ABSTRACT
An important gas trend within the southern Rocky Mountain Foothills of northeast British Columbia in under current exploration and development. The presence of gas reserves has been established in Lower Cretaceous / Jurassic sandstones and Upper Triassic carbonates, with locally important reserves in Middle Triassic sandstones.
This paper deals with Upper Triassic gas reserves and potential present in complexly folded and faulted low-grade carbonate reservoirs of the Pardonet and Baldonnel Formations. The geological, geophysical and reservoir parameters pertaining to these accumulations are best illustrated in the Sukunka/Bullmoose area where five discoveries have been made, three of which are partly defined by development drilling.
These Upper Triassic sour gas accumulations are believed to have formed in the following manner: Organic matter was deposited contemporaneously with the Pardonet-Baldonnel carbonates and with shales of the immediately overlying Jurassic Fernie Formation. The organic matter was transformed into hydrocarbons, which migrated a short distance into locally permeable and porous carbonates as the Triassic became buried by a thick Jurassic and Cretaceous clastic sequence. As a result of deep burial and the Laramide Orogeny, the mature stage of organic diagenesis was reached, leaving only gaseous hydrocarbons and bitumen. The Laramide tectonic event created a series of compressional-type structures and an extensive fracture system, allowing the gas to re-migrate into anticlinal traps. This fracture network is also responsible for significantly enhanced permeability and thus excellent productive capability. AOF tests as high as 6 300 × 103m2 (223 MMcf) per day have been recorded. Proven and probable reserves of sour gas in the general Sukunka/Bullmoose area defined to date are estimated at 28 328 × 106m3 (1.1 Tcf). Because of the high H2S and CO2 content, sales gas is estimated to be in the order of 16 544 × 106m3 (584 Bcf).
The area’s exploration history has been long and difficult, hampered by a combination of high-cost operations and complex geology. Although exploration was undertaken in the late 1950s and a discovery made at Sukunka in 1965, it was not until the mid-1970s that progress was made in defining the extent of the original Sukunka discovery and in discovering other fields. The increase in commodity price for natural gas, improved technology, and persistence in exploration have been factors in the emergence of this promising gas trend in British Columbia.
