CHAPTER 4 WOODBEND GROUP RESERVOIRS N.L. Anderson, Department of' Geological Sciences, Ohio University; D. White, Canadian Occidental Petroleum Ltd, Calgary, Alberta; R. Hinds, Department of Geology, University of Pretoria 3 9 1 INTRODUCTION estimated to be 490 x 10(' m of oil and 240 x 10 m of gas. All of authors prefer to classify the pinnacles and atolls as stratigraphic (Leduc-Woodbend) but are difficult to differentiate elsewhere the example seismic lines incorporated into this chapter cross Leduc traps and the fringing reefs generally as combination structural and (Morinville/St. Albert-Big Lake). These data are more thoroughly Fm reservoirs. stratigraphic traps. discussed within the interpretations of the specific examples. The stratigraphy and the geological history of the Woodbend Gp (Fig. 4.1) are described in the Introduction to this Atlas. It is The Leduc Fm developed as fringing reef complexes, linear The seven Leduc Fm reservoirs analyzed in this chapter are PENHOLD FIELD therein noted that the Woodbend Gp consists principally of chains of reefs, isolated atolls and isolated pinnacles (Fig. 4.2). In geographically and morphologically diverse. Included are reservoirs carbonates and shales, with the carbonates, typically of organic the subsurface of central Alberta these build-ups overlie a regional within fringing reef complexes (Penhold), atolls (Redwater, abed, origin, forming the reservoir facies whereas, the shales, generally platform facies, the Cooking Lake Fm, whereas in the Sturgeon Sturgeon Lake, Leduc-Woodbend), pinnacles (Rich, Leduc­ INTRODUCTION basinal infill, are primary source rocks. Evaporites are locally L1ke area, they rest on the Beaverhill Lake Gp. The Leduc Fm in Woodbend) and reefs (Sturgeon Lake, Morinville/St. Albert-Big interbedded with the carbonates (Klovan, 1964: Mountjoy, 1980; central Alberta is typically encased and sealed by impermeable shales Lake). These build-ups are distributed throughout southcentral and Penhold field is located in the southern part of the east Ireton Stoakes, 1980; Stoakes and Wendte, 1987). of the Duvernay and Ireton formations. In contrast the reefs to the westcentral Alberta. Sediments of the Alberta basin dip to the shale basin, along the western margin of the Bashaw complex, a northeast are capped hy and in communication with Grossmont Fm southwest and consequently, post-reef strata in the examples range northern extension of the southern Alberta shelf (Fig. 4.2). The field There are three principal reservoir units within the Woodbend carbonates. As a result of differential compaction of reef and from a minimum thickness of 950 m at Redwater to a maximum is divided into 14 assigned and unassigned pools (Table 4.1), six of Gp: 1) the Leduc Fm 2) Grossmont Fm and 3) Camrose Mbr of the off-reef facies, overlying strata typically drape across Leduc Fm thickness of 4000 m at abed. As expected, both the depth of burial which are in the Penhold fie Id area (Fig. 4.3, Tables 4.1 and 4.2). Ireton Fm (Fig. 4.1). Economically the Leduc Fm is the most build-ups. Drape is a function of the height of the reef, the thickness and the lithology of the encompassing shales profoundly affect the Two of these six pools, D-3A and D-2A are Devonian reservoirs significant of the three units with initial recoverable reserves of the overlying sedimentary section and the relative cOl11pactibilities morphology of the reef and the adjacent sedimentary section, (Leduc Fm and Nisku Fm respectively). The other four, the Lower of the reef and off-reef facies. specifically with respect to the magnitude of differential compaction and the resultant drape. ACKNOWLEDGEMENTS EAST WEST Leduc Fm rcscrvoirs generally develop within the up-dip edges of SHALE BASIN SHALE BASIN I ~ both the fringing reef complexes and the larger atolls and throughout The Leduc Fm examples are morphologically diverse and The authors gratefully acknowledge the following individuals z NISKU FORMATION the smaller atolls and the pinnacles. Whether these are stratigraphic consequently their seismic signatures are diverse. Time-structural and companies for their colltribution to this chapter: Len Hills for 0 z AMRosE MEMB traps or a combination stratigraphic and structural trap is arguable. drape, velocity pull-up and the contrast between the seismic images reviewing submissions; Dave Waddington (Canadian Occidental < rr\ C > Z Indeed isolated reefs (pinnacles and atolls) are encased in of the reef and the off-reef shales are characteristically associated Petroleum Ltd.) for his assistance in defining the geology of the w (/) C IRETON Jl-EDU$... FORMATION ~~ impermeable shale scals and could form traps regardless of the scnse with the seismic signatures of the Leduc Fm. In the suite of the abed Area; Don Dodds (Canadian Occidental Petroleum Ltd.) for a:: tr: FM -j~ CO W ~ DUVERNAY FM of regional dip. In contrast, reservoirs within the fringing reef Leduc Fm reef examples it will be shown that the Wabamun event computer generating the contour maps and profiles for the 8! complexes are generally confined to the up-di p edges of these drapes by as little as 5 ms (Rich Field) and by as much as 20 ms Redwater and Sturgeon Lake reefs; Barry Frandsen (Virtual a: ~ ;:) -MAJEA~~A"r-~ COOKING LAKE FORMATION build-ups and hence have a structural component. Within both the (Penhold Field); the Beaverhill Lake event is pulled up by as little as Computing Services Ltd.) for providing oil and gas production BRI I isolated and fringing reef reservoir examples, the distribution of 10 ms (Morinville/St. Albert-Big Lake) and by as much as 40 ms data; Jerry Buzahora (Riley's Datashare) for reproducing the log Figure 4.1. Stratigraphy of the Woodbend Gp of central Alberta hydrocarbons is influenced by post-depositional structure (due to (Leduc-Woodbend) and that the seismic images of the Leduc Fm and curves; Geophysical Microcomputer Applications for plotting (Stoakes, 1980). both differential compaction and basin subsidence) however, the the Ireton Fm contrast sharply on some of the examples some of the synthetics and Lori Harman for typing. 101 Table 4.1. Production data for the six assigned pools in the Penhold Bashaw complex, whereas the Ellerslie Fm pools (Lower Mannville) IRETON study area are basinward (Fig. 4.3). All of these reservoirs are strongly LEDUC FlELD eoo, P~OOUC1~G ~L!'4SER ClMllATIVE P~(x)UCT1~ influenced by the differential compaction of reef and off-reef ,~, OF \/EllS 0; I (,.3) Gas (E3 .,3) ~Bter (,.3) sediment. For example, the Leduc Fm, Nisku Fm and Viking Fm OFF REEF PeMold O-3A ,~ 3,3a3.7 2,171.5 ',761.1 pools are structurally closed across the reef rim whereas the fluvial Pernold D-U ~;SKU 10,079.3 4,21'.0 3.798.0 SHALES Pernold Lowe' Mamville A EI lersl;e 52,5%.S 49,8".3 42.6 sandstones of the Ellerslie Fm were preferentially deposited Penhold Lower Mannville S EI, lersl;e 56.3 347,438.4 1,255.6 immediately to the west (basinward). Apparently, relief along the Penhold Viki"ll C Vikir.g 20.1 U 62.9 Pre-Cretaceous unconformity, during Lower Mannville time, COOKING LAKE Penhold Viking 0 Vik;"'l. ,,u 0.0 STAGE 1 reflected drape along underlying strata. This concept is illustrated in Figure 4.4. TOPPRE-CRETACEOUS The Leduc Fm in the Penhold field area (Fig. 4.5) is herein differentiated into full reef and basinal carbonate. The full reef -------~ MISSISSIPPIAN towers some 250 m above the platform facies and is easily distinguished from off-reef shales on the basis of seismic image, velocity pull-up and drape. In contrast, without well control the basinal carbonates could be misinterpreted as either Duvernay Fm or IRETON lower Ireton Fm shales. 1---: LEDUC Penhold field was selected as an example Woodbend Gp reservoir for two reasons: COOKING LAKE STAGE 2 1) The Leduc Fm, D-3A pool illustrates that reservoirs within the fringing reef complexes are not restricted to the main up-dip -~--~~-,/""--- MISSISSIPPIAN edges; and 22 2) The D-3A, D-2A, Lower Mannville and Viking pools illustrate IRETON o 100 , KMS. I that structural and/or stratigraphic traps can form within LEDUC 1:36 Leduc Fm and/or post-Leduc Fm strata as a result of ALBERTA Figure 4.3. Penhold study area. Pool outlines, the four wells differential compaction of reef and off-reef sediments. UNITED STATES incorporated into the geological cross-section and the approximate 1 COOKING LAKE location of the seismic line are shown (L.M.A. - Lower Mannville A GEOLOGICAL CROSS-SECTION STAGE 3 1. Rich 6.0bed pool; L.M.B. - Lower Mannville B pool). 2. Penhold 7. South Sturgeon The locations of the four wells incorporated into the geological MISSISSIPPIAN Table 4.2. Production data for the Penhold area ---~~;.....,. 3. Leduc Woodbend 8. Lanaway/Garrington cross-section (Fig. 4.5) and the example seismic line (Fig. 4.6) are superimposed, in Figure 4.3. Three of these wells are within 200 m CRETACEOUS ~ELL FIELD '00' PROOUCI~G P~OOUCTl~ ClJHIJlATlVE PROOUCTION 4. Morinville 9. Ricinus ,~, DATE 0; I ,~, Gas (n 11'I3) ~ale; (m3) of the seismic line, whereas the fourth (14-31), lies about one FLUVIAL SANDS 9-28-36-27'M4 pemold 0-3A ,~ 2,173.5 1,761. 1 IRETON 5. Redwater '1/68 3,383.7 kilometre to the north. Such extrapolation is necessary for 13-28-36-27\14 penhold 0-2A ~; sku 07/61 7,321.0 3,640.1 .- lEDUC 10-29-36-21\14 PeMold Lower lIamvi lie 8 Ellerst ie 02/78 0.0 180,606.7 723.7 interpretative and illustrative purposes as this well is the deepest test pennold LOoWer lIanrw; lie B 139,585.2 420.1 1::==:== 10-30-36-27\14 Ellerslie 11/TI 56.3 in the study area.