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When placed within the context of their depositional setting and compared to modern analogs, the proven hydrocarbon reservoirs of the Middle Triassic Halfway Formation provide models for future exploration of similar sequences in the stratigraphic record. The Halfway sandstones accumulated along the northeastern margin of the Triassic seaway. Barrier-strandplain deposits amassed along a depositional embayment in western Alberta downdrift of an area of sediment influx into the basin in eastern British Columbia.
Along the Halfway coastline, porous deposits accumulated either in the wave-reworked upper shoreface-foreshore zone of barrier islands or in tidal-inlet areas. The barrier-island reservoir sandstones are thin (less than 5 m) and elongate with depositional strike, whereas the tidal-inlet deposits are thick (up to 20 m) with abundant shell-hash lag conglomerates and elongate with depositional dip. Similar to modern coastal configurations, the frequency and thickness of tidal-inlet sequences increase toward the center of the depositional embayment because of tidal amplification. There, more conduits through the barriers were necessary to exchange the larger volumes of water during a tidal cycle.
Most of the significant Halfway hydrocarbon reservoirs have been inlet-fill sequences. An excellent example is the Wembley field. Positioned near the center of the Halfway depositional embayment, this field contains 37.5 million bbl of oil. A majority of the reserves are found in inlet deposits. Porosities and permeabilities have been significantly enhanced by secondary solution of the shell lags. Other Halfway inlet reservoirs exist along depositional strike. They are most abundant near the axis of the embayed shorelines where tides were amplified. Future hydrocarbon exploration along other embayed coasts should emphasize the locations and abundance of inlet-fill deposits.
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