Devonian Swan Hills Research Articles

Oil and Gas Developments in Western Canada in 1986

Western Canadian petroleum industry activity slumped in 1986 in response to oil prices that fell to less than half of their 1985 levels. The federal and provincial governments attempted to support the industry with the introduction of new incentive programs and the elimination of the petroleum and gas revenue tax (PGRT). Total number of wells drilled decreased 51% to 5,384 wells. Exploratory drilling fell 41% to 1,955 wells, and development drilling was down 56% to 3,429 wells. Exploratory success rate dropped marginally from 57% to 55% with 634 oil completions and 444 gas completions. Development success rate also dropped (from 89% to 84%) with 2,044 oil completions and 851 gas completions. Exploratory drilling activity fell in every area except the Northwest Territories Arctic region, where it increased slightly. Land sale revenues fell by 67% to $33.8 million (FOOTNOTE 6). Alberta's 25 Crown land sales generated $251 million, Saskatchewan's 4 Crown land sales generated $18 million, British Columbia's 8 Crown land sales generated $28 million, and Manitoba's 2 Crown land sales generated $900,000. Average price per hectare decreased in all provinces. Exploration and development drilling in Alberta continued to dominate western Canada with 78% of the total activity. The premier discovery of the year was made by Shell in the Devonian Swan Hills Formation at Caroline with potentially 56.6 billion m3 of gas in the reservoir. Other Devonian completions were made at Medicine River, Simonette, Kenzie, Gift, Panny-Senex, Hutch, and Shekilie, whereas Cretaceous targets were successfully completed at Enchant, Pageant, and Ferrier. British Columbia activity declined 30% while the average well depth increased by 24%. Active areas included Noel/Kelly, Flathead Valley, and the Halfway trends in the vicinity of Fort St. John. Two interesting dry holes were drilled by BP Canada on Vancouver Island. In Manitoba, no significant discoveries were made. Most of the activity centered around the Waskada, Pierson, and Daly areas. In the Northwest Territories-Arctic region, total drilling activity decreased almost 20%. Exploration drilling increased, however, by 15%, with all of that increase coming from onshore activity. The most significant discovery was the Gulf et al Amauligak I-65A well, which has proven additional reserves on the Amauligak structure. This structure, with its estimated 110-125 million m3 of recoverable oil, could well qualify as the lead project for the development of the Beaufort Sea. The most significant gas discovery of 1986 was made by Esso at the Hansen G-07 well, which tested gas and condensate from the Tertiary Kugmallit Formation. Saskatchewan activity plummeted to 27% of its record high 1985 levels. A rebirth of hope for prospects of deep Saskatchewan oil was caused by the Home et al Tableland discovery in the Devonian Winnipegosis of southeastern Saskatchewan. Exploration activity was concentrated in areas of lighter crude oil and gas potential such as the Dodsland, Plato, and Hatton areas. At year end, it was still uncertain if the Husky Oil heavy oil upgrader at Lloydminster would proceed.

Tectonic Control of Devonian Reef Sedimentation, Alberta: ABSTRACT

Kaybob is one of a group of geologic reefs which underlie west-central Alberta and which comprise the Upper Devonian Swan Hills Formation of the Beaverhill Lake Group. Kaybob is a flat north-south elongate lens, 250 ft thick, 11 mi long, and 3 mi wide, built on the Slave Point Formation, a widespread platform carbonate. Detailed core study of sedimentary structure, texture, and constituents reveals that the carbonate sediments composing the can be grouped into 3 environmentally controlled facies groups: reef-slope, reef-margin, and shelf-lagoon facies. The reef-slope facies is a stromatoporoid-crinoid-brachiopod grainstone. The marginal deposits consist of a groundmass of massive stromatoporoid grainstone containing varied concentrations of different stromatoporoid growth forms (ranging from slender branching to large massive heads). The interior facies includes several rock types arranged in repeated vertical sequences. A basal unit of massive wackestone is overlain by combinations of massive, thin-bedded, and laminated mudstones, mudclast grainstones, and amphiporid carbonate conglomerate. Submarine and subaerial scoured surfaces are present within the upper units. The outer slope sediments intertongue with contemporaneous open-marine deposits seaward and with the reef-marginal facies on the inner side of the reef. This pattern changes laterally in vertical section, as the thickness of the changes from place to place. The upper half of the shows a marked westward displacement. Position of the various facies within the geologic mass, and comparison with Holocene carbonate sediments from several Caribbean localities, together provide a paleoenvironmental interpretation. The interior facies includes most of the sediment types which have been described from recent shallow shelf-lagoon environments. Sequential arrangements are the same and result from similar processes. The marginal realm includes many facies comparable with those observed in Holocene reef tracts, ranging from scattered coral growth on a sand bottom to coral constructed buttresses of ecologic reefs. Circumferential variations in geologic development, the westward displacement of the upper part, and a thick pile of open-marine deposits on the southwest are attributed to prevailing nor h winds during the Devonian. Tectonic control is exhibited at 4 levels. 1. The interior shelf-lagoon sequences are initiated by small-scale pulses of subsidence, perhaps complicated by eustatic sea-level changes. 2. Larger scale subsidence variations account for the thickening and thinning of the geologic body as a whole. 3. An orthogonal pattern of sharp elongate folds trending NE-SW and NW-SE is expressed clearly at the base of the reef. The folds are confined to the area of reefing, where they controlled initiation by forming mud mounds during upper Slave Point deposition. The pattern may reflect Slave Point block faulting. 4. This and others in the region, together with their associated carbonate-shelf deposits, fit into a well-expressed orthogonal tectonic pattern controlled by larger scale ba ement features. The basement features include a family of NE-SW-trending, relatively stable arches revolving about a NW-SE-trending major arch, the West Alberta ridge. They form part of the system of stable arches that provides the tectonic framework of the continent. End_of_Article - Last_Page 854------------

Devonian stromatoporoids from central Alberta, Canada

The Devonian Swan Hills reef complexes of western Canada contain a prolific and well-preserved stromatoporoid fauna. Species of the genera Hermatostroma, Atelodictyon, Stromatopora, Parallelopora, Ferestromatopora, and Clathrocoilona are common constituents of the reef, fore-reef, and reef platform limestones. Specimens from six reef complexes (Snipe Lake, Goose River, Kaybob, Virginia Hills, Swan Hills, and House Mountain) are described. Most species occur in several growth forms although one growth form is usually predominant. Two new species, Clathrocoilona sp. and Stromatopora sp., are recognized in the Swan Hills material.

Stratigraphy, Devonian Swan Hills reef complexes of central Alberta

ABSTRACT Devonian reef complexes in the subsurface of the Swan Hills area of central Alberta are some of the most prolific oil-producing reservoirs in Canada. The complexes, composed of carbonate rocks and collectively forming the Swan Hills Formation, contain rich, varied, and well-preserved stromatoporoid faunas and other associated fossils, including ostracodes. Six discrete reef complexes (Snipe Lake, Goose River, Kaybob, Virginia Hills, Swan Hills, and House Mountain) lend themselves in particular to detailed stratigraphic analysis. From the many available cored sections, the rock sequences can be established readily, and divisions of the sequences correlated from one reef complex to another. Moreover, the rocks of these complexes are negligibly altered, so that various facies can be recognized, and facies relationships established with little difficulty. Nine separate stages of growth can be recognized in the Swan Hills reef complexes, and these are designated conveniently, from bottom to top, Divisions I to IX. A distinct break is apparent at the boundary between Divisions V and VI, expressed in part by a perceptible southwesterly shift in the loci of reef growth. Each division consists of as many as four main facies, which contain characteristic rocks and fossils. Thirty-one species of stromatoporoids have been recognized in the Swan Hills Formation, and five of these (Euryamphipora sp. A, Trupetostroma sp. A, Trupetostroma sp. B, Clathrocoilona sp., and Stromatopora sp.) are new. From examination of the many stromatoporoid colonies present in the rocks, it is apparent that growth forms intergrade, and dendroid stromatoporoids are allied genetically to both subspherical and tabular forms. It is proposed, therefore, that, in contrast to the importance accorded it by many palaeontologists, growth form be relegated to a position of little importance for taxonomic purposes. Three distinct species of Amphipora, (A. ramosa, A. pervesiculata, and A. angusta) can be recognized in the collections from the Swan Hills Formation. A progressive loss of stromatoporoid species occurs at the end of each stage of reef growth (top of each division) except for Division I. The most significant faunal break occurs at the boundary between Divisions V and VI, where seven stromatoporoid species disappear. Significantly, diagnostic Middle Devonian ostracode species also disappear at this level. No ostracodes diagnostic of either Middle or Late Devonian age were recovered from the rocks above this boundary. The shales of the Waterways Formation, which enclose the reef complexes and locally underlie Divisions VI to IX, where these lie to the southwest of the main centres of the complexes, contain a Late Devonian microfaunal assemblage. Lithological and faunal evidence points to a disconformity, marking a considerable time lapse, between Divisions V and VI, and there is little doubt that this hiatus contains the Middle-Late Devonian boundary. Fluctuations in sea level, preceding retreat of the Middle Devonian sea, resulted in the development of Divisions I to V. Similar fluctuations of the Late Devonian sea, after deposition of early Waterways Shale, resulted in the development of Divisions VI to IX. End_Page 444------------------------

An oil producing reef-fringed carbonate bank in the Upper Devonian Swan Hills Member, Judy Creek, Alberta

ABSTRACT A reef-fringed carbonate bank, the Swan Hills Member, of probable early Late Devonian age, is present in the subsurface of west-central Alberta, at Judy Creek. Five million barrels of 41° API gravity oil were produced from this bank in 1963. In 1964, there were 169 producing oil wells and reserves were estimated at 770 million barrels of oil in place. Thirty-two diamond cores from the Swan Hills Member were studied. Three hundred and thirty thin sections and one hundred and fifty acetate peels were examined petrographically in order to determine grain origin, grain/micrite ratios, types of fossils present and diagenetic history. The Swan Hills Member limestones are composed of: (1) Organic framebuilders--dominantly massive and tabular stromatoporoids with locally significant quantities of solenoporid algae and tabulate corals. The dendroid stromatoporoids, mainly Amphipora and Stachyodes, are not considered to be framebuilders although they were exceedingly important rock builders. (2) Grains--mostly skeletal, but pellets dominate locally. Rare intraclasts and coated grains are also present. (3) Micrite. (4) Sparry calcite. (5) Void space. The Swan Hills Member is divisible into nine informal stratigraphic units. The major rock types and environments of deposition of these informal units are given below in ascending order. The basal biomicrite beds consist mainly of micritic-skeletal limestone which contains a brachiopod-gastropod-echinoderm fauna. The environment of deposition is essentially similar to that of the Waterways Formation but is believed to represent shallower water. The coral beds are composed mainly of stromatoporoidal limestone with large quantities of Amphipora, Stachyodes and lesser quantities of Thamnopora; these beds form a widespread biostromal deposit. During deposition of the next unit, the Amphipora-stromatoporoid beds, a broad shelf lagoon developed over a wide area; stromatoporoid reefs grew on the eastern margin of the shelf. The lagoon was densely populated with Amphipora and bulbous stromatoporoids which grew, in part, on a pelleted lime-mud bottom. Local areas of supratidal conditions prevailed. The overlying Amphipora-spar beds, characterized by Amphipora limestone with abundant sparry calcite and interbedded with micritic-Amphipora limestone, represent a transition between the underlying lower energy and the overlying higher energy environments. Emergent conditions appear to have prevailed in some areas after deposition of this unit. The next depositional unit, the dendroid stromatoporoid beds, consists mainly of stromatoporoidal limestone, which was deposited on a relatively flat surface interpreted as a table reef. The succeeding Amphipora beds, chiefly micritic-Amphipora limestone, were deposited in a shallow central lagoon surrounded by reefs (Unit 8) on the bank margins. This differentiation into a shallow central lagoon and marginal reefs ceased during sedimentation of the grey limestone-green shale beds; deposition occurred in brackish ponds, supratidal flats and subtidal environments. 1 Manuscript received January 5, 1966; revised manuscript received February 22, 1966. 2 Department of Geology and Institute of Oceanography, University of British Columbia. End_Page 1-------------------------- Reef growth on the bank margins was contemporaneous with the deposition of Unit 5, and most of Unit 6. These reefs were built primarily of massive and tabular stromatoporoids with lesser amounts of solenporid algae and tabulate corals; they form an important petroleum reservoir which encircles Judy Creek field. The culmination of the Swan Hills depositional history was the formation of a widespread skeletal and pelleted limestone over the entire Judy Creek bank. This unit forms an important petroleum reservoir through Judy Creek field.

Paleoecology of Devonian Swan Hills Reef, Alberta, Canada: ABSTRACT

The Limestone reef reservoir at Swan Hills consists essentially of a buildup of successively smaller atoll-like layers. Precipitation of calcium carbonate within the lagoonal area of each layer essentially kept pace with growth of the outer organic lattice. Within the reef mass, six depositional environments characterized by specific suites of fossils (or fossil fragments) and associated limestone textures are recognized as follows. 1. Aerated moderately agitated water of normal marine salinity (widespread shelf or submerged reef-built platform). Thamnopora-type corals, Amphipora, stromatoporoids, crinoids, articulate brachiopods, rare rugose cup corals, and ostracods occur in light gray-buff skeletal microgranular limestone of low permeability. 2. Semi-stagnant quiet water of normal marine salinity (leeward side of reef). Crinoids, articulate brachiopods, rare thamnopora-type corals, Amphipora, pancake and bulbous stromatoporoids, rugose cup corals, ostracods, and gastropods occur in impermeable dark brown argillaceous skeletal calcilutite with thin black bituminous shale beds and rare dark chert nodules. 3. Aerated highly agitated water of normal marine salinity (organic lattice). Light buff stromatoporoid bulbs and Amphipora, rare thamnopora-type corals, rugose cup corals, crinoids, and articulate brachiopods form permeable patch reefs and interbedded skeletal calcirudites. 4. Semi-stagnant quiet marine water of slightly increased salinity (partly restricted shelf). Dark gray biostromal buildups of stromatoporoid bulbs and minor Amphipora occur in impermeable black shaly matrix. 5. Aerated, quiet to highly agitated marine water of increased salinity (mud flats, tidal channels, and shoals within atoll-lagoon). Amphipora, rare ostracods and gastropods occur in light buff impermeable to highly permeable precipitated limestone (lithographic, microgranular, pseudo-oolitic, and intra-formational conglomerate). 6. Semi-stagnant quiet marine water of increased salinity (deeper protected pools in atoll-lagoon). Amphipora, rare stromatoporoid bulbs and ostracods occur in impermeable dark brown slightly argillaceous calcilutite of precipitated origin. Mapping of these environments is of great value in outlining field extensions and evaluation of acreage during development drilling. Use of these techniques, in addition to contruction of isopach maps of critical intervals, should also be highly effective in exploration for undiscovered reef oil and gas fields. End_of_Article - Last_Page 265------------