Internal Breakers for Viscoelastic-Surfactant Fracturing Fluids

Abstract

Over the past two decades, viscoelastic surfactant (VES) fluids used for gravel packing, frac-packing and conventional hydraulic fracturing have primarily relied on external or reservoir conditions to break the fluid's viscosity. Unlike polymeric fluids, no internal breakers have been used. Relying on external conditions to break VES fluid has been a point of contention and questionable, especially for dry gas applications. This paper describes how new internal breaker technology has been developed that allows VES fluids to be broken into easily producible fluids, without the need for contacting reservoir hydrocarbons. The reservoir pressure required to produce VES fluid is no longer compromised: very little pressure or time is required when an internal breaker is present. Mechanisms for internally breaking VES viscosity are discussed. New internal breakers have been found to work over a wide fluid temperature and mix water salinity range, and have compatible with newly developed VES stabilizers and fluid loss control agents. Presented are laboratory results that compare VES fluids with and without an internal breaker. Rheological data is presented that show the performance of internal breakers in degrading VES fluid viscosity, in particular at low fluid shear rates. Core clean-up tests were performed at 150°F, using 3% KCl brine and nitrogen gas as the displacement (clean-up) fluid. The results show that use of an internal breaker significantly improves VES fluid clean-up. This paper also presents VES system compatibility and proppant conductivity results. Introduction During the 1980's a VES fluid was developed for gravel packs1. Introduced with this fluid was the concept that no internal breaker was required. This same concept was also applied to VES fluids developed for frac-packing and conventional hydraulic fracturing during the 1990's2,3. The stated reason for not requiring internal breaker was that the VES micelles which impart fluid viscosity are sensitive to and will break upon contacting reservoir hydrocarbons, including gas hydrocarbons like methane, ethane and propane. During production the reservoir hydrocarbons are said to come in contact with the VES fluid in the pores of the reservoir and thereby will readily break the VES fluid viscosity and allow the once viscous fluid to then be easily removed. This concept of externally breaking VES fluids is still promoted today4. However, it should be noted that viable internal type breaker technology has not existed for VES fluids until recently5. With the introduction of internal VES breaker technology has come the ability to evaluate the need for such technology. This paper presents laboratory data for evaluating the cleanup of VES fluids with and without internal breaker. The data shows internal breakers may substantially improve VES fluid cleanup without the need for relying on an external breaking mechanism, and how VES fluids without internal breaker under certain conditions may be difficult to move and cleanup. Internal Breakers In a broad sense internal breakers are compounds placed within the VES fluid during surface mixing that will:go wherever the fluid goes;ensure the VES fluid breaks; andbreak the VES fluid into an easily producible fluid. From one point of view, using internal breaker is like adding the required amount of reservoir hydrocarbons to the VES fluid at the surface, ahead of time, so complete break in VES fluid viscosity will occur over time at reservoir temperature without the need for contacting reservoir hydrocarbons. The use of internal breakers should also improve:the rate and ease of VES fluid cleanup; andprevent viscous emulsions from forming when problematic reservoir hydrocarbons contact, mix with, and break VES-laden fluid in the reservoir.

Understanding viscosity reduction of a long-tail sulfobetaine viscoelastic surfactant by organic compounds

“…17 But the reduction of the viscosity by reservoir oil is inefficient. 18,19 Moreover, the gels are detrimental to natural gas production if le in the reservoir.…”

Numerical analysis of non-Newtonian rheology effect on hydrocyclone flow field

“…Tom B A [16] thought turbulent drag reduction effect of non-Newtonian fluid and its application were to add high molecular polymer solvent to clear water and make it to be shear thinning non-Newtonian fluid, and then raised its head of delivery at a certain rate of turbulent flow field; Toms and Krame successively found polymer dilute solution or elastic protective material could achieve viscosity drag reduction. Other articles [17,18] studied the mechanism of turbulent drag reduction, water due to minimum molecular viscosity, should have the highest degree of freedom, namely the combination vortex motion index should be the biggest, but due to the minimum molecular viscosity, it led to high turbulence and fast kinematic velocity when entering the cyclone. In the process, the friction between the molecules intensified and high turbulent viscosity led to serious internal loss.…”

Propagation and Retention of Viscoelastic Surfactants Following Matrix-Acidizing Treatments in Carbonate Cores

“…9 is that the amount of surfactant retained in the core following acid treatment was significant. This means that there is a need to use external (mutual solvent) or internal breakers (Crews 2005;Crews and Huang 2007) to reduce surfactant retention, especially if a surfactant-based acid is used in a power-water injector or a dry-gas well. …”

“…This is exactly what Mohamed et al (2002) noted in the field. Another solution is to use internal breakers to remove the surfactant (Crews 2005;Crews and Huang 2007).…”