| Popis: |
In the Lloydminster area, oil and gas are produced from the deltaic sands of the Lower Cretaceous Mannville Group, which has been subdivided into three formations; Dina, Silverdale and Colony, respectively. The subdivisions were based on slight lithological variations reflecting minor changes in the environment of deposition and the source of sediments. The deposits of the Dina Formation are non-marine beach sands, having little economic importance. They are overlain by mostly marine sediments of the Silverdale Formation, which contains the main oil producing horizons, the Sparky and General Petroleum Sand Members. Most of the gas is produced from the upper sands of the non-marine Colony Formation. The oil was formed "in situ" and accumulated in two types of traps, i.e., a number of simple convex traps resulting from differential thickness and permeability pinch-out traps. The development of channel systems on the delta front by tidal action formed the trap conditions. The oil was probably produced by the chemical transformation of the humic acid, transported by streams from the marginal alluvial plains of Lower Cretaceous times to the delta front. There the acid was precipitated out and settled in the bottom sands and bars of the channel system. When the strata of the Mannville were tilted towards the Rocky Mountain Geosyncline during the Laramide and later orogenies, same of the oil from the area soutwest of Lloydminster probably migrated up dip and gathered in the traps in the Lloydminster region, thus adding to the reserves of this area. Note:This thesis contains maps that have been sized to fit the viewing area. Use the zoom in tool to view the maps in detail or to enlarge the text. |
