[14]

The Viking is a regional formation with a thickness of 15-45 meters in central Alberta to approximately 65 meters in southern Alberta where it merges with the Bow Island Formation. To the east the Viking thins to the east, south east and pinches out around St. Paul, MN.[15] The incised valley systems have been of interest to hydrocarbon exploration and production, yet the Viking has yet to become the prolific producer the oil in place numbers suggest.  This could be because of the depositional history of local transgression and regression cycles created heterolithic sand bodies that prevent vertical extraction over large zones. The purpose of this project is to identify the different facies and their associations with in the Viking Formation of central Alberta (townships 30-33, ranges 25W4- 27W4) to better understand the depositional history and unique challenges of producing hydrocarbons from this formation.

 

Facies Interpretations

Facies 1 – Facies 1 represents the initial deposition sandstone during the global lowstand. Facies 1 is a coarsening upward very fine to fine grained prodelta sandstone that was deposited as the result of the first lowstand within the Viking succession. Facies 1 ends with the minor transgression of sea level following the lowstand.

 

Facies 2 – Facies 2 is a bioturbidated mud that represents the local transgression after lowstand 1 within the major transgressive cycle of the Kiowa-Skull Creek Transgression.[16] This facies represents a partial retreat of the shoreline and a minor flooding event.

 

Facies 3 – Facies 3 represents a period of slightly fluctuating sea level, higher than lower, but overall a period with relative stability, The alternating thin beds of mud and silt indicate an alternating energy environment, and a relatively slower rate of sedimentation.

 

Facies 4 – Facies 4 represents a massive sandstone that is fine grained and slightly fining upwards. Facies 4 was deposited as a the result of distributary channels reworking and incising during the transgressive periods. Facies 4 was deposited in the final transgressive period of the Viking and its termination represents lowstand 2.

 

Facies 5 – Facies 5 represents the end of the transgressive periods within the Viking deposition and is the beginning of a global sea level rise. Facies 5 is a shale deposited as the inland sea began to regress and eventually lead to the deposition of the marine shales that overlie the Viking.

 

Facies 6 – Facies 6 marks the end of the Viking Formation. Facies 6 is a pebble conglomerate transgressive lag, which refers to large grain sedimentary clastics that resulted from incised valley fills during the previous regression period, but are sufficiently large in grain size that the current energy of global transgression was insufficient to remove the pebble clasts and instead deposited mud as the matrix. This Facies marks the termination of the regressive periods following lowstand 2.

 

Facies Association

Within the Viking formation there is two facies associations. The first facies associations includes Facies 1-3 representing the first regression and transgression cycle of the local regression/transgression cycle due to the tectonism of the Cordilleran orogeny.[17] Facies 1 represents the initial progradation of the delta after the global transgression that created the Joli Fou marine shales. Facies 1 is the initial sedimentation of the foreland basin as the Joli Fou Seaway begins to recede. As the prodelta begins to advance to the east coarsening upward fine grain sandstone is deposited. Facies 3 is a siltstone that represents the tidal influence and the ending of the minor transgression that happened within the Kiowa-Skull Creek Transgression. During the minor transgression interbedded shale and silt were deposited, however, when the regression cycle returned the deposition of Facies 5 was overlain the first facies association.

 

The second facies association consists of Facies 4, massive fine grained sandstone that represents the final progradation of the prodelta system. As the local transgression cycle, represented by Facies 5 came to an end, the regression facies of Facies 5 and Facies 6 were deposited. Facies 5 represents the initial flooding of estuarine valleys, depositing very finer grained shale on top of the massive sandstone represented by Facies 4. Facies 6 is a pebble conglomerate transgressive lag. This conglomerate transgressive lag marks the end of the regressive period and is a remnant of the erosion and deposition of the global sea level increase.

 

Sequence Stratigraphic Interpretation

The Viking Formation is local transgression and regression cycle of about two million years with in a larger global transgression, the Kiowa-Skull Creek Marine Cycle[18] (see logs 1-5 in the Appendix for the transgression and regression cycles). This creates two facies associations, identified above. The first is a coarsening upward progradational beginning by Facies 1. Facies 2 represents the beginning of the transgression with in the lower Viking, while Facies 3 is the return to regression. After the flooding surface indicated by Facies 2 and the siltstone of Facies 3,  the deposition of sandstone returns with the deposition of Facies 4, a fine to very fine sandstone as the process of regression returns. Facies 4 is massive sand that is deposited during the final regression prior to the global transgression. Facies 4 is deposited as the Joli Fou seaway is regressing at a faster rate than during Facies 1 and two, leading to a more coarse grained and massive sandstone interval. Following the deposition of Facies 2 and 3 the local transgression of Facies 5 and 6 are deposited before the global transgression leading to the Westgate shales and Colorado shales.

 

The Viking formation is broken into two facies associations based on transgressive and regressive cycles. The Viking has been identified to have two lowstand within the deposition prior to the termination of the formation by the global transgression. The transgressions are identified in the core by shale overlaid by a pebble conglomerate. The pebble conglomerate is a transgressive pebble lag[19] that caps estuarine deposits and indicating a highstand, local when in regression and transgression cycle one and a global highstand in transgression and regression cycle two (see well logs 1-5 in the Appendix for the cycle).  

 

Depositional History

In the foothills the Viking thickens and overlies the Hulcross Formation.[20] In central Alberta the Viking overlies Joli Fou Formation and underlies the Westgate Formation and in south western Saskatchewan the Viking thins out and is overlain by Colorado shales and while overlying Joli Fou shales. The Viking is identified on logs by a sharp unconformity at its base succeeding a marine shale package and is terminated by a flooding surface at its top leading to being overlain by shales. The unconformity at the base is identified to be a major lowstand in sea level, post of the Mannville unconformity.[15] Prior to the mid Albian the Joli Fou Seaway split North America in two along the Transcontinental Arch.[21] The Viking was deposited in response to this lowstand in a due to a minor transgression and regression cycle with in a global major sea level highstand. The highstand in the Late Albian terminates the Viking and deposits Westgate Shales and Colorado shales over top. There is two local lowstands within the Viking deposition. The local transgression and regression cycle is postulated to be in response to basin subsidence and crustal shortening created by the Cordilleran orogeny.

 

The Viking Formation is a coarse grained clastic wedge with interbedded shale and silt facies and a transgressive pebble zone. The sediment for the Viking was derived to the west from the Cordilleran orogeny[22]. The cycles of regression and transgression, with in the global eustacy lead to an east ward prograding delta . As the prodelta prograded to the east, into the foreland basin, the flood plains of north east BC prograded to the east as well, this left a shallow shelf over the remaining basin.[23] This lead to the deposition of a series of transgressive shorelines with tide dominated deltas and deposits. During the period of deposition there was at least two identified sea level lowstands that allowed fluvial channels to incise Mannville sands and shales, cutting and filling these channels. The subsequent local transgressive period following the incision of the shelf and Manville Group rocks reworked the sands and deposited a layer of shale and mud. The regression, transgression cycle with in a larger global transgression is of interest to hydrocarbon exploration as incised valley systems are major hydrocarbon producing systems and the transgressive period floods estuarine valleys deposition muds and shales and creating possible stratigraphic traps.

 

Implications for Hydrocarbon Exploration

Despite the large OOIP, estimates of 1.8 billion barrels of oil, light sweet crude of 36˚ API[24] and over 13 TCF, the Viking has not been a prolific producer in Alberta. The Viking formation averages about 40,000 boe/d production from three main locations, Provost and Redwater, Alberta and Doddsland, Saskatchewan.  The main similarity of these three locations is they are all east of Edmonton and well into the foreland basin that existed in the Albian. The difference in success from the above mentioned areas and the rest of the Viking is related to the depositional history. In south western Saskatchewan the marine shales are overlain entirely by prodelta, coarsening upwards sandstone successions, as the local regression and transgression did not interbed prodelta sands and foreshore sands with shale and silt layers, as the minor transgressions during the local regression did not affect the mostly shallow marine deposition. In west to central Alberta, the minor transgression and regression cycles flooded prodelta and incised valley before large scale homolithic sands could be deposited. This suggests that vertical migration of hydrocarbons is restricted by thin beds of lower permeability that restrict flow. However, in south western Saskatchewan, where the minor transgressions and regressions only affected marine deposited sands and shales, as the delta was yet to prograde to that location, the prolific producing zones are above the first transgression and regression cycle and so the sands that were deposited after the first transgression are homolithic, coarsening upward prodelta sands, overlain by channel mouth bar sands and minor distributary channel sands that fine upwards before being flooded in the global transgression that created the Colorado shales to the east and Westgate shales to the west. This created a very desirable reservoir, as it coarsens upwards until it fines into a stratigraphic trap. This explains the success of Saskatchewan Viking versus the central and western Alberta Viking formation (see production graph in Appendix). However, by understanding the depositional history and exploration and production model can be constructed.

 

The regional Viking sands possess all the required inputs to create a petroleum system. The system has a sediment and organic input. The depositional environment is conducive to forming reservoir bodies. The Viking was buried to a depth to allow it to be within the oil and gas window and there exists a stratigraphic trap. The key to increasing production is related to understanding the depositional history. Within the study area of the Viking, the large sand beds, related to the local lowstands are interbedded with shale and mud due to the transgression and regression cycle related to the Cordilleran Orogeny. This creates a heterolithic sand reservoir where thin beds of lower permeability restrict vertical migration of hydrocarbons. The high bioturbidation and fine lamination of interbedded shale and silt make the net to gross sand calculation from logs misleading, however neutron density logs suggest porosity of 15-20%, indicating that production should be possible.

 

To produce the Viking Formation to the extent that it can be exploited a different model is required for different regions based on paleo-depositional history. To the west where the prodelta began the progradational cycle, heterolithic sand with shale interbeds cannot be produced vertically as the vertical permeability is impeded by interbed shales, but the horizontal permeability is high. However, in the east (south western Saskatchewan) the sands are much more homolithic and well placement is of lower concern. To maximize Alberta Viking production, horizontal wells should be drilled into Facies 1 and Facies 3, both sandstones. Within Facies 1, the middle to upper sands are the cleanest and within Facies 3, the middle sands are the cleanest. The key is to avoid the interbedded shales that divide the sand bodies.

 

 

References

Boreen, Thomas Dale. 1989 Sedimentology, Stratigraphy, and Depositional History of the Lower Cretaceous Viking Formation at Willesden Green, Alberta, Canada McMaster University, Hamilton, ON.

 

Leckie, Dale. Schroder-Adams, Claudia. Rosenthal, Lorne. And Wall John. 2000. An outcrop of the Albian Viking Formation and a southerly extension of the Hulcross/Harmon interval in west-central Alberta, Bulletin of Canadian Petroleum Geology. Volume. 48, No. 1, P, 30-42

 

MacEachern, James A. Zaitlin, Brian. Pemberton, George. 1999.  A Sharp-based Sandstone of the Viking Formation, Joffre Field, Alberta Canada: Criteria for Recognition of Transgressively Incised Shorface Complexes. Journal of Sedimentary Research, Volume. 69, NO. ,  P. 876–892

 

Power, Bruce. 1988. Coarsening Upward Shoreface and Shelf Sequences: Examples From the lower Cretaceous

Viking Formation at Joarcam, Alberta, Canada. Sequences, Stratigraphy, Sedimentology: Surface and Subsurface. Canadian Society of Petroleum Geologists, Memoir 15, p. 185-194.

 

Singbeil, Pete and Seifert, Mike. 2012 Review of Viking Resource Plays and Redwater Case Study. Canadian Discovery Ltd and Introspec Energy Group Inc.

Reinson, G.E., Warters, W.J., Cox, J. And Price, P.R. Cretaceous Viking Formation of the Western Canada Sedimentary Basin; in Geological Atlas of the Western Canada Sedimentary Basin, G.D. Mossop and I. Shetsen (comp.), Canadian Society of Petroleum Geologists and Alberta Research Council, URL <http://www.ags.gov.ab.ca/publications/wcsb_atlas/atlas.html

 

Hwang, In-Gul and  Heller, Paul  L.  202Anatomy of a transgressive lag: Panther Tongue Sandstone, Star Point Formation, central Utah. International Association of Sedimentologists, Sedimentology, Volume 49, 977–999