Unfortunately, some believe that the reservoirs have been...

Unfortunately, some believe that the reservoirs have been charged from deeper source rocks along faults caused by the shale diapirs. This is how the CO2 is found in shallower formations. The shallow reservoirs in the Chinese fields did not have a CO2 problem and I believe this is true of the NEN well also.
High pressure formations can be caused by at least 2 situations. Pressure increases as depth increases. If a deeper, isolated reservoir is pushed upward by a process such as a diapur, the pressure within that reservoir is higher than what would be expected at that depth. By definition, this would be a high pressure formation. Second is more likely. Rapid deposition causes a fluid filled, high porosity formations to be compressed. Since fluids are not compressible, the only thing that can happen is the pressure increases and the formation becomes over pressurized. It is very true that shales can be very susceptible to this process as they have high porosity and low permeability. High pressure shales are big problem in the Gulf of Mexico and have caused the loss of several wells.