This paper describes the development and field-testing of a new high-temperature epoxy resin system (new HT epoxy) that effectively consolidates sand and synthetic proppants. This new system has several advantages over previous epoxy systems: it is significantly safer to handle, it is more compatible with fracturing treatment fluids, and it provides superior unconfined compressive strengths.
The epoxy resin and hardener can be premixed and stored safely for an extended time and used when needed. As a result, pot life cautions and special metering systems are unnecessary. This resin system has a reduced impact on gel breakers and does not change fluid pH. In addition, the system has a lower cure rate at high temperatures, providing the operators sufficient time to place the resin treatment before hardening occurs. This cure rate can be catalyzed for lower-temperature applications with excellent consolidation properties, but the catalyzed formulation results in reduced pot life.
Results of laboratory and field testing are presented. A number of mechanical testing procedures that are not normally used to study plastic consolidations were used as a means of comparing this new HT epoxy formulation with both an earlier HT epoxy formulation and some curable precoated proppants. These tests include (1) the effect of stress cycling on consolidation strength, (2) creep studies, and (3) the variation of Young's modulus with temperature.
The earlier HT epoxy formulation provides excellent curable coatings on both sand and ceramic proppant in applications up to 400 F. The new HT epoxy is expected to provide similar capabilities, but will be much easier for operators to handle.
Curable resin-coated proppants are used in hydraulic fracturing treatments to reduce proppant flowback after fracture stimulation treatments. To control proppant flowback, the resin coating must bond proppant grains to one another at closure stresses and bottomhole temperatures that are available based on the formation being fracture-stimulated. For best performance, the resin coating should not cure so quickly at a temperature that it does not have time to become a "tight" proppant pack because of formation closure. Instead, the resin should remain mostly uncured until after fracture closure has occurred and then harden into a strong consolidated proppant bed. Conversely, the resin must be reactive enough to harden, even in very cool formations at a rate sufficient to allow normal well operations.
Several curable resin-coated proppants (RCPs) are based on a partially precured coating of a phenolic resin. At the treatment site, these precoated proppants are handled as bulk sand; operators use conventional equipment to mix the proppants with fracturing fluid and pump them downhole. While precoated RCP is a convenient material for use with conventional proppant handling equipment, some problems do exist. The resin coating may be damaged during shipping and handling, resulting in reduced consolidation properties and possible generation of resin dust, which complicates handling. In addition, the resin coating may cure too fast or slow to result in good consolidation properties. Achieving good consolidation properties is dependent on the fracture treatment design, the formation temperature and fracture closure rate.
These limitations justified development of a new process for coating proppants "on the fly" with liquid resin at the treatment location. In this system, sand is continuously coated in the blender during hydraulic fracturing. Fig. 1 (Page 5) shows a schematic of this process.