Swan Hills Formation Research Articles

Reservoir evaluation of dolomitized Devonian strata in the Western Canada Sedimentary Basin: implications for carbon capture, utilization, and storage

Abstract Differentially dolomitized carbonate strata in the Western Canada Sedimentary Basin (WCSB) are increasingly targeted for carbon capture, utilization, and storage (CCUS), yet few studies have evaluated the petrophysical characteristics of these conventional hydrocarbon reservoirs for this purpose. To address this, this study uses drill-core analysis (sedimentology, diagenesis, pore morphology, and distribution), together with core-plug and production data, to evaluate the properties of five depleted oil and gas fields in the Middle to Upper Devonian Swan Hills Formation, Leduc Formation and Wabamun Group. The Swan Hills and Leduc formations are composed of reef, shoal, and lagoon deposits that are predominantly fossil-rich (e.g., stromatoporoid-dominated rudstones and boundstones). In contrast, the carbonate-ramp deposits of the Wabamun Group are fossil-poor, consisting instead of variably bioturbated carbonate mudstones, wackestones, and packstones. Replacement dolomitization is variable throughout each stratigraphic unit, but generally occurs within fossil-rich and/or heavily bioturbated intervals. Fracture densities are broadly comparable in limestone and dolostone. Porosity in the Swan Hills and Leduc formations is predominantly moldic and vuggy, occurring where fossils (e.g., stromatoporoids) are partially or fully dissolved. Pore space in the Wabamun Group is mostly restricted to intercrystalline porosity in burrows. In general, burial cements (e.g., calcite and dolomite) are volumetrically insignificant and only partially fill pores. Exceptions to this include porosity-occluding cements associated with fractures and breccias in the vicinity of faults. Dolomitization and depositional facies are found to exert a strong control on pore morphology, distribution, and interconnectivity. Porosity is principally controlled by the relative abundance of skeletal grains and by the presence of burrows. These highly porous facies acted as fluid pathways during burial diagenesis, resulting in their preferential dolomitization, solution enhancement of pre-existing pores, and creation of volume reduction-related porosity. The high CO2 storage capacity and low unplanned plume migration risk (due to depositional and/or diagenetic baffles) of dolomitized reefal reservoirs (e.g., Swan Hills and Leduc formations) make them more attractive targets for CCUS than those with limited capacity and/or potential migration pathways (e.g., fault-related fractures and breccias in the Wabamun Group). These results demonstrate that drill-core analysis, in combination with legacy data, can provide valuable insights into the factors that control reservoir CO2 injectivity, plume migration, and storage capacity.

Burial dolomitization driven by modified seawater and basal aquifer‐sourced brines: Insights from the Middle and Upper Devonian of the Western Canadian Sedimentary Basin

AbstractDolomitization in the Western Canadian Sedimentary Basin has been extensively researched, producing vast geochemical datasets. This provides a unique opportunity to assess the regional sources and flux of dolomitizing fluids on a larger scale than previous studies. A meta‐analysis was conducted on stable isotope, strontium isotope (87Sr/86Sr), fluid inclusion and lithium‐rich formation water data published over 30 years, with new petrographic, X‐ray diffraction, stable isotope and rare‐earth element (REE+Y) data. The Middle to Upper Devonian Swan Hills Formation, Leduc Formation and Wabamun Group contain replacement dolomite (RD) cross‐cut by stylolites, suggesting replacement dolomitization occurred during shallow burial. Stable isotope, REE+Y and 87Sr/86Sr data indicate RD formed from Devonian seawater, then recrystallized during burial. Apart from the Wabamun Group of the Peace River Arch (PRA), saddle dolomite cement (SDC) is more δ18O(PDB) depleted than RD, and cross‐cuts stylolites, suggesting precipitation during deep burial. SDC 87Sr/86Sr data indicate contributions from 87Sr‐rich basinal brines in the West Shale Basin (WSB) and PRA, and authigenic quartz/albite suggests basinal brines interacted with underlying clastic aquifers before ascending faults into carbonate strata. The absence of quartz/albite within dolomites of the East Shale Basin (ESB) suggests dolomitizing fluids only interacted with carbonate strata. We conclude that replacement dolomitization resulted from connate Devonian seawater circulating through aquifers and faults during shallow burial. SDC precipitated during deep burial from basinal brines sourced from basal carbonates (ESB) and clastic aquifers (WSB, PRA). Lithium‐rich formation waters suggest basinal brines originated as residual evapo‐concentrated Middle Devonian seawater that interacted with basal aquifers and ascended faults during the Antler and Laramide Orogenies. These results corroborate those of previous studies but are verified by new integrated analysis of multiple datasets. New insights emphasize the importance of basal aquifers and residual evapo‐concentrated seawater in dolomitization, which is potentially applicable to other regionally dolomitized basins.

A preliminary statistical model for hydraulic fracture‐induced seismicity in the Western Canada Sedimentary Basin

AbstractWe characterize the statistical relationship between hydraulic fracturing and seismicity in western Canada by using the concept of cellular seismicity. We determine the regionally averaged probability that hydraulic fracture operations will be associated with M ≥ 3 seismicity within a 10 km grid cell. This rate is 0.01 to 0.026 at the 95th percentile confidence limit. Monte Carlo simulations confirm that the observed correlations are extremely unlikely (≪1%) to have been obtained by chance. Proximity to a disposal well and proximity to the Swan Hills Formation, which has been suggested as a proxy for basement controlled faults, appear to increase the likelihood that hydraulic fracturing will trigger seismicity.

Evolution of Li-enriched oilfield brines in Devonian carbonates of the south-central Alberta Basin, Canada

There is a long and extensive history of study regarding the origins and characteristics of brines within the Alberta Basin of Canada. This study focuses on the origins of Li-enriched (>50 mg/kg) brines of the late Devonian Swan Hills, Nisku and Leduc Formations of the southwestern Alberta Basin. Available data show that two Li-enriched brines having distinctly different geochemical characteristics, and thus distinct evolutionary histories, exist within the late Devonian carbonates of the southwestern Alberta Basin. Li-enriched brine of the Swan Hills Formation appears to have been formed by dissolution of halite and mixing with Li-enriched fluids expelled from Precambrian crystalline basement. The degree of mixing between Swan Hills brines and meteoric water is unknown. Formation of Li-enriched brines in the Nisku and Leduc Formations could be explained by preferential dissolution of Li-enriched late-stage evaporite minerals, likely from the middle Devonian Prairie Evaporite Formation, into evapoconcentrated late Devonian seawater. Dense Li-enriched brine migrated downward into the underlying early Devonian Winnipegosis Formation and then westward in response to westward tilting beginning in Jurassic time. Li-enriched brine was then diluted by mixing with meteoric water driven into the Devonian of the southwestern Alberta Basin in response to hydraulic gradients created by the effects of Laramide tectonics.

Palaeosols and palaeokarst beneath subaerial unconformities in an Upper Devonian isolated reef complex (Judy Creek), Swan Hills Formation, west‐central Alberta, Canada

AbstractSubaerial unconformities are used widely for palaeoenvironmental and palaeogeographic reconstructions, sequence stratigraphy and petroleum reservoir assessments. Recognition and interpretation of these unconformities, particularly those with associated palaeosols, may be problematic in Lower and Middle Palaeozoic carbonate successions because of the collective effect of limited land plant development, superficial similarities between some pedogenic and marine features, and overprinting by later diagenesis. The isolated Judy Creek reef complex in the Lower Frasnian Swan Hills Formation in west‐central Alberta, Canada, contains two subaerial unconformities, R0.5 and R4, which formed as a consequence of relative sea‐level falls of at least regional scale. Deposits beneath these unconformities have distinctive palaeosol and palaeokarst features. The lower unconformity, R0.5, occurs at the top of a progradational reefal phase of stromatoporoid rudstones–floatstones and peloidal packstones–grainstones and has been recognized in at least one other isolated Swan Hills reef complex (Snipe Lake). Palaeosol–palaeokarst profiles beneath this unconformity extend as deep as ca 2 m below the unconformity. These profiles are characterized by the presence of small rhizoliths, laminar calcretes, ferroan dolomite glaebules, desiccation cracks, breccias, green shale and solution vugs. The upper unconformity, R4, occurs at the top of a backstepping phase of reef growth and has been correlated widely between isolated reefs and carbonate banks on both the western and eastern shelves of the Central Alberta Basin. Palaeosol–palaeokarst profiles, extending as deep as ca 9·5 m beneath the R4 unconformity, are distinguished by abundant, sub‐horizontal desiccation cracks filled with green shale, occurring in peloidal wackestones–packstones. Comparison of the R0.5 and R4 profiles indicates that the major intrinsic controls on the development and modification of the profiles are parent‐material lithology, particularly the prior degree of induration and particle size; the low topographic relief at the top of the reef interior; and limited vegetation of the exposed reef top due to unfavourable growth conditions and geographic isolation. In addition to climate, the major extrinsic controls are the extent of relative sea‐level fall, estimated to be 2·5 to 3 m and 13 to 14 m associated with the R0.5 and R4 unconformities, respectively, and the degree of shoreface erosion during the ensuing marine transgression, estimated to be up to 3 m. This study highlights the complex interplay of mainly physical and chemical processes influencing the formation of subaerial unconformities in carbonate environments during the Devonian, before major evolutionary innovations among vascular land plants led to more intense pedogenesis.

Depositional facies analysis and modeling of the Judy Creek reef complex of the Upper Devonian Swan Hills, Alberta, Canada

Judy Creek, located in west-central Alberta, is one of the largest reservoirs in the Swan Hills oil field. Judy Creek is an isolated reef complex of the Upper Devonian Swan Hills Formation. This mature field has about 350 wells drilled and nearly 6000 m (19,685 ft) of cores and thus provides a good database for depositional facies analysis and testing methods for integrating descriptive and quantitative data in facies modeling. General depositional facies and sequence stratigraphy of Judy Creek have been studied quite extensively. However, no three-dimensional numeric facies model has been built to guide the field development. One of the objectives in constructing such a model for this study was to establish a close linkage between the facies depositional analysis and modeling. As a matter of fact, there have been significant disconnects between descriptive analysis and numeric modeling in the exploration and production. Depositional facies analysis has focused on conceptual understanding for prospect generation and reservoir delineation, whereas facies modeling has emphasized data mining for field development. In this study, a method that integrates the spatial propensity from the depositional conceptual models and facies data from the wells is used to bridge the gap between the depositional analysis and stochastic modeling. Such integration has proven to be critical in building realistic subsurface models in Judy Creek because it helped improve the estimation of subsurface resources.

A case for renewed development of a mature gas field: the Devonian Swan Hills Formation at Kaybob South field, Alberta, Canada

Abstract In 1961 approximately 104,772 × 106m3 (3.7 trillion ft3) of in-place sour gas resources were discovered within the Late Devonian Swan Hills Formation (Beaverhill Lake A pool) at Kaybob South field of west-central Alberta. Production at Kaybob South is managed as three operational units (Gas Units #s 1, 2 and 3) and commenced in 1968 at Gas Unit #1 with the secondary recovery of natural gas liquids and condensate from produced gas and re-injection of by-product lean sweet gas. Liquid and gas production through this process of gas cycling continued at Gas Unit #1 until 1983, after which gas was harvested through pressure depletion. Cumulative gas production to date at Gas Unit #1 suggests that only 47–56 percent of the in-place gas will be ultimately captured by the remaining productive wells. This relatively low recovery is attributed to wellbore mechanical failure resulting from corrosive formation fluids, and both wellbore and reservoir permeability loss caused by the precipitation of hydrocarbon liquids and various mineral precipitants. Work presented in this study suggests that the drilling of 17 infill development wells may capture between 1,183 × 106m3 (42 bcf) and 5,192 × 106m3 (183 bcf) of by-passed gas resources. These reserve additions, combined with the 651 × 106m3 (23 bcf) reserves that are anticipated to be recovered by the current producing wells in their remaining well life, will increase the ultimate recovery at Gas Unit # 1 to 63–77 percent of OGIP. This recovery factor is comparable to analogous Swan Hills Formation gas pools within the region. The Swan Hills Formation at Gas Unit #1 accumulated as a platform margin succession of shallow marine carbonates that are partitioned into five high-frequency depositional sequences (HFS-2 through HFS-6). HFS-2 through −4 are characterized by an aggradational to slightly retrogradational stacking pattern, whereas HFS-5 and −6 are stacked in a more strongly retrogradational fashion. The priority assigned to future development wells should take into account the geologic attributes that influence well performance. The best reservoir quality and production performance is associated with dolomitized reef margin and stromatoporoid shoal facies associations. Due to pervasive fracturing, sequence boundaries and associated facies distributions are not thought to compartmentalize flow units. Future development wells may be ranked according to their likelihood of favourable well performance by considering their location relative to the predicted distributions of dominant facies, structural position, gas-saturated pore-volume thickness, Kmax permeability, fracture density, and proximity to currently producing wells. Following assessment of all prospective development wells, three prospects were successfully drilled during the 4th-quarter of 2006 and 2007 and serve as an independent test that strengthens the geologic interpretation and confirms the existence of significant bypassed gas resources that may be captured through infill development.

Phase Behaviour and Compositional Changes Associated With Residual Oxygen in a Miscible CO/Light Oil Reservoir

Abstract Concern about the effects of global greenhouse gases has made people aware of the need to reduce the atmospheric concentration of industrial waste gas. Alberta, as the centre of Canada's petroleum industry, is strongly impacted by the politics of greenhouse gases. One way Alberta can achieve the goals of the Kyoto Protocol is to capture CO2 from stack gases and to inject it into oil reservoirs to enhance recovery while sequestering at least a portion of the CO2. This paper will concentrate on oil from the Swan Hills Formation reservoir operated by Devon Oil Corporation. The phase behaviour of different concentrations of CO2/O2 mixtures injected into the Swan Hills reservoir was investigated. Two PVT (Pressure-Volume-Temperature) apparatus were used to visually observe phases and to determine bubble points and swelling of the oil rich phase. The PVT measurements were performed to develop a basic understanding of the phase behaviour for the CO2 / O2 /oil system. The composition of oxidized oil was predicted using a previously developed low temperature oxidation model coupled with phase equilibrium calculations. Introduction Carbon dioxide flooding is a well established enhanced oil recovery process in regions where CO2 is available. Canada has been slow to implement CO2 floods due to the lack of natural sources. However, the public's concern with greenhouse gas emissions and Canada's support for the Kyoto Protocol provide sufficient environmental incentives to allow for the application of CO2 floodingas a combined EOR/sequestration process. Capturing the CO2 from stack gas is an expensive process and the actual cost will depend on the purity of the CO2 stream that is required. Oxygen is an important factor as its impurity can modify the native oil properties through low temperature oxidation reactions, promotion of corrosion in the injection and production piping and alter the phase behaviour of the reservoir fluids. The study described in this paper will examine how oxygen is consumed in the reservoir, and it will concentrate on the impact of oxidation reactions with regard to the composition and emulsification characteristics of the oil. Lee(1) studied the phase behaviour and displacement efficiency of a carbon dioxide-hydrocarbon system which consisted of various mixtures of n-pentane/n-hexane. The results demonstrated that multiple phase behaviour involving two liquids with and without a vapour phase occurred during carbon dioxide injection in low temperature reservoirs. A number of studies on the effectiveness of carbon dioxide displacement under miscible and immiscible conditions have been reported by Wilburn et al.(2), Dyer et al.(3), Srivastava and Huang(4, 5) and Srivastava et.al.(6). The results showed that CO2 /oil miscibility could be developed and that the swelling behaviour depended on the chemical composition of the oil. Wilburn et al.(2) also found that miscibility is strongly dependent on the volatility or boiling point distribution of the oil. Dyer et al.(3) investigated the phase behaviour of typical Saskatchewan heavy oils with carbon dioxide. Their study was divided into two categories: stock tank oil and reservoir oil, which were mixed with CO2 in different ratios. Parameters studied included viscosity, density, swelling factor and gas-oil ratio (GOR).

Origin of molds in dolostones formed by the dissolution of calcitic grains: Evidence from the Swan Hills Formation in west-central Alberta and other Devonian formations in Alberta and northeastern British Columbia

Abstract Molds or partial-molds formed by the dissolution of calcitic grains selectively occur in dolostones and are virtually ubiquitous in Phanerozoic strata throughout the world. The preferential position of partial-molds the centre of originally calcitic grains in pure dolostones is direct evidence of mineralogically controlled dissolution of calcite either during or following dolomitization. Furthermore, the selective occurrence of these calcitic grain partial-molds or molds in dolostones rather than in limestones or partially dolomitized limestones and their occurrence in the middle of thick dolostone successions provides good evidence to support the interpretation that the dissolution of calcitic grains to form these pores occurred both as part of and during the dolomitization process. Investigation of pores within the zone of transition from limestone to dolostone in a core (well 10-3-61-24 W5) from the Swan Hills Formation of west-central Alberta links the evolution of micro-pores of leached origin in undolomitized portions of stromatoporoids in partially dolomitized limestones to the origin of macro partial-molds in pure dolostones. In the zone of transition from limestone to dolostone, micro-pores of leached origin in the undolomitized walls of stromatoporoids increase in abundance, with the advancing degree of dolomitization, toward the pure dolostone. In the transition between extensively dolomitized limestone and pure dolostone, both the undolomitized walls of the stromatoporoids and chamber-filling equant calcite cements are extensively dissolved, producing a near partial-mold. In the pure dolostone, the undolomitized walls of stromatoporoids and chamber-filling equant calcite cements are completely dissolved, creating macro partial-molds. I interpret this distribution of porosity and pore types to be a snapshot of that immediately following the dolomitization process. Because dolomite replacement occurred as a dolomite front advanced through time, it is reasonable to assume that a similar distribution of porosity and pore types existed at earlier phases of dolomitization, when the pure dolostone bodies were significantly smaller. From this, I conclude that macro-moldic pores in pure dolostones formed by the formation and coalescence of micro-pores of leached origin along the peripheral halo of a migrating dolomite front. Dissolution of calcite is interpreted to have occurred throughout the duration of the dolomitization process, with increasing degrees in any given position as the dolomite front advanced through. Speculative models to account for the dissolution of calcite during dolomitization are offered.

Fault and conduit controlled burial dolomitization of the Devonian west-central Alberta Deep Basin

Abstract Devonian reservoirs in the Swan Hills, Leduc and Wabamun formations in the west-central Alberta deep basin occur at present day depths of 3000 m to 3600 m and are generally restricted to dolomitized strata. Pervasive dolomite occurs; 1) along bank margins (Kaybob South Field and Fox Creek Field) of the Swan Hills Formation; 2) in the Leduc Formation rimmed reefs (Pine Creek and Pine Creek Northwest fields) and; 3) in the Wabamun Formation above the up dip edge of the Pine Creek Leduc Field. Dolomites have variable crystal size (50 to 800 μm) and morphology (planar euhedal rhombs to non-planar anhedral). Type I dolomite (< 5% of all dolomite) is a fine-grained (planar subhedral–euhedral) dolomite that overlaps with low amplitude stylolites and is prevalent as a burrow replacement at the Wabamun Pine Creek Field. Type II pervasive dolomite that postdates low amplitude stylolites is a medium to coarse-grained (non-planar, subhedral–anhedral) dolomite that occurs as the predominant replacement of matrix and fossils in all the fields. The pervasive replacement dolomite Type II has low δ18O values of −7.9 to −3.6‰ (relative to PDB) and low to moderate Sr ratios (87Sr/86Sr of 0.7083 to 0.7118). Wabamun Fm Type I dolomite of burrow mottled intervals (Type IA), have depleted δ18O (−8.78 to −9.77 ‰, mean −9.15 ‰) and moderately radiogenic 87Sr/86Sr signatures (0.7095). Type I dolomite from pervasive dolomite intervals (Type IB), have less depleted δ18O (−3.86 to −7.34 ‰ PDB, mean −5.67 ‰) and moderate 87Sr/86Sr signatures (0.7099). Although there is a wide spread in oxygen isotope values, estimated temperatures of Type II dolomite formation range from 45 to 75°C, equivalent to burial depths of 700–1500 m. Samples with 87Sr/86Sr ranging from Devonian sea water values to more radiogenic (0.7093 to 0.7118), indicate that pore waters were modified by water-rock reactions during burial and dolomitization. Type IA dolomites may have undergone neomorphism during burial at high temperatures. Type IB dolomites may have been altered from fluids that precipitated the Type II dolomites, or formed from fluids that precipitated the Type II dolomite. Seismic evidence, detailed log marker correlation and fractured and brecciated dolomite occurrences indicate that fault-controlled conduits may have controlled local and restricted dolomite occurrences in the Swan Hills and the middle Wabamun Fm. Widespread dolomite in the Leduc level indicates that porous Leduc dolomites may also have been connected via the underlying dolomitized part of the Lower Leduc platform, forming a basin-wide conduit system. Basin fluid flow could have been initiated by tectonically stacked thrust sheets and sedimentary loading by a clastic wedge causing mechanical compaction that squeezed the fluids out of the still compactable basin sediments. This may have occurred during two orogenies, the Late-Devonian to Early-Carboniferous Antler Orogeny, and the Late-Jurassic to Early-Tertiary Columbian/Laramide Orogeny. Presumably, the basin fluids flowed laterally updip along the conduit systems and vertically up fault systems until they reached stratigraphic conduits along the eastern flank of the Alberta Basin.

Facies control on dolomitization and porosity in the Devonian Swan Hills Formation in the Rosevear area, west-central Alberta

ABSTRACT Cores from Rosevear Field and surrounding areas were studied to determine controls on reservoir porosity and hydrocarbon distribution in the Swan Hills Formation (Middle to Late Devonian; Givetian to Frasnian) in west-central Alberta. Most reservoir porosity (3-15%) in the Rosevear area is in dolomites of the middle Swan Hills Formation. Dolomitization was facies-controlled, occurring mainly in peloid-bioclast and Amphipora-peloid grainstones. Porous dolomitized grainstones at Rosevear accumulated along the rims of a trough initiated by structural downwarp during Swan Hills time. The depositional trough is recognized by the distribution of facies as well as a 20 m thickening of the Swan Hills Formation within and on the flanks of the trough. Porous dolomitized grainstones also occur along the middle Swan Hills shelf margin. Lime mud-rich shelf-interior limestones and lime mud-rich slope to basinal limestones are generally not porous. Previously published geochemical and petrographic data suggest that most dolomite precipitated at relatively high temperatures during moderate to deep burial. The geochemical signature and stratigraphic distribution of dolomite may have been produced by (1) pervasive recrystallization of an early facies-controlled dolomite, or (2) dolomitizing fluids moving laterally and preferentially through porous shelf-margin and trough-margin grainstones after substantial burial. The geometry of the Swan Hills dolomite is critical for the stratigraphic trapping of gas. In Rosevear's southwestern pool, porous dolomitized grainstones pinch out updip (to the northeast) into nonporous slope to basinal limestones of the trough. In the northeastern pool, porous dolomitized grainstones pinch out updip (to the northeast) into nonporous shelf interior limestones. The gas-water contacts at Rosevear are at elevations that approximate the spill-point of Rosevear dolomites into a porous shelf margin dolomite trend. Many wells south and west of Rosevear have porous dolomite filled with water. The Rosevear dolomite bodies have enough of a north-south orientation to trap gas migrating from the south along the shelf margin. RESUME Des carottes provenant du champ de Rosevear et des regions environnantes ont ete etudiees pour determiner les controles regissant la porosite de reservoir et la distribution des hydrocarbures dans la Formation de Swan Hills (Devonien moyen a superieur, Givetien a Frasnien) dans le centre-ouest de l'Alberta. La plupart de la porosite de reservoir (3-15%) dans la region de Rosevear est dans des dolomies de la Formation de Swan Hills moyen. La dolomitisation a ete controlee par les facies, se presentant surtout dans les grainstones a bioclastes-peloides et a Amphipora-peloides. Les grainstones poreux dolomitises de Rosevear se sont accumules le long des marges diune fosse initiee par l'affaissement structural durant la periode Swan Hills. La fosse de sedimentation est reconnaissable par la distribution des facies et un epaississement de 20 m de la Formation de Swan Hills a l'interieur et sur les flancs de la fosse. Les grainstones dolomitiques poreux se presentent aussi le long de la marge de la plate-forme de Swan Hills moyen. Les calcaires riches en boue calcareuse de l'interieur de la plate-forme et les calcaires riches en boue calcareuse de la pente et de bassin sont generalement non-poreux. Les donnees geochimiques et petrographiques publiees precedemment suggerent que la plupart de la dolomite se soit precipitee a des temperatures relativement elevees durant un enfouissement modere a profond. La signature geochimique et la distribution stratigraphique de la dolomite ont possiblement ete produites par: (1) une recristallisation intense d'une dolomite precoce controlee par les facies, ou (2) les fluides dolomitisants se sont deplaces lateralement et preferentiellement a travers les grainstones de marge de plate-forme poreuse et de marge de fosse apres un enfouissement substantiel. La geometrie de la dolomie de Swan Hills est critique pour le piegeage du gaz. Dans le reservoir du sud-ouest de Rosevear, les grainstones dolomitises poreux se biseautent en amont-pendage (vers le nord-est) pour passer a des calcaires non-poreux de pente a bassin de fosse. Dans le reservoir du nord-est, les grainstones dolomitises poreux se End_Page 458------------------------ biseautent en amont-pendage (vers le nord-est) en calcaires non-poreux d'interieur de plate-forme. Les contacts gaz-eau a Rosevear sont a des elevations qui sont approximativement a la hauteur du point de debordement des dolomies de Rosevear dans un axe de dolomies poreuses de marge de plate-forme. Plusieurs puits au sud et a l'ouest de Rosevear ont des dolomies poreuses remplies d'eau. Les corps de dolomie de Rosevear ont une orientation suffisamment nord-sud pour pieger du gaz qui migre a partir du sud le long de la marge de la plate-forme. Traduit par Lynn Gagnon

Fault‐controlled dolomitization at Swan Hills Simonette oil field (Devonian), deep basin west‐central Alberta, Canada

The partly dolomitized Swan Hills Formation (Middle‐Upper Devonian) in the Simonette oil field of west‐central Alberta underwent a complex diagenetic history, which occurred in environments ranging from near surface to deep (&gt;2500 m) burial. Five petrographically and geochemically distinct dolomites that include both cementing and replacive varieties post‐date stylolites in limestones (depths &gt;500 m). These include early planar varieties and later saddle dolomites. Fluid inclusion data from saddle dolomite cements (Th=137–190 °C) suggest that some precipitated at burial temperatures higher than the temperatures indicated by reflectance data (Tpeak=160 °C). Thus, at least some dolomitizing fluids were ‘hydrothermal’. Fluorescence microscopy identified three populations of primary hydrocarbon‐bearing fluid inclusions and confirms that saddle dolomitization overlapped with Upper Cretaceous oil migration. The source of early dolomitizing fluids probably was Devonian or Mississippian seawater that was mixed with a more 87Sr‐rich fluid. Fabric‐destructive and fabric‐preserving dolostones are over 35 m thick in the Swan Hills buildup and basal platform adjacent to faults, thinning to less than 10 cm thick in the buildup between 5 and 8 km away from the faults. This ‘plume‐like’ geometry suggests that early and late dolomitization events were fault controlled. Late diagenetic fluids were, in part, derived from the crystalline basement or Palaeozoic siliciclastic aquifers, based on 87Sr/86Sr values up to 0·7370 from saddle dolomite, calcite and sphalerite cements, and 206Pb/204Pb of 22·86 from galena samples. Flow of dolomitizing and mineralizing fluids occurred during burial greater than 500 m, both vertically along reactivated faults and laterally in the buildup along units that retained primary and/or secondary porosity.

Devonian hydrocarbon source rocks and their derived oils in the Western Canada Sedimentary Basin

Research Article| March 01, 2001 Devonian hydrocarbon source rocks and their derived oils in the Western Canada Sedimentary Basin* Martin G. Fowler; Martin G. Fowler Geological Survey of Canada, 3303 - 33 Street NW, Calgary, AB, T2L 2A7 Search for other works by this author on: GSW Google Scholar Lavern D. Stasiuk; Lavern D. Stasiuk Geological Survey of Canada, 3303 - 33 Street NW, Calgary, AB, T2L 2A7 Search for other works by this author on: GSW Google Scholar Mark Hearn; Mark Hearn Shell Canada Ltd., 400 - 4 Avenue SW, Calgary, AB, T2P 2H5 Search for other works by this author on: GSW Google Scholar Mark Obermajer Mark Obermajer Geological Survey of Canada, 3303 - 33 Street NW, Calgary, AB, T2L 2A7 Search for other works by this author on: GSW Google Scholar Author and Article Information Martin G. Fowler Geological Survey of Canada, 3303 - 33 Street NW, Calgary, AB, T2L 2A7 Lavern D. Stasiuk Geological Survey of Canada, 3303 - 33 Street NW, Calgary, AB, T2L 2A7 Mark Hearn Shell Canada Ltd., 400 - 4 Avenue SW, Calgary, AB, T2P 2H5 Mark Obermajer Geological Survey of Canada, 3303 - 33 Street NW, Calgary, AB, T2L 2A7 Publisher: Canadian Society of Petroleum Geologists Received: 12 Sep 2000 Accepted: 16 Nov 2000 First Online: 02 Mar 2017 Online ISSN: 2368-0261 Print ISSN: 0007-4802 © The Society of Canadian Petroleum Geologists Bulletin of Canadian Petroleum Geology (2001) 49 (1): 117–148. https://doi.org/10.2113/49.1.117 Article history Received: 12 Sep 2000 Accepted: 16 Nov 2000 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Martin G. Fowler, Lavern D. Stasiuk, Mark Hearn, Mark Obermajer; Devonian hydrocarbon source rocks and their derived oils in the Western Canada Sedimentary Basin. Bulletin of Canadian Petroleum Geology 2001;; 49 (1): 117–148. doi: https://doi.org/10.2113/49.1.117 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract Devonian strata within the Western Canada Sedimentary Basin contain large reserves of oil and gas. These vast hydrocarbon reserves can be largely attributed to the occurrence of abundant mature, excellent to good quality Devonian source rocks. The Middle Devonian Elk Point Group contains several units with hydrocarbon potential including the Evie Formation in British Columbia, the Keg River Formation in northern Alberta, and the Winnipegosis Formation in east-central Alberta and southern Saskatchewan. Many of these are proven source rocks of oils occurring in Middle Devonian reservoirs. Elk Point Group potential source rocks contain a wide variety of organic matter types reflecting the diversity of their depositional environments. No hydrocarbons have been definitively linked to a Beaverhill Lake Group source rock but it is possible that such a unit is the source of Slave Point Formation reservoired oils in northwest Alberta. The Late Devonian Woodbend Group contains the Duvernay Formation, the most prolific Devonian source rock in the Alberta Basin. It is characterized by marine Type II/I organic matter with TOC contents up to 15% in immature samples and is the source of most oils in the Bashaw Reef Complex, the Rimbey-Meadowbrook Reef Trend, and in the Swan Hills Formation in Alberta. The stratigraphically equivalent Muskwa Formation in northern Alberta has a much lower hydrocarbon potential than the Duvernay Formation. Oils have been correlated to Winterburn Group source rocks within the Nisku Formation of east-central Alberta, Camrose Member/Nisku Formation of southern Alberta, and the time-equivalent Birdbear Formation of southeast Saskatchewan. Winterburn Group potential source rocks in central to southern Alberta can have high TOC contents (up to 15%) and contain Type I and Type II organic matter deposited in open marine to lagoonal palaeoenvironments. The Cynthia Member shale of the Nisku Formation in west-central Alberta, previously thought by some workers to be a source rock, is actually organic-lean. The underlying Bigoray Member is more organic-rich and may be a minor contributor to hydrocarbons in the West Pembina area. The Wabamun Group contains no regionally extensive potential source rocks. Almost all the oil generated from Devonian source rocks appears to have remained within Devonian-aged reservoirs and very little is biodegraded. In contrast, where Exshaw Formation sourced oil is found in Devonian reservoirs, such as in the Grosmont and Nisku formations in the vicinity of the Athabasca Mannville Group bitumen deposit (i.e. “Carbonate Trend”), it tends to be biodegraded. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Late Cretaceous-Early Tertiary Remagnetization of the Devonian Swan Hills Formation Recorded in Carbonate Cores from the Caroline Gas Field, Alberta, Canada

Limestone and dolomite samples obtained from four unoriented Swan Hills Formation cores from the Caroline gas field were examined with the goal of dating both dolomitization and emplacement of solid hydrocarbon. Detailed analysis of 110 specimens showed no difference in the magnetic components in limestone, dolomite, and bitumen-bearing rocks. The first-removed component (A) appears to have been acquired during sampling and is not considered further. The second component (B) is interpreted as a record of the present-day Earth's magnetic field. The third component (C) is a steeply dipping vector acquired during a period in the past when the Earth's magnetic field was reversed, and is recovered from almost all specimens. Declination values of component C were resolved by using component B as a fossil compass needle in cases where these two occurred together. This yielded an in-situ direction of declination/inclination = 155.7°/-73.3°, k = 26.4, a95 (the cone of 95% confidence) = 7.1° for the C component. The corresponding paleopole (74.7N, 192.3E, with 95% confidence limits of dp = 11.4, dm = 12.7) plots directly on the apparent polar wander path for (APWP) stable North America yielding a Late Cretaceous-early Tertiary age for the C component. Because the C component is not unique to the dolomite or bitumen-bearing rocks, but is shared by limestone far removed from the dolomite reservoir, we are hesitant to assign this Late Cretaceous-early Tertiary age to the dolomitization or bitumen formation; however, this record does testify to a fluid pulse at the end of Laramide orogeny. Such pulses currently are believed to be common events proximal to orogenic fronts and may participate in the migration of petroleum. If we accept the flow of fluids through the reservoir at Caroline as being responsible for the remagnetization, then this suggests that the gas charge was not in place (or completely in place) until after this event. This constrains the time of charging to during or after the Late Cretaceous-early Tertiary.

Dolomite Fluorescence and Its Exploration Significance in the Swan Hills Formation, Upper Devonian, Western Canada Sedimentary Basin: ABSTRACT

Dolomite Fluorescence and Its Exploration Significance in the Swan Hills Formation, Upper Devonian, Western Canada Sedimentary Basin: ABSTRACT

Simonette Beaverhill Lake Oil Pool: Discovery History, Reservoir Characterization and Depletion Strategy: ABSTRACT

A significant light oil discovery was made in reefal carbonates of the Middle-Upper Devonian Swan Hills Formation of the Beaverhill Lake Group in west-central Alberta in September, 1993. The discovery well, Chevron Simonette 7-20-64-26W5, encountered a dolomitized Swan Hills reef margin with 28 meters of net oil pay and was capable of producing 750 ml (4700 barrels) of oil per day. A total of eighteen wells have been drilled into the pool to date. The accumulation at Simonette is divided into two pools (Beaverhill Lake A and B) by a north-south trending fault. The pools are the twelfth and fourteenth largest Swan Hills oil pools discovered to date and the largest Swan Hills oil pools discovered since 1962. The pools have an average net pay of 13.5 meters, with average porosity of approximately 9% and average water saturation of 7%. Porosity is present within both dolomite and limestone and the distribution of the reservoir is controlled by depositional facies. The density of the oil is 808 kg/m[sup 3] (43[degrees] API) and the gas/oil ratio is 325 m[sup 3]/m[sup 3]. The solution gas has an H[sub 2]S content of 1.5%. Initial reservoir studies indicate that 48% of the oil in placemore » in the A Pool can be recovered with a hydrocarbon miscible flood, which was initiated in March, 1995. A water flood, with anticipated recovery of 41% of the oil in place, will be initiated in the B Pool in early 1996.« less

Solvent Tracers And The Judy Creek Hydrocarbon Miscible Flood

Abstract Radioisotopic liquid hydrocarbons have been successfully used as solvent tracers for the Judy Creek Beaverhill Lake "'A" Pool horizontal hydrocarbon miscible flood. Tritiated toluene and tritiated normal alkanes from pentane to octane were selectively injected as tracers into miscible flood patterns during solvent injection cycles. Subsequent tracer production at wells surrounding the miscible injectors provided a means to confirm each pattern's contribution to tertiary oil response at those wells. Communication with pattern injectors was an important factor to consider when solvent sweep was estimated and candidate areas were evaluated for pattern reconfiguration. Tracing program results were used to identify solvent migration from pattern areas. Field engineers used the information on flow distributions to advantage when they made changes to injection and production rates in order to improve pattern balancing. This paper includes a description of a new analysis technique which uses fractional distillation and gas chromatography to determine tracer activities in produced oil samples. Details of tracer injection and sampling strategies are also discussed. Introduction The Judy Creek Beaverhill Lake (BHL) "A" Pool is located 240 Ian northwest of Edmonton. The pool is an atoll-like reefal limestone complex of upper Devonian age. The reef has an areal extent of approximately 115 km2 and is up to 70 m thick. Together, the reef and platform limestones comprise the Swan Hills Formation of me Beaverhill Lake Group. Figure 1 shows a structural cross section of the reef along a line drawn from the northeast to the southwest. It is divided into live growth cycles. The uppermost production interval is the R-5, which is generally continuous with 90% of its porosity greater than 6%. This interval contained 41%of the pool's original-oil-in-place (OOIP). The remaining four cyclescan be grouped into interior and margin areas based on facies, with 32% of the pool's OOIP in the highly continuous reef margin. The best reservoir is found in the forereef, to the northeast. In the stratified reef interior, porosity is discontinuous and occurs as patches and lenses(1). The pool was discovered in 1959. Water injection commenced in 1964 into down-dip pool edge locations to help maintain reservoirressure. It was found that the injected water followed the highly permeable reef rim; the relatively impermeable interior facies presented barriers to fluid movement to the reefs interior. The severe pressure gradients that developed provided convincing evidence of the reservoir's complexity. In 1974 a pattern waterflood was initiated and water injection into the peripheral injectors was reduced. These actions gradually corrected the pressure imbalance across the reservoir. Approval for a horizontal hydrocarbon miscible flood was received from Alberta's Energy Resources Conservation Board in 1983. In Mar 1985, solvent injection commenced into four patterns of what was then planned to ultimately be a 56-pattern commercial project. Figure 2 shows the miscible flood patterns in relationship o the project boundaries as of February 1990. Hydrocarbon miscible flood surveillance included an extensive solvent radioisotope tracing program. As described by Jonasson(2), the program's objectives were to provide information on continuity, directional now trends and solvent flow beyond miscible patternboundaries.

The East Swan Hills Unit Waterflood Optimization Study: A Multi-Disciplinary Approach

Abstract The East Swan Hills Unit No. 1 is located on the eastern flank of the Swan Hills Beaverhill Lake "A" and "B" Pools. The reservoir is now in an advanced stage of depletion like many of Alberta's oil reservoirs. Optimization of a geologically complex reservoir, such as is found in the Beaverhill Lake, is a major undertaking and requires a multi-disciplinary approach. To evaluate waterflood performance a study consisting of petrophysical data reduction, geological mapping, spreadsheet analysis of recovery and reservoir simulation was carried out. This paper highlights three major contributions which were essential in the analysis.The significance of geological mapping which has identified layerirlg/ heterogeneity within the Swan Hills formation and the potential in the underlying Slave Point formation.Manual waterflood calculations have enhanced the understanding of the reservoir and confirmed Slave Point production, prior to proceeding with numerical simulation.The methodology used to simulate a multilayer reservoir under waterflood is described. Incremental recovery is predicted by improved waterflooding in selected areas of the Unit. A program consisting of injection testing, production testing, single well tracers and selective cased-hole logging has been designed, prior to proceeding with field implementation. Introduction The East Swan Hills Unit is located in the province of Alberta approximately 200 km northwest of Edmonton as shown in Figure 1. This field was discovered in early 1963 with primary production commencing in the same year. Commingled production is derived primarily from the Swan Hills formation as well as from the underlying Slave Point formation. There are 76 wells in the Unit. The field was produced by primary fluid expansion drive since there was no gas cap or no acquifer support. Unitization occurred in 1967 for the purposes of waterflooding. Peak oil production of 1959 m3/day occurred in 1969 after which oil production declined at 20% per year. An aggressive workover program was initiated in 1984 to arrest the production decline. The program was successful as indicated by the oil production rate which has remained flat over the last five years. The current oil rate is 100 m3/day with a water cut of 90%. As the Unit was approaching its economic limit, it was concluded that a detailed reservoir engineering study should be carried out to determine if improved waterflooding could be achieved. This paper documents the results of the study and the methodology used.. The paper has been divided into three main sections: Geological - Petrophysical Studies, Conventional Reservoir Engineering Review and Reservoir Simulation. The Optimization Program developed from these three studies is then discussed. Finally, the conclusions of the paper are presented. Geological- Petrophysical Studies Method of Study When the East Swan Hills pool was being developed and unitized a fairly simple geological model was used. Two reservoirs, the Swan Hills member and the Slave Point member were recognized, These became known colloquially as the "Light Brown" and "Dark Brown". respectively. The Light Brown member was known to be of substantially better reservoir quality; hence most development was aimed at this pay.

Three Gas-Water Contacts in a Stratigraphically Trapped Pool: Swan Hills Formation, Caroline Area, Alberta

Three Gas-Water Contacts in a Stratigraphically Trapped Pool: Swan Hills Formation, Caroline Area, Alberta

Devonian Swan Hills Formation Carbonate Platform Facies and Cyclicity, Caroline, Alberta, Canada

Devonian Swan Hills Formation Carbonate Platform Facies and Cyclicity, Caroline, Alberta, Canada