Northwest Alberta Research Articles

Depositional, stratigraphic and structural controls on the geometry of Montney Formation reservoirs: Lower Triassic, northeast British Columbia, northwest Alberta

Abstract The Lower Triassic Montney Formation is a world-class unconventional hydrocarbon reservoir that spans the border of northeast British Columbia and northwest Alberta. Integrated sedimentological and ichnological analyses suggest that the Montney Formation was deposited in a predominantly prodeltaic setting that was commonly influenced by both river flood and storm processes. Riverine processes include the local occurrence of normally- and inversely-graded siltstone and sandstone interbeds, interpreted as the record of sediment-laden hyperpycnal flows. Episodic storms are recorded by the local occurrence of hummocky cross-stratified interbeds, as well as normally graded, parallel and wave-ripple laminated beds, which are commonly draped by structureless carbonaceous mudstones. These mudstone drapes represent river-flood-derived fluid muds that collapsed from hypopycnal plumes following the passage of the storms and suggest the intimate linkage between storms and heightened fluvial discharge. The basin in which the Montney Formation was deposited began as three sub-basins, northern, central and southern, each of which experienced different patterns of subsidence and uplift that varied both spatially and temporally during sedimentation. Subsidence of the northern sub-basin was compartmentalized by deep seated faults that provided accommodation for the basal sequence of the Montney Formation, Sequence 1. Subsequent fault movement resulted in reduced accommodation in the northern sub-basin and accelerated subsidence in the central sub-basin, providing accommodation for deposition of Sequence 2, the basal sequence in the central sub-basin. The northern sub-basin remained paleotopographically elevated throughout deposition of Sequence 2 and early Sequence 3 successions, and these younger units did not extend beyond the northern limit of the central sub-basin. During subsequent deposition of the late Sequences 3 and Sequence 4 successions, compartmentalization between the north and central sub-basin was greatly reduced and these intervals were deposited relatively more uniformly along-strike. The unconventional and conventional reservoirs in both the northern and central sub-basins occur at the scale of systems tracts within the four depositional sequences of the Montney Formation. Reconstructing the depositional history of the component systems tracts of Sequence 1 through early Sequence 3 reveals the dynamic interplay between syndepositional tectonism, fluctuating relative sea-level and deltaic depositional processes in controlling the character, geometry and distribution of prolific Montney Formation reservoirs. The recognition of these key geological controls enhances predictability in this valuable resource and may be applicable to other fine-grained reservoirs elsewhere.

The Regulation and Litigation of Cumulative Effects on Indigenous Rights Following the Yahey Decision and Blueberry River First Nation Settlement and the Potential Effects on the Energy Industry

The British Columbia Supreme Court issued a groundbreaking decision in Yahey v. British Columbia: the Crown had failed to uphold its treaty obligations due to the cumulative effects of over 100 years of development. In response to the 2021 decision, British Columbia and Blueberry River First Nation have reached a multi-million dollar investment agreement which includes joint decision-making powers regarding future development. Yahey’s novel reasoning has significant implications for energy and resource development, treaty relations, and litigation across Canada. Similar claims have now been filed in Alberta, Saskatchewan, and Ontario, including Duncan’s First Nation seeking to apply Yahey’s reasoning in northwest Alberta. If courts across Canada adopt Yahey, land management decision-making could fundamentally change across much of the country.

Constraint strategies for estimating in-situ stress from borehole measurements

In this study, we describe strategies to reduce uncertainties in the estimation of in-situ stresses. The strategies are based on the commonly used poro-elastic model with strain corrections for in-situ stress estimation. In addition to the calibration of the minimum horizontal stress magnitudes from measurement data, we further constrain the magnitude of maximum horizontal stress quantitatively with (i) a critical stress state model, (ii) (non)-occurrences of breakout and/or drilling-induced fracture observed from image logs, and (iii) qualitatively with elliptical borehole shapes observed from multi-arm caliper logging data. The methodology is demonstrated using wells near Dawson Creek, Northeast British Columbia and Northwest Alberta, in Western Canada Sedimentary Basin (WCSB). The uncertainty of the estimated maximum horizontal stress magnitude was reduced and the range of the maximum horizontal stress was narrowed after the application of these constraint strategies. It is also observed that in the east of the study area, the in-situ stress regime is a normal fault stress regime. The presence of a normal fault stress regime is unexpected since a strike–slip fault stress regime is typically considered for the entire region. Yet, analysis of caliper data in two horizontal wells has confirmed its presence.

The impact of mountain pine beetle outbreaks and their treatment methods on the abundance of plant-foods important to caribou and grizzly bears

In Alberta, Canada, mountain pine beetle (MPB) infestations overlap with threatened caribou and grizzly bear ranges. While MPB is a natural part of the ecosystem, increased intensity of infestation due to fire suppression and a changing climate has required mitigating actions in the form of MPB control treatments, including accelerated forest harvesting, prescribed burns, and single-tree cut and burn. However, little is known on how MPB and MPB treatments affect understory shrub and forb forage taxa important to threatened caribou and grizzly bear populations. Using data collected in west-central and north-west Alberta, we investigated how the occurrence and abundance of 25 shrub and forb taxa varied among MPB kill, MPB treatments: single-tree cut and burn, harvesting, fire, and uncut forest strata. We determined that MPB kill and MPB treatments impacted 13 forage taxa preferred by threatened caribou and grizzly bear populations. These caribou and grizzly bear forage taxa generally had a positive response to MPB kill and single-tree cut and burn, a positive response to fire, or a positive response to MPB kill, single-tree cut and burn, and fire. Our results suggest that less-intensive MPB treatments like single-tree cut and burn might balance the threat of MPB against maintaining food resources and habitat for threatened species. As MPB continues to be a significant problem in Alberta and across the boreal forest, the results from our study, combined with ongoing assessments on the impact of MPB on wildlife species will provide essential information for evidence-based landscape management.

Effect of variable retention forestry on wood frogs (Lithobates sylvaticus) in early successional boreal mixedwood forests

Variable retention forest harvesting aims to reduce negative effects of harvesting on forest biodiversity, but knowledge gaps remain regarding its effects on some taxa over longer post-harvest time frames. To better understand effects of variable retention and environmental features on amphibians, we used pitfall traps to capture wood frogs ( Lithobates sylvaticus (LeConte, 1825)) across four levels of retention (clearcut (0%), 20%, 50%, and unharvested control (100%)), and two forest types (deciduous and coniferous), in 17-year post-harvest forests in northwest Alberta. We mapped breeding sites and used a LiDAR-based terrain moisture index (depth-to-water) to examine relationships between relative abundance, breeding site proximity, and soil moisture. Retention level alone had no effect on relative abundance of adult wood frogs, but in late summer (July and August), there was a significant interaction between retention level and forest type: capture rates decreased with retention level for deciduous forests, but increased with retention level in conifer forests. During late summer, capture rates were higher in conifer forests than deciduous forests, with soil moisture (lower depth-to-water) positively related to capture rates. Though timber retention may be beneficial to wood frogs in the short term, any impacts of forest harvesting on wood frog abundance were undetectable in stands 17 years post-harvest.

The dinosaur tracks of Tyrants Aisle: An Upper Cretaceous ichnofauna from Unit 4 of the Wapiti Formation (upper Campanian), Alberta, Canada.

The Wapiti Formation of northwest Alberta and northeast British Columbia, Canada, preserves an Upper Cretaceous terrestrial vertebrate fauna that is latitudinally situated between those documented further north in Alaska and those from southern Alberta and the contiguous U.S.A. Therefore, the Wapiti Formation is important for identifying broad patterns in vertebrate ecology, diversity, and distribution across Laramidia during the latest Cretaceous. Tracksites are especially useful as they provide a range of palaeoecological, palaeoenvironmental, and behavioural data that are complementary to the skeletal record. Here, we describe the Tyrants Aisle locality, the largest in-situ tracksite known from the Wapiti Formation. The site occurs in the lower part of Unit 4 of the formation (~72.5 Ma, upper Campanian), exposed along the southern bank of the Redwillow River. More than 100 tracks are documented across at least three distinct track-bearing layers, which were deposited on an alluvial floodplain. Hadrosaurid tracks are most abundant, and are referable to Hadrosauropodus based on track width exceeding track length, broad digits, and rounded or bilobed heel margins. We suggest the hadrosaurid trackmaker was Edmontosaurus regalis based on stratigraphic context. Tyrannosaurids, probable troodontids, possible ornithomimids, and possible azhdarchid pterosaurs represent minor but notable elements of the ichnofauna, as the latter is unknown from skeletal remains within the Wapiti Formation, and all others are poorly represented. Possible social behaviour is inferred for some of the hadrosaurid and small theropod-like trackmakers based on trackway alignment, suitable spacing and consistent preservation. On a broad taxonomic level (i.e., family or above), ichnofaunal compositions indicate that hadrosaurids were palaeoecologically dominant across Laramidia during the late Campanian within both high-and low-latitude deposits, although the role of depositional environment requires further testing.

Working Together for Grizzly Bears: A Collaborative Approach to Estimate Population Abundance in Northwest Alberta, Canada

Grizzly bears are a threatened species in Alberta, Canada, and their conservation and management is guided by a provincial recovery plan. While empirical abundance and densities estimates have been completed for much of the province, empirical data are lacking for the northwest region of Alberta, a 2.8 million hectare area called Bear Management Area 1 (BMA 1). In part, this is due to limited staff capacity and funding to cover a vast geographic area, and a boreal landscape that is difficult to navigate. Using a collaborative approach, a multi-stakeholder working group called the Northwest Grizzly Bear Team (NGBT) was established to represent land use and grizzly bear interests across BMA 1. Collectively, we identified our project objectives using a Theory of Change approach, to articulate our interests and needs, and develop common ground to ultimately leverage human, social, financial and policy resources to implement the project. This included establishing 254 non-invasive genetic hair corral sampling sites across BMA 1, and using spatially explicit capture-recapture models to estimate grizzly bear density. Our results are two-fold: first we describe the process of developing and then operating within a collaborative, multi-stakeholder governance arrangement, and demonstrate how our approach was key to both improving relationships across stakeholders but also delivering on our grizzly bear project objectives; and, secondly we present the first-ever grizzly bear population estimate for BMA 1, including identifying 16 individual bears and estimating density at 0.70 grizzly bears/1,000 km2-the lowest recorded density of an established grizzly bear population in Alberta. Our results are not only necessary for taking action on one of Alberta's iconic species at risk, but also demonstrate the value and power of collaboration to achieve a conservation goal.

Seismic line edge effects on plants, lichens and their environmental conditions in boreal peatlands of Northwest Alberta (Canada)

Boreal peatlands of Alberta (Canada) are heavily dissected by a large network of linear disturbances, including seismic lines used for Oil and Gas exploration. Edge effects resulting from these linear disturbances can increase their footprint and affect wildlife habitat, including the quality and quantity of plant and lichen forage. In 2012, seismic line restoration became a priority in Alberta, under the realm of restoration of habitat of threatened boreal woodland caribou. More accurate understanding of biotic and abiotic interactions leading to edge effects can be important in choosing appropriate restoration practices and prompting natural regeneration. We assessed the extent of edge effects of seismic lines on the adjacent boreal peatland near Peace River, northwestern Alberta. We compared plant and lichen community composition and environmental conditions on seismic lines and along 22 transects, which extended perpendicularly 75 m into the peatland from both lines edges. Soil moisture and light were higher on the lines, but frozen ground was less frequent than in the adjacent peatland. Seismic lines were also subsided by approximately 1.2 cm. Lichens were less abundant in the 2–25 m zone from the edge—indicating edge effects. On the lines,Sphagnumconstituted a nearly 100% cover while lichens, trees, herbs, and other bryophytes were less abundant than in the peatland. We demonstrate how knowledge of edge effects on plants and lichens could be applied in assessing caribou habitat quality based on forage availability and predation risk, and how such knowledge could inform restoration practices of seismic lines in peatlands.

Best of both worlds: hybrids of two commercially important pines (Pinus contorta × Pinus banksiana) combine increased growth potential and high drought tolerance

Over 18 million hectares of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) forests have been affected by a massive mountain pine beetle outbreak in western Canada. The ensuing need for reforestation compels forest managers to deploy more drought-resistant stock in anticipation of a hotter and drier future climate. Recent studies suggest that naturally occurring lodgepole pine × jack pine (Pinus banksiana Lamb.) hybrids may be more drought-resistant than pure lodgepole pine. We used single-nucleotide polymorphism markers to determine the level of jack pine introgression present in the region J lodgepole pine seed orchard, in northwest Alberta, and we identified six hybrid genotypes with 10%–18% jack pine introgression for further study. We compared the performance of open-pollinated seedlings of lodgepole, jack, and hybrid pines under well-watered and drought conditions in a greenhouse experiment. Seedlings were subjected to repeg ated drought cycles, withholding water for either 2 or 3 weeks. We found that hybrid pines grew significantly faster than lodgepole pine under well-watered conditions while retaining the high tolerance to prolonged drought exhibited by lodgepole pine seedlings, a particularly beneficial combination of traits during the critical stage of establishment. We therefore suggest the deployment of hybrid lodgepole pine as a strategy to promote adaptation to hotter and drier future climates.

Application of paleoporosity and bitumen saturation concepts to tight-gas accumulations containing solid bitumen

Solid bitumen significantly influences reservoir quality in many unconventional tight and shale hydrocarbon accumulations. In the siltstone-dominated Montney Formation of northeast British Columbia and northwest Alberta organic matter is mostly in the form of solid bitumen and represents an original pore-filling oil phase that was later thermally cracked. Here, we show that the influence of solid bitumen on reservoir quality can be further understood by applying the concepts of paleoporosity and bitumen saturation. Paleoporosity is defined as the sum of present-day porosity and total organic carbon (TOC) volume, and conceptualized as the porosity available at the time of oil charging. Bitumen saturation is defined as TOC volume divided by paleoporosity, and conceptualized as the fraction of paleoporosity filled with oil/bitumen. We introduce the paleoporosity-bitumen saturation cross-plot and use it, together with organic petrography and scanning electron microscopy observations, to investigate how different combinations of paleoporosity and bitumen saturation impact rock properties. Solid bitumen in the Montney Formation influences pore throat size, porosity, permeability and wettability. Understanding such key rock properties benefits from recognizing paleoporosity and bitumen saturation as inherent rock attributes with wide-ranging combinations. The concepts of paleoporosity and bitumen saturation elucidated here can likely be applied to other tight hydrocarbon accumulations that contain organic matter dominantly in the form of solid bitumen.

Temporal segregation among sympatric boreal predators

Mechanisms that decrease niche overlap, whether dietary, spatial, or temporal, are important in facilitating the coexistence of sympatric competitors. Since predators commonly partition resources via temporal segregation, we investigated whether it plays a significant role in mediating the coexistence of four common boreal predators: black bear (Ursus americanus), Canada lynx (Lynx canadensis), wolverine (Gulo gulo luscus), and fisher (Pekania pennanti). We examined their daily activity patterns at camera traps (19 sampling sites) in the boreal forest of northwest Alberta (2380 km2). Fishers were distinctly diurnal, while black bears, Canada lynx, and wolverines were cathemeral, resulting in high overlaps among the species (∆ = 0.62 to ∆ = 0.86). Fishers showed the lowest overlap with other species, while other pairs of species were relatively higher. Our results suggest that temporal partitioning plays a smaller role in the coexistence of these predators than anticipated, while revealing some interesting trends and suggesting other factors that may play a role in their niche segregation.

Spatial structure of boreal woodland caribou populations in northwest Canada

Local population units (LPUs) were delineated in Canada’s recovery strategy for threatened boreal woodland caribou (Rangifer tarandus caribou). Population viability analyses central to contemporary integrated risk assessments of LPUs implicitly assume geographic closure. Several LPUs in northwest Canada, however, were in part delineated by geopolitical boundaries and/or included large areas in the absence of evidence of more finely resolved population spatial structure. We pooled >1.2 million locations from >1200 GPS or VHF-collared caribou from northeast British Columbia, northwest Alberta and southwestern Northwest Territories. Bayesian cluster analysis generated 10 alternative candidate LPUs based on a spatial cluster graph of the extent of pairwise co-occurrence of collared caribou. Up to four groups may be artifacts in as yet under-sampled areas. Four were mapped LPUs that were conserved (Prophet, Parker, Chinchaga and Red Earth). One small group between Parker and Snake-Sahtaneh known locally as the “Fort Nelson core,” and outside any mapped LPU, was also conserved. Finally, one large group, at >136000 km2, spanned all three jurisdictions and subsumed all of six delineated LPUs (Maxhamish, Snake-Sahtaneh, Calendar, Bistcho, Yates, Caribou Mountains) and part of southern Northwest Territories. These results suggest less geographic closure of LPUs than those currently delineated, but further analyses will be required to better reconcile various sources of knowledge about local population structure in this region.

Can retention harvests help conserve wildlife? Evidence for vertebrates in the boreal forest

AbstractRetention harvesting, or the approach of leaving live mature trees behind during forest harvest, is used in natural disturbance‐based management to mitigate the effects of logging on biodiversity. However, responses of many boreal vertebrates to variable retention harvesting are unknown. We investigated the influence of different retention levels in forest harvests on stand use by wildlife 15–18 yr post‐harvest using a combination of surveys of wildlife signs (scats, middens) and camera trapping. Site‐level measures of forest structure, including canopy cover, horizontal cover, tree height, tree diameter, basal area, cover of downed coarse woody material, and understory plant cover, were used to describe post‐harvest differences in habitats used by common wildlife species in northwest Alberta's boreal forest. Stand use of six species (black bear, coyote, fisher, red squirrel, wolverine, woodland caribou) increased with level of retention, while stand use of two species (grouse, snowshoe hare) declined with retention level. Retention level did not significantly affect stand use of five species (American marten, Canada lynx, deer, gray wolf, moose). Higher levels of retention characterized by greater canopy cover, basal area, and abundance of deadwood were associated with use of forest habitats by late‐seral species. Woodland caribou, a species of conservation concern, was detected only in harvested stands with at least 20% retention. Greater understory and horizontal cover characterized lower levels of retention being attractive for early‐seral species. These findings demonstrate the value of retention harvesting for conservation of wildlife species in boreal forest, while highlighting the challenge of managing forests for multiple species with different habitat preferences.

Geoelectric structure of the Great Slave Lake shear zone in northwest Alberta: implications for structure and tectonic history

The study of ancient plate boundaries can provide insights into the past and present-day tectonic processes. Here, we describe a magnetotellurics (MT) study of the Precambrian basement of the Hay River Fault (HRF) in northwest Alberta, which is the southwest segment of the Great Slave Lake shear zone. New broadband MT data were collected to give a clearer image of the crustal structure. The Western Canada Sedimentary Basin was imaged as a low-resistivity layer above the resistive crystalline basement. Four basement conductors were defined, and correlate with the terrane boundaries delineated with aeromagnetic data. These are (1) a major conductor in the Kiskatinaw domain, (2) a conductor on the boundary of the Ksituan and Chinchaga domains, (3) a conductor on the boundary of the Chinchaga and Buffalo Head domains, and (4) a conductor near the HRF. Both (1) and (2) correspond to areas of high seismic reflectivity. The low resistivity can be explained by interconnected grain boundary graphite or sulfide phases deposited by metamorphic fluid migration. The HRF was not definitively located in previous studies. The new data show that the HRF could be thin (1 km) or wide (10 km) and located at the boundary of the contrasting aeromagnetic anomalies or further to the north. Various tectonic processes are proposed to interpret the possible locations of the HRF. No electrical anisotropy structure is required to interpret the MT data in this study.

Bryophyte abundance, diversity and composition after retention harvest in boreal mixedwood forest

Abstract Variable‐retention harvest is widely recognized as an alternative to more intensive methods such as clear‐cutting. However, present information is inadequate to judge the impact of variable retention on biodiversity of indigenous forest organisms intolerant of canopy removal, such as forest‐inhabiting bryophytes. We examined how bryophyte species cover, richness, diversity and composition change with time in response to a broad range of dispersed retention harvest treatments (2% [clear‐cut], 10%, 20%, 50%, 75% retention of original basal area) contrasted with uncut controls [100% retention]) in broadleaf deciduous, mixedwood and conifer‐dominated boreal forests in North West Alberta, Canada. Bryophytes were studied in 432 permanent sample plots within 72 compartments before harvest and at 3, 6 and 11 years after harvest. Clear‐cut and lower (10% and 20%) retention levels resulted in lower cover and richness of bryophytes than in unharvested control compartments in mixed and conifer‐dominated forests, but less so in deciduous‐dominated forests, which generally supported low cover and richness. Species composition in each forest type varied along the gradient of harvesting intensity; clear‐cuts and lower levels of retention supported similar composition, as did control plots and those representing higher retention levels. Over time, the retention harvest treatments became more similar to uncut controls. Synthesis and applications. Variable‐retention harvests can better maintain bryophyte biodiversity in managed boreal mixedwood forests, as compared to clear‐cuts. We found the efficacy of retention harvest scaled with harvest intensity. Higher levels of retention better moderated the negative impacts of harvesting on bryophyte assemblages across all forest types. Our results suggest, however, that even 10% retention will facilitate faster post‐harvest recovery of bryophytes, as compared to clear‐cutting.

Stratigraphy of the Middle Devonian Keg River and Prairie Evaporite formations, northeast Alberta, Canada

Stratigraphy of the Middle Devonian Keg River and Prairie Evaporite formations, northeast Alberta, Canada

Hot water flooding and cold water flooding in heavy oil reservoirs

ABSTRACTMurphy Oil’s Seal asset in the Peace River Oil Sands region in North West Alberta, Canada, has a remarkable capacity for implementation of Enhanced Oil Recovery (EOR) processes. Some wells in Seal have shown strong historical production due to excellent permeability and the foamy solution gas drive mechanism. The reservoir characteristics in this portion are highly variable where determining the most suitable EOR method is very challenging. Two of the potential EOR candidates which have been evaluated for this portion include conventional cold waterflooding and hot waterflooding. Results of EOR core analysis, logging, detailed seismic and petrophysical studies, and history-matched reservoir simulation and forecast indicate that cold waterflooding outperforms hot waterflooding. This is surprising as hot waterflooding is believed to outperform cold waterflooding in most medium heavy oil reservoirs.

Water Distribution in the Montney Tight Gas Play of the Western Canadian Sedimentary Basin: Significance for Resource Evaluation

SummaryWater distribution in unconventional gas reservoirs is a key parameter that influences many aspects of resource exploitation including selecting geographic areas for multiwell development programs, identifying target zones for horizontal wells, calculating reserves, estimating permeability, and understanding variability in gas and water production. Insights on water distribution in the Montney tight gas play of northeast British Columbia and northwest Alberta were gained by integrating reliable water-saturation measurements from full-diameter core samples with other core, well-log, and geologic data. Water distribution in the studied Montney section was found to be related to stratigraphic architecture and rock fabric (defined by degree of bioturbation), and is interpreted to have been influenced by the displacement efficiency of mobile formation water updip through tight Montney siltstones during hydrocarbon charging. Low-gradient clinoform units with few shaly zones in the Lower Montney section enabled efficient water displacement and led to water contents at or close to irreducible water saturation. Higher-gradient clinoform units with greater facies variation and common shaly zones in the Upper Montney allowed less-efficient water displacement, and significant volumes of mobile water were retained in parts of the section. Water saturation varies widely and directly influences gas effective permeability. A simple method for determining gas effective permeability from well logs was developed on the basis of empirical relationships derived from the core and log data set. Gas-effective permeability logs generated by this method help to identify target zones with superior reservoir quality for exploitation by use of horizontal multistage-fracturing technology. A Pickett plot with gas-effective-permeability lines was found to be a useful tool for a log-based comparison of Montney rock quality by stratigraphic zone or geographic area. This work shows that understanding water distribution and its influence on gas effective permeability leads to the improved delineation of "sweet spots" for resource development in unconventional gas plays.

A stratigraphic framework for Late Jurassic-Early Cretaceous gas-bearing strata (Monteith Formation) in the subsurface of northwest Alberta

Abstract The entire Late Jurassic–Early Cretaceous stratal package between the Fernie Formation and the Cadomin Formation, from Townships 62–74 in the subsurface of northwestern Alberta, is assigned to the Monteith Formation (Minnes Group). Three mappable units are present, informally termed Monteith A, B and C, from youngest to oldest. The Monteith C was deposited in a marginal marine–deltaic depositional setting. Upward, the transition to coastal plain (Monteith B) and fluvial (Monteith A) depositional settings records a continuous progradation of a long-lived depositional system. Mapping of these units is aided by identification of regionally extensive marine flooding surfaces in the Monteith C, which are used as stratigraphic datums. The thickness of the Monteith Formation decreases from 450 m in the southwestern portion of the study area to a zero-edge in the northeast. The Monteith A, B and C are up to 160 m, 100 m and 200 m thick, respectively. Depositional thinning to the northeast is prevalent, but the primary reason for gross stratal thinning is substantial incision associated with the overlying sub-Cadomin unconformity. The Monteith Formation in Alberta was deposited in a foredeep setting. Regional thickness trends suggest increased accommodation to the southwest and the strata are interpreted to have accumulated on the cratonward side of the foredeep axis. These observations, as well as evidence for basin axial channel flow to the northwest during deposition of the Monteith C, support an interpretation that the foreland basin had initiated prior to Monteith Formation deposition. Basin physiography, as well as uplift and denudation of the Cordillera, affected the depositional evolution of units in the study area. Ultimately, these factors strongly influenced the distribution of reservoir rocks (primarily sandstones of the Monteith A and C), which are part of the Deep Basin Gas System. The presence or absence of permeability enhancing fractures also impacts reservoir quality and well deliverability in the Monteith Formation.

Geologist-controlled trends versus computer-controlled trends: introducing a high-resolution approach to subsurface structural mapping using well-log data, trend surface analysis, and geospatial analysisA companion paper to Mei, S. 2009. New insights on faults in the Peace River Arch region, northwest Alberta, based on existing well-log data and refined trend surface analysis. Canadian Journal of Earth Sciences, 46(1): 41–65.

This paper introduces a refined trend surface analysis (TSA) for detecting faults with small, metre-scale offsets (5–20 m). Conventional TSA uses a global polynomial method to model the trend; the power of the polynomial (e.g., first, second, or third order) is the only parameter for input. The refined approach is different in that it uses local-fit techniques to generate the trend. The refined approach provides greater flexibility for inputting geological knowledge in the trend surface modelling process. This results in a trend surface with the maximum amount of unwanted information, which is removed from the residual surface after removal of the trend from the data, leaving features of interest optimally highlighted in the residuals. Such a trend is referred to as a geologist-controlled trend to differentiate it from the trend surface modelled by conventional TSA, which is primarily a computer-controlled global polynomial surface. The refined approach goes one step beyond conventional TSA by incorporating advanced geostatistics for modelling the trend, interpolating the resultant residuals, and then extracting formation-top offset patterns from the residual surface using spatial analysis. Modelling the geologist-controlled trend in the refined approach results in higher resolution in detecting formation-top offsets and higher accuracy in digitizing fault locations, compared with various techniques that have been traditionally used in subsurface structure mapping of the West Canada Sedimentary Basin (WCSB) (e.g., structural and isopach contour mapping, cross-section construction, and seismic and aeromagnetic data interpretation). The refined approach is demonstrated using the Basal Fish Scale Zone in the Peace River Arch region as an example.