This report demonstrates a refined approach to the mapping of subsurface structures that incorporates trend-surface analysis and surface-fitting techniques into the conventional well-log interpretation workflow. The trend-surface analysis is first used to separate formation picks into a component of regional dip/trend and a residual component of local structures using polynomial regression. Then, the residuals are fitted by a representative surface using kriging. In both steps, existing geological knowledge about the regional and local structures is incorporated as constraints in both modelling the trend and interpolation of the residual surface. Finally, the linear patterns of formation-top offset are extracted from the residual surface using a moving window neighbourhood statistics method. Lineaments are then interpreted and digitized from the resultant maps. The trend-surface analysis is also applied to the isopach data calculated from two formation-top picks, in order to differentiate syndepositional faults from postdepositional faults.
The methodology developed has a higher resolution in detecting formation-top offsets and higher accuracy in digitizing fault locations compared to the conventional contour map, seismic section and aeromagnetic data interpretation techniques in structure mapping for the sedimentary cover. The result is a significant update to the structure framework of the Peace River Arch region, which has been the focus of structure study for decades. Lineaments, interpreted from the linear offset pattern of formation tops extracted with the refined approach, have been identified from each of 14 formation tops (including the Precambrian top) and traced through most of the sedimentary cover. Many of these lineaments were found to be associated with known major faults that had been previously interpreted from well-log and seismic interpretations. This suggests that the linear offset patterns extracted with the refined approach in the study area are related mainly to faults rather than differential compactions. The effect of the possible differential compaction has been mostly removed with the trend. The Dawson Creek Graben Complex (DCGC) has been reinterpreted using this new approach. A different structure pattern was identified from the Triassic and Lower Jurassic formation tops. Activation of the DCGC in the Late Cretaceous has been identified with direct evidence. Some of the faults (e.g., Josephine Creek, Farmington, Gordondale, Belloy, Fairview, Bluesky, Berwyn, Normandville, Whitemud, Hines Creek and Beaton Creek faults) were identified as steep and/or listric faults and have offset formation tops from the Upper Cretaceous through the Paleozoic and down to the top of Precambrian. They could be the possible pathways/conduits for the hydrothermal venting hypothesis for the origin of the ooidal ironstone deposit.
Mei, S. (2006): Structure mapping for the Clear Hill-Smoky River region using well-log data and geostatistical analysis; Alberta Energy and Utilities Board, EUB/AGS Earth Sciences Report 2006-04, 98 p.