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"Epsilon cross-stratification" refers to large-scale, alternating sand and mud couplets that dip at right angles to the paleocurrent direction. This feature is of major concern when producing oil from ancient meandering river point-bar deposits. Mud epsilon cross-strata act as impermeable barriers to the movement of hydrocarbons within the reservoir. This and other related problems have been prevalent in steam enhanced recovery from the bitumen-rich middle member of the McMurray formation.
Research on epsilon cross-stratified lateral accretion deposits has been focused for the most part on the study of ancient deposits. Investigation into the modern occurrence of these features has been limited in scale (0.5 m or 1.6 ft deep channels) and numbers of observations. Many unanswered questions remain as to the location of depositional environment (meanders in fluvial, tidal, or deltaic systems) and detailed sedimentologic characteristics.
A recent investigation has found mud epsilon cross-strata in lateral accretion point-bar deposits in the Athabasca upper delta plain in northeastern Alberta. The overall sedimentologic trends of these particular lateral accretion deposits, including the variability, continuity, thickness, and geometry of the mud epsilon interbeds, has given new insight into the complex nature of these deposits and occurrence of depositional setting.
Many aspects of the lateral accretion in the Athabasca upper delta plain appear very similar to the ancient lateral accretion deposits of the middle McMurray. Comparative sedimentology of the modern and ancient deposits may lead to a better understanding of these deposits. This may in turn allow for optimum site selection for in-situ steam injection and recovery wells as well as prediction of potential fluid movement patterns.
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