Conventional vs Unconventional Oil and Gas

There are several types of geological formations that trap naturally occurring energy resource. They are categorized as either ‘conventional’ or ‘unconventional’ resources.

Conventional	Unconventional
Conventional oil and gas is trapped in naturally porous reservoir formations that are capped with impermeable rock strata. When intercepted by a well, oil and gas is able to move to the surface without the need to pump.	Unconventional oil and gas is formed in more complex geological formations which limit ability of gas to migrate and therefore different methods are required to extract the oil and gas.

There are several types of unconventional gas including shale gas and tight gas, which occurs in reservoirs with very low permeability compare to conventional reservoirs. Horizontal drilling and hydraulic fracturing is needed in the case of such energy extractions. Other form of gas is CBM (coal bed methane) that is trapped within the coal seem under the pressure of overlying formations.

Tight Gas Reservoir : Tight gas reservoirs characterized with low porosity (3-6%)and permeability (from microDarcies to a few mili Darcies), small drainage radius and low productivity, require significant well stimulation-hydraulic fracture treatment- or the use of horizontal or multilateral wells to produce at economic rates. Sandstones and Shales of tight gas gets its tightness due to different geological events like loss of porosity through diagenesis, mineralogical composition, shorting, depositional environment, cementation, dissolution tectonics etc.

• Shale gas : Shale gas refers to natural gas that is

REFERENCES :

• www.epa.nsw.gov.au