Comparison of Sources, Maturities and Alteration of Gases from Three Mud Gas Depth Profiles Across the Western Canada Sedimentary Basin

Barbara Tilley and Karlis Muehlenbachs
University of Alberta, Edmonton, AB

A correlation of carbon isotopic depth profiles from three wells, spanning a distance of about 200 km across the western part of the Western Canada Sedimentary Basin, includes wells from the OJAY Field in the easternmost part of the disturbed belt (eastern British Columbia), a Kakwa Field well in the undisturbed ‘Deep Basin' of Alberta, and a well from the Belloy Field in the Peace River Arch area. Each depth profile is composed of 100 or more mud gas analyses which represent the Mississippian to Cretaceous stratigraphic section, in three different post-depositional tectonic settings.

Although definite groupings of carbon isotope and molecular compositional data do occur, it is evident that the genetic and post-genetic history of these gases is complex. Near-surface biogenic gases, biodegraded thermogenic gases, deeper unaltered thermogenic gases from type II and type III kerogens can all be identified in these wells. In the deepest section of the OJAY well, late-stage thermally cracked gases are also apparent. Gases in the Triassic to Mississippian section in the three wells were generated from Type II kerogen at increasing levels of maturity as expected for their burial depths. Gases in the Cretaceous section were generated from Type III kerogen, although many have been bioaltered. We see no evidence for regional gas continuity across this region or cross formational flow of gas at the OJAY and Belloy wells. At Kakwa, the gas is homogenized from the Mississippian into the Lower Cretaceous section.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005