The term “tight gas sands” refers to low permeability sandstone reservoirs that produce primarily dry natural gas. A tight gas reservoir is one that cannot be produced at economic flow rates or recover economic volumes of gas unless the well is stimulated by a large hydraulic fracture treatment and/or produced using horizontal wellbores (Holditch, 2006). Tight gas includes basin-centred gas systems, defined by Law (2002) as low-permeability, gas-saturated reservoirs that are abnormally pressured, regionally pervasive, and lack down-dip water contacts.
In the United States tight sands produce about 6 trillion cubic feet (TCF) of gas per year, which is 25% of the total gas produced (AAPG). As of January, 2009, the U. S. Energy Information Administration (EIA) estimates that 310 TCF of technically recoverable tight gas exists within the U.S, representing over 17% of the total recoverable gas.
Cooper Basin – Pervasive Tight Gas Accumulation
The presence of a Basin Centred Gas Accumulation (BCGA) in the Nappamerri Trough has been suspected for over two decades. Beach Energy has stated that the Encounter and Holdfast wells confirm the presence of gas in sands outside of structural closure and estimate that gas in place potentially exceeds 200 Tcf in sands across PEL 218.
Cooper Basin – Discrete Tight Gas Accumulations
In the Cooper Basin gas reserves are at commercial rather than technical recovery limits and explorers recognise significant upside reserve potential from unconventional sources. These unconventional sources include Early Permian Patchawarra Formation tight gas sands in the Moomba and Big Lake fields on the southern end of the Nappamerri Trough. Tight gas is the most mature unconventional play in the Cooper Basin. The Santos JV has been exploring the Nappamerri Trough since the mid 1990s and has utilised a range of drilling, development and production technologies to extract tight gas from its existing Cooper Basin fields. Tight gas sands have also been intersected at Wimma 1 in the centre of the Patchawarra Trough.