gel breaker

When an aqueous gel is contacted under appropriate conditions, chemical gel breakers can degrade the gel back to a low-viscosity and watery solution. The use of gel breakers and the types of gel breakers used in the industry were describe as following:

1 Use of gel breakers
1.1 Two possible reasons to use a gel breaker after a conformance-improvement gel treatment are: 1.1.1 To remove gel from the wellbore or perforations, 1.1.2 To undo a gel treatment in the near-wellbore region if it was determined after its placement that the emplaced gel was not beneficial.
2 Problems in using chemical gel breakers for gels in fractured reservoir
There are several reasons why a chemical gel breaker cannot be used to successfully and fully degrade a gel that has been placed deeply in either a matrix-rock or a fractured reservoir. First, successfully delivering the chemically reactive gel breaker solution deeply in an oil reservoir is a daunting task. Second, and more fundamentally problematic, even if a chemical breaker solution could be 100% effective in the reservoir during its entire gel-breaking life, once injected into the reservoir, the gel breaker solution would tend to wormhole through the emplaced gel. Thus, the chemical breaker would only be able to regain a small fraction of the pregel-treatment fluid-flow capacity within the gel-treated reservoir volume.
3 Types of gel breakers
3.1 Strong acid solution
Strong acid solution gel breaker is one of the common gel breaker. Many biopolymer gels and freshly placed inorganic gels can be chemically broken and reversed by contacting them with a strong acid solution. However, acids are usually ineffective at chemically breaking down metal-crosslinked synthetic-organic-polymer gels, such as metal-crosslinked acrylamide-polymer gels. Acrylamide-polymer gels can be chemically degraded back to a watery solution by contacting them with a free-radical chemical gel breaker, such as hydrogen peroxide, sodium hypochlorite of bleach, and ammonium peroxide. Free radicals chemically degrade polymer gels by a polymer backbone scission mechanism.
3.2 Hydrogen peroxide
Hydrogen peroxide is, in many instances, the most chemically powerful of the chemical gel breakers commercially available. However, its decomposition is catalyzed by tubular rust and many other oilfield substances, such that the injected hydrogen peroxide can be rendered essentially spent before it can be delivered to the downhole gel. The use of hydrogen peroxide may be favored when plastic-coated well tubulars have been used. Hydrogen peroxide is an extremely reactive chemical. It is advised to not inject concentrations exceeding 10% hydrogen peroxide; however, a concentration of less than 5% is ill advised, because ineffectively low concentration of hydrogen peroxide will often result downhole. Hydrogen peroxide decomposes to water and free oxygen during the gel-degradation process. The creation of oxygen in the wellbore and/or the reservoir after the hydrogen peroxide is injected raises safety issues that need to be addressed as part of the hydrogen peroxide selection process.
3.3 Bleach
Bleach (containing sodium hypochlorite) as a gel breaker, is probably the most widely used material to chemically breakdown acrylamide-polymer gels. It is more chemically robust downhole than hydrogen peroxide. A note of caution: when hydrogen peroxide or bleach is used to break gels crosslinked with a chromium (III)-containing crosslinking agent, some of the chromium (III) will be converted, at least temporarily, to chromium (VI). Because any Cr (VI) that might be formed in the chemically reducing reservoir environment is rapidly converted back to relatively nontoxic Cr (III), field experience has shown that this is often only a theoretical concern. Most oil reservoirs are characterized as having a chemically reducing environment. It should be noted that certain types of metal-crosslinked polymer gels, under certain conditions, can be degelled when contacted with an aqueous solution containing a high concentration of either a caustic chemical (e.g., sodium hydroxide) or a strong ligand (e.g., oxalate).
3.4 Encapsulated (Delayed) gel breaker
3.4.1  Encapsulated gel breaker is also called delayed gel breaker. If an effective delayed and single-fluid reversible-gel technology, especially a reversible-polymer-gel technology, were to be developed in which the gel chemical breaker or gel-breaking mechanism were chemically built directly into the gel structure itself, there would be numerous oilfield applications for such reversible gels. The delayed gel reversal/degelation time would need to be controllable.
Encapsulated gel breaker is a new kind of gel breaking technology. It is based on one or several common gel breaker as capsule-core and coated on the surface of a layer of waterproof material to become a tiny capsules. It could release breaker slowly and could be used in high concentration without any negative influence.
Ammonium persulfate is a kind of common gel breaker in well fracturing. Nevertheless it can make the fracturing fluid viscosity loss in advance when it be added too early or too much. Then do the negative influence to width generation capacity of the fracturing fluid, even cause the sand out untimely and result in the failing of the treatment. What was worse, the gel breaking will be not completely when gel breaker is added not enough. This matter do damage to the oil rock caused by the residue and the liquid in the reservoir, reducing the flow conductivity, influencing the fracturing effect.
3.4.2 The advantages of encapsulated gel breakers are as following:
(1) Encapsulated gel breakers can thoroughly break the gel, reduce the viscosity quickly, flow back easily and causes no damage to the formation.
(2) The external encapsulation is impermeable, resistant to temperature, and allows a delayed break down of the gel polymer chains.
(3) Encapsulated gel breakers decreases viscosity after the proppant placement which minimizes return of proppant and maximizes return of stimulation fluids to the surface.
3.4.3 The encapsulated gel breaker manufacturing process involves the use of special process:
To coat a special material on the surface of ammonium persulfate (shell), the ammonium sulfate and fracturing fluid in the water isolation, at room temperature, pressure conditions are placed, the outer layer of the shell is broken, broken glue effective components. Wrapped in a coat does not play a role, only when the layer crack closure of pressure and impact, or with the temperature rise, after long time immersion, the outer coat of hair is not the same degree of broken or solution will have to release. Put out, it will send the gel breaking in. This is also the capsule gel breaker can be high enough concentration to use and does not affect the flow of the important reasons.
With conventional gel breaking agent than its advantages that can prevent the fracturing fluid gel breaking before a construction failure. But if the capsule shell material is not good, the capsule gel breaker release speed too fast will lead to the breaking of fracturing fluid, causing the construction fails, the capsule gel breaker release rate is the product of one of the main energy. In the room where the capsule gel breaker can correct and effective in the evaluation of field application tools have guiding significance.
3.5 Water-soluble chemical gel breaker
If a water-soluble chemical gel breaker (breaker not built into the gel structure itself) were incorporated into an aqueous gel formula and the gel were placed downhole under a differential pressure (as usually is the case), then as the chemical gel breaker begins to break down the gel, the differential pressure would begin to squeeze water, including the dissolved breaker, out of the gel. Unfortunately, increasing breaker concentration is required as the concentration of the polymer increases in the gel. When a water-soluble breaker is being squeezed out of the partially broken gel, the opposite trend is occurring. Thus, the use of water-soluble chemical breakers incorporated into a single-fluid aqueous gel under differential pressure always results in an incomplete gel break and always leaves a significant gel residue. To date, the addition of a water-soluble chemical breaker into a single-fluid aqueous gel formula has not proven effective in fully degrading a gel when the gel is broken under differential pressure.
3.6 Borate-gum gel breakers
A typical fracturing fluid having a delayed breaking time can be formed by first mixing the borate and gum chemicals in an aqueous solution to form a water-gel of the desired consistency. A fracture propping agent, like sand, can be added. Thereafter, a predetermined amount of sized gel breaker will be suspended in the gel. In utilizing the gel, the resulting mixture is injected into the well bore and pressurized into the desired formation thereby creating or extending fractures in the formation. After fracturing the formation, the formation fluids are either produced immediately or the well bore is shutin and the formation allowed to remain quiescent until the gel has broken before the formation fluids are produced. When a binding agent is used, the method of producing the well will depend on the type of binding agent used. If a temperature-sensitive or water-soluble binding agent is used, the formation can be allowed to remain quiescent until the gel breaks. If an oil-soluble binding agent is used, the formation fluids are produced until the binder is dissolved. Thereafter, either the well is shut-in until the gel breaks or the production is continued and the gel gradually breaks and gel chemicals are removed.
Ammonium Persulfate Gel Breaker

Shale Gas Hydraulic fracturing is a proven technology to enhance productivity and maximize recovery in oil and gas wells. Guar gum is generally used for making the frac-fluid and keep the sand particles or proppant in suspension. The high viscosity fracking or fracing fluid is pumped in and the pay zone is fractured. After fracturing , the viscous guar gum is required to be broken for reducing the viscosity and get hydrocarbons to flow out of the fractured formation. This decrease is achieved by using an oxidizer like Ammonium Persulphate. It is often referred to as gel breaker. In delayed and single-fluid reversible-gel technology, gel-breaking mechanism is chemically built directly into the gel structure itself and for this delayed gel reversal time is controllable.
When an aqueous gel is contacted under appropriate conditions, breakers can degrade the gel back to a low-viscosity and watery solution.

Coated or Encapsulate Ammonium Persulfate, based coated chemical for low to high temperature delayed release gel breaker is used for breaking gel up to temperatures of 200°F or 93C or a little more. 75% to 90% active matter is generally offered depending upon down-hole temperature. The release rate can be customized to give quick or medium or fast release.

Encap Ammonium Persulfate is generally demanded for 3 different temperature ranges.
LT Encapsulated Breaker for downhole temperature of 100F (38C) to 120F (49C). This will have a coating of about 10.5 to 12.5% and active matter about 87 to 89%.
MT Encapsulated Breaker for for downhole temperature of 120F (49C) to 140F (60C). This will have a coating of about 13 to 16% and active matter about 83 to 86%.
HT Encapsulated Breaker for for downhole temperature of 140F (60C) to 200F (93C). This will have a coating of about 16.5 to 23% and active matter about 76 to 78%.

Coated or Encapsulate Potassium Persulfate based coated chemical to be active at 195F or 90C called high temperature delayed release gel breaker is used when significantly higher down-hole temperatures up to 300°F or 150°C are expected.
Coated or Encapsulated Sodium Bromate based gel breaker for very high temperatures. It will not be active up to 240°F or 115°C and is suggested for use at 280°F to 330°F or 138°C to 165°C.

Oxidizing agents can be used in 4 ways for breaking gel.
1. As it is chemical Ammonium Persulfate
2. Coated chemical to be active at 140°F or 60°C medium temperature delayed release gel breaker.
3. Coated chemical to be active at 195°F or 90°C high temperature delayed release gel breaker.
4. Coated chemical to be active above 250°F or 120°C very high temperature delayed release gel breaker.

Applications:
Oil field – Oxidizing Gel Breaker for Guar slurries used in fracturing. In frac jobs, after proppant is placed, fluid viscosity needs to be reduced.  All Guar based systems can be broken using oxidizing breakers. It generates free radicals of oxygen to efficiently oxidize and break all types of guar gels.
Manufacturing – Polymerization initiator
Water Treatment - It is used in water treatment.