[ckilmer]

It is going to be hard to ‘shoot’ to that depth,
.........
according to the article to get to the required depth —they shoot more than one shell—or however many it takes where each shell punches deeper

[Smokin' Joe]

Multiple shots? Unless ejecta are carefully controlled, the borehole internal dimensions will change with every shot. That will be a complication, as it will affect trajectory, efficiency, terminal impact force, and the ejecta evacuation from subsequent shots. There remains the problem of controlling formation fluids at reservoir pressures of 4500 psi in an open hole with no fluids.

Even air resistance would become a more complex problem with depth.

For Shell, a million dollars indicates interest, but that is small money in the big picture. It may well work in areas where producing formations are shallow (3000 ft. or less) and large numbers of vertical holes are desirable versus horizontal drilling.