--> Abstract: Basinward Increase in Prolificacy of Shallow Continuous Type Gas Plays – Importance of Facies, Stratigraphy and Structure, by Per Kent Pedersen; #90039 (2005)

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Basinward Increase in Prolificacy of Shallow Continuous Type Gas Plays – Importance of Facies, Stratigraphy and Structure

Per Kent Pedersen
Apache Canada Ltd, Calgary, AB

Large shallow, continuous type, gas accumulations within the upper Cretaceous Alderson Member (Milk River Formation) contain large reserves of biogenic generated gas, estimated 10-12 TCF in eastern Alberta and western Saskatchewan. Stratigraphic and structural influence on gas trapping in these sheet-like sands has largely been even considered insignificant or ignored. The recent discovery of a large (~0.5 TCF over 400 miles2) gas accumulation at Shackleton, Saskatchewan, has however caused a change in exploration concept for these continuous type gas plays: Although the continuous character of the Shackleton gas accumulation, detailed sequence stratigraphic mapping shows that the gas is stratigraphic trapped in a detached sandy lowstand and the sweet spot of the gas production is closely related to the present of a structural high within the extend of the lowstand. At Shackleton, the gas is mainly produced from a specific facies consisting of 2-15 mm thick siltstone and very fine-grained sandstone beds interbedded with silty mudstones. Gas production from these thin beds has in several wells exceeded 1.2 mmcf/d/well, proving these distal sedimentary facies at Shackleton several orders more prolific than the more proximal, sedimentary facies of muddy sandstones within the Hatton Pool 50 km to the southwest. This successful change in exploration strategy, looking for economic gas basinward of previously mapped boundaries, may apply elsewhere in the mature basins of the Canadian and US plains. Exploration for these continuous type gas plays require detailed, high-resolution mapping of stratigraphic units and sedimentary facies as the gas is not directly detectable on well logs.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005