Kethane is indeed a very useful resource however the problem with it is that it is very useful for space craft, that are up moving around in space and kethane originates under the surface of terrestrial planets and moons. This is where the problem comes into play – getting the kethane from the surface to the spacecraft.
There are many variables that determine what is best for a particular mining operation. One thought is to build an orbital fuel depot where space craft can come to top off their tanks before continuing forward on missions deeper into space and fuel tugs can top off to move vast amount of fuel into other locations around the solar system.
The ultimate requirement is to land a craft that is capable of mining kethane to the surface. From there, the options begin to show their faces. Once you have the kethane stored onboard the craft, do you refine it into fuel there or do you launch the kethane into orbit to some sort of orbital refinery? Common sense says to refine it in place because the mass of kethane going into the kethane converter is much higher than the mass of fuel output. This design is more complicated, however, and requires not only kethane storage but kethane conversion capabilities and fuel storage capabilities.
Kethane isn’t available everywhere on the surface of a terrestrial planet or moon – it is scattered in deposits across the surface and deposits tend to run out. This creates a second problem for long-term mining operations. How do you mine from multiple locations?
One thought is to establish a stationary refinery on the surface that doubles as a launch center for refined fuel from kethane. Then have mobile drilling rigs that can travel out to the deposits, collect the kethane, and return to the refinery. This is definitely a time consuming process but it saves fuel because the mobile drilling platforms can be powered by solar energy instead of fuel. A fuel tug can then land nearby the refinery to be filled by a fuel truck that carts fuel between the refinery and the fuel tug and then the fuel tug launches to go wherever the fuel is needed.
The large determining factor in what method is most efficient overall is the amount of delta-v required to launch off of the body being mined. In a case like Gilly, where very little delta-v is needed to get into a stable orbit, it is more feasible to have a mining operation that launches the kethane into orbit to rendezvous with an orbital refinery and fuel depot. In the case of of a body with moderator gravity and an atmosphere, like Duna, it is more feasible to prefer using less fuel by refining on the surface and transporting the refined fuel into space with large fuel tugs.
There are multiple solutions to acquiring and utilizing kethane. What solutions did you use?