The adverse effects of inadequate fluid-loss control associated with gravel-packed completions is well known. Controlling fluid losses to the formation before and after pack placement is critical to ultimately achieving optimum productivity from a given well for the following two reasons:
Fluid-loss control is necessary to prevent losses of expensive high-density brines, sometimes used for well control in high-permeability, unconsolidated formations. The costly loss of expensive brines can also lead to critically unsafe well conditions, where high overbalance pressures are required to control highly geopressured zones.
Dense brines have been reported as being difficult to unload from formations once losses have occurred. Calcium and zinc-bromide brines can form highly stable, acid-insoluble compounds when reacted with some formation brines. Because of the high density of these brines, stratification tends to further inhibit their removal. The most effective means of preventing the formation damage described is to limit completion brine losses to the formation.
A variety of fluid-loss control materials have been used and evaluated, including foams, oil-soluble resins, acid-soluble particulates, graded salt slurries, linear viscoelastic polymers, and heavy metal-crosslinked polymers. Their comparative effectiveness is well documented. Most attain their fluid-loss control from the presence of solvent-specific solids, or from hydrated linear polymers that rely on filter-cake buildup and on viscoelasticity to inhibit flow into and through the formation.
Oil-soluble resins generally clean up well when they are thoroughly contacted with solvent. Tests have shown, however, that such resin, lodged in perforation tunnels, may remain isolated from solvent for extremely long periods, thus restricting well production.
Recent testing has shown that particulate systems, i.e., graded salt slurries, particularly those using polymers and gums for particle suspension, can be quite damaging to formations and difficult to remove from perforation tunnels. Himes et al. reported less than 10% regained permeability after treatments into a Berea core with a salt system containing graded salt in a xanthan gum base in a 10% NaCl solution.