Rainbow lake basin

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Introduction

Rainbow Lake (Also known as Beaver Hill Lake Group) is located approximately 900 kilometers northwest of Edmonton, Alberta. Rainbow Lake consists of two distinct areas, Rainbow Lake and Bivouac, with assets including two natural gas plants and multiple field facilities, including compressor stations with over 1,100 kilometers of pipelines. The area that surrounds Rainbow Lake Basin is known as Middle Devonian Keg River Formation. Around this area, there are other basins that have some of the same source rocks, seals, traps etc... [1]

Reference of where Rainbow Lake area is in comparison to its surrounding geography. [2]

Depositional History

The Depositional History of Rainbow Lake, in Alberta goes all the way back to the Devonian age. The area shows the presence of biohermal reefs (ancient organic reef of mound like form built from a variety of marine invertebrates). The reefs are characterized by either a pinnacle or an atoll. The evaporites and carbonates of the Muskeg Formation are believed to have been deposited subsequent to reef growth. Crinoidal beds are present in the uppermost Lower Keg River and lowermost Upper Keg River. Structural control in the form of low-relief warping and normal faulting is believed to have exerted considerable influence on the initiation, distribution, and geometry of these crinoidal beds and reef growth. Fourteen broad but distinct lithofacies, representing six depositional environments, are recognized in Rainbow Member reefs. The stromatoporoid organic-reef facies developed to within 30 ft of the top of the Rainbow Member. Deposition of skeletal rudite and lutite, predominant in the upper reef complex, was controlled by the configuration of the wave-resistant organic reef. [3]

Paleogeography of Northwestern Canada. Rainbow Lake is located inside the light blue color representing shallow-marine carbonates. [4]

Primary Geological Risks and Uncertainties

The Uncertainties of this Basin aren't necessarily factored on weather its dangerous or not. The Risks and uncertainties come from the layout of the land, and the geographic challenges that this particular area has. These challenges include the Watt Mountain formation, the equivalence relations of the Dawson bay formations, the overall relation between transgressive, and regressive phases, and the non-equivalence of the tops of Beaver Hill lake area, and Manitoba groups. [4] These risks more include risking money on equipment in order to accommodate for the geographical difficulties.

Petroleum Elements

Source Rocks

The primary Source rock found in rainbow lake basin is Biohermal reefs, and organic rich carbonate facies. The reefs are are more well known for producing oil, and therefore are paid more attention nowadays. An integrated approach using stratigraphy, sedimentology and organic petrology to study these bituminous laminites has facilitated regional stratigraphic correlation and interpretation of the depositional history, paleoenvironments, and paleoecology of the Keg River ramp and reef foreslope successions. This work provides insight into the influence of depth-related anoxia, high productivity and sedimentation rates as primary controls on organic matter accumulation and preservation in Keg River source rocks. The lowermost bituminous laminite unit in the Lower Keg River Member in the Rainbow Sub-basin (LRL) occurs at the base of a decameter-scale shallowing-upward cycle. The LRL represents the onset of a transgressive event, possibly related to local subsidence along a widespread carbonate ramp. The middle bituminous laminite unit in the Rainbow Sub-basin (MRL) and the lower laminite unit in the Zama Sub-basin (LZL) occur at the base of reefal successions near the top of the Lower Keg River Member and they are considered to be correlative. [5]

Seal

Seals are represented by salts of the Muskeg and Prairie formations. It is believed that the seals are salt domes that slowly migrate upwards when it can. This results in salt domes forming plug or bulge shapes as it tries to fit through weak spots in the overlying rock layer. As the salt forces its way upwards and begins to dissolve, a cap rock forms on top of the dome. Anhydrite is an evaporite mineral that is not as easily dissolved as salt. It reacts with bacteria and other substances in the ground to change into sulphur, dolomite, limestone, and/or gypsum, all of which build up to make the cap rock. [6]

Trap

The traps in the Beaver hill lake groups are known to be Anticlines. These anticlines are shaped like the letter A because of movement of beds underground. In this specific area, these anticlines are believed to have formed from Salt Domes. The domes move upwards because of evaporation leading to the movement of rock later on creating an anticline shape.

Cross section of Keg River "pool B" in the Rainbow Lake area.[7]

Migration

The occurrence of a basinally-restricted source facies between a series of pinnacles which are capped by shale and/or evaporites provides an ideal generation/ migration/entrapment situation. Local sourcing in these pinnacles results in a systematic progression of oil properties from low gravity, lower maturity oils at the eastern end of the Zama sub-basin to high gravity oils, condensates, and gases as the onset of overmaturity is approached to the west. No evidence exists to date that any Elk Point-sourced hydrocarbons have migrated out of the Middle Devonian strata and this, therefore, represents a closed system. [8]

Reservoir

The pattern of lithofacies distribution is distinctive for each type of reef; in reefs of a specific type, lithofacies distribution is similar. There may be considerable variation in reservoir properties because of differences in diagenetic history. The most significant diagenetic process is dolomitization.

Lithofacies studies, supplemented by capillary-pressure data, are the bases on which five reservoir facies have been identified. Each reservoir facies has a distinctive pore system and system of conveying canals. [9]

Porosity and Permeability

In the Rainbow Member reefs a variety of pore systems is recognized in both limestone and dolomite reservoirs. They are (1) intergranular pores in clastic limestone, (2) intergranular pores in microgranular to chalky limestones, (3) intercrystalline pores created by dolomitization, (4) intrastromatoporoid and coralline pores, (5) original intrafossil pores or voids (gastropods and rarely brachiopods), (6) voids produced by selective solution of skeletal material (brachiopods, gastropods, amphiporids, and dendritic corals), (7) voids due to the indiscriminate solution of fine matrix, (8) banded pores or vugs in laminites, (9) shrinkage voids in lutites, (10) solution voids associated with fracture planes, and (11) fracture porosity. Fractures, presumably of tectonic and atectonic origin, are present in all Rainbow Member reefs. They are particularly abundant in the “F” pool atoll reef. Original porosity in the Rainbow Member reefs is mainly intergranular, but includes intrastromatoporoid and intracoralline pores and more rarely intrafossil pores in other skeletal material such as gastropods. [9]

Resistivity

Seismic data was processed at U of A using a conventional processing flow. The shallow nature of the targets made proper velocity analysis difficult; a standard semblance analysis was essentially confirmed by close analysis of the first break refractions, however. Both indicated low velocities to the top of the pre-Cretaceous unconformity, consistent with weakly consolidated channel fill materials, to the east and evolved to higher velocity Cretaceous sediments to the west. Only a portion of the seismic profile is provided here. Preliminary interpretation of seismic profile reveals the Pre-Cretaceous unconformity and shows the presence of stacked Quaternary channel margins. [10]

Engineering Aspects

Rainbow Lake area has 300 wells spread out across the area. Major material stockpiles, a central operating camp, and an all weather airstrip serving aircraft as large as the Lockheed Hercules have allowed program continuity. Drilling costs are high due largely to well pressure and lost circulation problems as well as the remote location.

Areas of exploration in northwestern Alberta, Canada. [11]

Future Petroleum Prospects

The Rainbow Lake Basin/ Beaver Hill lake group has been drilled for many years now. There isn't much else that companies can do other than go more east, or southbound, or add more wells to their respective land.

1. Southbound of Rainbow lake has very good potential knowing that it has been drilled for many years.

2. Back side of the rainbow reefs, because the way the waves used to flow, the dead debris built up on the backside of these reefs.

3. Northwestward of Rainbow lake holds a lot of oil. Near the Horn River Basin has a lot of potential due to the presence of reef formations.

References

The western Canada Sedimentary  Basin (WCSB) Geological Atlas

Lithology and Mineral Resources, 2018, Vol. 53, No. 3, pp. 236–251

GEOLOGICAL SURVEY OF CANADA BULLETIN 452 DEVONIAN GAS RESOURCES OF THE WESTERN CANADA SEDIMENTARY BASIN PART I: GEOLOGICAL PLAY ANALYSIS AND RESOURCE ASSESSMENT G.E. Reinson, P.l. Lee, W. Warters, K.G. Osadetz, L.L. Bell, P .R. Price, F. Trollope, R.I. Campbell, and J.E. Barclay

Chapter 10 - Devonian Elk Point Group of the Western Canada Sedimentary Basin

External Links

Langton, J. R. and George E. Chin. “Rainbow Member Facies and Related Reservoir Properties, Rainbow Lake, Alberta.” Bulletin of Canadian Petroleum Geology 16 (1968): 104-143.

  1. https://www.cenovus.com/Our-operations/Conventional-oil-and-natural-gas
  2. https://www.rbauction.com/cms_assets/images/property/rainbow-lake-ab-2017296-property2/img-400x300-rainbow-lake-auction-location-map.jpg
  3. https://www.semanticscholar.org/paper/Rainbow-Member-Facies-and-Related-Reservoir-Rainbow-Langton-Chin/26fd40db4361c11b05673872476714b597462174
  4. 4.0 4.1 https://static.ags.aer.ca/files/document/Atlas/chapter_11.pdf
  5. https://www.semanticscholar.org/paper/Origin-of-source-rocks-in-the-Middle-Devonian-Keg-Wiebe-Chow/5114370eb435b9c2f67c4ec7da6b0b5cb853f3ac
  6. https://energyeducation.ca/encyclopedia/Cap_rock
  7. https://engineeringdesignfair.ucalgary.ca/petroleum/wp-content/uploads/sites/9/2021/04/image-120.png
  8. https://www.lyellcollection.org/doi/pdf/10.1144/gsl.sp.1990.050.01.9
  9. 9.0 9.1 https://pubs.geoscienceworld.org/aapgbull/article/52/10/1925/554740/Rainbow-Member-Facies-and-Related-Reservoir
  10. https://csegrecorder.com/articles/view/seismic-and-resistivity-imaging-for-quaternary-channels-rainbow-lake-nw-ab
  11. https://gsw.silverchair-cdn.com/gsw/Content_public/Journal/aapgbull/52/10/10.1306_5D25C53F-16C1-11D7-8645000102C1865D/1/m_aapg_1968_0052_0010_1925_page_3_1.jpeg?Expires=1673314952&Signature=46HlkO4F2BKKLG4qQ2zM6daCvEn-cvL0Lu1uguC2sX-aND0pVyCYE26F2zwh2naKysgUpA0N9jNlhH275FtjhtmrMC-MhXjadaMOzrB2-DWDBcCF1Hoq2RVbNZAs3fmBwNRkvt07ypqlWX~7gxV4fMjacr8hC4KY929IY3SdCJb9McscoUAl77R6vl3bEa7h~HGxVGzBiUfG6Cnty5KxLgfwisxHrFWLBanDuO0FHezCwnUaMl9Ot3hum~Jfdxjg0zAR3OBbAIOdE9WLE4PrPe6RAYIIP0h9KJ51P3M4PPXjNGYHaDLFUji1dO9vht6tlfqEdCRSOiZO-zDIJknLmw__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA