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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 673

Last Page: 674

Title: Geophysical Case History of Two Hills Colony Gas Field of Alberta: ABSTRACT

Author(s): F. E. Baker, G. W. Focht

Article Type: Meeting abstract

Abstract:

Seismic waveform changes, which in their most obvious form are known as "bright spots," have been known for some years to give direct indications of hydrocarbons. An example of the successful application of waveform analysis and direct detection of gas in a shallow Lower Cretaceous formation of east-central Alberta, Canada, is detailed.

At a depth of approximately 2,000 ft (610 m), the Colony formation typically consists of only thin (10 ft; 3 m) blanket sands interbedded with shale. However, in 1976 Hudson's Bay Oil and Gas Co. investigated a 100-ft (31 m) thick occurrence of channel sand (with substantial gas pay) in this formation. After some hit and miss attempts at extending the channel trend on geologic interpretation, seismic methods were applied. A seismic line over the channel well revealed a classic "bright spot." Several other lines also showed bright spots in the Colony zone. The results of seismic modeling can be summarized as follows. The lateral consistency of the sediments above the Colony provided a stable boundary of modeling and permitted the detection of gas. The inconsistency and complexity of th sediments underlying the Colony resulted in interference patterns that prevented exact quantitative analysis of gas pays. Furthermore, other geologic phenomena provided waveform changes that were similar to that of

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gas sand. Through detailed examination of the geology and evaluation of alternative explanations of the waveform changes, successful interpretation was accomplished.

Total gas reserves geophysically discovered to date in the Colony formation are estimated at 110 Bcf.

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