Present and Past Geothermal Regimes and Source Rock Maturation, Peace River Arch Area, Canada (1)

Abstract

Present and past geothermal regimes in the Peace River arch area in the Western Canada sedimentary basin were studied using stratigraphic, hydrogeological, geothermal, and geochemical data from about 22,000 wells drilled in the area. The analysis of the main characteristics of heat flow and of the flow of formation waters showed that conduction is the main mechanism for the transport of the terrestrial heat to the surface. The regional-scale distribution of the integral geothermal gradient (from the base to the top of the sedimentary column) shows a north-northwest increase from 25 degrees C/km to more than 35 degrees C/km, caused by increased heat flow of crustal origin. Some local anomalies superimposed over this trend are related to variable radiogenic heat production n the basement. The thermal history was reconstructed for the last 70 m.y. since the Laramide orogeny, during which maximum burial was attained. The paleoheat flow was lower than at present, with a warming trend since the Late Cretaceous or the Tertiary. The reason for this warming trend is not examined in this paper. Analysis of the level of maturation of the source rocks showed that the Upper Cretaceous rocks are generally immature, the Lower Cretaceous rocks are in the oil window, the Jurassic to Mississippian rocks are in various stages of oil and gas generation, and the Devonian source rocks are generally overmature. The maturation history shows that the Paleozoic source rocks entered the oil window during the Late Cretaceous and early Tertiary, whereas the Cretaceous rocks matured during the post-Eocene regional uplift.