Cement degradation processes in coal seam gas wells in Queensland

Community and landholder groups in Queensland have expressed concerns about potential failures in the integrity of CSG wells, and the possibility of failed wells providing a pathway for contamination of aquifers and gas leaks. Communities have asked for assurance as to how the construction of these wells ensures their integrity.

Well integrity is provided by barriers that are designed to prevent unintended flow of fluids (such as water or gas) into, out of or along the well bore.

The two main structural barriers are well casing and annular cement.

Well casing prevents the flow of fluids into or out of the well, keeps the well open through weak or broken rock layers, and provides a pathway to move gas and water from the reservoir to the surface.

Casing is cemented into the well to provide support to the casing and the wellbore and to create a seal between the casing and the surrounding rock. These components act together as a multi-barrier system that greatly reduces the risk of loss of well integrity.

Cement plays a vital role as both a primary barrier and in providing support and protection to the casing throughout the well’s lifecycle, continuing once a well has been decommissioned.

Cement used in natural gas wells is distinctly formulated for the unique requirements of bonding to casing and geological formations, differing significantly from common construction materials like structural concrete.

Unlike household concrete, which is designed primarily for strength and durability under everyday conditions, well cement must ensure a robust and impermeable seal, resisting extreme subsurface environments.

It is engineered to withstand high pressures, corrosive fluids, and varying temperatures, ensuring well integrity and preventing leaks between underground layers or to the surface.

This project will investigate the potential for cement degradation and their processes in CSG wells in the Surat Basin under conditions (pressure, temperature, groundwater chemistry) typically encountered in this region.

The project will be laboratory based, using ageing and accelerated ageing experiments to evaluate the extent of potential cement degradation. Cement samples are exposed to groundwater with compositions found in CSG fields at the pressures and temperatures representative of reservoir conditions for an extended period of time.