Well stimulation allows to increase the inflow of hydrocarbons from the reservoir into the wellbore. In oil and gas production, various stimulation techniques are utilized depending on the reservoir properties.
In traditional oil fields, where the rock formation is porous, hydrocarbons flows freely from natural reservoirs into the wellbore for extraction. When the bedrock is more impermeable, as is the case with fine-grained but fissile shale, hydraulic fracturing is a way to stimulate a well to produce a greater yield.
The process begins with vertical drilling. About halfway into the target shale formation, the drilling curves (at the kick-off point) and starts drilling into the rock horizontally (at the landing point). After the drill string is removed and the casing is inserted and cemented in place, a perforating gun creates holes through the shale layers and into the rock wall – preparing the way for hydraulic fracturing. This process consists of sending a mixture of water, sand, and chemicals under ultra-high pressure through the perforations to crack open the shale, which then allows oil and natural gas to flow into the production casing.
Hydraulic fracturing requires the use of specialised machinery to mix and inject the fracturing fluid deep underground. These pieces of equipment work together and include:
Pressure transmitters and gauges, temperature sensors, and force transducers play an important role in the proper function and control of these upstream industrial machinery.
After a perforating gun has punctured holes in the formation, it is time to crack the shale rock and create the fissures that will allow oil and natural gas to flow into the well. Fracturing equipment – mounted on a truck, trailer, or skid for easy mobility – include high-pressure pumps that send the liquid from the fluid end down the shaft and into the perforations. A high-horsepower diesel engine with cooling system and heavy-duty transmission provide power for the triplex or quintuplex pump, whose pressure also prevents the fracturing fluid from shooting back up the well.
Specialised pressure transmitters containing rugged measuring elements are designed to measure fracturing fluids that are corrosive, abrasive, and under very high pressures. Also, these instruments must withstand difficult working conditions, which include extreme weather, high vibration, and severe pulsation from the pump.
The fluid used for hydraulic fracturing is custom-mixed onsite for the specific conditions of each well and the type of fracturing desired. Fracturing blending units are the control centers for receiving the right quantities of hydrated fluid from the hydration unit, proppant (usually sand, treated sand, or ceramic material) to keep the cracked fissures propped open, and chemical additives to reduce corrosion, inhibit bacterial growth, maintain viscosity, and so on. This tailor-blended fluid is then transferred to the fracturing truck with pump units for injecting down the wellbore.
This blending system comprises a sand hopper and dry-chem and liquid-chem feeders. Specialised pressure transmitters help control and monitor the suction and discharge pumps, while pressure gauges on the control panel allows technicians to easily oversee operations. Temperature transmitters and compact resistance thermometers monitor the condition of the fracturing blending unit’s hydraulics, engines, and cooling systems.
Water comprises about 90% of fracturing fluid. But before it reaches the fracturing blending unit, it is first mixed with certain polymers:
In a mobile hydration unit, the polymer – in gel or powder form – is combined with water to produce a compound that is higher performance than ungelled fluid. This process uses load cells to accurately measure the weight of guar gum or another polymer in a hopper before it is hydrated. Pressure transmitters help control the suction and discharge pressures, while pressure gauges allow operators to monitor the hydraulically driven pumps.
Hydraulic fracturing calls for circulating an enormous amount liquids – mostly water but also chemicals and drilling mud – in and out of wells. Frac tanks are capacious yet mobile vessels designed to store vast quantities of fluids. A variety of level sensors can be used to ensure that a frac tank remains full enough for efficient operations, but not so full that it overflows.
There are many considerations when choosing level sensors for frac tanks, including:
Float sensors are commonly used in frac tanks due to the instruments’ high accuracy, ease of installation, and low maintenance. Usually mounted at the top of a tank, float sensors have a guide tube that extends all the way to the bottom. Around the tube is a hollow float that moves vertically along the shaft with the liquid level. Float sensors come in two types:
If top mounting is an issue, use a submersible pressure sensor for hydrostatic level measurement. This specialized type of level sensor, placed at the bottom of a tank, measures the pressure of a liquid column (e.g., inches of water), which is then converted into the liquid’s volume. When turbulence or sludge is an issue, an attachment like the LevelGuardTM provides extra durability and stability.
If the fluid is too turbulent or viscous for a submersible pressure sensor, or if the fluid is corrosive or otherwise incompatible with the sensor, a foolproof solution is to move level measurement from inside the tank to outside of it. In this type of measurement, load sensors – like load pins, bending beams, or shear beams – are mounted to the tank’s support structure for the static and dynamic weighing of liquids; the measurements are then converted into a volume measurement.