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