Polymer Applications for Oil & Gas
Polymer flooding is the most widely used Chemical Enhanced Oil Recovery (CEOR) method. It is relatively simple to apply and has a long history of successful field applications. Field implementation requires specialized mixing and injection equipment to avoid polymer degradation and viscosity loss. Most CEOR technologies require the addition of polymer for mobility control.
Polymer is added to the injection water to increase viscosity which improves sweep efficiency and provides mobility control between water and oil. Polymer flooding can yield a significant increase in oil recovery compared to conventional water-flooding. Polymer is mixed and injected continuously for an extended period of time until about 30 to 50 percent of the reservoir pore volume in the project area has been injected. The polymer slug is followed by continued long-term water-flooding to drive the polymer slug and the oil bank in front of it toward the production wells.
CHEMICAL ENHANCED OIL RECOVERY
In CEOR, recovery of residual oil is achieved by adding surfactants and alkali to the injection water. Surfactants decrease the interfacial tension between oil and water, and alkali agents can be added to generate in-situ surfactants to help reduce the high level of surfactant adsorption to the reservoir rock. Due to the high pH brought about by the addition of alkali a water softening system is needed to eliminate precipitation of hardness ions.
SELECTING THE RIGHT POLYMER
SNF produces a wide range of EOR polymers in both powder and emulsion form. These cover the majority of reservoir conditions. All the polymers used for EOR are anionic, and product selection for field testing depends on 3 main parameters: temperature, water composition, and permeability. SNF has expertise and guidelines to fine-tune the chemistry in order to limit chemical, mechanical, and thermal degradation. SNF EOR polymers include:
- Anionic co-polymers for below 85°C (185°F)
- Sulfonated co- and ter-polymers for below 100°C (212°F) and/or salty brines
- N-Vinyl Pyrrolidone based ter-polymers for up to 140°C (284°F)
- Associative polymers
- Thermo-associative polymers
- Iron and H2S resistant polymers
- Salt-resistant polymers
- Protective packages
SNF has a long history of supplying the Oil & Gas industry with polymers used for well completions and hydraulic fracturing:
- Friction Reducers
- Guar Alternatives
- Scale Inhibitors
Drag reducing agents (DRA) are used in water injection wells, irrigation networks, and municipal sewer systems to increase their capacities as well as in firefighting to extend the range of fire hoses and water spray.
In Completions and Hydraulic Fracturing, Drag Reducers:
- Reduce corrosion by up to 30%
- Increase injection rates and oil production rates
- Promote energy savings and reduce carbon footprint of oil production
DRAs are widely applied for hydraulic fracturing to produce shale oil and gas. Polyacrylamide is used throughout the fracturing process to reduce the pressure drop in the surface piping and wellbore tubing to help increase the bottom hole pressure. The polymer is added in the range of 150-300 ppm depending on water and field characteristics and injection rates.
SELECTING THE RIGHT POLYMER
SNF produces a wide array of polymers in powder and emulsion form that can be applied in the majority of field conditions, including cationic, non-ionic, or anionic polymer. Selection of the best polymer for a given field application depends on temperature, water composition (salts, contaminants), and rock type.
SNF Polymers for Completions include:
SNF manufactures a unique polymer dissolution unit called PowderFrac™, which is a self-contained and automated hydrating and dosing system designed for rapid hydration of powder-grade polymer. It offers enhanced performance and cost-savings, and has a environmental benefits over traditional emulsion systems.
PowderFrac™ X Gen II Dry Friction Reducer Hydration Unit
Hydraulic fracturing of shale increases productivity by creating, connecting, and propping deep fractures. Design of the fracturing fluid is key to the success. The main functions of the fracturing fluid are to open the fractures and transport the proppant along the length of the fractures.
Guar gum was one of the first polymers used as a viscosifier for fracturing fluids. It is well known for its ability to thicken ice cream, however, there are significant price fluctuations and it has become more expensive as supplies have tightened around the world.
SNF produces a range of synthetic polymers that can be substituted for guar in this application. SNF believes that one product can be used for drag reduction in both linear and cross-linked modes which reduces chemical handling and associated logistics.
The advantages of these products are as follows:
- Viscosity performance is equal to or better when compared to guar gum in both linear and cross-linked systems
- Products can be fine-tuned for high temperature applications
- Viscosity can be broken with conventional oxidizers
- Can be cross-linked with zirconium over a wide range of salinities and pH
- Cleaner than guar, as shown by regain conductivity tests
- Good friction reduction properties
- Biocide not required to protect from polymer degradation
SNF produces a wide range of scale inhibitors to mitigate the damage caused by precipitation of minerals during the completion or production phases of oil and gas wells. These products can be tagged or non-tagged and supplied in powder or liquid form.
Economic drilling of oil wells requires specific properties for drilling fluids. Many requirements are placed on these fluids to achieve multiple purposes, such as:
- Transport cuttings from the drill bit to the surface and permit their separation
- Cool and clean the drill bit
- Reduce friction between the drill string and sides of the wellbore
- Prevent inflow of formation fluids such as gas, oil, or water
- Maintain stability of uncased sections of the borehole
- Form a thin and impermeable filter cake layer that seals the formation and prevents fluid loss
SNF produces a wide range of polymers for water-based drilling fluid systems. Each series of polymer meets one or several requirements such as fluid loss control, viscosity improvement, and shale inhibition. These polymers are produced in a variety of forms, molecular weights, and compositions for specific applications. For example, the same partially hydrolyzed polyacrylamide (PHPA) can be used to provide viscosity or thixotropic behavior, drag reduction, or fluid loss properties to the fluid.
SNF drilling fluid polymers include:
- Shale Inhibitors (clay anti-swelling agents)
- Bentonite Extenders
- Fluid-Loss Control Agents for mud and cement
- Scale Inhibitors
SNF’s years of experience in the creation, manufacturing, and supply of polymers to the oil and gas industry has led to the development of a series of polymers specifically designed for cementing applications. Different additives are often needed as drilling operations go deeper into the formation:
- HTHP fluid-loss control up to 260°C (500°F)
- Gas migration control
- High levels of salt tolerance
- Improved cement placement in the annulus
- Improved adhesion to casing and formation
- Improved density control
SNF provides products to solve multiple challenges in fracturing oil and gas wells. Our products include both liquid and dry friction reducers which perform in a range of produced waters, clay, and shale stabilizers compatible with most frac formulas and scale inhibitors that do not hinder that performance of other additives. Multiple manufacturing and warehousing locations allow SNF to provide products on time, where needed.
- Performance in freshwater to heavy brine
- Low dose clay stabilizers reduce additives and lower costs
- Compatibility with most fracturing formulations
- Reliable supply
SNF offers scale inhibitors to handle the most challenging problems from calcium carbonate to barium/strontium sulfate scales in down-hole or in surface equipment. Additionally, SNF offers dewatering and de-oiling agents proven to solve the toughest separation problems. These products are available in both liquid and dry versions to meet your transportation and product application needs:
- Designed to prevent multiple scale types
- Performance in HTHP conditions
- Improved water/oil separation
- Global product supply
Conformance treatments are applied to injection wells to reduce the permeability in high-permeability zones to increase sweep efficiency of a water or chemical flood. Water shut-off treatments are applied to production wells to reduce or totally shut off water production. Chemicals such as polymer gels can be used for these applications.
SNF offers a wide range of products for these techniques:
- Polymers reactive with organic or inorganic crosslinkers (Chromium, Aluminum, Zirconium, Titanium)
- Crosslinked microgels
- Micro-particles with delayed uncoiling
At the pilot stage (with only a small percentage of injecting wells under polymer flooding), there is generally no need to assess the effect of the back-produced polymer since dilution in the reservoir will lead to negligible concentration of polymer within the water treatment facilities.
When dealing with a full field project, two different aspects have to be considered in treatment processes. The first is related to the separation of crude and produced water. The next one deals with the treatment of water once it has been separated from the crude, in order to be re-used or disposed of.
IMPACT ON THE SEPARATION OF OIL AND WATER
Influence on the separation process
On the production side, depending on the design of the production facilities and the type of injected fluid (presence of surfactant or alkali or both) an emulsion is produced. Demulsifiers, or “breakers”, are needed to break this emulsion. The presence of polymer can interact with the breaker and may result in altered separation. Skilled service companies generally select the most appropriate and compatible breaker using bottle tests. Since polyacrylamide-based polymers are water-soluble, they are considered absent from the oil phase.
Presence of suspended solids
Anionic polyacrylamides are efficient flocculating agents of mineral-based suspended solids. Thus, if the TSS (Total Suspended Solids) are high in the produced fluid, some agglomerates should appear in the water phase in the presence of polymer. These precipitates can deposit on the surface of specific equipment such as heater treaters used in the separation of oil and water. This contributes to the creation of hot points and can lead to accelerated corrosion issues. These deposits should be removed on a regular basis.
TREATMENT OF PRODUCED WATER
Once oil has been recovered from the produced fluid, a small amount of oil and TSS still remain in the produced water. Devices for produced water treatment are usually sized to operate with water viscosities below 4 mPa·s. Polymer breakthrough on the production side will contribute to an increase in viscosity and will reduce the efficiency of the treating devices to separate the oil and suspended materials. With produced water viscosities of 10 mPa·s, the residence time required is five times longer and devices required are five times larger.
Different methods can be applied to decrease the viscosity of the fluid containing polymer in order to improve water treatment efficiency. The principle is to drastically decrease its molecular weight and thus, the associated viscosity of the fluid by means of mechanical and/or chemical degradations.
Mechanical Degradation of the Polymer
Mechanical degradation can be performed to decrease the molecular weight of the polymer and decrease the viscosity of the solution. A shearing pump or choke valve can be used to achieve the necessary results.
Chemical Degradation of Polymer
Polyacrylamides degrade in the presence of oxidizers. Radicals are formed from oxidizers that react with the backbone chain of the polymers, resulting in a decrease of the molecular weight and viscosity reduction. A preferred oxidizer is sodium hypochlorite (NaClO).
Achieving sufficient injection pressure is a major problem in deep wells. Both bottom hole pressure required to fracture a formation and pressure loss due to friction, increase directly with well depth. This is due to the cumulative effect of overburden pressure and tube or casing length the fluid has to travel through in order to reach the bottom hole. If the injection rate is below a critical value, proppant may fall out of the fracturing fluid and cover the perforations. This would force the treatment to be stopped.
Drag reduction additives such as polyacrylamides are used to reduce frictional pressure loss so that higher bottom hole pressures and injection rates are realized. The drag reduction effect achieved can be 50 to 75% during a fracturing treatment.