The exciting prospect regarding hydrocarbon recovery with our GFCs technology is the idea of self-fueling. Initially, GFCs are fueled by natural gas or propane. After the resource is brought into production, the GFCs operate off of fuel derived from the resource.
There is a pre-production phase during which the ground around the GFC heaters is warmed sufficiently to establish full production from the collection wells. As the formation is warmed, available fuel gas from the formation gradually increases such that the GFCs become self fueling. Natural gas or propane provides the supplemental fuel for the GFCs during the warm up phase.
The variance between gas yields produced by Fischer assay and those resulting from in-situ heating, like that employed by IITRI (The IIT Research Institute of Chicago), is due to the thermal history of the shale oil as it is extracted. The Fischer assay process is a small batch laboratory procedure which involves rapidly heating oil shale in a closed vessel with an inert atmosphere. The Fischer assay method involves heating a small shale sample to 500°C at the controlled rate of 12°C per minute. At this heating rate the shale sample is raised to maximum retorting temperature in just over 40 minutes. In-situ retorting, by contrast will raise the temperature of oil shale or other hydrocarbon resources much more slowly. This longer temperature regime results in some fundamental changes to oil and gas yields and compositions.
The table below shows the variation between gas composition under Fischer assay (FA) conditions and those under in-situ (IS) conditions.
Table: in-situ Gas Composition
|Gas||% – FA||% – IS|
|Carbon dioxide – CO2||24||15|
|Hydrogen – H2||26||45|
|Methane – CH4||18||20|
|Higher carbons – C2+||26||17|
Under the long heating regimes that will prevail under in-situ conditions, like those that will be created by GFCs, oil shale and other hydrocarbons will show decreases in oil yield and corresponding increases in gas yields. Under the longer heating regime, oil yield falls from 100% of assay to 80%. This is due to degradation of the oil as it is exposed to heat for longer periods of time. Oil degradation leads to increased production of “char”, or fixed carbon, which remains on the shale in solid form. By injecting steam into the pre-heated formation, we can produce “syngas” that can be collected and used by the GFC as fuel. This allows us to recover an estimated, 18 units of energy for each unit of energy spent.