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Stratigraphic Controls on Gas Production from the Cadotte, Deep Basin*
Tim McCullagh1 and Bruce Hart1
Search and Discovery Article #10151 (2008)
Posted October 29, 2008
*Adapted from oral presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008
1Earth and Planetary Sciences, McGill University, Montreal, QC, Canada ([email protected])
We integrated core, wireline log, 3-D seismic, and production data to examine the controls on gas production from the Lower Cretaceous Cadotte Member in the Deep Basin of Alberta, considered by some to be the “type area” for basin-centered gas accumulations. The Cadotte was deposited as part of a prograding wave-dominated strandplain. Cadotte shoreface and foreshore deposits can be either chert-rich or quartzose. Chert-rich units lack quartz overgrowths, have relatively high permeability and can produce gas, whereas the overgrowths are well developed in the quartzose units which are tight. A sonic and density porosity log crossover technique can be used to distinguish quartz-rich from chert-rich facies. The physical properties of the two lithologies are sufficiently different that they can be distinguished seismically. A map of seismic amplitudes for the Cadotte shows curvilinear high-amplitude anomalies up to a few 100 m wide and several km long, that are parallel to depositional strike. The amplitude anomalies represent stratigraphic compartments in the Cadotte shoreface that are similar in scale to beach ridges of the modern Nayarit coast of Mexico. Seismic, log, and pressure data indicate that shale-filled channels incising through the shoreface can compartmentalize the reservoir. Like other basin-centered gas accumulations, the Cadotte produces gas downdip from areas that are wet. The contact between these two phases cuts through our study area. Our work suggests that the location of this contact is controlled by the interplay of regional structure and depositional processes that control the mineralogy, permeability, and stratigraphic architecture of the Cadotte.
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· Importance of stratigraphy o Detrital mineralogy controls diagenesis. o Depositional processes control distribution of mineralogy. o Stratigraphic sweet spots. o Combination of structure and stratigraphy controls location of regional gas-water contact. · Differences in physical properties make porous units visible seismically, · Integration of geology, geophysics and engineering data and concepts is essential. · “Basin-centered gas” concept doesn’t apply in area where it originated (!?!?) o Can’t drill “anywhere” to get production. § Although all rocks are gas saturated downdip from gas/water contact.
Connolly, E.T., and P.A. Reed, 1983, Full spectrum formation evaluation: Journal Canadian Well Logging Society, v. 12/1, p. 23-69.
Masters, J.A., 1979, Deep basin gas trap, western Canada: AAPG Bulletin, v. 63/2, p. 152-181.
Masters, J.A., 1984, in Elmworth; case study of deep basin gas field: AAPG Memoir 38, 316 p..
Smith, R.D., 1984, Gas reserves and production performance of the Elmworth Wapiti area of the deep basin: in Elmworth; case study of deep basin gas field, AAPG Memoir 38, p. 153-172.
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