Abstract
The drill-out, clean-up, and testing of a hydraulically fractured well is critical to ensure stimulation success. This period is important both for production and environmental reasons, due to the high risk of gas release. Most wells require a sand separator during clean-up, which are a source of fugitive emissions. These emissions often go unreported during flowback due to the challenge in their quantification.
This work improves on a study by Wasfy et al (SPE, 2019) which investigated sand separator fugitive emissions. The analysis is improved by categorizing the differences in draining mechanisms between four different separator styles: vertical cyclonic separators, horizontal separators, spherical separators, and vortex separators. A simple 3-stage mathematical model is presented to calculate emissions based on drain duration for online sand separators which are drained without isolating the vessel. A vortex separator was found to provide the lowest overall fugitive emissions release. Prior work was found to have significantly underestimated the emissions released by horizontal separators.
Field experiments were performed using freestanding atmospheric gas plume sensors to validate the model. Measured gas releases were within 6% of the volume predicted by the 3-stage model at field conditions. This model can be used by engineers to accurately assess different styles of sand separators in hydraulic fracturing, allowing for more accurate reporting and quantification of fugitive emissions.
The following is a summary of the published technical paper.
Introduction
In the wake of advancements in hydraulic fracturing, the drill-out, clean-up, and testing phase of a well carry immense significance, both for operational success and environmental preservation. However, this phase also poses a considerable risk of gas release, often overlooked and unreported due to the complexity of quantification.
Recent advancements, building upon the groundwork laid by Wasfy et al (2019), delve deeper into the understanding of sand separator fugitive emissions. This new study meticulously categorizes and analyzes four distinct separator styles: vertical cyclonic separators, horizontal separators, spherical separators, and Sandtinel vortex separators.
Fugitive emissions were modeled using 3D transient numerical simulations for typical flowback conditions in each of these four separator styles. Based on the simulation results, a simple yet effective 3-stage model was developed to estimate emissions that can be expected from the separators in different dumping scenarios: on a per dump basis, timed or acoustic method, or sand volume removed.
Field experiments conducted using state-of-the-art atmospheric gas plume sensors validated the model's accuracy. The measured gas releases closely aligned, within 6% of the volumes predicted by the 3-stage model under field conditions. This validation opens doors for engineers to accurately evaluate different sand separator styles, enabling precise reporting and quantification of fugitive emissions in hydraulic fracturing operations.
The objective: To comprehend the variances in draining mechanisms and their subsequent impact on fugitive emissions to provide a useful and practical model for engineers and decision-makers to be able to estimate an expected volume of fugitive emissions from sand separators during oil and natural gas production.
Understanding Sand Separator Types
The study delves into four types of sand separators: vertical cyclonic, horizontal, spherical, and vortex. Each style boasts unique features influencing the emission release dynamics during sand separation. For instance, vertical cyclonic separators employ rotation to expel sand against the vessel wall, while horizontal separators require isolation from the production stream for manual sand removal.
Refining Fugitive Emissions Modeling
The study's methodology rectified prior analysis shortcomings, addressing factors like separator size, gas compressibility, dissolved gas in oil, and flow rates. Such improvements significantly altered previous emission estimations, exposing the need for a more comprehensive understanding of separator effectiveness.
Practical Application and Field Trials
Beyond theoretical advancements, the study translates findings into practical applications. It introduces the concept of an efficient storage capacity (ESC) for sand separators, defining optimal sand volume levels to minimize fugitive emissions during sand removal. A rigorous 26-day field trial in the Bakken basin validated the model's efficacy, showcasing how human-operated sand separator dumps closely align with predicted emission volumes.
Key Takeaways and Future Implications
The research provides engineers with essential equations to estimate fugitive emissions from sand separators accurately. Notably, Sandtinel vortex separators consistently exhibit superior performance, releasing the lowest emissions among the studied equipment. These insights offer a more accurate assessment of emissions during cleanout, emphasizing the critical role of precise sand measurement in optimizing cleanout frequency and environmental safety.
Conclusion
In conclusion, this study marks a pivotal step in understanding and minimizing fugitive emissions during post-fracturing sand separation. By refining models, validating predictions through field trials, and showcasing the superiority of certain separator styles, this study reveals how and why Sandtinel vortex separators consistently outperform other available technologies, showcasing the lowest overall fugitive emissions release and paving the way for enhanced environmental safety measures in the oil and natural gas industry.
References
Minimizing Fugitive Emissions In Post Fracturing Sand Separation Using A Vortex Separator; C. Johnston, A. Natarajan, Energera Inc.
Xie et al, 2021; Duan and Mao, 2006; Wasfy et al, 2019; Wasfy et al, 2023
Why upgrade to a spherical sand separator? Vertical cyclonic sand separators have been around for years, and everyone is comfortable with them. That was the conventional wisdom we set out to challenge when we brought Sandtinel sand separators into the field in 2014. Since then, we’ve learned a lot about how cyclonic separators work – and what we’ve found is that just because one way of doing things is comfortable and familiar, doesn’t mean it’s the right choice. In our newest study, we dig into the seven most important factors in sand separator performance and compare Sandtinel’s Vapor Lock spherical separators to the generic vertical cyclonic separators which have been on the job for decades.
Although they are widely used, vertical cyclonic separators really have two main advantages over other separator designs. First, it’s easy to remove sand from them, as you can simply open the drain line on the bottom. Second, they are easy and cost-effective to build for very high pressures, up to 10 ksi or even 15 ksi pressure ratings. These factors make them a convenient and low-cost option for sand removal. However, convenient and low-cost doesn’t necessarily translate into the separator’s real job, which is actually removing sand. In many cases, operators have had to stack two, three, or even larger numbers of cyclonic sand separators in front of each other to try to approach the effectiveness of a single high efficiency sand separator.
Sandtinel’s spherical sand separators were found to outperform cyclonic separators on four key performance criteria: sand removal efficiency, sand storage capacity, fugitive emissions release, and turndown operation at low flow rates. Vertical cyclonic separators were found to have a poor separation efficiency; in one featured trial in our study in the Permian basin, a downstream Sandtinel spherical separator actually caught more sand than an upstream cyclonic sand separator.
The storage capacity of vertical cyclonic separators is sharply limited, requiring frequent dumping to remove accumulated sand. These frequent dumps also come with a cost: Sandtinel found a high fugitive emissions release during the dump stage of a vertical cyclone, between 2x and 55x more gas than is released during a comparable sand dump operation on a Sandtinel sphere. Vertical cyclones were also found to be vulnerable to turndown at low flow rates, dropping sharply in efficiency once the flow rate of a well fell below a critical threshold.
Just because vertical cyclonic sand separators are common, doesn’t make them a good choice for your well. As wells are seeing higher flowrates and sand sizes are getting smaller in recent years, sand separators are becoming an ever more important component of a successful flowback operation. You need a high efficiency sand separator which can keep up with the demands of the modern flowback and production environments – and the cyclones of 40 years ago aren’t cutting it anymore. Take a look at our newest comparison report where we dig into the specific improvements Sandtinel spherical sand separators bring to the field compared to generic vertical cyclones. Contact our sales staff today to see how Sandtinel’s separators can upgrade your flowback and production and save you on dangerous erosion, costly downtime, and unnecessary chargebacks.
Not all spheres are created equal.
That’s the lesson that producers have learned in the Permian basin. Traditionally, options for sand separators have been limited to using either low storage and flow-sensitive vertical cyclonics, or low efficiency generic spheres to manage sand. Functional differences in technology, design, innovation, and quality of material may not be apparent on the surface but ultimately impacts overall production in addition to bottom-line. Making it crucial for decision makers to understand the differences between separator technologies and how to manage produced sand most effectively.
Our newest report in the Sandbox shows proven field results comparing Sandtinel’s spheres using patented Vapor Lock technology against generic spherical separators that have been on the ground for more than 10 years. Generic spheres, such as the “Super Sand Hog” or “NOV Sand Trap”, have proven to have low separation efficiency and high back pressures which lead to reduced overall production.
A recent paper from Occidental Resources submitted at URTeC found in the Wolfcamp that “an aggressive flowback strategy can speed up the production rate tremendously early in the life of a well.” “An aggressive flowback […] opens the choke quickly to full capacity if there is no sand control issue.”1 One of the biggest limits on running an aggressive strategy is having sand management that you can rely on at high rates of production.
Sandtinel is a sphere that you can trust, with an operating envelope up to 4,000 BBL/day higher than generic spheres. Our efficiency promise is a minimum of 95% sand removal of 100 mesh sand, and producers all over North America have seen the difference. Generic spheres are old technology with low storage capacity, low efficiency, and high fugitive GHG emissions. Our Sandtinel team is excited and eager to show you the difference that Vapor Lock technology can make for your flowback.
Don’t let a subpar sphere be the bottleneck in your flowback. Take a look at our newest report and decide for yourself which sand separator you want to trust your equipment with.