Five types of replacement silica are recognized in the Lower Mississippian Virden Member carbonates on the northeastern flank of Williston basin： microcrystalline quartz, chalcedonic quartz, anhedral megaquartz, euhe...Five types of replacement silica are recognized in the Lower Mississippian Virden Member carbonates on the northeastern flank of Williston basin： microcrystalline quartz, chalcedonic quartz, anhedral megaquartz, euhedral megaquartz, and stringy megaquartz. Silica tends to replace various bioclasts, and all except the stringy megaquartz also occur as non-replacive void-filling cement or as silica forming chert nodules and silicified limestone. Although crinoids, brachiopods, corals, bryozoans, molluscs, trilobites, forams, and ostracodes are present in the sediments studied, only the first three show evidence of silicification. Crinoids are commonly replaced by microcrystalline quartz whereas brachiopods typically by spherules of length slow chalcedony. Coalesced spherules, often in concentric rings （beekite rings）, may form sheet-like masses on the surface of corals and brachiopods. Although bryozoans are common in the Virden Member, none showed any evidence of silicification. The difference in the susceptibility to silicification may be related to the shell microstructure, biological group, size of organism, skeletal mineralogy, and organic content of the bioclasts. Biogenic silica derived from the dissolution of siliceous sponge spicules is considered to be the most likely silica source for silicification. Most silica is believed to be released during early diagenesis before the sediments were deeply buried. The Virden Member carbonate may have experienced two episodes of replacement, the first affecting the bioclasts, the second producing silicified limestone and chert nodules.展开更多
A workflow that helps identify potential production sweet spots in the Middle Bakken tight oil play is proposed based on analysis of large amounts of production data. The proposed approach is a multivariate statistica...A workflow that helps identify potential production sweet spots in the Middle Bakken tight oil play is proposed based on analysis of large amounts of production data. The proposed approach is a multivariate statistical model that extracts relevant information from a training dataset of production wells to facilitate geological similarity comparison between economic and sub-economic production wells. The model is applied to the Middle Bakken tight oil play in southeastern Saskatchewan. Data screening for diagnostic geological indicators for sweet spots reveals that several geological factors indicative for conventional oil reservoirs seem to work for the Middle Bakken tight oil play as well. These factors include: a) the NE Torqunay-Rocanville Trend serving as a preferred regional migration path for connecting mature source rock in southern Williston Basin and the Middle Bakken tight reservoir in southeastern Saskatchewan; b) the oils in the Bakken tight reservoirs along the U.S. and Canada border are more likely from local matured Bakken source rocks; c) subtle structural components enhancing the convergence of dispersed hydrocarbons over a large area; d) top seal and lateral barrier improving preservation, thus favouring oil productivity; e) orientation of maximum horizontal stress coincident with the direction of the variogram spatial continuity in ultimate recoverable reserves, so the direction of horizontal well has a significant impact on the oil productivity.展开更多
基金supported by the Natural Sciences and Engineering Research Council of Canada (No. 327092-06)Brandon University (BU) Research Committee for financial support
文摘Five types of replacement silica are recognized in the Lower Mississippian Virden Member carbonates on the northeastern flank of Williston basin： microcrystalline quartz, chalcedonic quartz, anhedral megaquartz, euhedral megaquartz, and stringy megaquartz. Silica tends to replace various bioclasts, and all except the stringy megaquartz also occur as non-replacive void-filling cement or as silica forming chert nodules and silicified limestone. Although crinoids, brachiopods, corals, bryozoans, molluscs, trilobites, forams, and ostracodes are present in the sediments studied, only the first three show evidence of silicification. Crinoids are commonly replaced by microcrystalline quartz whereas brachiopods typically by spherules of length slow chalcedony. Coalesced spherules, often in concentric rings （beekite rings）, may form sheet-like masses on the surface of corals and brachiopods. Although bryozoans are common in the Virden Member, none showed any evidence of silicification. The difference in the susceptibility to silicification may be related to the shell microstructure, biological group, size of organism, skeletal mineralogy, and organic content of the bioclasts. Biogenic silica derived from the dissolution of siliceous sponge spicules is considered to be the most likely silica source for silicification. Most silica is believed to be released during early diagenesis before the sediments were deeply buried. The Virden Member carbonate may have experienced two episodes of replacement, the first affecting the bioclasts, the second producing silicified limestone and chert nodules.
基金The Program of Energy Research and Development (PERD) funded this study
文摘A workflow that helps identify potential production sweet spots in the Middle Bakken tight oil play is proposed based on analysis of large amounts of production data. The proposed approach is a multivariate statistical model that extracts relevant information from a training dataset of production wells to facilitate geological similarity comparison between economic and sub-economic production wells. The model is applied to the Middle Bakken tight oil play in southeastern Saskatchewan. Data screening for diagnostic geological indicators for sweet spots reveals that several geological factors indicative for conventional oil reservoirs seem to work for the Middle Bakken tight oil play as well. These factors include: a) the NE Torqunay-Rocanville Trend serving as a preferred regional migration path for connecting mature source rock in southern Williston Basin and the Middle Bakken tight reservoir in southeastern Saskatchewan; b) the oils in the Bakken tight reservoirs along the U.S. and Canada border are more likely from local matured Bakken source rocks; c) subtle structural components enhancing the convergence of dispersed hydrocarbons over a large area; d) top seal and lateral barrier improving preservation, thus favouring oil productivity; e) orientation of maximum horizontal stress coincident with the direction of the variogram spatial continuity in ultimate recoverable reserves, so the direction of horizontal well has a significant impact on the oil productivity.
