased, they get a subsurface easement and buffer out the tract and drain you again.
This is another great example of the non-equitable pooling in Texas. See here for the tragic effect:
http://www.mineralrightsforum.com/profiles/blogs/pooling-in-texas-part-3