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March 2013

Fracking and Flow Metering

Fracking Background
Fracking first started in the United States in the early 1860s in relatively shallow oil wells and in a very simple fashion. Later in the 1940s more modern versions of fracking were developed and then further developed in the 1970s as wells were being drilled at much greater depths. In North America as oil sources became deeper and deeper, it became common to drill wells to great depths considerably deeper than 25,000 feet (7 600 meter) deep to find crude. And, these deep wells required stimulation of some form to allow the crude oil or natural gas become un-trapped from the underground formation and flow freely.

With the deeper wells it became critical to keep the drill pointed precisely in the right direction and aimed perfectly at the desired formation. Eventually the process of drill directional control became very well developed and operators eventually realized they could drill in any direction desired. A key part of this is pressurizing the drilling mud to move the drill bit in the desired direction. Eventually this led to horizontal drilling and in a precisely controlled and positioning fashion.

Horizontal drilling became the key breakthrough in the shale oil/gas production as shale deposits are hugely horizontally but typically of very shallow depth.

Besides fracking to stimulate production over the years other methods of formation stimulation were developed including such processes as “acidizing”, down hole steam production, explosives and others. However, fracking gained favor as it typically uses very benign substances to perform the fracking process, the process can be very well controlled to develop effective flow passages and it is the smallest environmental footprint.

In the 1980s and 1990s a large fracking site for a very deep well (>15,000 foot or 4 500 meter) would consist of several flatbed semi-trailers each with a large Caterpillar diesel engine driving a very large triplex piston pump. Each pump output would be hooked together in parallel flow output and the fracking fluid pumped deep into the well. Eventually the well piping would become full and start to pressurize the fracking fluid deep in the underground formation. As the formation started to fill with fracking fluid the pressure would build up, the fluid itself would start to compress and eventually reach the formation’s fracture point. Once the formation fractured the fracking fluid would decompress flow into the fracture formation and the sand in the fluid would create fluid flow paths. The peak fracking pressure would be upwards of 17,000 PSI (pounds per square inch) (1 175Bar).

Fracking fluid is not particularly complex. It has a base polymer to keep various chemicals in suspension and is similar in feel to human hair conditioners but with the silica sand additive. It is designed to have minimum compressibility and if you look at a list of chemicals listed in fracking fluids you will see some of them also in your hair conditioners. They are simply polymer bases that keep the various components suspended in the fluid.

Depending upon which shale formation is being drilled; horizontal drilling can targets depths from 2,500 (760 meter) to over 11,500 feet (3 500 meter). Generally, these horizontal drilling rigs are smaller than rigs for drilling to 5 or 6 mile depths. And, the weight of drill pipe hanging on the rig (about 16 pounds per foot or 23 kilogram per meter) is dramatically less there is much less drilling mud required and much less stimulation fluid required. Thus the production footprint for a horizontal drilling is smaller than a very deep well.

Fracking and Flow Meters
Instrumentation in general and flow meters in particular are used in several applications in the fracking process and play crucial roles in fracking. Most rotary drilling rigs are hydraulically driven and flow meters are used extensively on the rigs monitoring drill rotational speed, hydraulic system performance, hydraulic pressures and temperatures. By measuring hydraulic pressure and flow at the same time the horsepower required to drill can be continuously monitored. Hydraulic pump case drain flow is continuously measured to carefully monitor pump efficiency and stay ahead of maintenance. Between measuring hydraulic system horsepower and case drain flow rates critical system performance is closely monitored.

Accuracy is important and generally most all flow meters will have accuracies of ±1% accuracy or better. Some fracking fluid has final components added on site and those injection systems require accurate injection ratios which dual flow meters can ensure.

When the fracking procedure starts flow meters are used to monitor the flow and amount of fluid put down hole along with pressure required to fill the formation. Once the fracking fluid pressure starts to rise, the profile of pressure versus flow is closely monitored and gives rig operators a good indication of formation filling, pressure buildup and progress towards fracture.

A whole variety of instrumentation is used throughout the drilling, fracking and production process to monitor results, address preventative maintenance issues and identify potential pipe or casing leaks. Overall, a fully instrumented well’s drilling, fracking and production equipment is the best insurance to minimize environmental impact. Such instrumentation can also include down hole sensors to monitor drill condition, ultrasonics to monitor drill pipe stress and potential pipe weakness or failure. Meteorological conditions are continuously monitored and the bulk of all instrumentation is a local control system with web based connection for remote monitoring.

Fracking and the Environment
Be it steel mills, electrical generation plants, mines or large chemical processing plants, all heavy industries including oil well drilling, fracking and production have their environmental issues and environmental footprints. For fracking it’s in a couple areas: the fracking fluid chemistry relative to its environmental impact; failures in the piping or casings and resulting leaks and in general site cleanup once the well goes into production or out of production.

Obviously fluid chemistry is important. In the USA the fluids used in fracking are regulated and generally quite benign. When a large volume of fracking fluid is used, even small or trace amounts of toxic chemicals can be problematic. Like any industry regulation and monitoring is the best way to ensure environmental considerations are met and environmental impact is minimized.

It is important to note that independent of the cost of a fracking fluid, the fluid should not be used indiscriminately and without producing oil or gas for which its use is intended. If society is going to accept a small environmental impact for the energy production they desire, any stimulation fluid should be used sparingly and with expected production results.

In reality, failures in the piping or casings are probably the most important environmental issue. Most North American shale deposits are between the depths of 2,500 foot (760 meter) to 11,000 foot (3 350 meter) and most aquifers are between 200 (61 meter) foot to about 1,000 foot (300 meter) depths. So, as a well is dug it typically, but not always, penetrates various aquifers. Because of this well casings and piping need to be leak free. The piping and casing must be secure to contain all the drilling fluid, stimulation fluids and all the produced oil and gas.

Failures in the well casing or production piping can cause crude oil or natural gas to leak into an aquifer and can easily pollute the water source. While this is statically rare there are notable cases where failure leaks have caused natural gas or crude to enter wells and literally people have had natural gas come out of their water faucets. This is about the worst case failure scenario in fracking. Generally this occurred when drillers or stimulators were not strictly adhering to quality control procedures and standards. Typically if this does occur the well can be resealed to stop the leak or alternative methods can be performed to divert the leaking into other piping. Expensive correction and the driller is on the hook for that cost plus fresh water for any contaminated well and for water filtration systems.

Site cleanup is another issue with fracking. At the drill site typically one or two ponds are dug and lined to be used for drilling fluids. One pond is used for drilling mud and another for well waste. Fracking fluids are typically containerized and pumped directly from the containers to the well.

Once the well has been drilled, the stimulation process complete and then put into production the key cleanup is to clean out the ponds, dispose or reuse contaminated waste water, remove the drilling equipment, put the well head in good production condition and then bring the area back to pre-drilling condition.

This recovery process started in the strip mining business in the Midwest USA and was very successful converting strip mines back into their native condition. In some parts of the USA drilling can place in park like setting or in other places of the country where, well, they call the “badlands” the “badlands” for a reason.

If you are reading this most likely you have an interest in instrumentation of some type. It is important to note that over the last few decades the advances in instrumentation is the key reason that environmental standards can be adhered to in the oil and gas industry.

TG Nelson