Conventional reservoirs are typically classified to porous / permeable sandstone and limestone, single or multi reservoir interval systems. They will produce naturally driven the pressure within the system and the reservoirs formation characteristics ability to naturally flow from the well to surface. After a period pressure support into the reservoir is then often required. Typically water or gas injection from separate strategically placed wells.
Wells can be classed on hydrocarbon type oil, gas, pressure, and complexity.
Tight gas / non conventional wells again can exist in different pressure regimes depths and environments in different types of sedimentary rock sequences eg shale. Due to limited permeability and porosity flow into a Well is restricted and to be able to produce from these systems viability to stimulate wells to be able to produce and be productive has to be verified.
While drilling tripping casing cementing one has to be extremely careful in regards to pressure management and well control assurance. Eg small influxes slowly entering a well can be very difficult to detect. Hence best and very specific drilling and operational best practices have evolved for these wells versus the standard norms.
What else, please ask where I am sure the SPREAD extended community can suitably further advise.