Encapsulated Breaker for Aqueous Polymeric Fluids

Abstract

Conventional breakers reduce fracturing-fluid viscosity much too rapidly, even at moderate temperatures (140 to 200°F), to be used at the high concentrations required to degrade polymers within proppant packs. A delayed-release, encapsulated breaker was developed that permits the use of high breaker concentrations and thus significantly increaSes fracture conductivity. AbstractPersulfates are commonly used as breakers for aqueous fluids viscosified with guar or cellulose derivatives. These breakers are necessary to minimize permeability damage to proppant packs at temperatures where there is little thermal degradation of the polymers. Unfortunately, dissolved persulfates are much too reactive, even at moderate temperatures (140 to 200 0 P), to be used at concentrations sufficient to degrade concentrated, high-molecularweight polymers thoroughly.New technology described in this paper was used to produce a "delayed" breaker. The breaker is prepared by encapsulating ammonium persulfate (APS) with a water-resistant coating. The coating shields the fluid from the breaker so that high breaker concentrations can be added to the fluid without causing the premature loss of fluid properties, such as viscosity or fluid-loss control. Critical factors in the design of encapsulated breakers (such as coating barrier properties, release mechanisms, and reactive chemical properties) are discussed. The effects of encapsulated breaker on fluid rheology were compared for several encapsulated persulfates. Only one material had a coating adequate to protect the fluid from premature degradation. Additional rheology and conductivity damage studies were done with this product. It was found that in a boratecrosslinked fluid at 160 o P, 2 Ibm/I ,000 gal of encapsulated breaker caused an improvement in retained permeability from 15% to 49 %, but caused only a 20 % loss in viscosity in 1 hour. These laboratory tests indicate that an encapsulated breaker may increase well production by improving proppant-pack cleanup.

Optimization of Post-Hydraulic Fracturing Flowback Cleanup Utilizing Polymer Content Determination in Flowback Liquid Samples

“…By the reaction of the thickening agent with the cross-linker, the viscosity of the fracturing fluids increases. Breakers of different types such as acids or enzymes or oxidizers are used to reduce the viscosity of the fracturing fluid by cleaving the thickening agent molecules into smaller fragments (Almond and Bland 1984; Gulbis et al 1992; Brannon and Tjon-Joe-Pin 1994; Reinicke et al 2012). The most widely common breakers are oxidizers, as used in the three wells in this study.…”

“…Subsequently, the fracturing fluid must degrade to a very low viscosity to allow flowback and fracture cleanup (Rae and Di Lullo 1996;Lu et al 1999). Any unbroken gel residue remained inside the fracture may cause damage resulting from chemical interactions with time (Almond and Bland 1984; Gulbis et al 1992). Over the past years, hydraulic fracturing in Saudi gas fields underwent significant improvements with regard to job design and execution, fracturing fluid recipes, proppant type and strength, number of fracturing stages, and treatment volume optimization that resulted in enhanced productivity (Al-Ali et al 2015; Rahim et al 2013).…”

“…There are three main types of most widely used breakers: oxidizers, acids, and enzymes. Many factors can affect the performance of the breaking agents, such as the type of breaker and loading, temperature, time, polymer content, and liquid or solid state of the breaking agent (Almond and Bland 1984;Gulbis et al 1992; Brannon and Tjon-Joe-Pin 1994; Reinicke et al 2012).…”

Novel Controlled-Release Breakers for High-Temperature Fracturing

“…Conversely, the encapsulated oxidizers released slowly from the polymer blend. The mechanism behind the diffusion-controlled release is comprised of i) the penetration of aqueous medium into the polymer matrix, ii) dissolution of the breaker, and iii) diffusion of the breaker into the aqueous medium caused by the difference in the concentration gradient (Satya Gupta and Cooney 1992; Aminabhavi et al 1996;Gulbis et al 1992). The desired release rate can be achieved by choosing the appropriate composition of polymer blend and breaker loading.…”

Development and Implementation of a Low-Polymer-Concentration Crosslinked Fracturing Fluid for Low-Temperature Applications

“…However, studies over the last decade have identified fluid degradation and clean up as the most serious weakness of the guar-based fracturing fluids. 4 As a result, the industry has focused on improving the controlled degradation of the fluids with various polymer (gel) breakers [5][6][7] .…”