Innovative solution for cold-temperature paraffin wax control

Paraffin wax deposition is a primary flow assurance challenge in the upstream oil and gas industry. Deposition occurs when temperature and pressure decline beyond a point that forces paraffins (waxes) out of the crude oil and onto the pipeline surface. This issue is more frequent and severe in areas with colder climates. Paraffin wax can precipitate out of the oil and lead to deposition at different stages during the oil production process. Some common places for deposition to accumulate are downhole, within the flowline, or the separator, in the fine screens, transport lines, or storage tanks. There are a few paraffin remediation approaches available to combat the challenges that they bring, which have their own unique cost benefit.

A common, and typically more cost-effective, way to address this challenge is with chemical inhibition and remediation programs—these can be used in combination with other mechanical techniques. Mechanical examples are knifing (downhole) and pigging (surface) the lines after paraffin deposition becomes so problematic that a decrease in production rate is observed. There are more proactive approaches that are often taken by producers, where a constant mechanical remediation program is in place that runs on a pre-defined set period (weekly, monthly). This can be very effective and can be the best option in some cases; unfortunately, this still requires a set downtime in production. There is also a chance of a pig becoming stuck, due to a high buildup of paraffin, which can require a very costly intervention and recovery to be undertaken.

Chemical remediation examples include solvent washes, typically with aprotic solvents that will dissolve the wax, and hot oil or hot water dewaxing jobs that will use thermal or solvating properties to remove paraffin wax deposition from the pipe surface. The challenge with this method is that if not properly selected and designed, then it can effectively remove only a portion of the lighter chain paraffins and leave behind heavier and harder-to-remove paraffins that cannot be dissolved easily. This thin deposit layer can build up over time and eventually lead to a more challenging case to handle in the future, and is a common reason for stuck pigs.

CONTROLLING WAX

Chemical inhibition relies on classes of specialty polymers that are designed to mitigate paraffin deposition in-situ. While the polymeric mitigation approach can be very effective, there is a challenge to maintain product stability in Arctic climates. These polymers, known as pour point depressants (PPDs), are themselves sensitive to temperature declines, often becoming unusable at freezing temperatures. With an increase in natural gas production projected in arctic regions, a real challenge emerges for oil producers.

The function of a PPD chemistry is to be structurally similar to the paraffin found in crude oil. This similarity allows the PPD to interact with the paraffin through key structural attractions and hinders paraffin build-up from occurring while also altering the temperature at which deposition occurs.

Fig. 1. Mechanism of paraffin deposition and PPD inhibition.

The main benefit of a PPD is in its ability to delay and limit the severity of paraffin deposition. To fully accomplish this, a PPD must co-precipitate with the paraffin in the crude oil, allowing the PPD to either hinder the paraffin from growing larger; modify the structure and reduce the size of the paraffin; or surround the paraffin and prevent a network from forming by repelling the paraffin crystals from each other. It is key for the deployment of the PPD chemistry to be applied above the temperature at which the paraffin will begin to form in solution, also known as the Wax Appearance Temperature (WAT). A schematic of the deposition and inhibition process is included in Fig. 1.

Producers in Arctic regions are faced with increased paraffin deposition challenges, due to the stark temperature declines during the winter months. The Montney formation in Canada, for example, has areas that reach as low as –50°C during winter. There is a large projected growth of production in the Montney area over the next 20 years. This highlights the need for a viable and effective solution for paraffin management, specific for the Arctic regions. They are faced with the challenge of having limited PPD treatment options, due to the thermal sensitivity of the polymers. This results in limited solutions, at higher dose rates, that still do not successfully and fully address the paraffin challenge to justify the increase in OPEX costs.

The current industry practice is to formulate very low amounts of PPD (< 5% by weight) into a suitable solvent matrix to ensure product stability at temperatures as low as 50°C below zero. The options available for such stringent conditions are extremely limited. Many PPD chemistries, such as some EVA types, are incapable of reaching such temperatures before gelling occurs. Due to the similarity to paraffin, a PPD will be sensitive to declining temperatures. This leaves pursuing more dispersant type chemistry, with minimal amounts of PPD diluted in high volumes of solvent as the only viable option. This results in increased chemical dose rate for problematic crude oils and relies more on diluting the paraffin wax than allowing the PPD to directly impact the paraffin wax.

These treatments are still needed to prevent plugging events, as temperatures decline and paraffin begins to deposit on the inner walls of the pipe. In some cases, the real challenge isn’t always simply finding the right chemistry, but rather being able to realistically apply a high enough concentration to be effective.

DELIVERY SYSTEMS

The current body of work reports an intensive R&D effort to identify a suite of PPDs that have shown to be top performers for a wide range of different crudes types encountered globally. The base principle behind the patented approach relies on micro-dispersion (colloid) science, which consists of dispersing the active chemistry within a solvent system, allowing product flowability at temperatures as low as –50°C.

Fig. 2. Non-winterized product versus WAXTREAT SubZero.

This micro-dispersion technology is the fundamental basis behind Clariant’s latest novel technology, WAXTREAT SubZero. When compared to the equivalent solution polymer products typically solid at < 25°C, this technology has led to the delivery of new products with a more robust temperature stability range (–50°C to +50°C), with no sacrifice in performance, Fig. 2.

The wax treatment technology has an average particle distribution < 2 micrometers, which ultimately allows for maximum product storage stability under both static and dynamic conditions. The unique micro-dispersion system enables an effective delivery of the PPD chemistry into the crude, regardless of the presence of water, that would typically impact the effectiveness of the PPD. The presence of water can potentially hinder the interaction of the paraffin and the PPD chemistry. The side groups of the PPD chemistry that are responsible for disrupting the paraffin network from properly forming will interact with the water molecules and will not properly migrate into the oil layer for effective treatment. The patented solvent system of the wax treatment technology has been shown to not be impacted by this same hinderance.

Fig. 3. Viscosity wax profile of non-winterized polymer and new wax solution versus traditional winterized incumbent on crude oil.

One of the key design criteria during the development of WAXTREAT SubZero, was maintaining the performance of the PPD when compared to the equivalent solution polymer, so that there is effectively no distinguishable performance difference. This was an important step to demonstrate, as one of the key features of the micro-dispersion system is that it can serve as a delivery system for the active PPDs and overcome the natural freeze tendency at colder temperatures. From testing, it was shown that there was no difference in performance between the two delivery systems, Fig. 3.

A review of viscosity versus temperature in Fig. 3. shows that treatment curves for the new wax technology and the non-winterized counterpart are similar. However, the effective dose rate of 150 ppm compares favorably to the incumbent, at the same dosage, while the other product could make only a slight improvement against the blank.

This was verified with additional laboratory testing utilizing the industry-standard cold finger technique. A cold finger device is an instrument designed to simulate paraffin deposition occurring within the inner wall of a pipeline. The inverted stainless-steel finger is set to the desired temperature and submerged into the crude to act as a chilled depositional surface (i.e. the pipe wall). Deposition is triggered by temperature differential between the crude and the cold pipe wall, which leads to paraffin wax diffusing out of the crude oil and onto the surface of the finger.

Test results showed that the innovative WAXTREAT SubZero chemistries were able to achieve 90% reduction in paraffin deposition and showed there was no difference in performance between the micro-dispersed product and the non-winterized counterpart. This demonstrates that the new wax control technology behaves as expected, and the delivery system for PPD to diffuse into the oil layer for effective paraffin mitigation is effective. This captures the added benefit of the increased activity made possible with WAXTREAT.

In summary, the development of the new micro-dispersion system lowered the (equivalent solution polymer) product pour point to –50°C. Additionally and uniquely, the range of different dispersion chemistries has been designed carefully to allow blending of different PPD chemistries without sacrificing product pour point or compatibility. This development has created an unparalleled flexibility in formulation design and, therefore, in provision of customized, and low-temperature stable, treatment options. The right PPD chemistries can first be screened to determine the best chemistries for mitigation of the paraffin challenge at hand, and then apply the micro-dispersion concept and products to ensure product stability and efficacy.

PROVEN FIELD PERFORMANCE

Several successful applications of WAXTREAT SubZero have been performed, and continue to be applied, in the field. The new products offer an innovative customization to mitigate paraffin wax deposition in pipeline systems while also reducing OPEX, due to significantly reduced dose rates and superior product performance. The wax control system has demonstrated effectiveness in a wide range of field trial applications throughout the yearly climate cycle.

A transport pipeline operator in Canada was flowing approximately 200,000 bpd of comingled crude oil and serviced over 100 producers in its region of operation. This geography saw temperatures decline to as low as –50°C during the winter months. The comingled crude flowed into a terminal and was then transported via a 22-km, 4-in. pipeline to the main transport line. During transport, the operator was experiencing severe wax deposition problems occurring throughout its pipeline. This had a significant increase in severity during the winter months, and the operator had an incumbent and rigorous paraffin mitigation program, including daily pigging combined with solvent washes and use of a continuously injected PPD chemical treatment.

Despite having the described incumbent program in place, the operator was still facing constant deposition challenges, as indicated by paraffin wax in the daily pig returns. The incumbent PPD chemical treatment program was not able to combat and reduce the paraffin deposition, due to it being a low-active winterized product. The incumbent product was designed to be mostly organic solvent-based to meet the low-temperature requirement, which meant that the main mitigation pathway was ineffective at inhibition of paraffin wax at low dosages.

For this reason, the operator was still experiencing the additional challenge of having stuck pigs occur during the daily remediation jobs, a costly investment for retrieval. The opportunity was given to review and revamp the incumbent paraffin control program. A systematic approach was used that involved a deep dive into the operating conditions, stock tanks, comingled crude, and pipeline paraffin wax deposits. By careful examination, it was deemed that the system required a high concentration of a specific type of PPD chemistry, which simply would not have been possible to deploy under the traditional approach (solution polymer). For this reason, the new wax treatment technology was recommended to address the challenge and was given the opportunity to trial on the most problematic line that averaged daily shipping volumes of 800 m³.

The overall performance improvement indicated in the laboratory testing led to an eight-month field trial, so that both winter and summer performance KPIs could be determined. During the trial, the ambient conditions dropped as low as –45°C, and the new cold temperature wax control technology remained stable and pumpable throughout the time period of the trial.

Fig. 4. Trial pig return volumes and paraffin wax hardness.

Figure 4 shows a summary of the field performance. A sharp reduction can be seen in the pig return volumes compared to the incumbent, which highlights the products’ ability to keep the paraffin in solution and limit deposition from occurring by reducing the size of the paraffin crystals. It can be further seen that the hardness of the pig return wax is also reduced significantly after treatment, when compared to the incumbent. This is due to the product targeting the problematic paraffin chains that led to harder deposits that weren’t being controlled by the incumbent. The performance benefit also yielded a field dose rate reduction of 63%, when compared to the historical treat rate of the incumbent during the same timeframe. The incumbent had a historical dose rate of 150–180 ppm during the harsh winter months, with significant wax deposition still seen, Fig. 4. WAXTREAT SubZero was optimized to 60 ppm during the trial and was shown to be very effective. The operator had never seen a chemical achieve the level of paraffin deposit reductions that the new product was able to achieve and independently validated the best-in-class nature of the new technology.

With the confidence gained from this extended field trial (now permanent application), further opportunities were explored to test the product’s limits. Another opportunity was provided, when a producer in the Western Canadian Sedimentary basin was experiencing significant paraffin wax deposition issues in its surface pipelines. This operator had a rigorous paraffin remediation program that also made use of frequent mechanical and chemical solutions. They had implemented a pigging schedule every other day in combination with PPD injection.

Despite this, the operator was still experiencing substantial amounts of wax deposition, as indicated by the volume of pig trash returns every other day, which showed the PPD chemical was not effective at mitigating the problem at a dose rate of 1,500 ppm. A field trial was granted on a problematic well using WAXTREAT SubZero. The product was optimized and injected down the annulus of the trial well at a dose rate of 500 ppm, a 66% reduction in comparison to the incumbent rate of 1,500 ppm.

Fig. 5. Pig return of 1,500-ppm incumbent (left) and 500-ppm WAXTREAT SubZero (right).

Figure 5 shows the paraffin wax deposition realized with the incumbent chemical treatment accumulated on the pig. After the deployment of the new cold temperature wax control product, there was negligible paraffin deposit recovered during the pig run. The operator was able to warrant a switch in the pigging frequency after treatment with the new wax control technology from every other day to twice per week. The reduced OPEX and assurance gained from the success of this trial allowed the remaining wells in the field to be treated with the new wax treatment polymer.

VALUE ADDED

The technology developed for WAXTREAT SubZero offers a superior degree of customization and flexibility that was previously unachievable for Arctic regions. The new paraffin control technology offers a highly active, winterized, and fully customizable PPD product that has been shown to provide best-in-class performance and offer a cost-effective solution for paraffin wax mitigation in regions that experience temperatures as low as –50°C.

Operators have seen an average dose rate reduction of 50%, when compared to traditional winterized low-active products, as well as a decrease of pigging frequency and solvent batch treatments if utilized. The technology offers a superior product activity level that translates to customers experiencing less production downtime, less chemical exposure, reduced lift costs and lower energy use. This all contributes to the reduction of OPEX through its effective paraffin wax mitigation performance that has shown to address operator concerns after selecting WAXTREAT SubZero as their chemical solution.