New Technology Improves Performance of Viscoelastic Surfactant Fluids
- James B. Crews (Baker Oil Tools) | Tianping Huang (Baker Oil Tools) | William Russell Wood (Baker Oil Tools)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 2008
- Document Type
- Journal Paper
- 41 - 47
- 2008. Society of Petroleum Engineers
- 4.6 Natural Gas, 3.4.1 Inhibition and Remediation of Hydrates, Scale, Paraffin / Wax and Asphaltene, 4.3.4 Scale, 2.2.3 Fluid Loss Control, 2.4.3 Sand/Solids Control, 4.3.1 Hydrates, 2 Well Completion, 5.9.1 Gas Hydrates, 2.4.5 Gravel pack design & evaluation, 1.10 Drilling Equipment, 5.4.10 Microbial Methods, 1.6 Drilling Operations, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.1.2 Separation and Treating, 2.4.6 Frac and Pack, 1.8 Formation Damage, 1.6.9 Coring, Fishing, 3 Production and Well Operations, 2.7.1 Completion Fluids
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For a number of years, viscoelastic surfactant (VES) fluids have been used for a variety of stimulation treatment applications, including hydraulic fracturing, acid diverting, and gravelpacking. VES fluid systems typically offer higher-retained permeability and conductivity of the formation sand and proppant pack than polymeric systems. However, preliminary cost, a 200°F temperature limit, excessive leakoff, and no internal breaker mechanism for dry gas applications have limited VES use.
New VES fluid technology has been developed that substantially improves product performance and cost effectiveness. The temperature range has been extended to 300°F by using newly developed VES stabilizer technology. The system works with high-density brines up to 14.4 ppg. Internal breakers have been developed that permit a controlled viscosity break from ambient to 300°F. Laboratory tests have determined that an internally broken fluid rapidly achieves >90% returned permeability and conductivity of the formation sand and proppant pack without the presence or need for contacting hydrocarbons. Fluid loss-control technology has been developed that reduces VES fluid leakoff similar to wall-building fluids, but without filtercake damage.
This paper discusses the development of the new VES system chemistry and its properties. The paper also addresses the merits of a viscous fluid that can work in a variety of base fluids for high-pressure applications, such as managing surface-treating pressure or for gas-hydrate inhibition in deep gas or deepwater environments. Breaker technology discussion addresses the ability to ensure and enhance VES fluid-viscosity breaking. Fluid loss-control technology effective to at least 2,000 millidarcies (mD) is presented. This paper also presents rheological, return permeability and conductivity, fluid loss control, treating pressure, and financial results.
VES fluid systems have been used for gravelpack completions since the mid 1980s and for frac-packs since the mid 1990s (Nehmer 1988; Brown et al. 1996). These fluid systems have been mainly applied to completions requiring treatment fluids that are relatively low-damaging to the reservoir. The viscosity developed by VES is created by the unique arrangement of the surfactants into elongated, or worm-like, micelle structures (Samuels et al. 1997). A select type and amount of counterion in the mix water is typically required for elongated micelle structures to form and retain their stability. These structures are typically sensitive to counterion concentration and fluid temperature. Type and amount of common counterions used are 4% potassium chloride, 3% ammonium chloride, 1.5% magnesium chloride, and 30 to 70 pptg sodium salicylate. The temperature stability for VES fluids used for frac-packs has increased to approximately 200°F. Because the viscosity of VES fluids is caused by the arrangement of low-molecular weight surfactants and not by high-molecular weight polymers like guar and hydroxypropyl guar, VES fluids are nonwall-building fluids (i.e., they do not form a filtercake on the formation face). Therefore, they readily leak into the reservoir matrix. The amount of leakoff is much higher than polymeric systems and is fluid-viscosity dependent. In times past, no internal breaker has been used within VES fluids (i.e., no breaker is added to the VES fluid to go wherever the VES fluid goes). Instead, the VES fluid has been considered to break by reservoir conditions. The two primary external conditions have been: 1) contact with reservoir hydrocarbons; and 2) contact and dilution with reservoir brine. However, relying on external or reservoir conditions to break down the leaked-off VES fluid to achieve quick and complete treatment fluid flowback has been a point of contention and is questionable, especially for dry gas reservoirs. Internal breaker technology for VES fluids has not existed until recently (Crews 2005). Additionally, conventional counterions that work within a low- and narrow-concentration range for VES viscosity yield and temperature stability have limited the range in salinity and density of VES fluids to only light brines.
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