A New, Low-Viscosity, Epoxy Sand-Consolidation Process

Abstract

This paper describes the development and field testing of a new, low-viscosity, sand-consolidation system. During experimental investigation, several new concepts were developed that are not available elsewhere, including the use of a bisphenol F epoxy resin, an extractable two-part diluent (acetone plus cyclohexane), and an improved placement procedure. Introduction Plastic consolidation continues to be an important Plastic consolidation continues to be an important technique for controlling sand during oil and gas production. New resin systems for sand consolidation have developed consistently for the past 20 years, which, in turn, have improved field performance. Epoxy resins long have been known to have properties desirable for sand consolidation - excellent adhesion to silica surfaces and good resistance to deterioration. Several commercial consolidation processes have been based on epoxy resins, but until now, none have achieved the desirable combination of being externally catalyzed and having low viscosity. All previous low-viscosity epoxy formulations have been catalyzed internally, that is, the curing agent was added to the resin just before it was pumped into the well. Major drawbacks of this technique arelimited pumping time before the resin hardens andthe need to blend chemicals at the wellsite. While externally catalyzed resins can eliminate pumping time and blending considerations, ail previous pumping time and blending considerations, ail previous externally catalyzed epoxy processes used resins with viscosities of more than 80 cp. The high viscosity of the resin caused high pumping pressures and increased the risk of forming a channel through an unconsolidated sand. Our experience has shown that a resin with viscosity of less than 30 cp (preferably less than 20 cp) is most desirable. A new process has been developed that has low viscosity and also eliminates blending at the wellsite. With a viscosity of 16 cp, the resin solution can be pumped readily through tubular goods and into the reservoir sand. All process components are premixed before their arrival at the wellsite. The elimination of field blending simplifies the procedure to an ordinary pumping operation. The shelf life of the premixed components is longer than 1 year, which can be important when operating in remote locations. Process Description, Process Description, The basic consolidation process requires that four fluids be injected sequentially through the sand:an organic preflush to remove water from the sand surface,an preflush to remove water from the sand surface, (2) an epoxy resin diluted to 16 cp,a spacer oil to flush excess resin from the pore space, andan oil containing a catalyst to harden the resin coating around each sand grain. The key to developing a successful externally catalyzed consolidation process is to harden the desired quantity of resin on the surface of the sand grain. Laboratory studies have shown that the optimal residual cured-resin saturation is 35% of the original pore volume. Values higher than this lower the permeability of the sand after consolidation, without substantially improving compressive strength. Saturations of less than 35% contain too little resin to coat effectively or to bond together all sand grains. Consequently, design criteria for the new process were to obtain a 35% residual resin saturation and process were to obtain a 35% residual resin saturation and then to pump enough oil with catalyst to harden all the resin. JPT P. 1805

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