What is tight gas?
#Tight Gas exploratory fracking has been occurring in Seaspray, Longford and Gormandale - Gippsland by Lakes Oil Pty Ltd and is near ready to proceed to a commercial stage.
- In Victoria, tight gas comes under petroleum guidelines and shale and coal seam gas come under mineral guidelines
- Fracking, which is used for all processes contain chemicals to assist in fracturing of rock and the free flow of gas to the surface
- Tight gas uses more water volume than CSG for the fracking process
Shale, tight and coal seam gas (coal bed methane) is the name used to categorise gas obtained from coal seams (coal seam gas) and certain types of low permeability rock formations (tight sands gas and shale gas) and are known as unconventional gases.
Coal seam gas (CSG) is found predominately on the surface with only minor amounts in the natural fractures of coal seams.
Tight gases are usually found in extraordinarily impermeable, hard rock or and low porosity sandstone and limestone making the underground formation extremely "tight."
Shale gas occurs within shale-type rocks that are commonly associated with traditional oil and gas sources.
Tight gas is a very different resource to coal seam gas. The main difference is that shale and tight gas resources are found at significantly greater depths of beyond 2000 metres than coal seam gas, which is generally found between 600-1000 metres.
Development of shale, tight and coal seam gas has resulted from technological developments, mostly originating in North America, over the past 30 years. Key technologies include very accurate horizontal drilling and hydraulic stimulation.
In order to overcome the challenges that the tight formation presents, there are a number of additional procedures that can be enacted to help produce tight gas. Deviating drilling practices and more specific seismic data can help in tapping tight gas, as well as artificial stimulation, such as fracturing and acidizing.
How does hydraulic stimulation work?
Hydraulic stimulation (also known as ‘fraccing’ or ‘hydraulic fracture stimulation’) uses high pressure to fracture rock formations and push carrying fluids containing proppants (typically sand or ceramic beads) into the fractures to improve permeability, or the ability of the gas to flow through the formation.
This allows gas trapped in rock formations to be accessed and extracted faster. After the pressure is reduced, the carrying fluids may flow back to the surface where they are treated or disposed of in accordance with accepted procedures.
Additionally, acidizing the well is employed to improve permeability and production rates of tight gas formations. Acidation involves pumping the well with acids that dissolve the limestone, dolomite and calcite cement between the sediment grains of the reservoir rocks. This form of production stimulation helps to reinvigorate permeability by re-establishing the natural fissures that were present in the formation before compaction and cementation.
Currently, not enough information is known about underground water aquifers.
Currently, no one knows where approx. 50% of the fraccing fluid flows underground.
Currently there are no guidelines for waste disposal (typically salts) and treated waste water.
Interestingly, the Gippsland area experienced a 5.3 scale earthquake in the Strezlecki fault line where exploratory fracking had recently commenced. This is an unstable fault line and it cannot be discounted that this process either contributed to the earthquake or will cause future destablising.
Furthermore, there is an updated seismic and subsidence report for Gippsland but DPI are refusing to release it to the public. Where is the transparency?
What is Gas?
Sourced © Geoscience Australia.
Natural gas is a combustible mixture of hydrocarbon gases.
It consists mainly of methane (CH4), with varying levels of heavier hydrocarbons and other gases such as carbon dioxide.
Natural gas is formed by the alteration of organic matter. This can be by biogenic or thermogenic processes. When accumulated in a subsurface reservoir that can be readily produced it is known as conventional gas.
Conventional gases (gas) fields can be dry (almost pure methane) or wet (associated with the “wet gas” components – ethane, propane, butanes and condensate). Dry gas has less energy content than wet gas. Conventional gas can also be found with oil in oil fields. Natural gas also occurs in more difficult to extract unconventional deposits, such as coal beds (coal seam gas), or in shales (shale gas), low quality reservoirs (tight gas), or as gas hydrates.
Liquid Natural Gas (LNG) is primarily composed of the lightest hydrocarbons, methane (CH4) and ethane (C2H6); it is a gas at surface conditions but is cooled and compressed to a liquid for transport in LNG tankers to export markets. LNG is natural gas that is cooled to around -160oC until it forms a liquid, making it easier to transport.
Australia has significant gas resources, with gas being Australia’s third largest energy resource after coal and uranium. Conventional gas resources are widespread both on and offshore, occurring in fourteen different basins, but most of the resource is off the north-west margin in the Bonaparte, Browse and Carnarvon basins.
Unconventional Petroleum Resources
Unconventional resources are natural resources which require greater than industry-standard levels of technology or investment to exploit. In the case of unconventional hydrocarbon resources, additional technology, energy and capital has to be applied to extract the gas or oil, replacing the natural action of the geological processes of the petroleum system.
Examples of unconventional oil resources include oil shales, oil sands, extra-heavy oil, gas-to-liquids and coal-to-liquids. Oil shale is an example where a thermally immature source rock has not generated and expelled hydrocarbons. Oil or tar sands occur where conventional crude oil has failed to be trapped at depth and has migrated near to the surface and has become degraded by evaporation, biodegradation and water washing to produce a viscous heavy oil residue.
In contrast to conventional gas reservoirs, natural gas can also be found in more difficult to extract unconventional deposits, such as coal beds (coal seam gas), or in shales (shale gas), low quality reservoirs (tight gas), or as gas hydrates. Unconventional gas accumulations reflect the failure or under-performance of the petroleum system.
•Shale gas and coal seam gas are examples where the natural gas is still within the source rock, not having migrated to a porous and permeable reservoir. •Tight gas occurs within low permeability reservoir rocks, which are rocks with matrix porosities of 10 per cent or less and permeabilities of 0.1 millidarcy (mD) or less, exclusive of fractures. Tight gas can be regionally distributed (for example, basin-centred gas), rather than accumulated in a readily producible reservoir in a discrete structural closure as in a conventional gas field. •Gas hydrates are naturally occurring ice-like solids (clathrates) in which water molecules trap gas molecules in deep-sea sediments and in and below the permafrost soils of the polar regions.
The recent developments of oil sands in Canada and of shale gas in the United States are examples where rising energy prices and technological development has facilitated the exploitation of unconventional hydrocarbon resources. In the Australian context, coal seam gas is the unconventional hydrocarbon resource that is most developed.