COMBINING DOWNHOLE AND SEDIMENT LOGGING TO UNDERSTAND THE RESERVOIR CHARACTERISTICS OF A LARGE-SCALE MISSISSIPPI RIVER POINT BAR, FALSE RIVER, LOUISIANA

Although the general processes by which meandering river point bars are constructed have been known for some time, there is a lack of clarity regarding why small scale heterogeneities develop. This is especially true in the largest meandering river systems, which are equivalent to some of the most important hydrocarbon reservoirs in the world. In this study, we combine shallow coring, geophysical logging, and grain size analysis to examine the 80 km² False River Point Bar System on the Lower Mississippi River. We evaluate the stratigraphic architecture of the point bar (and associated channel tie system) and use the knowledge gained to better comprehend point bar construction at different phases. Previous studies of small to medium-scale systems have not been able to predict the degree of lateral heterogeneity of larger systems— where data on a scale of 1 m to approximately 300 m is needed. Guided by a high resolution DEM, this study combines sediment coring and gamma ray, hydraulic profiling, and electrical conductivity logging at 19 sites (12 sites with sediment coring) in the bar head, bar apex, bar tail, and channel plug. Results show not only large scale differences in lithology and permeability between these areas but also show differences on a finer scale within these locations. This is especially true at the bar apex where an abandonment facies is observed. At the bar tail, where data was collected from closely spaced sites (approximately 30 m apart), data shows a rapid deterioration in permeability towards the youngest parts of the bar. The channel fill, which once connected the present oxbow lake to the Mississippi River, shows even more pronounced changes over 10’s of meters and generally poor reservoir characteristics. The False River system— and presumably other major river point bar deposits— show coherent differences across their width with a fining and reduction of reservoir quality going downstream and a sharp decrease immediately before the final abandonment of the channel.