West-Central AB
NWSG
October 31, 2005

To evaluate the hydrocarbon potential in the uppermost Cretaceous and Tertiary in Alberta, a new model has been been developed to explain the source, emplacement and trapping of unconventional shallow gas reserves. It has long been known that these reserves are biogenic in origin and that large volumes of gas were generated from in situ organic sources early on in the depositional history of the reservoir units. Subsequently, these reservoirs were rapidly and deeply buried and this gas was forced into solution in the interstitial water of the sediments. In the late Tertiary, much of the overlying sediments were eroded and the entire stratigraphic section rebounded and decompacted. This removal lowered the reservoir pressures and allowed the gas to come out of solution and migrate into the reservoirs. This forced the water out of the system and these reservoirs became almost completely gas-saturated. With nowhere to go, the gas column became overpressured until the seal capacity of the reservoir was exceeded. At this point, the gas began leaking out of the system, however, significant water was able to imbibe to replace it. Subsequently, the reservoirs became underpressured but still gas-saturated. Using hydrogeological data, and applying this model, it is possible to predict those areas and formations which are gas-saturated.

Fluid(s): 
Area: 
West-Central AB
DLS/NTS: 
T45-65, R1W5-13W6