Coal is a natural bioreactor that generates a proportion of its gas through biological action, and stores that gas within the microscopic pores of the coal.
For CSG, a high degree of gas saturation is preferred because it only takes a modest reduction in pressure for the gas to flow. When the coal is undersaturated, or has been depleted, the pressure at which gas can be produced becomes low and yields fall dramatically.
Verso Energy’s process allows the coal seam to be stimulated to produce new gas. The ideal application is to restore depleted fields, where the wells, collection systems, delivery network and end users are already in place.
A wellfield can be stimulated back to pre-production gas levels in as little as 6 months, after which time the operator can repeat the original production process to recover secondary gas. In most cases the dewatering time for secondary gas production will be negligible.
How it Works
Coal samples from a target site are provided to Verso Energy, where our proprietary microbial adaptation process is undertaken in simulated coal bed reactors. This takes 4 - 6 months, during which time the reservoir stimulation is designed for a particular field.
The stabilised and adapted consortia developed in the lab are then scaled to large volumes in field units. They are injected into the reservoir in combination with a specifically designed nutrient medium to support rapid proliferation of microbial biomass within the reservoir. A series of proprietary process phases, known as shunts, are used to maximise the underground coverage and control different aspects of the bioconversion process.
The coal acts as both a source of carbon as the storage tank for the gas. When the reservoir is suitably saturated the system is flushed and is ready to be produced at the discretion of the operator. Gas will stay in place until it is needed for production.
Verso Energy’s CSG stimulation process allows a CSG site to be produced multiple times, which equates to a much higher return on capital.
In rejuvenating a site for secondary production, the need to explore and develop new fields may be reduced. This is beneficial for landowners where CSG developments are in conflict with existing land use.
Re-using and recycling co-produced water in the process will help to reduce costs of water treatment and the maintenance of coal seam water levels may benefit from lower overall groundwater production.