There are many advantages to using a single component, non-ionic viscoelastic surfactant gel (VES) for sand control and stimulation applications. The VES is highly compatible with a wide range of completion brines and crude oils, is virtually non-damaging to the formation and demonstrates shale-stabilizing characteristics with many types of shale. Another advantage of having a single additive VES system is that it requires a small equipment footprint. With this combination of compact equipment set-up and simplified fluid mixing, complex, high rate, high sand concentration frac jobs are possible where rig space is limited or equipment is limited because of the remote location from full stimulation service. A treatment using a single additive system can typically be performed with only one or two frac pumps, a frac blender, proppant silo or a modified sand infuser and data acquisition equipment.
Many offshore facilities have commingled gathering systems many of which must be treated for emulsions with chemicals. This treatment process may be substantially reduced or simplified when a non-ionic VES fluid is used for stimulation compared to a crosslinked gel fluid. The high compatibility with completion brines and crude oils, coupled with the non-damaging nature of the VES itself, reduces the likelihood of formation damage in the well. The VES promotes a fast and more thorough recovery of the stimulation fluid from the formation and if emulsions are generated, it will allow for easier treatment in the surface facility.
Since December 2000, non-ionic VES gels have been used in over 30 applications in the Adriatic Sea and in the Gulf of Mexico in brines ranging from seawater with varying amounts of KCl to 10.5 ppg CaCl2. Each application has resulted in enhanced production due to the excellent performance of the fluid. Clean-up rates have been directly related to bottom hole pressure, and have not been complicated with typical clean-up problems such as clay swelling, water blocks, and filter cake plugging of proppant packs. This type of treatment with a minimum equipment set-up has made high rate/volume frac treatments possible without the need of a stimulation vessel.
The fracturing industry has focused on polymer-based fracturing fluids as their chemistry of choice for years1. The benefits of high viscosity and proppant placement have outweighed the disadvantages of formation damage and fluid complexity and sensitivity. Recently, polymer-free VES fluids have emerged as a possible alternative to the polymer-based chemistry2; however, compatibility issues between the VES fluids and various completion brines3 and with crude oils have caused some concern. New developments in VES technology have yielded non-ionic VES fluids that are highly compatible with completion brines and crude oils, without compromising their viscosity, proppant carrying capacity or non-damaging characteristics. These new generation VES fluids require only the base brine and concentrated surfactant for sufficient viscosity generation. The VES fluid can easily be mixed on a stimulation vessel using a standard blender setup, or on a rig from skid mounted equipment. The system requires a minimal amount of rig space due to its single additive design.
Most polymer-based fracturing fluids are gelled in low weight brine such as 2% KCl4; however, the completion fluid controlling the well is typically a heavier brine. The compatibility of the fracturing fluid with this completion fluid is very important. Emulsion tendencies between the fracturing fluid and the completion brine would cause problems downhole. It is possible to gel polymer-based fracturing fluids in heavy weight brines and seawater; however, special formulas must be developed in order to offset the negative effects of the brine on the system5. An ideal fluid system would be one that is compatible with the completion brine.