Open hole gravel packing for sand control can offer productivity and cost reduction advantages over cased-hole completions, particularly in thick, high permeability sands. The filter cake formed by the reservoir drilling fluid can be trapped by the gravel, resulting in high drawdown requirements, non-uniform inflow profiles and/or low productivity. Effective clean-up and flow-back of this filter cake is necessary to fully realize productivity advantages of open-hole completions.

A comprehensive series of over 20 laboratory experiments were carried out to better understand filter cake flow-back in sand control completions. Variables investigated included mud weight and type, gravel size, additives like enzymes and acids, gravel size, and screen type. Results from 12 of these experiments are summarized in this paper.

Key findings include:

  • Tested synthetic oil base muds resulted in filter cakes which were much easier to remove than those formed from tested water-based muds.

  • 40/60 mesh gravel can severely inhibit filter cake removal compared to larger gravel sizes, which still maintain sand control.

  • An expandable screen pressed into the filter cake does not inhibit filter cake flow-back as long as solids are sized correctly, i.e. the drill-in mud is properly conditioned at the rig site.

Experiments were conducted in a standard cell where filter cakes were dynamically deposited and allowed to flow back through gravel and/or screens at scaled flow rates – many with gas. Following each experiment, the entire cell was saturated with epoxy and thin sections were cut across the filter cake and gravel. These visual images dramatically complement return permeability and "lift-off" pressure measurements and help illustrate the mechanics affecting return permeability performance.

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