RE:why would they do that ?I would be very surprised if they bought another rig. They need to know what the reservoir "looks" like (commercial hydrocarbon intervals, depth, expanse of the reservoir, the homogeneity of the reservoir, the appropriateness of utilizing horizontal and pad drilling) before they can determine what type of rig is necessary for future development (that's likely a few years off). It's likely going to have to be a rig more substantial than a carrier mounted rig, but appropriate rig moving equipment/crews would be needed for just about any other type of rig (super single, tele-double, jack knife double, triple, pad/walking triple).
I would guess that rig(s) would be mobilized once appraisal and development wells are planned to be drilled. Economies of scale has the potential to be a big help when securing services required for development. I would guess the added funds would be used for further exploration or strat wells, as well as more comprehensive G&G data gathering.