Stress Changes and Coal Failure Analysis in Coal Seam Gas Wells Accounting for Matrix Shrinkage: An Example from Bowen Basin, East Australia

The production of coalbed methane, or coal seam gas (CSG) in Australia increased 250-fold since the 1990s to around 1502 petajoules in 2019 and continues to expand. Groundwater flow in the aquifers intersected by gas wells could potentially facilitate a transport pathway for migration of contaminants or poorer quality water from deeper formations. While regulatory and mitigation mechanisms are put in place to minimize the risks, quantitative environmental impact assessments are also undertaken. When many gas wells are drilled in a wide area where many potential receptors are also spatially distributed, potential source-receptor combinations are too numerous to undertake detailed contamination risk assessment using contaminant transport modelling. However, valuable information can be gleaned from the analysis of groundwater flow directions and velocities to inform and prioritise contamination risk assessment and can precede computationally challenging stochastic contaminant transport modelling. A probabilistic particle tracking approach was developed as a computationally efficient screening analysis of contamination pathways for a planned CSG development near Narrabri in northern New South Wales, Australia. Particle tracking was run iteratively with a numerical groundwater flow model across a range of plausible parameter sets to generate an ensemble of estimated flow paths through the main Great Artesian Basin aquifer in the area. Spatial patterns of path lines and spatial relationships with potential receptors including neighbouring groundwater extraction wells and hydrologically connected ecological systems were analysed. Particle velocities ranged from 0.5 to 11 m/year and trajectories indicated dedicated contaminant transport modeling would be ideally focused at the local scale where wells are near potential receptors. The results of this type of analysis can inform the design of monitoring strategies and direct new data collection to reduce uncertainty and improve the effectiveness of adaptive management strategies and early detection of impacts.

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Field trials of the use of hydrated bentonite for decommissioning oil and gas wells

The APPEA Journal ◽

10.1071/aj15067 ◽

2016 ◽

Vol 56 (2) ◽

pp. 561 ◽

Cited By ~ 1

Author(s):

Brian Towler ◽

Mahshid Firouzi ◽

Amin Mortezapour ◽

Paul Hywel-Evans

Keyword(s):

Coal Seam ◽

Oil And Gas ◽

Laboratory Data ◽

Field Trials ◽

Gas Wells ◽

Coal Seam Gas ◽

Water Wells ◽

The Us ◽

Oil And Gas Wells ◽

The Many

Bentonite is widely used for plugging shallow water wells in the US. In the past 15 years Chevron has been plugging oil and gas wells with bentonite in the San Joaquin Basin in California, and has successfully plugged about 10,000 wells. In several previous publications the authors’ research team has reported laboratory data to predict pressure containment using bentonite to underpin the fundamentals for plugging both oil and gas wells. The authors propose bentonite as an alternative medium for decommissioning coal seam gas wells in Queensland. Gas producing companies in Queensland are proposing to drill and produce about 40,000 coal seam gas wells in the state, and all of these will have to be plugged eventually. Water wells are shallow and are usually plugged with coarse granulated bentonite that is simply poured down the hole and hydrated. The authors propose a process for compressing bentonite into cylinders of various shapes, which promises to improve the use of bentonite for plugging deeper wells. Oil and gas wells are presently plugged and abandoned with cement. Bentonite has a number of advantages when plugging oil and gas wells. It is cheaper and easier to deploy and it is more reliable than cement. In this extended abstract the application of bentonite for plugging conventional oil and gas and coal seam gas wells will be discussed. The many field trials will be reviewed and the fundamental theory for plugging wells with bentonite will be outlined.

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