As menacing as it may be, sand is often required during hydraulic fracturing (fracking) operations. With no alternatives typically available to serve as a proppant, sand is generally utilized along with water to prop open underground fractures for purposes of bringing oil and natural gas to the surface.
The unwanted flow back mixture that sand can cause, including a combination of water, debris, and hazardous chemicals, has created difficulty among hydraulic frackers for more than 70 years — from impairment of surface piping and hazardous leaks to lost time and revenue, and it has been a burden in general to fracking much longer than that.
The need to manage sand flow back, which can accumulate significantly, becomes critical for the successful harvesting of oil and gas, as well as for protecting the environment and those who are conducting the work. Mismanagement of sand while on the job can necessitate frequent cleanups of equipment and the workspace, which results in more downtime and lost production. In order to minimize these negative consequences, appropriate process management can go a long way toward improving the bottom line and having a positive environmental impact. A willingness to take a holistic approach to fracking is ideal for avoiding common complications and maximizing effort.
Common complications and mistakes
Some may be surprised that fracking dates back to at least the 1860s. But, it wasn’t until the 1940s that the practice of hydraulic fracturing actually began as an experiment, followed by the first commercially successful application in 1950.
Some of the commonly occurring mistakes, however, have been timeless and associated with the tendency to try collecting as much as possible in the shortest period of time. This practice is a misstep, often leading to high velocities in the piping. Especially in the initial phase of flowing, an abundance of sand that has been used for fracking comes back through the piping, which can cause erosion and corrosion. In addition, increased velocity often causes holes in the piping — namely in the bends, due to an abrupt change in the direction of flow. In this instance, sand impinges on the wall and creates a hole, which can lead to spills and/or fires. Surface production equipment damage, sand buildup, production deferment, reduction in processing capacity and added costs related to sand disposal are also consequences of the shortcuts that some have taken during the fracking process.
A holistic approach
The controversies associated with fracking are nothing new. While the validity of each can be debated, there are proven technical measures that mitigate the negative effects on the environment and society. In addition, there are operational and functional processes that make the job easier and improve the financial outlook of those in the industry.
Proactive mitigation of the issues faced while fracking can be accomplished in three general steps that are commonly overlooked:
Controlling flow velocity to minimize erosion and corrosion in surface piping. The secret here is to maintain the optimal, critical velocity in surface piping and equipment. Flowing at a higher velocity can lead to a higher rate of erosion. Erosion models based on industry standards, such as those established by API (RP 14E – Design & Installation of Offshore Production Platform Piping Systems) and other proprietary tools, such as those from DNV, can be used to calculate velocity limit.
Optimal sand separating. This can be accomplished by installing high-pressure sand filters in the well flow line. The intent is to remove the majority of produced sand collected there. This will prevent having to manage sand in other surface production equipment, such as in the separators.
Modifying internal design of separators. For example, install additional sand weirs and sand flushing connections so that sand can be cleaned out while the separator is operational. This eliminates the need to shut down the separator, thus reducing downtime and deferment. Also, installing additional instrumentation in the separator helps to detect sand levels.
The positives to this methodology include minimized piping erosion and corrosion, less likelihood of hazardous exposure to workers and nearby residents, and long-term cost savings for those conducting the work.
There are cons to consider too. Generally, these are short-term tradeoffs that should be anticipated to develop into long-term positives. For example, additional equipment, such as sand filters, will increase costs and temporarily lower production, but the long-term goals should outweigh those considerations. That said, companies should conduct research and utilize trial equipment before deciding on a plan. While there is science behind this methodology, tapping into consulting and academia expertise is important too.
Managing the menace
A typical fracking operation can use 2-10 million pounds of sand, and approximately one to two percent of that sand will return to the surface. With a lack of control being the standard, the expectation should also be that the sand separator will stop functioning at some point, due to sand build up, because separating oil, gas and water from the sand is not sustainable for the duration of the job. Shutting down the separator is inevitable if proactive measures are not taken, as are real risks to safety.
Even though just one to two percent of the total sand used returns to the surface, in real terms it could be hundreds of pounds that must be managed and disposed of. If measures are in place, such as an upstream hydro cyclone sand filter, then less sand will go into the separator and a total temporary or permanent shutdown is less likely. When design modifications are made in the separator, even when sand accumulates, service can continue by running a hose occasionally for cleaning while operating.
Emerging trends and future implications
The following list of novel technologies could have interesting impacts on the industry’s future:
No-man entry tank cleaning technologies, including robotics such as Re-Gen
Automated, mobile and modular, non-man entry oil tanks, such as the BLABO® system
Online desanding systems, such as Altrad vacuuming
Sand level detection technologies, such as Acoustic Sand Detectors
Vessel sparging systems, such as Stork
Vibrating fork technology, such as Emerson
Flow testing services, such as TechnipFMC
Hydraulic fracturing requires a precise approach and a willingness to focus on long-term outcomes versus the short-term rush to collect. Holistic processes can mitigate common difficulties associated with the presence of sand, and trending modalities may help navigate the nuances of the strategies suggested in this article, which will go a long way to impacting businesses and the environment.
About the Author: Vikash Dixit, P.Eng., is an engineering professional with 35 years of experience specializing in the upstream sector for the oil and natural gas industry. Adept in process engineering, flow assurance, discipline management, sour gas, offshore operations, production and drilling, he is a recognized industry expert who helps to improve processes and equip engineers with best practices.
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