Kevin W. Hall

Frozen subduction in Canada's Northwest Territories: Lithoprobe deep lithospheric reflection profiling of the western Canadian Shield

Lithoprobe deep seismic reflection data from the northwestern Canadian Shield provide images of structures to the base of the lithosphere between the Archean Slave Province on the east and the Cordillera on the west. Mantle reflections dip eastward from the lower crust to about 100 km depth beneath the ∼1.88–1.84 Ga Great Bear magmatic arc and almost certainly represent a subduction surface associated with arc development. Where the mantle reflections flatten into the lower crust, they merge with prominent west dipping crustal reflections thus delineating a lithospheric-scale wedge that formed as a result of Proterozoic plate convergence between the Slave craton on the east and the ∼1.84 Ga Fort Simpson terrane on the west. The crust throughout the 725 km survey is highly reflective, and the Moho remains at a constant level between about 11.0 and 12.0 s beneath both Archean craton and Proterozoic accreted rocks; the most significant Moho deflection occurs beneath the ∼1.8–0.7 Ga Fort Simpson basin where it appears to rise to about 9.0 s (about 27 km). Within the crust of the Slave Province, east dipping, low-angle reflections near the surface beneath the Yellowknife basin may be shallow detachments, and lower crustal geometry is consistent with low-angle imbrication during Late Archean (∼2.65 Ga) tectonism associated with development of the Yellowknife basin volcanic rocks. West of the Slave craton, accreted Proterozoic crust is characterized by gently folded upper crustal layers overlying apparent thrust duplexes above detachment surfaces that flatten near the Moho. These lower crustal rocks were likely inserted as a tectonic wedge above the Moho and beneath the Slave Province during the contractional phase (∼1.90–1.88 Ga Calderian orogeny) of the Wopmay orogen. On the western end of the profile, the Fort Simpson extensional basin has up to 20–25 km of Proterozoic (meta) sedimentary rocks and sills(?) that are younger than 1.84 Ga.

Images of a lower-crustal oceanic slab: Direct evidence for tectonic accretion in the Archean western Superior province

The Archean western Superior province in Canada is the type area for proposed Archean plate tectonics. Seismic images from this region provide direct evidence for assembly of the craton by terrane accretion and for a large slab of remnant oceanic crust preserved at the base of the crust. This slab, with inferred garnet amphibolite composition, adds a critical piece of evidence to previous suggestions that Archean subduction was at a shallow angle and that some Neoarchean tonalite-trondhjemite-granodiorite suites, distinct from most modern-day suprasubduction magmas, are melts primarily derived directly from subducted slabs.

Tectonic delamination and subcrustal imbrication of the Precambrian lithosphere in northwestern Canada mapped by LITHOPROBE

Seismic reflection profiling of the Precambrian lithosphere in northwestern Canada has produced images of delamination structures (tectonic wedges) at crustal scale (to about 30 km depth) and, for the first time, at lithospheric scale (to about 100 km depth), and has further delineated subcrustal structures that were likely caused by imbrication of subducted lithosphere. Coupled with observations of similar structures in thrust and fold belts, delamination and lower plate imbrication are persistent features at many scales.

VP/VS characterization of a heavy-oil reservoir

This article demonstrates a VP/VS application for a heavy oil field near Plover Lake, Saskatchewan, where Nexen has applied both hot and cold production methods. Plover Lake Field is about 8 km east of the Alberta-Saskatchewan border and about 320 km north of the Canada-U.S. border. Oil sands of the Devonian-Mississippian Bakken Formation are found in NE-SW trending shelf-sand tidal ridges that can be up to 30 m thick, 5 km wide, and 50 km long. Overlying Upper Bakken shales are preferentially preserved between sand ridges. The Bakken Formation is disconformably overlain by Lodgepole Formation carbonates (Mississippian) and/or clastics of the Lower Cretaceous Mannville group. Since sandstones have larger S-wave velocities (and hence lower VP/VS ratios) than shales, VP/VS maps should help to identify thickening sand layers within the target zone. We also intend to examine changes within the reservoir due to cold production. Unlike the steam injection processes used in enhanced heavy oil recovery, cold prod...

Seismic physical modeling at the University of Calgary

The seismic physical modeling facility at the University of Calgary has existed since 1985. Recently, we upgraded it by replacing obsolete components with modern alternatives. We constructed a 3D positioning system based on high-precision linear electric motors, and coupled it to arrays of multiple transmitting and receiving piezoelectric transducers. We wrote customized software executing on the latest generation of desktop computers for controlling transducer movements, selecting and activating individual transducers, and acquiring and recording files of digital seismograms. The modernized facility enables us to collect scale-model seismic gathers at rates of thousands of traces per hour. We present examples of data from modeled 2D marine and land seismic surveys.

Geophysical transect of the Eagle Plains foldbelt and Richardson Mountains anticlinorium, northwestern Canada

A 250-km-long east-west geological and geophysical transect has been constructed at about lat 66°40′N, from near the Yukon-Alaska border, across the Eagle Plains foldbelt and Richardson Mountains anticlinorium, to the Interior platform in northwestern Canada. It includes reprocessed industry seismic reflection profiles, regional gravity data, and drill hole information. The north-trending Richardson Mountains anticlinorium is interpreted to be a contractional (pop-up) structure, having a core of Proterozoic and lower Paleozoic rocks; the structure is bounded on the east and west by post-Early Mississippian, pre- or syn-Cretaceous thrust faults. Contractional deformation in the Eagle Plains foldbelt is probably the same age. The location of the pop-up may have been controlled by a preexisting west-facing crustal scale ramp at the top of the crystalline basement. A horizontal displacement of about 33 km is required to accommodate the pop-up; the displacement probably occurs above regional detachment(s) that project westward beneath the Eagle Plains.

Time-lapse seismic analysis of a heavy oil cold production field, Lloydminster, Western Canada

Alberta, Canada has enormous heavy oil deposits, which represent the majority of Canada’s future oil reserves. In heavy oil recovery, cold production is less expensive than steam drive methods and has become more popular due to the development and widespread use of progressive cavity pumps (Lines at al., 2003). The distribution of “wormholes” formed during cold production is a major concern for reservoir engineers. Through their modeling work, Lines et al. (2003) have concluded that the resolution of individual wormholes is almost impossible using the normal surface seismic frequency range. However, they suggested that it should be possible to detect the presence of wormhole zones. Figure 1: Locations of the two time-lapse 3D seismic surveys.

Comparison of low‐frequency data from co‐located receivers

A low-frequency sensor comparison survey was acquired at the University of Calgary’s test site near Priddis Alberta in August 2009. Portable calibrated broadband seismometers, analog 3C 10 Hz geophones and two makes of digital 3C accelerometers were deployed at 1 m receiver line spacing, and used to record weight-drop and EnviroVibe (this report) sources at two source points located 50 m from the end of the receiver lines. This study shows that leastsquares-subtraction scalars (LSSS) depend on amplitude, frequency, phase, source-receiver offset, quality of sensor placement in or on the ground. LSSS show good promise for future use in quantitative sensor comparison studies.

Progress on Ultra-Wideband (UWB) Multi-Antenna radar imaging for MIGA

Progress on the development of the multi-channel, ground penetrating radar imaging system is presented from hardware and software perspectives. A new exponentially tapered slot antenna, with an operating bandwidth from 100 MHz to 1.5 GHz was fabricated and tested using the eight-port vector network analyzer, designed by Rhode and Schwarz Incorporated for this imaging project. An eight element antenna array mounted on two carts with automatic motor drive, was designed for optimal common midpoint (CMP) data acquisition. Data acquisition scenarios were tested using the acoustic version of the NORSAR2D seismic ray-tracing software. This package enables the synthesis and analysis of multi-channel, multi-offset data acquisitions comprising more than a hundred thousand traces. Preliminary processing is in good agreement with published bistatic ground-penetrating radar images obtained in the tunnels of the Low-noise Underground Laboratory (LSBB) at Rustrel, France.

VSP survey in a shallow well using a small vibrator source

Summary A shallow VSP survey was conducted in the University of Calgary Test Well using an EnviroVibe vibrator source and a downhole clamping 3C geophone. The goal was to evaluate VSPs for imaging thin-bed stratigraphy in the nearsurface environment. Two offset VSPs were obtained with the vibrator located 15m and 30m south of the wellhead. The vertical component data were subjected to wavefield separation to remove down-going P and S waves, and laterarriving (low-velocity) up-going and down-going events. The residual up-going P-wave reflections were further processed and mapped using a simplified VSP/CDP procedure. Features on the resulting reflectivity maps corresponded closely to the near-surface stratigraphy of the Paskapoo formation close to the well as identified by sonic velocity, resistivity, and natural gamma-ray logs. The project confirmed that the EnviroVibe vibrator used in nearsurface VSP surveys produces enough high-frequency energy to be effective for imaging relatively thin lithological beds in the upper 100m.