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Chert Reservoirs of North America |
1 Burlington Resources Canada Energy Ltd., 3700 Bow Valley Square IV, 250-6th Avenue SW, Calgary, Alberta T2P 3H7, Canada; Jeff_Packard{at}br-inc.ca
2 Earth Sciences, School of Physical Sciences, University of Windsor, Windsor, Ontario, Canada, N9B 3P4
3 Earth Sciences, School of Physical Sciences, University of Windsor, Windsor, Ontario, Canada, N9B 3P4
4 Image Interpretation Technologies Inc., #2010, 520-5th Avenue SW, Calgary, Alberta, Canada, T2P 3R7; zeev{at}iitech.ab.ca
5 Image Interpretation Technologies Inc., #2010, 520-5th Avenue SW, Calgary, Alberta, Canada, T2P 3R7; jim{at}iitech.ab.ca
Jeff Packard has a B.Sc. degree in geology from Concordia University in Montreal and received his Ph.D. in carbonate sedimentology from the University of Ottawa in 1985. Following a stint as an NSERC research fellow with the Geological Survey of Canada, he joined Texaco Canada (and subsequently Imperial Oil) as a carbonate specialist. From 1992 to 1998 Jeff worked in Calgary, principally as a partner with Rhomb Carbonate Consulting. More recently he has been employed as a senior geologist with Burlington Resources Canada Energy Limited. His research interests embrace all aspects of carbonate reservoir creation and modification.Ihsan Al-Aasm earned his B.Sc. (1974) and M.Sc. (1977) degrees in geology from the University of Baghdad and his Ph.D. (1985) in geology from the University of Ottawa. From 1985 to 1986 he was a postdoctoral fellow with the University of Ottawa, then assistant professor from 1986 to 1988. In 1988 he joined the Department of Earth Sciences at the University of Windsor, and he is presently a full professor at that university, as well as being an adjunct with the University of Western Ontario. His principal area of research is on petrologic and chemical attributes of carbonate rocks, siliciclastic diagenesis, dolomitization, and environmental geochemistry. He has acted as an associate editor for the Journal of Sedimentary Research and holds memberships in AAPG, SEPM, and the Geological Association of Canada. http://www.cs.uwindsor.ca/units/geol/research/alaasm.html
Iain Samson received a B.Sc. degree in applied geology in 1979 and a Ph.D. in economic geology in 1983 from the University of Strathclyde. From 1983 to 1986 he was a research associate with the Mineral Exploration Research Institute (IREM-MERI) at McGill University. In 1986 he joined the faculty of the University of Windsor, where he is currently an associate professor and program chair in the Department of Earth Sciences. His research interests include the microanalysis of fluid inclusions and the geochemistry of crustal fluids and their role in the formation of mineral deposits and in diagenesis.
Zeev Berger is the president of Image Interpretation Technologies Inc., a Calgary-based company that is dedicated to the integrated analysis of remote sensing data for hydrocarbon exploration. Prior to forming IIT he was a member and group leader of the remote-sensing group at Exxon Production Research Company, a senior exploration specialist with Imperial Oil of Canada, and president of Paz Energy Ltd.
Jim Davies attended the University of Wales, College of Cardiff, where he attained a B.Sc. (hons) degree in exploration and mining geology. He subsequently attained his M.Sc. degree from McGill University, Montreal, studying structural geology and reactivation episodes in the Canadian shield. His research interests include the role of basement structures in controlling the occurrence of hydrocarbon and mineral deposits and the influence of basement structures on the geometry of thrust belt margins.
The 225 bcf (original gas in place [OGIP]) Parkland A pool was discovered in 1956 with the drilling of Imperial Pacific 6-29-81-15w6. This well initially production tested at 19 mmcf gas/day and has produced more than 95 bcf of sweet gas. The Parkland play type (as defined by the Geological Survey of Canada) consists principally of fracture-associated hydrothermally karsted and dolomitized reservoirs hosted in the Upper Devonian (Famennian) Wabamun Group medial ramp carbonates resting on the axis of the Peace River arch and includes major fields such as Tangent, Teepee, and Gold Creek. Ironically Parkland itself owes little of its production to hydrothermally dolomitized carbonates; instead, most of the reservoir pore volume can be attributed to microintercrystalline porosity within a pervasive replacement microquartz (chert) that occurs at the dolomite-limestone interface. The thickness of this chert zone in the 6-29 well is 35 m and occurs near the top of the Wabamun.
The origin of the chert is problematic. It postdates matrix dolomitization and crosscuts the early Tournaisian (Mississippian) Exshaw Ash but is in turn truncated by later saddle dolomite and calcite veins. The replacement chert is composed of a microporous (up to 30%) meshwork of microquartz crystals averaging 5-10 µm in size and is texturally distinct from early diagenetic chert nodules also found in the Wabamun. The two cherts are also distinguishable isotopically, with the replacement microquartz showing significantly more depleted oxygen values (22 vs. 25 
18O standard mean ocean water [SMOW]), consistent with precipitation from hot fluids having a temperature range from about 140 to 200°C. Silicification has had the greatest impact on slightly dolomitized limestone at the outer margin of the hydrothermal dolostone pod. Entrapped floating euhedral crystals of dolomite within the replacement chert show little evidence of microdissolution, suggesting that the silicic acid-charged fluid, although undersaturated with respect to the microspar lime matrix, was saturated with respect to dolomite. We postulate that hydrothermal fluids of common parentage, only marginally evolved in composition-if at all, were responsible for both dolomitization and silicification. Both replacement processes occurred in relatively rapid succession at shallow burial depths and were related to an early Tournaisian period of hydrothermal activity associated with both wrench and minor extension structuring linked with the nascent development of the Fort St. John graben. The source of the silica is thought to be the immediately subjacent Granite Wash or possibly the Precambrian basement. Stratigraphic proximity to the Granite Wash is likely a prerequisite condition for chert reservoir development within the Wabamun and serves to explain, along with significantly different hydrothermal fluid temperatures (much hotter to the west), why Parkland is such a distinct field compared to Tangent and Teepee.
Hydrocarbon reservoirs that are dominantly chert-hosted are relatively uncommon, but where recognized (e.g., Monterey Formation, California) they are related to the redistribution and transformation of biogenic opal-A silica derived from diatoms, spicules, and/or radiolarians in deeper water sediments. To our knowledge, Parkland is the only hydrothermal chert reservoir that has been reported anywhere in the world.
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G. R. Davies and L. B. Smith Jr. Structurally controlled hydrothermal dolomite reservoir facies: An overview AAPG Bulletin, November 1, 2006; 90(11): 1641 - 1690. [Abstract] [Full Text] [PDF]
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