An Innovative Approach to Gel Breakers for Hydraulic Fracturing

Abstract

Gelled fluids are routinely used in hydraulic fracturing to deliver fractures with higher propped width, due to the fluids' abilities to deliver higher proppant concentrations than their lower-viscosity analogues. The most common of these gels (borate-crosslinked polymers) have been used successfully in fracturing for decades, routinely exhibiting viscosity >100cP in conventional high-pressure, high temperature (HPHT) viscosity measurements. Recent studies have found that the viscosities of borate gels at actual downhole pressure conditions may be 80% less than that measured using standard HPHT rheometer measurement (which uses 400 psi top-pressure). A proposed mechanism for this phenomenon is a pressure-induced shifting of the crosslink/temperature stability near the "melt temperature" of borate-crosslinked gels, leading to a reversible thinning. A novel approach is posed in the current work to exploit the "pressure effect", by capturing the pressure-thinned fluid in a thin state and irreversibly breaking the gel viscosity. As existing crosslinked-gels with oxidative breakers rarely achieve >50% retained pack-permeability, an improved break mechanism based on pressure could yield sizeable productivity-gain in propped fractures. A series of candidate breaker materials with potential affinity for the crosslinker was screened for gel-breaking performance in the current work. Preliminary screening of these additives led to one preferred alternative gel breaker material which demonstrated superior performance in pressure-induced breaking behavior. This study will illustrate advanced characterization of the breaker performance utilizing realistic sequences of temperature, pressure and shear rate that would be expected for a fracturing treatment. The advanced characterization also included fracture-conductivity measurements comparing a control gel with and without the alternative breaker. Under these conditions, the fluids containing the candidate breaker material showed persistent viscosity-break, while the control fluids recovered their viscosities upon pressure-release. The preferred breaker material performance was further confirmed through a series of experimental conditions varying temperature, pressure (up to 10,000 psi), gel concentration, and breaker concentration. In fracture conductivity measurements, the gel which contained the preferred breaker also showed improved conductivity compared to control fluids without breaker. The current study proposes a new method of achieving break of gelled fracturing fluid, which avoids some of the risks and disadvantages of oxidizer chemicals. These results will suggest the most preferred fluid conditions for applying the new breaker material in hydraulic fracturing.

Supramolecular dynamic binary complexes with pH and salt-responsive properties for use in unconventional reservoirs

“…After the fluid injection step is completed and the proppant is deposited in the fractures, the fracturing fluid must attain a lower viscosity to allow flow back and efficient cleanup [ 70 ]. The use of oxidizers and enzymes have sometimes been utilized for this purpose in linear and crosslinked gels, but their incompatibility towards certain fracturing fluids and additives prompted the search for alternatives [ 71 , 72 ]. The dynamic binary complex presented in this paper, which can be switched down to a lower viscosity by decreasing the pH has the potential to address the gel breaking requirements of industry in a facile manner.…”

A Review of Advanced Molecular Engineering Approaches to Enhance the Thermostability of Enzyme Breakers: From Prospective of Upstream Oil and Gas Industry

“…The acids lower the pH of the liquid solution and decrease the viscosity. In one study, tannic acid encapsulation could gradually break the fluid viscosity up to 275 • F. Acid breakers work effectively at higher temperatures compared to oxidizer breakers [10]. Enzyme breakers, first introduced in 1992 for lowtemperature and high-temperature fracturing applications, are bioactive polymers of amino acids that can reduce hydraulic fluid viscosity by degrading glycoside bonds of guar-based gel polymers.…”

Viscosity-Reducing Agents (Breakers) for Viscoelastic Surfactant Gels for Well Stimulation

“…Polymers and viscoelastic surfactants (VES) are used to improve well productivity in carbonate and sandstone reservoirs. − These compounds are used in matrix acidizing and hydraulic fracturing. ,− In matrix acidizing, polymers and VES are used as chemical diverters and are known as self-diverting agents. ,− Using diverters ensures that the low viscosity acid pumped into the well goes into the low-permeability zones and not in the high-permeability zones, thus increasing the effectiveness of matrix acidizing. ,− , Diversion by gels replaces mechanical diversion techniques because mechanical diversion methods are not always recommended, especially for long horizontal or extended-reach wells. , In hydraulic fracturing, polymers and VES act as a fracturing fluid and a proppant transporter as a result of their high viscosity. ,,,, They are pumped at or above the formation fracturing pressure to create fractures in the wellbore, thus improving well productivity, especially in low-permeability zones . However, the usefulness of gels is not only based on their diversion or fracturing abilities.…”

“…First, polymer-based fluids are not easily cleaned up by reservoir oils after being fully viscosified when compared to VES. ,− This is because viscosity of VES fluids can be reduced by reservoir oils, leading to less formation damage. Moreover, polymer-based fluids need more resources to prepare at the surface when compared to VES. ,, VES solutions only need salt to viscosify the solution and a co-surfactant to promote or inhibit gelling if necessary. ,, The calcium ions (Ca 2+ ) released during the acid reaction with carbonate in carbonate reservoirs help viscosify the low-viscosity VES/acid mixture pumped during acidizing diversion. ,, Meanwhile, polymers usually require cross-linkers to build their high viscosity at reservoir conditions . However, the efficiency of these cross-linkers is also dependent upon reservoir conditions, such as the temperature and hydrogen sulfide. , Moreover, VES-based gels have lower losses in pressure in pipes compared to polymer gels. , With these advantages, VES-based stimulation fluids have been applied in the field, as discussed in the reviews of Hull et al and Kang et al …”

“…3,6,7,23,24 They are pumped at or above the formation fracturing pressure to create fractures in the wellbore, thus improving well productivity, especially in lowpermeability zones. 25 However, the usefulness of gels is not only based on their diversion or fracturing abilities. Another criterion for their value is their ability not to block the acidized or fractured wells.…”