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.
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.
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.
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.
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.
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.
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.
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
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