"Grass Roots" where wells are drilled from the surface and then go horizontal.  These are new field development wells where as Oilmanbob noted they wouldnt produce anything otherwise.  These are drilled horizontal or they are not drilled at all.

Then there are "re-entry" wells in existing fields where a whipstock is set in an existing vertical well, a window is cut in the casing and a slimhole tool is used to drill out at a very high build rate.  These in my experience are only somewhat successful in increasing production and are high risk and expensive.    It requires highly skilled people and most hands decline to work these jobs simply because of the stress involved.  The better people can pretty much pick and choose where they want to work now anyway.

I can't speak for what is going on in Texas but in my part of the country...the Rockies,  re-entry work is very limited.      Most of the work going on in the older fields is simply workover.  As far as increasing depletion I don't think anyone knows at present on horizontal re-entry on old fields.  

Maybe this doesnt clear this up, but to people in my business it is considered apples and oranges between these types of horizontal wells.