Internal Phase Breaker Technology For Viscoelastic Surfactant Gelled Fluids
- J.B. Crews (Baker Oil Tools)
- Document ID
- Society of Petroleum Engineers
- SPE International Symposium on Oilfield Chemistry, 2-4 February, The Woodlands, Texas
- Publication Date
- Document Type
- Conference Paper
- 2005. Society of Petroleum Engineers
- 5.2.2 Fluid Modeling, Equations of State, 4.1.2 Separation and Treating, 2.7.1 Completion Fluids, 5.4.10 Microbial Methods, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.4.6 Frac and Pack
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Past viscoelastic surfactant (VES) gelled fluids used for fracpacking and conventional hydraulic fracturing have primarily relied on external or reservoir conditions to break (reduce) the fluids gel viscosity. This paper describes an internal phase breaker system developed for breaking viscoelastic surfactant gelled fluids. Laboratory rheological data is presented that shows controlled viscosity reduction can be achieved from 80°F to 225°F by the use of two or three aqueous breaker solutions. The mix waters evaluated were KCl, CaCl2, and ASTM synthetic seawater. The results show that break times typical for polymeric fluids can now be achieved for VES gelled fluids.
Crosslinked-polymer fluid systems are routinely used for fracpacking and conventional hydraulic fracturing of oil and gas wells. These polymeric-based fracturing fluids have gel breakers added to them, such as oxidizers and enzymes, in order to reduce the fluids' viscosity downhole once a treatment is completed. An extensive amount of breaker technology has been developed to enhance and optimize the quality of break for polymeric-based fracturing fluids1,2,3,4,5,6.
VES gelled fluids have been used in frac-packing and conventional hydraulic fracturing since the 1990's7,8. Several references point out that an internal breaker is not required in order for VES viscosified fracturing fluids to break d,8,9,10ownhole7. These references mention any one of two reservoir conditions will readily break the VES gel viscosity. The breaker mechanisms listed are: (1) contact with reservoir hydrocarbons; and (2) reduction of salt concentration by reservoir brine.
Because of reliance on external factors rather than internal components, or the combination of external breaking factors with internal breaker components, there have been cases where the VES gelled fracturing fluid does not readily flow back or appear to break downhole after a treatment. When the reservoir fails to produce or unload fluids after a VES based fracturing treatment the reservoir is treated with a remedial fluid containing mutual solvents or alcohols in order to try and clean-up the unbroken or poorly broken VES gelled fracturing fluid left within the reservoir. For over a decade there has been an industry need for an "internal phase" breaker for VES gelled fluids to help insure and better optimize the breaking of VES gelled fluids; where the breaker components are aqueous solutions and go wherever the VES fluid goes during a stimulation treatment; and can function alone to give quick gel break times or in combination with reservoir conditions for enhanced breaking of VES gelled fluids.
This paper presents laboratory rheological data that show a breaker system composed of two or three aqueous products can be used for a quick, complete, and controllable reduction of VES gel viscosity for temperatures from 80°F to at least 225°F. Also presented is how the breaker system works within a fairly wide range of mix water salinity. The results additionally show that the breaker chemistry can give "industry expected" break times like crosslinked-polymer fracturing fluid systems, with complete reduction of VES gel viscosity in time as short as 15 minutes.
Viscosity break tests were performed using Brookfield Engineering PVS and Grace Instruments 5500 rheometers, configured with hastelloy steel wetted parts and B-5 bobs. Tests temperatures ranged from 80°F to 225°F and test pressure was regulated at 300 psi. Fluid viscosity was measured over time at a constant shear rate of 100 sec-1, with periodic shear rate ramps of 100, 75, 50, and 25 sec-1 for power-law fluid modeling.
A non-ionic viscoelastic surfactant, labeled WG-3L, was the VES product used for the gel break tests listed in this paper. The non-ionic VES product was selected for its ability to yield and retain its VES viscosity within high salinity aqueous fluids. The mix waters tested were 3% bw (by weight) KCl, 12% bw KCl (~9.0 ppg), 30% bw CaCl2 (~10.8 ppg), and ASTM synthetic seawater (Sea-Salt ASTM D-1141- 52 by Lake Products Company, INC.). All VES gelled fluids were premixed in a Waring blender and let set within an enclosed container for 16 to 48 hours to deaerate. Breaker products were added just prior to rheometer testing.
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