Sand Consolidation Preflush Dynamics
Authors: Penberthy W.L. , Shaughnessy C.M. , Gruesbeck C. , Salathiel W.M. 
Published: December 2007

Penberthy Jr., W.L., SPE-AIME, Penberthy Jr., W.L., SPE-AIME, Exxon Production Research Co. Shaughnessy, C.M., SPE-AIME, Exxon Production Research Co. Gruesbeck, C., SPE-AIME, Exxon Production Research Co. Salathiel, W.M., SPE-AIME, Exxon Production Research Co.
For effective sand consolidation, resin must wet the surface of sand grains. When plastic resins do not have this ability, preflushing is essential. Model studies demonstrated that preflushing effectiveness depended on preflush volume, viscosity, and sand permeability. Results indicated that an optimum volume of 100 gal/ft was required for an effective preflush.

Introduction
Experience with sand consolidation for the past 30 years has shown that candidate wells should have relatively thin, clean, homogeneous, undamaged sand zones. Proper preflushing also is essential for effective sand Proper preflushing also is essential for effective sand consolidation. A variety of aqueous and organic preflushes have been used to remove formation fluids ahead preflushes have been used to remove formation fluids ahead of sand consolidation resins. Proper preflushing can contribute significantly to the strength of the consolidated sand by improving the adhesion between the resin and sand matrix. Because of increased emphasis on sand consolidation performance and lifetime, a considerable incentive exists for improving preflush selection and volume.
To be effective, a sand consolidation resin first must wet and then must adhere to the surface of the sand grains. Because the sand grains in most reservoirs are water wet originally, it is critical for the resin to replace water on the surface of the grains. Fig. 1 shows the effect of residual water saturation on the strength of sand consolidated with an epoxy resin. As water saturation increases, compressive strength decreases. At 6-percent water saturation, resin is prevented from wetting the sand matrix and consolidation has little compressive strength.
While studying all available sand consolidation processes, laboratory tests showed that some resins were processes, laboratory tests showed that some resins were able to displace water by themselves. Others depended heavily on preflushing for water removal. Although oil removal appears desirable, most sand-consolidation resins exhibit good sand-grain wetting in the presence of oil. Consequently, mutual solvents that preferentially remove water are more desirable for sand consolidation preflushing, particularly where epoxy resins are preflushing, particularly where epoxy resins are concerned.
Preflush Study Preflush Study A series of tests identified solvents that preferentially remove water in the presence of oil. Solvents were characterized on the basis of their phase behavior with brine and oil. Fig. 2 illustrates four possible types of phase behavior for the preflush-brine-oil system. Dashed phase behavior for the preflush-brine-oil system. Dashed lines represent tie lines connecting equilibrium phases in the two-phase region. Of the four types of phase behavior, Type 2 solvent is the most desirable because it preferentially removes water and also removes oil. Type preferentially removes water and also removes oil. Type 1 solvent results in a residual oil saturation, Type 3 solvent preferentially removes oil, and Type 4 solvent has no water miscibility.
Most tests were conducted with 6-percent NaCl brine and diesel oil. Promising candidates were studied further using combinations of twine, 15-percent HC1, spent mud acid, and diesel and crude oil. Tests were conducted on three classes of compounds - alcohols, glycol ethers, and glycol ether acetates. Results showed that, of the alcohols, only isopropyl alcohol demonstrated mutual miscibility for brine and oil. The glycol ether acetates were all oil miscible. Many glycol ethers, however, were mutually miscible with brine and diesel.
JPT
P. 845