Diagenesis and Petrographic Reservoir Characterization of the Mission Canyon Formation, Southeastern Saskatchewan
Congwei Ji 1 and Osman Salad Hersi 1
Information from this publication may be used if credit is given. It is recommended that reference to this publication be made in the following form: Ji, C. and Salad Hersi, O. (2016): Diagenesis and petrographic reservoir characterization of the Mission Canyon Formation, southeastern Saskatchewan; in Summary of Investigations 2016, Volume 1, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2016-4.1, Paper A-5, 16p.
Abstract In southeastern Saskatchewan, the Mississippian Mission Canyon Formation was deposited on the northern platform margin of the Williston Basin and includes, from bottom to top, Tilston Beds, Alida Beds, Kisbey interval and Frobisher Beds. The formation is dominated by carbonate lithofacies; subordinate evaporites and sandstone lithofacies also occur within the formation. The lithologic properties and sedimentary structures of the formation indicate a depositional system of subtidal carbonate sand shoals to supratidal muddy carbonates and evaporites (Tilston, Alida and Frobisher beds) and localized sandy tidal creeks (Kisbey Sandstone). The depositional system developed on a ramp-type carbonate platform with a vertical stacking pattern controlled by relative sea-level fluctuations. The formation preserves a complex diagenetic history that affects the reservoir qualities of the various stratigraphic intervals of the formation. In this study, petrographic examination of cores and thin sections from the formation identified the diagenetic features in the rocks, and their paragenetic sequence and effects on the reservoir quality of the strata. Four major diagenetic processes profoundly affected porosity development of the Mission Canyon Formation. Cementation, compaction, dolomitization and dissolution were active throughout the evolution of the formation. Different degrees of porosity-destruction and porosity-enhancement features result in porosity and permeability differences among the lithofacies of the Mission Canyon Formation. The Tilston Beds and Kisbey interval show good porosity and permeability, the Alida Beds and Frobisher Beds exhibit moderate porosity and permeability. The tidal channel siliciclastics and carbonate sand shoal show good porosity and permeability.
Keywords: Mission Canyon Formation, southeastern Saskatchewan, Alida Beds, Kisbey interval, Frobisher Beds, Tilston Beds, porosity, diagenesis, reservoir quality, petrography, dolomitization, calcite cement
1. Introduction The Mississippian strata of southern Saskatchewan and adjacent North Dakota and Montana are prolific hydrocarbon producers that have been studied for many decades (Yurkowski, 2013). These strata were deposited on the northern flanks of the Williston Basin, a subcircular basin with a depocentre in North Dakota (Figure 1). The Madison Group forms the bulk of the Mississippian succession and consists of the Lodgepole, Mission Canyon and Charles formations, in ascending order (Figure 2). The Mission Canyon Formation of southeastern Saskatchewan consists of four stratigraphic units: Tilston Beds, Alida Beds, Kisbey interval and Frobisher Beds, in ascending stratigraphic order (Marsh, 2006; Nickel and Yang, 2011; Ji and Salad Hersi, 2014; Ji, 2016; Figure 2). The Mississippian Mission Canyon Formation of the Williston Basin comprises a mixed carbonate-siliciclastic-evaporitic succession (Figure 2). Carbonate lithology prevails in these rocks in regions both north and south of the Canada–USA border. Thinner, laterally extensive siliciclastic and evaporitic strata are also present. The stratigraphic nomenclature and interpretation of the depositional environments of these strata have been addressed by different researchers over the years (Thomas, 1954; Fuller, 1956; Edie, 1958; Fuzesy, 1960; Roberts, 1966; Kent, 1987, 2004, 2007; Kent et al., 1988; Witter, 1988; Legault, 1999; Howard, 2000; Halabura, 2006). Oil accumulations occur in the porous carbonate and subordinate sandstone units of the Mission Canyon Formation, and have been truncated and sealed by the pre- Mesozoic unconformity.
1 University of Regina, Department of Geology, 3737 Wascana Parkway, Regina, SK S4S 0A2 Although the Saskatchewan Ministry of the Economy has exercised all reasonable care in the compilation, interpretation and production of this product, it is not possible to ensure total accuracy, and all persons who rely on the information contained herein do so at their own risk. The Saskatchewan Ministry of the Economy and the Government of Saskatchewan do not accept liability for any errors, omissions or inaccuracies that may be included in, or derived from, this product.
Saskatchewan Geological Survey 1 Summary of Investigations 2016, Volume 1 Figure 1 – A) Location map showing the study area in southeastern Saskatchewan, configuration of the Williston Basin, and the location of the Sweetgrass Arch, Montana Trough and Antler foreland basin (modified from Nimegeers, 2006). B) Map showing the distribution of the wells examined in the study area. Numbered well locations are keyed to Table 1.
Saskatchewan Geological Survey 2 Summary of Investigations 2016, Volume 1 Figure 2 – Stratigraphic chart of Mississippian strata in southeastern Saskatchewan (modified from Nimegeers, 2006). The Williston Basin in Saskatchewan, North Dakota and Montana is a major intracratonic basin (Fowler and Nisbet, 1985; Kent and Christopher, 1994). The basin was created by uplift and erosion of the cratonic arches surrounding the basin in periods between transgressive-regressive cycles, as a result of differential subsidence of the basin during the cycles (Porter et al., 1982). Four major transgression and regression events occurred across the basin from the Cambrian to the Jurassic (Wilson, 1975). Mississippian sediments evolved as a transgressive-regressive cycle equivalent to the upper part of Sloss’s (1963) Kaskaskia Supersequence (Wilson, 1975). The Mississippian Madison Group of the Williston Basin in southern Saskatchewan contains a 400 to 700 m thick section of mainly carbonate succession with minor evaporite and sandstone sediments (Wegelin, 1984). The sedimentation pattern of the group is typical of a major upward-shoaling sequence, deposited as a thick basin-ward migrating wedge of sediments (Lake, 1991). Superimposed on this sequence are smaller-scale transgressive-regressive parasequences, which are interpreted to be the result of sea-level fluctuations (Wilson, 1975; Ji, 2016). Sediments of the
Saskatchewan Geological Survey 3 Summary of Investigations 2016, Volume 1 Mississippian Mission Canyon Formation were deposited in a relatively stable, broad, and shallow epicontinental sea in a periodically restricted environment (Richards, 1989; Rott and Qing, 2005). Several studies of the Mission Canyon Formation in North Dakota and Montana have emphasized the occurrence of solution-collapse breccias and their effect on porosity, permeability and hydrocarbon production (Roberts, 1966; Sando, 1974, 1988; Gargallo-Quinones, 1985). Studies of the depositional and diagenetic history of the Mission Canyon Formation include Lindsay and Kendall (1980); Lindsay (1982); Lindsay and Roth (1982); Vice (1988, 1993); Vice and Utgaard (1989, 1996); Smith (1991); and Smith and Dorobek (1993a, 1993b). Vice et al. (2000) established a paragenetic sequence for the Mission Canyon Formation in south-central Montana and northern Wyoming. Mundy and Roulston (1998) studied the diagenesis and porosity development within the Alida Beds in southeastern Saskatchewan. Despite the many studies addressing the lithologic, stratigraphic and diagenetic aspects of the Mission Canyon Formation in the northern Williston Basin, more detailed work on the diagenetic evolution of the formation and reservoir characterization is required. The present study is part of an M.Sc. thesis project by the senior author (Ji, 2016) to interpret the diagenetic features preserved in the various units of the formation, and establish their paragenetic sequence, diagenetic realms and effects on the reservoir qualities of the various lithologic units of the formation.
2. Methodology The study area is within Townships 1 to 8 and Ranges 30W1 to 6W2 in southeastern Saskatchewan (Figure 1). Cores from twenty-five wells and drill cuttings from four wells containing the Mission Canyon Formation were examined (Figure 1, Table 1). Eighty-five thin sections from nine of these cores were examined, and the microfacies and diagenetic properties of the rocks identified. The porosity and reservoir quality study is based on integration of petrographic attributes from core samples and thin sections with porosity and permeability data obtained from geoSCOUT for a few select wells (wells 9, 11, 13, 16 and 24 in Table 1) from the various strata of the Mission Canyon Formation.
Table 1 – List of wells studied in southeastern Saskatchewan, of which 25 have core available for examination (wells 1 to 25) and 4 have only drill cuttings available (wells 26 to 29). Well Number Well ID Licence Cored Interval Drill Cutting Number (m) Interval (m) 1 101/04-09-008-06W2 67B002 1228.0 to 1243.6 2 111/13-13-008-06W2 87I040 1181.0 to 1199.0 3 101/03-08-001-06W2 57D025 1759.8 to 1891.0 4 121/03-32-007-05W2 84A107 1224.0 to 1241.4 5 101/03-26-004-05W2 55J092 1374.0 to 1483.2 6 141/03-24-007-04W2 93H085 1208.0 to 1226.8 7 141/04-22-007-03W2 08J439 1195.0 to 1213.3 8 101/06-01-006-03W2 62L012 1220.7 to 1246.8 9 101/07-34-005-02W2 85G245 1227.0 to 1245.0 10 101/09-23-002-02W2 56J006 1371.0 to 1440.1 1475.2 to 1490.2 11 101/05-20-006-01W2 00F231 1190.0 to 1208.2 12 101/02-27-005-01W2 85K115 1183.0 to 1202.3 13 141/10-09-004-01W2 08C362 1238.5 to 1256.8 14 141/09-33-005-34W1 87K208 1152.0 to 1154.8 1155.0 to 1173.0 15 131/06-02-004-33W1 97G141 1173.5 to 1192.8 16 101/04-12-004-33W1 96I248 1164.6 to 1182.6 1183.0 to 1201.0
Saskatchewan Geological Survey 4 Summary of Investigations 2016, Volume 1 Well Number Well ID Licence Cored Interval Drill Cutting Number (m) Interval (m) 17 111/06-12-004-33W1 96K245 1164.0 to 1199.0 18 101/16-10-005-32W1 55C028 1074.4 to 1116.5 19 101/08-01-004-32W1 67F004 1091.2 to 1106.5 20 121/16-05-003-32W1 98F112 1192.8 to 1211.2 21 111/15-18-001-32W1 90G125 1281.5 to 1300.5 22 102/16-27-002-31W1 56K120 1100.5 to 1127.2 23 150/11-19-002-30W1 72L015 1075.0 to 1092.8 24 101/01-11-006-33W1 86J054 1133.0 to 1177.2 25 101/12-29-001-05W2 54D007 1859.3 to 1889.8 26 141/13-16-003-05W2 08G476 1595 to 1615 27 141/15-16-002-04W2 08J206 1602 to 1620 28 191/16-32-001-05W2 08H550 1720 to 1735 29 141/09-32-001-03W2 08C328 1623 to 1635
3. Lithology of the Mission Canyon Formation The lithology of the Mission Canyon Formation is dominated by carbonates, with subordinate sandstone and evaporite lithofacies. Ji and Salad Hersi (2013a, 2013b, 2014) identified eight lithofacies within the formation. They include i) oolitic, oncolitic and bioclastic packstone to grainstone; ii) oncolitic rudstone; iii) bioclastic mudstone to wackestone; iv) dolomudstone; v) sandstone; vi) sandy dolomudstone; vii) sandy packstone to grainstone; and viii) anhydrite. Descriptions of these lithofacies are summarized in Table 2. The nature of the framework grains and sedimentary structures indicate that these lithofacies were deposited in a subtidal to supratidal environment on a ramp-type carbonate platform (Ji and Salad Hersi, 2013a, 2013b, 2014; Ji, 2016).
Table 2 – Lithofacies description of the studied strata.
Stratigraphic Facies Lithofacies Description Sedimentary Structures Occurrence Mainly in Tilston, Light to dark grey Fenestral structure and microbial Alida and Frobisher PG Packstone/grainstone bioclastic packstone and laminations beds; locally in grainstone Kisbey interval Fenestral structure and microbial RD Rudstone Grey oncolitic rudstone Frobisher Beds laminations Fenestral structure, horizontal Mainly in Frobisher, Light to dark grey MW Mudstone/wackestone laminations, microbial Alida and Tilston mudstone/wackestone laminations beds Distributed Pale grey to grey Fenestral structure, mudcracks throughout the DS Dolomudstone dolomudstone and stromatolites Mission Canyon Formation Yellowish grey to dark Massive, burrows, some partial grey fine SS Sandstone/siltstone cross-bedding or horizontal Kisbey interval sandstone/siltstone to laminations quartz arenite Pale to dark grey sandy SD Sandy dolomudstone Massive Kisbey interval dolomudstone Sandy Grey sandy packstone/ SP Fenestral structure Kisbey interval packstone/grainstone grainstone Frobisher, Alida AH Anhydrite White and red anhydrite Massive and mosaic texture and Tilston beds
Saskatchewan Geological Survey 5 Summary of Investigations 2016, Volume 1 4. Diagenesis The Mission Canyon Formation has undergone a complex and extensive evolution. The diagenetic processes that can be identified within the Mission Canyon Formation are micritization, episodic calcite cementation, dolomitization, anhydritization, dissolution, compaction and fracturing.
a) Micritization Micritization accounts for the earliest changes to the framework grains in rocks of the Mission Canyon Formation. In a study of thin sections of core samples, total to partial micritization (Figures 3A, 3B), as well as formation of a thin micrite coating on some grains (e.g., skeletal grains within Figures 3A and 3B), is evident and micritization is seen to form centripetally. Micrite envelopes around grains result from incomplete micritization (Bathurst, 1966), whereas completely micritized grains show no trace of original microstructure (Swinchatt, 1965). Micritization is a diagenetic process that commonly occurs in shallow-marine phreatic zones (Longman, 1980; Tucker and Wright, 1990). Micritization mainly develops in the packstone to grainstone and sandy packstone to grainstone lithofacies, which are more common in the Kisbey interval and Alida Beds. Production of micritic particles during micritization may have contributed to the overall matrix content within a lithofacies, thereby reducing the original intergranular effective porosity of the sediments.
b) Episodic Calcite Cementation Calcite cement is the most common diagenetic feature in rocks of the Mission Canyon Formation, occurring as three different types: isopachous fibrous calcite cement, bladed calcite cement and equant calcite cement (Figures 3A, 3B, 3C). The isopachous fibrous calcite cement and bladed calcite cement appear as a thin cement rim around the grains and occlude both interparticle and intraparticle pore spaces. The crystal shape of the isopachous fibrous calcite is usually micro-sized, needle-like or columnar crystals. The bladed calcite crystals grow perpendicular to the edges of the grains, and generally show a gradual increase in width away from the grains along their length. Both fibrous and bladed calcite cements are non-ferroan. Equant calcite cement is characterized by equant to elongate, anhedral to subhedral, non-ferroan crystals. The crystal size of the equant calcite is usually larger than 0.1 mm. This cement occurs in primary and secondary pore spaces and postdates both fibrous and bladed calcite cements. Primary intragranular and interparticle porosity is often partially or completely filled by this equant calcite cement (Figures 3A, 3B, 3C). The three types of cement show a diagenetic evolution from marine to meteoric realms. The fibrous calcite cement, which precipitated from marine water, represents an early-diagenetic feature (Tucker and Wright, 1990). This was followed by the bladed calcite, which may indicate a precipitant of mixed marine and meteoric water (Folk, 1974; Tucker and Wright, 1990). Equant calcite cement has been interpreted as a precipitate from meteoric phreatic water (Folk, 1974; James and Choquette, 1990; Tucker and Wright, 1990; Flügel, 2004). The fibrous and bladed calcite cements are more common in the Kisbey interval and Alida Beds, the equant calcite cement occurs in all intervals of the Mission Canyon Formation. The calcite cements are mainly distributed within the packstone to grainstone, sandy packstone to grainstone, and rudstone lithofacies throughout the study area. Because the three types of calcite cement have filled the primary and secondary pore spaces in the rocks, they have negatively affected the reservoir quality of the formation.
c) Dolomitization Dolomitization is an important diagenetic process in rocks of the Mission Canyon Formation and is characterized by two different types of dolomite (Figure 4): fine crystalline dolomite (Figure 3C) and fine to medium crystalline replacive dolomite. Both stages of dolomite are recognized in most of the carbonate lithofacies (including dolomudstone and lime mudstone to grainstone lithofacies) throughout the Mission Canyon Formation. The dolomitization within the Mission Canyon Formation locally creates porosity, thereby increasing the overall potential reservoir quality of the various stratigraphic intervals it has affected.
Saskatchewan Geological Survey 6 Summary of Investigations 2016, Volume 1
Figure 3 – A) Photomicrograph of oolitic bioclastic grainstone showing micrite envelope (Me) and equant calcite cement (Ec). Photo was taken under plane-polarized light. Kisbey interval, 1195.5 m, 111/13-13-008-6W2; 87I040. B) Photomicrograph of bioclastic peloidal grainstone showing micritization (Mi), micrite envelope (Me), fibrous calcite cement (Fc), bladed calcite cement (Bc) and equant calcite cement (Ec). Photo was taken under plane-polarized light. Kisbey interval, 1191.0 m, 101/04-12-004- 33W1; 96I248. C) Photomicrograph of oolitic grainstone showing equant calcite cement (Ec), anhydrite (An) and fine dolomite (Fd); the thin section is stained with Alizarin Red. Photo was taken under plane-polarized light. Alida Beds, 1185.5 m, 111/06-12- 004-33W1; 96K245. D) Photomicrograph of sandstone showing anhydrite cement (An). Photo was taken under cross-polarized light. Kisbey interval, 1223.1 m, 101/04-12-004-33W1; 96I248. E) Core photograph showing vuggy porosity filled by anhydrite (An). Frobisher Beds, 1103.5 m, 101/16-27-2-31W1; 56K022. F) Photomicrograph of bioclastic oolitic grainstone showing stylolite (St) and suture contact (Sc). Photo was taken under plane-polarized light. Tilston Beds, 1870.6 m, 101/12-29-001-05W2; 54D007.
Saskatchewan Geological Survey 7 Summary of Investigations 2016, Volume 1 The fine crystalline dolomite (dolomite event I) generally exhibits loosely packed, fine anhedral to subhedral crystals (Figure 3C) that are commonly pervasive, obscuring most of the original textures and grains; however, outlines of bioclastic and peloidal fragments can still be observed in some samples. This dolomitization event created intercrystalline microporosity and microvuggy porosity, potentially leading to an enhancement of porosity and permeability. This fine crystalline dolomite is interpreted as the product of early, near-surface diagenetic processes comparable to the penecontemporaneous dolomitization well documented in the literature (e.g., Landes, 1946; Friedman and Sanders, 1967; Butler, 1969; Hsu and Siegenthaler, 1969; Gregg and Sibley, 1984; Saller, 1984; Hardie, 1987; Moore, 1989; Tucker and Wright, 1990; Purser et al., 1994; Morrow, 1998; Flügel, 2004; Marsh, 2006). The fine to medium crystalline replacive dolomite (dolomite event II) is characterized by fine to medium, subhedral to euhedral crystals that postdate compaction features (such as stylolites) and other diagenetic features. The replacive dolomite tends to be fabric-selective and preferentially replaces the micritic matrix rather than allochems and burrows. Intercrystalline porosity, genetically related to the dolomitization, is also well developed and associated with this dolomite event. This dolomite also precipitates as cement that partially fills previously existing pore spaces (e.g., inter- and intragranular pores). The degree of dolomitization in this event ranges from rare floating dolomite rhombs to partial replacement of the micritc matrix, to locally complete replacement of original rock constituents. The characteristics of the fine to medium dolomite can be used to suggest that this type of dolomite formed within a shallow to medium burial environment (Sibley and Gregg, 1987; Amthor and Friedman, 1991).
d) Anhydritization Anhydritization is also a very common diagenetic process within rocks of the Mission Canyon Formation. The anhydrite, when seen in hand specimen, is commonly white in colour, and in thin section it typically has a medium to coarse blocky or bladed crystalline appearance (Figures 3C, 3D). There are two stages of anhydrite cement in the studied strata: medium blocky or coarse bladed crystals filling interparticle or intraparticle porosity (Figures 3C, 3D), and coarse bladed crystals filling vuggy porosity (Figure 3E) that is older than the anhydrite cement filling the inter- and intraparticle spaces (the former is dissolved and the latter fills in the dissolution pores). Based on the studied core, anhydrite is most common in the sandstones of the Kisbey interval, and subordinate in the other units of the Mission Canyon Formation. Diagenetic anhydrite destroys much of the secondary porosity, reducing the overall reservoir quality of the formation.
e) Dissolution Dissolution within the Mission Canyon Formation occurred in two stages. The initial stage postdates the fibrous and bladed calcite cements (Figure 4; as evidenced by etched outlines of calcite). Although porosity enhancement accompanied this initial dissolution stage, later events (e.g., precipitation of anhydrite cement, equant calcite cement and dolomite event II, and compaction; Figure 4) partially destroyed the pore spaces that had been created earlier. The second dissolution event, during which relatively large moldic pores were formed, occurred at a later stage (Figure 4). Petrographic evidence (such as etched outlines of calcite and dolomite cements) shows that the second stage of dissolution postdates the precipitation of equant calcite and fine to medium crystalline dolomite. The two stages of dissolution occur in all four stratigraphic units of the Mission Canyon Formation and are common in the mudstone to wackestone lithofacies in the northeast corner of the study area. Dissolution is one of the most important events related to creating porosity for the reservoir and increasing the overall reservoir quality of the formation, especially in the Frobisher Beds.
f) Compaction There are two types of compaction features recognized from core and thin-section studies of rocks of the formation: mechanical, and chemical. Mechanical compaction caused deformation and breakage of grains (e.g., ooids), and chemical compaction led to the generation of dissolution seams and stylolites (Figure 3F). Chemical compaction features such as stylolites and microstylolites are common within the Mission Canyon Formation, especially in the packstone/grainstone lithofacies (Figure 3F). Compaction destroyed a good portion of the porosity, reducing the overall reservoir quality of the formation.
Saskatchewan Geological Survey 8 Summary of Investigations 2016, Volume 1 g) Fractures Fractures in the studied rocks are typically vertical and partially filled by white anhydrite cement (anhydrite I and II). Fractures are more common in the fragile limestone lithofacies in the Mission Canyon Formation (e.g., mudstone and bioclastic wackestone). Although later partially plugged by the anhydrite cement (anhydrite I and II), fracture generation contributed to increasing the original effective secondary porosity of the sediments.
h) Paragenetic Sequence Based on the petrographic study of the diagenetic features in the rocks of the Mission Canyon Formation, the paragenetic sequence (from earliest to latest) is as follows: micritization and micrite envelope; fibrous calcite cement; bladed calcite cement; fine crystalline dolomite (dolomite event I); physical compaction; dissolution event I; fractures; equant calcite cement; fine to medium crystalline dolomite (dolomite event II); anhydrite cement I; dissolution event II; and anhydrite cement II (Figure 4).
Figure 4 – Paragenetic sequence of the diagenetic features observed in the Mission Canyon Formation in southeastern Saskatchewan, and their effect on porosity.
5. Porosity and Reservoir Quality Porosity and permeability in rocks of the Mission Canyon Formation is determined in part by depositional facies (Lindsay, 1988; Petty, 1988); however, diagenetic events have a significant effect on the present-day reservoir conditions of the formation. Thus, both diagenesis and original textures of the various lithofacies of the formation must be taken into account to achieve better hydrocarbon production. Following the porosity scheme of Choquette and Pray (1970), seven types of porosity can be recognized: interparticle, intraparticle, intercrystalline, fenestral, fracture, vuggy and moldic, several of which are shown in the photos in Figure 5. Primary interparticle porosity is one of the most common porosity types in rocks of the Mission Canyon Formation. The packstone/grainstone, rudstone, and sandstone/siltstone lithofacies exhibit good interparticle porosity (10%; Figure 5A), although most of the pore spaces are occluded by calcite, dolomite and anhydrite cement. Intraparticle
Saskatchewan Geological Survey 9 Summary of Investigations 2016, Volume 1 pores are also common in the studied strata and usually develop in the packstone/grainstone lithofacies (Figure 5B). Intercrystalline porosity is related to the pervasive replacement of limestone by dolomite (Figure 5C). Fenestral porosity (Figure 5E) is one of the important types of porosity in the study area. It is common in the packstone/grainstone lithofacies. Fracture porosity is also present throughout the Mission Canyon Formation (Figure 5D). Although vuggy and moldic porosities are mainly due to dissolution event II, the vuggy porosity is the principle type of porosity in the study area (Figure 5F). Moldic porosity is a minor contributor to the enhancement of porosity throughout the formation and mainly occurs in the bioclastic mudstone/wackestone lithofacies. Both moldic and vuggy porosities are partially filled by later anhydrite cement (anhydrite II). The porosity types in the Tilston Beds are mainly interparticle (Figure 5A) and vuggy. Porosity is influenced by burial depth and calcite cement dissolution, which partially reinstates the porosity. However, the highest porosity values are associated with natural fractures. Higher values of permeability are also associated with natural fractures. Porosity within the Tilston Beds is generally very well developed (Figure 5A); however, permeability is very low. As an example, in well 101/01-11-006-33W1; 86J054 porosity ranges from 8.7 to 28.7% (average 19.7%, n = 25), but permeability varies from 0.19 to 76.2 millidarcies (mD) (average 33.7 mD, n = 25). The packstone/grainstone lithofacies shows relatively good porosity in the Tilston Beds, but the dolomudstone lithofacies appears denser, with lower porosity (Figure 6A). The representative porosity types in the Alida Beds are interparticle, intraparticle, moldic and vuggy. In the northeast part of the study area, the Alida Beds have porosity ranging from 6.6 to 25% (average 14.5%, n = 90), and permeability varying from 0.01 to 96.7 mD (average 11.0 mD, n = 90) but concentrated in the 0 to 40 mD range (Figure 6B). These strata can develop into excellent reservoirs, with up to 25% porosity. The micritic coatings that formed on the bioclasts tend to suppress the syntaxial overgrowths of the calcite cement that normally destroy the interparticle porosity in the crinoid-rich grainstone/packstone lithofacies (Figure 5B). Interparticle and intercrystalline porosity types are dominant in the Kisbey interval. Moreover, dark-coloured, dolomitized mudstone intraclasts, which are often dissolved, contribute microporosity to the Kisbey interval. Near the eastern end of the Kisbey erosional line (e.g., in wells 101/04-12-004-33W1; 96I248, 101/05-20-006-01W2; 00F231, and 141/10-09-004-01W2; 08C362), the Kisbey interval exhibits porosities of up to 29.5% (average 18.2%, n = 68) and permeabilities from 0.02 to 780 mD (average 199.3 mD, n = 68; Figure 6C). Porosity increases with increasing permeability in the Kisbey interval. The sandstone/siltstone lithofacies shows the best porosity and permeability of all the lithofacies in the Mission Canyon Formation (Figure 6C). The main reservoir lithology in the Kisbey interval is a clean, well-sorted, and fine- to medium-grained quartz arenite (lithofacies v) with anhydrite, calcite and dolomite cement. The primary interparticle porosity is well interconnected. The Frobisher Beds contain a large amount of moldic, fenestral, vuggy and interparticle porosity within the packstone and grainstone lithofacies (Figures 5D, 5E and 5F). As the Frobisher Beds are adjacent to the top of the Mississippian unconformity surface in most of the study area, anhydrite has cemented and occluded many of the interparticle, vuggy, and fenestral pores (Figures 5D, 5E and 5F). The wackestone intervals exhibit scattered moldic porosity (e.g., bioclasts). In well 101/07-34-005-02W2; 85G245, the porosities range from 5.7 to 24.2% (average 11.3%, n = 18) and permeabilities from 0.02 to 127 mD (average 45.5 mD, n = 18; Figure 6D). The mudstone/ wackestone lithofacies shows relatively good vuggy porosity (Figure 5F).
Saskatchewan Geological Survey 10 Summary of Investigations 2016, Volume 1 Figure 5 – A) Photomicrograph of peloidal grainstone showing interparticle porosity (It). Photo was taken under cross-polarized light. Tilston Beds, 1158.5 m, 101/01-11-006-33W1; 86J054. B) Photomicrograph of bioclastic grainstone showing intraparticle porosity (Ia). Photo was taken under plane-polarized light. Alida Beds, 1122.9 m, 101/01-11-006-33W1; 86J054. C) Photo- micrograph of dolomudstone showing intercrystalline porosity (Ic). Photo was taken under plane-polarized light. Kisbey interval, 1222.7 m, 101/03-24-007-4W2; 93H085. D) Core photograph of oncoidal grainstone showing fracture porosity (Fr). Frobisher Beds, 1232.1 m, 101/04-09-008-06W2; 61J038. E) Core photograph showing fenestral porosity (Fe) filled by anhydrite. Frobisher Beds, 1157.1 m, 141/09-33-005-34W1; 87K208. F) Core photograph showing vuggy porosity (Vu). Frobisher Beds, 1185.5 m, 101/02-27-005-01W2; 85K115.
Saskatchewan Geological Survey 11 Summary of Investigations 2016, Volume 1 Figure 6 – Crossplots of Mission Canyon Formation porosity and permeability in samples from A) the Tilston Beds; B) the Alida Beds; C) the Kisbey interval; and D) the Frobisher Beds. Abbreviations: K-Max = maximum permeability (in millidarcies (mD)); lithofacies DS = dolomudstone; lithofacies PG = packstone/grainstone; lithofacies SS = sandstone/siltstone; lithofacies MW = mudstone/wackestone.
6. Conclusions Based on petrographic investigation of the Misson Canyon Formation in southeastern Saskatchewan, the following conclusions are drawn:
1) The recognized diagenetic features and their paragenetic sequence are as follows: micritization and micrite envelope; fibrous calcite cement; bladed calcite cement; fine crystalline dolomite (dolomite event I); physical compaction; dissolution event I; fractures; equant calcite cement; fine to medium crystalline dolomite (dolomite event II); anhydrite cement I; dissolution event II; and anhydrite cement II. Fracture, dissolution and dolomitization events create porosity and permeability in the rock and thus have increased the overall reservoir quality of the formation. 2) Seven types of porosity are recognized: interparticle; intraparticle; intercrystalline; fenestral; fracture; vuggy; and moldic. 3) The Tilston Beds and Kisbey interval show good porosity (Tilston: average 19.7%; Kisbey: average 18.2%) and permeability (Tilston: average 33.7 mD; Kisbey: average 199.3 mD). In comparison, the Alida Beds and Frobisher Beds exhibit moderate porosity (Alida: average 14.5%; Frobisher: 11.3%) and permeability (Alida: average 11.0 mD; Frobisher: average 45.5 mD). The permeability correlates positively with the porosity. The strata in the tidal channel (Kisbey interval) and carbonate sand shoal (Tilston, Alida and Frobisher beds) environments show good porosity and permeability.
Saskatchewan Geological Survey 12 Summary of Investigations 2016, Volume 1 7. Acknowledgments This project is financially supported by the Government of Saskatchewan through the Saskatchewan Geological Survey. The authors extend their gratitude to the Saskatchewan Ministry of the Economy’s Subsurface Geological Laboratory for providing free access to core, as well as providing pertinent data and materials. We also thank the staff of the core facility for their core handling and support. We would like to thank Hairuo Qing and Maria Velez for their helpful suggestions. My special thanks go to Arden Marsh and Melinda Yurkowski for reviewing and editing this paper.
8. References Amthor, J.E. and Friedman, G.M. (1991): Dolomite – rock textures and secondary porosity development in Ellenburger Group carbonates (Lower Ordovician), west Texas and southeastern New Mexico; Sedimentology, v.38, p.343-362. Bathurst, R.G.C. (1966): Boring algae, micrite envelopes and lithification of molluscan biosparites; Geological Journal, v.5, p.15-32. Butler, G.P. (1969): Modern evaporite deposition and geochemistry of coexisting brines, the Sabkha, Trucial Coast, Arabian Gulf; Journal of Sedimentary Petrology, v.39, no.1, p.70-89. Choquette, P.W. and Pray, L.C. (1970): Geologic nomenclature and classification of porosity in sedimentary carbonates; AAPG Bulletin, v.54, no.2, p.207-250. Edie, R.W. (1958): Mississippian sedimentation and oil fields in southeastern Saskatchewan; AAPG Bulletin, v.42, p.94-126. Flügel, E. (2004): Microfacies of Carbonate Rocks: Analysis, Interpretation and Application; Springer-Verlag, New York, 976p. Folk, R.L. (1974): The natural history of crystalline calcium carbonate: effect of magnesium content and salinity; Journal of Sedimentary Petrology, v.44, p.40-53. Fowler, C.M.R. and Nisbet, E.G. (1985): The subsidence of the Williston Basin; Canadian Journal of Earth Sciences, v.22, p.408- 415. Friedman, G.M. and Sanders, J.E. (1967): Origin and occurrence of dolostones; Chapter 6 in Carbonate Rocks: Origin, Occurrence and Classification, Chilingar, G.V., Bissell, H.J. and Fairbridge, R.W. (eds.), Developments in Sedimentology, Volume 9, Part A, Elsevier B.V., p.267-348. Fuller, J.G.C.M. (1956): Mississippian Rocks and Oilfields of Southeastern Saskatchewan; Saskatchewan Department of Mineral Resources, Report 19, 72p. Fuzesy, L.M. (1960): Correlation and Subcrops of the Mississippian Strata in Southeastern and South-Central Saskatchewan; Saskatchewan Department of Mineral Resources, Report 51, 63p. Gargallo-Quinones, M. (1985): Study of the ancient karstification and brecciation in the Madison Limestone (Mississippian) in Wyoming; M.Sc. thesis, State University of New York at Stony Brook, New York, 208p. Gregg, J.M. and Sibley, D.F. (1984): Epigenetic dolomitization and the origin of xenotopic dolomite texture; Journal of Sedimentary Petrology, v.54, p.907-931. Halabura, S.P. (2006): The Mississippian of southeastern Saskatchewan: regional considerations; in Saskatchewan and Northern Plains Oil & Gas Symposium 2006, Gilboy, C.F. and Whittaker, S.G. (eds.), Saskatchewan Geological Society, Special Publication No. 19, p.146-164. Hardie, L.A. (1987): Dolomitization: a critical view of some current views; Journal of Sedimentary Petrology, v.57, p.166-183. Howard, P. (2000): Mississippian sedimentology, depositional and diagenetic control on the Kisbey Sandstone petroleum reservoir development, Williston Basin; M.Sc. thesis, University of British Columbia, Vancouver, British Columbia, 250p. Hsu, K.J. and Siegenthaler, C. (1969): Preliminary experiments on hydrodynamic movement induced by evaporation and their bearing on the dolomite problem; Sedimentology, v.12, p.11-25.
Saskatchewan Geological Survey 13 Summary of Investigations 2016, Volume 1 James, N.P. and Choquette, P.W. (1990): Limestones – the meteoric diagenetic environment; in Diagenesis, McIlreath, I.A. and Morrow, D.W. (eds.), Geological Association of Canada, Reprint Series 4, Ottawa, p.35-74. Ji, C. (2016): Lithofacies, cyclicity and diagenetic characteristics of the Mississippian Mission Canyon Formation, southeast Saskatchewan; M.Sc. thesis, University of Regina, Regina, Saskatchewan, 140p. Ji, C. and Salad Hersi, O. (2013a): Sedimentary and facies description of Mississippian Alida-Kisbey-Frobisher stratigraphic interval, Mission Canyon Formation, southeast Saskatchewan; abstract in Proceedings of the Twenty-first Williston Basin Petroleum Conference, April 30 to May 2, 2013, Regina, Saskatchewan. Ji, C. and Salad Hersi, O. (2013b): Lithofacies distribution of the Mississippian Alida-Kisbey-Frobisher stratigraphic interval, southeastern Saskatchewan; in Summary of Investigations 2013, Volume 1, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2013-4.1, Paper A-6, 15p. Ji, C. and Salad Hersi, O. (2014): Lithofacies and cyclicity of Mississippian Alida-Kisbey-Frobisher interval, southeastern Saskatchewan; Geoconvention 2014: FOCUS, May 12 to 16, Calgary, Alberta, talk abstract, Canadian Society of Petroleum Geologists, URL
Saskatchewan Geological Survey 14 Summary of Investigations 2016, Volume 1 Lindsay, R.F. and Roth, M.S. (1982): Carbonate and evaporite facies, dolomitization and reservoir distribution of the Mission Canyon Formation, Little Knife Field, North Dakota; in Fourth International Williston Basin Symposium, Proceedings of a Symposium Held in Regina, Saskatchewan, October 5, 6, 7, 1982, Christopher, J.E. and Kaldi, J. (eds.), Saskatchewan Geological Society, Special Publication No. 6, p.153-179. Longman, M.W. (1980): Carbonate diagenesis as a control on stratigraphic traps (with example from the Williston Basin); AAPG Bulletin, v.64, p.461-487. Marsh, A.K.A. (2006): Sedimentology and diagenesis of the Frobisher succession in the Steelman field in southeast Saskatchewan; M.Sc. thesis, University of Regina, Regina, Saskatchewan, 177p. Moore, C.H. (1989): Carbonate Diagenesis and Porosity; Developments in Sedimentology, Volume 46, Elsevier Science, New York, 338p. Morrow, D. (1998): Regional subsurface dolomitization: models and constraints; Geoscience Canada, v.25, no.2, p.57-70. Mundy, D.J.C. and Roulston, P.E. (1998): Diagenesis and porosity development of subcropped Mississippian carbonate oil reservoir, an example from the Alida beds of the Pheasant Rump Pool, southeast Saskatchewan; in Eighth International Williston Basin Symposium, Proceedings of a Symposium Held in Regina, Saskatchewan, 19, 20 and 21 October 1998, Christopher, J.E., Gilboy, C.F., Paterson, D.F. and Bend, S.L. (eds.), Saskatchewan Geological Society, Special Publication No. 13, p.86-102. Nickel, E. and Yang, C. (comps.) (2011): Mississippian subcrop map and selected oil-production data, southeastern Saskatchewan; Saskatchewan Ministry of Energy and Resources, Open File 2011-56, poster. URL
Saskatchewan Geological Survey 15 Summary of Investigations 2016, Volume 1 Smith, T.M. (1991): Diagenesis of shallow marine carbonate rocks: isotopic and trace element constraints from the Mississippian Mission Canyon Formation, central and southwestern Montana; Ph.D. thesis, Texas A&M University, College Station, Texas, 126p. Smith, T.M. and Dorobek, S.L. (1993a): Alteration of early-formed dolomite during shallow to deep burial, Mississippian Mission Canyon Formation, central to southwestern Montana; Geological Society of America Bulletin, v.105, no.11, p.1389-1399. Smith, T.M. and Dorobek, S.L. (1993b): Stable isotopic composition of meteoric calcites, evidence for Early Mississippian climate change in the Mission Canyon Formation, Montana; Tectonophysics, v.222, no.3-4, p.317-331. Swinchatt, J.P. (1965): Significance of constituent composition, texture and skeletal breakdown in some recent carbonate sediments; Journal of Sedimentary Petrology, v.42, p.162-167. Thomas, G.E. (1954): The Mississippian of the northeastern Williston Basin; Transactions of the Canadian Institute of Mining and Metallurgy, v.57, p.68-74. Tucker, M.E. and Wright, V.P. (1990): Carbonate Sedimentology; Blackwell, Oxford, UK, 482p. Vice, M.A. (1988): Depositional environments and diagenesis in an interval of the Mission Canyon Limestone (Madison Group, Mississippian), south-central Montana and northern Wyoming; M.Sc. thesis, Southern Illinois University at Carbondale, Carbondale, Illinois, 149p. Vice, M.A. (1993): Deposition and diagenesis of the Mississippian Mission Canyon Limestone, northern Bighorn Basin region, southcentral Montana and northern Wyoming; Ph.D. thesis, Southern Illinois University at Carbondale, Carbondale, Illinois, 281p. Vice, M.A. and Utgaard, J.E. (1989): Depositional environments in the Mississippian Mission Canyon Limestone (Madison Group, Mississippian), northern Bighorn Basin region, Montana and Wyoming; in Geological Resources of Montana, 1989 Field Conference Guidebook: Montana Centennial Edition, Volume 1, French, D.E. and Grabb, R.F. (eds.), Montana Geological Society, p.55-64. Vice, M.A. and Utgaard, J.E. (1996): Sedimentation and early diagenesis on the Mississippian Mission Canyon Platform in the northern Bighorn Basin region; in Resources of the Bighorn Basin, Bowen, C.E., Miller, T. and Kirkwood, S. (eds.), Wyoming Geological Association, Guidebook No. 47, p.145-157. Vice, M.A., Fifarek, R.H. and Utgaard, J.E. (2000): Diagenesis of the Mississippian Mission Canyon Formation, northern Bighorn Basin region, south-central Montana and northern Wyoming; abstract in Montana Geological Society: 50th Anniversary Symposium: Montana/Alberta Thrust Belt and Adjacent Foreland: Volume II, Montana Geological Society, p.32. Wegelin, A. (1984): Geology and reservoir properties of the Weyburn field, southeastern Saskatchewan; in Oil and Gas in Saskatchewan, Proceedings of a Symposium Held in Regina, Saskatchewan, 11 and 12 October 1984, Lorsong, J.A. and Wilson, M.A. (eds.), Saskatchewan Geological Society, Special Publication No. 7, p.71-82. Wilson, J.L. (1975): Carbonate Facies in Geologic History; Springer-Verlag, New York, 471p. Witter, D.N. (1988): Stratal architecture and volumetric distribution of facies tracts, Upper Mission Canyon Formation (Mississippian) Williston Basin, North Dakota; M.Sc. thesis, Colorado School of Mines, Golden, Colorado, 142p. Yurkowski, M. (2013): Saskatchewan oil and gas update; URL
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