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Weyburn field, in the Williston basin of Saskatchewan, produces oil from the Midale Member of the Mississippian Mission Canyon Formation.<ref name=ch09r9>Chetin, A. K., and W. W. Fitkin, 1959, Geology of the Weyburn field, Saskatchewan: Canadian Mining and Metallurgical Bulletin, December, p. 751–761.</ref>

 

Weyburn field, in the Williston basin of Saskatchewan, produces oil from the Midale Member of the Mississippian Mission Canyon Formation.<ref name=ch09r9>Chetin, A., K., Fitkin, W., W., 1959, Geology of the Weyburn field, Saskatchewan: Canadian Mining and Metallurgical Bulletin, December, p. 751–761.</ref>

Weyburn has ultimate recoverable reserves of about 300 million bbl of oil (48 × 10⁶ m³). The main pay interval is the lower part of the Midale, called the Midale vuggy beds. The Midale vuggy beds underly the Midale marly beds, which produce only minor amounts of oil.

Weyburn has ultimate recoverable reserves of about 300 million bbl of oil (48 × 10⁶ m³). The main pay interval is the lower part of the Midale, called the Midale vuggy beds. The Midale vuggy beds underly the Midale marly beds, which produce only minor amounts of oil.

==Weyburn trap problem==

==Weyburn trap problem==

To determine the trap type of Weyburn field, we have to know what forms the lateral closure. It is not structural because [[dip]] is homoclinal to the southwest. The field lies southeast of the truncation edge of the Midale Member, where it wedges out beneath Triassic rocks and above older Mississippian rocks. Early workers understood this truncation to be the cause of the trap. Yet there is an area lying downdip from the truncation edge of the Midale and updip from the oil pool in which porous Midale vuggy rocks were present but tested wet with shows of oil.

To determine the trap type of Weyburn field, we have to know what forms the lateral closure. It is not structural because [[dip]] is homoclinal to the southwest. The field lies southeast of the truncation edge of the Midale Member, where it wedges out beneath Triassic rocks and above older Mississippian rocks. Early workers understood this truncation to be the cause of the trap. Yet there is an area lying downdip from the truncation edge of the Midale and updip from the oil pool in which porous Midale vuggy rocks were present but tested wet with shows of oil.

This raises the possibility that either a stratigraphic change;<ref name=ch09r70>Winland, H. D., 1972, Oil accumulation in response to pore size changes, Weyburn field, Saskatchewan: Amoco Production Company Report F72-G-25, 20 p. (unpublished).</ref><ref name=ch09r71>Winland, H. D., 1976, Evaluation of gas slippage and pore aperture size in carbonate and sandstone reservoirs: Amoco Production Company Report F76-G-5, 25 p. (unpublished).</ref> Wegelin, 1986; <ref name=ch09r33>Kent, D. M., Haidl, F. M., MacEachern, J. A., 1988, Mississippian oil fields in the northern Williston Basin, in Goolsby, S., M., Longman, M., W., eds., Occurrence and Petrophysical Properties of Carbonate Reservoirs in the Rocky Mountain Region: RMAG Symposium, p. 193–210.</ref> or [[hydrodynamics]]<ref name=ch09r43>Petroleum Research Corporation, 1961, Hydrodynamic exploration for unconformity traps: Research Report A-11, 47 p. (unpublished report, available at Colorado School of Mines Library, Golden, CO).</ref><ref name=ch09r13>Dahlberg, E., C., 1982, Applied [[Hydrodynamics]] in Petroleum Exploration: New York, Springer Verlag, 161 p.</ref><ref name=ch09r24>Hannon, N., 1987, Subsurface water flow patterns in the Canadian sector of the Williston Basin: RMAG 1987 Symposium Guidebook, p. 313–321.</ref> or perhaps both provide the updip, transverse (lateral) seal. From producing wells at Weyburn and nearby Steelman, the oil column height appears to be [[length::600 ft]] [[depth::(183 m]]). This raises the next question: Could the Midale marly beds provide a seal for a 600-ft oil column, or must hydrodynamics be present to augment the seal quality of the Midale marly beds?

This raises the possibility that either a stratigraphic change;<ref name=ch09r70>Winland, H. D., 1972, Oil accumulation in response to pore size changes, Weyburn field, Saskatchewan: Amoco Production Company Report F72-G-25, 20 p.</ref><ref name=ch09r71>Winland, H. D., 1976, Evaluation of gas slippage and pore aperture size in carbonate and sandstone reservoirs: Amoco Production Company Report F76-G-5, 25 p.</ref><ref>Wegelin, A., 1984, Geology and reservoir properties of the Weyburn field, southeastern Saskatchewan, ''in'' J. A. Lorsong and M. A. Wilson, eds., Oil and Gas in Saskatchewan: Saskatchewan Geological Society Special Publication 7, p.71-82.</ref><ref name=ch09r33>Kent, D. M., F. M. Haidl, and J. A. MacEachern, 1988, Mississippian oil fields in the northern Williston Basin, ''in'' S. M. Goolsby, and M. W. Longman, eds., Occurrence and Petrophysical Properties of Carbonate Reservoirs in the Rocky Mountain Region: RMAG Symposium, p. 193–210.</ref> or [[hydrodynamics]]<ref name=ch09r43>Petroleum Research Corporation, 1961, Hydrodynamic exploration for unconformity traps: Research Report A-11, 47 p.</ref><ref name=ch09r13>Dahlberg, E. C., 1982, Applied hydrodynamics in petroleum exploration: New York, Springer Verlag, 161 p.</ref><ref name=ch09r24>Hannon, N., 1987, Subsurface water flow patterns in the Canadian sector of the Williston Basin: RMAG 1987 Symposium Guidebook, p. 313–321.</ref> or perhaps both provide the updip, transverse (lateral) seal. From producing wells at Weyburn and nearby Steelman, the oil column height appears to be 600 ft (183 m). This raises the next question: Could the Midale marly beds provide a seal for a 600-ft oil column, or must hydrodynamics be present to augment the seal quality of the Midale marly beds?

==Weyburn structure map==

==Weyburn structure map==

[[file:predicting-reservoir-system-quality-and-performance_fig9-98.png|300px|thumb|{{figure number|3}}Diagrammatic dip-oriented cross section of Weyburn field.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-98.png|300px|thumb|{{figure number|3}}Diagrammatic dip-oriented cross section of Weyburn field.]]

[[:file:predicting-reservoir-system-quality-and-performance_fig9-98.png|Figure 3]] is a diagrammatic dip-oriented [[cross section]] of Weyburn field. It shows the truncation of the Midale marly and vuggy beds and the updip facies change in the Midale vuggy beds from a vuggy grainstone to a vuggy mudstone to an anhydrite.

[[:file:predicting-reservoir-system-quality-and-performance_fig9-98.png|Figure 3]] is a diagrammatic dip-oriented [[cross section]] of Weyburn field. It shows the truncation of the Midale marly and vuggy beds and the updip facies change in the Midale vuggy beds from a vuggy grainstone to a vuggy [[mudstone]] to an [[anhydrite]].

==See also==

==See also==

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting reservoir system quality and performance]]

[[Category:Predicting reservoir system quality and performance]]