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. Introduction Many new prolific reservoirs are being found and developed in high permeability sands. Completion of wells in these sands often requires some type of sand control to maintain sand-free, high-rate production. An increasing number of these wells requiring sand control are completed using open-hole techniques. Completing the well as an open hole offers several advantages over other completion techniques including:Provide a simple lower cost and risk way of completing long intervals without complicated stacked multiple frac-packs and gravel packs;Provide an efficient completion in high mobility formations where the stimulation benefits of fracs are lost;Allow completion of long horizontal or high-angle wells. Several studies have demonstrated the impact and dominance of perforation tunnels on the inflow performance of high rate wells.1–4Turbulence and limited in-flow area can hurt in-flow potential. Stimulation benefits of fracturing can be lost in high mobility (kh/viscosity) reservoirs as flow is choked by perforations. Area open to flow is significantly greater in an open hole relative to cased and perforated completions. Until recently, many of these open-hole completions would have been accomplished with only screens in the open hole.5,6Several wells completed in this fashion have suffered premature failures due to screen plugging leading to productivity loss. In some cases this plugging led to such small inflow areas that screens were eroded and no longer able to hold back formation sand. Stand-alone screens are still a viable option for high permeability, well-sorted sands; but many heterogeneous formations require that the annulus between the screen and formation be stabilized by gravel or an expandable screen.
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