Abstract

The “Meramec-Osage” trap is not definable by standard definitions of permeability barriers. Nor does it perform as uniformly as it should on the assumption that the production is dominated entirely by fracture porosity.

Instead, the trapping mechanism is the finite nature of the permeability in a fracture system where it is extended laterally through massive beds of low-matrix porosity. In the Sooner Trend field, the noncontinuous lateral nature of fracture permeability is combined with a conventional top and bottom seal. The limit of the field is determined by the position of the truncated edge of the upper seal.

In addition, the field productivity appears to be associated with the presence of porosity trends related to regional depositional and facies trends, and combined with the regional fracture pattern, rather than to be associated with fractures alone. Production within this system is limited by reservoir problems arising from the concentration of permeability within fractures. Fracture-dominated reservoir systems have the highest recovery in a reservoir with a low gas-oil ratio and are most inefficient in a reservoir with a high gas/oil ratio at a pressure below the bubble point.

The role of fractures as a form of permeability barrier and the importance of low gas/oil ratios to the economics of fracture-dominated reservoirs have not been given the attention which they merit.

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