Shale, Tight and Coal Seam Gas

Unconventional Gas

Shale, tight and coal seam gas 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).

Coal seam gas (CSG) is found predominately on the surface with only minor amounts in the natural fractures of coal seams.  CSG has low potential for development in Western Australia.  Tight gases are usually found in low permeability and low porosity sandstone and limestone, while shale gas occurs within shale-type rocks that are commonly associated with traditional oil and gas sources.

Technical developments over the past thirty years, including horizontal drilling and hydraulic fracturing, have made these gas sources commercially viable.. These techniques were developed and refined in North America and have been continuously improved so that additives such as chemicals are relatively safe and able to be used.

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Western Australia has a high prospectivity for shale and tight gas, which are very different resources to coal seam gas being targeted in Queensland.  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.

It is believed that shale gas resources are spread across the Perth, Carnarvon and Canning basins. DMP estimates that known Perth Basin tight gas fields hold between nine and twelve trillion cubic feet of recoverable gas located in the vicinity of existing pipelines, which would be used to transport the gas.  It is generally assumed that one trillion cubic feet of gas can provide enough energy to power a city of one million people for a period of 20 years.

An assessment of world shale gas resources by the United States Energy Information Agency has estimated that Western Australia is holding the world's fifth-largest reserves of shale gas at 288 trillion cubic feet.  This is approximately twice the gas that is held in Western Australia’s offshore areas.

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.

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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. 

When the pressure is reduced the proppants remain in place and hold the fractures open.  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.

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Hydraulic stimulation was commercially established in the late 1940s in the United States. Since then it has been used globally by the industry. The use of hydraulic stimulation in accessing shale, tight and coal seam gas is a relatively recent phenomenon.

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Hydraulic stimulation increases the rate at which fluids can be produced from a reservoir. Hydraulic stimulation provides access to resources that would otherwise be inaccessible or commercially unviable.

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Hydraulic fracturing has only been used four times to target unconventional gas in typically remote areas of Western Australia.  This is in contrast to the United States, where it is used approximately 10,000 times per year.

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The department is aware of issues in Queensland and the United States with using hydraulic stimulation in close proximity to an aquifer to target CSG.

Within Western Australia, it is expected that hydraulic stimulation will primarily be used to target shale and tight gas resources, which are typically not found within 1000 metres of aquifers.  However, the Western Australian Government is working closely with other governments to learn from experiences in Queensland and New South Wales.

Western Australia is considered not very prospective for CSG and there are currently no coal seam gas operations in Western Australia. However, any operation would be assessed thoroughly before approval, and conditions added where appropriate.

However, a few companies have indicated that CSG may be a potential secondary target during exploration for other primary targets.

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Western Australia’s shale and tight gas resources are located at significantly greater depths than in Queensland or the United States and are typically separated from potable water aquifers by more than 1000 metres.  In other parts of the world, gases are known to occur at the same depth or near to an aquifer.

However, regardless of the depth of underground aquifers in Western Australia, DMP applies a rigorous and transparent approvals process to all projects to ensure that they meet the State’s high operational standards.

The geological nature of shale and tight gas reservoirs prevents gas migrating into the water table. Additionally, well design and drilling programs are thoroughly assessed to ensure integrity and no uncontrolled flow of fluids. However, as part of the approvals process each operation is assessed thoroughly and conditions are added to approvals where appropriate to ensure that all precautions are taken to protect the environment. This can include extra precautions such as monitoring of an aquifer.

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Shale, tight and coal seam gas are regulated using a similar process to conventional oil and gas activities under the Petroleum and Geothermal Energy Resources Act 1967.
Companies intending to carry out drilling and stimulation operations need to submit a number of applications to DMP, including:

• Drilling Application
• Environmental Management Plan; and
• Safety Management Plan.

Assessment of these plans will determine if additional conditions are required as a result of the activity proposed, such as monitoring of an aquifer.  For any activities using hydraulic stimulation, DMP will require a list of chemicals to be used and detailed information on how aquifers will be protected.

If an activity is proposed in or within 500 metres an environmentally sensitive area, the proposal will be referred to the Environmental Protection Authority (EPA).  DMP will liaise with the EPA if a proposed activity is within two kilometres of a town site, the coastline or likely to impact a water resource area (including a water reserve, water catchment area, groundwater protection area and declared or proposed water supply catchment area).

If a proposal is referred to the EPA, the EPA will subsequently determine the level of assessment required under the Environmental Protection Act 1986 (WA).

While applications are not normally made public, if the EPA requires a Public Environmental Review then an application will be made public.

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Chemicals used in hydraulic stimulation assist with inserting a propping agent and protecting any drilling equipment.  These chemicals vary depending on the conditions that a well is going to be hydraulically stimulated through and often vary from well to well.

DMP requires the disclosure of all chemicals to be used in a Drilling Application and Environmental Management Plan.  Any chemical solutions identified as being potentially harmful are not approved.

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While the department has a well established database containing information on all petroleum wells in the State, the Petroleum and Geothermal Energy Resources Act 1967 (the Act), does not contain separate provisions for oil, conventional gas, coal seam gas, tight gas or shale gas.

Companies apply for Exploration Permits, which cover all types of naturally occurring petroleum. Hydraulic stimulation activities can also be associated with conventional oil and gas developments.

However, during the administration of titles the department may become aware of particular targets. Based on this evidence it estimates there are fewer than 20 wells whose operators may currently be targeting shale, tight or coal seam gas.

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