Fracking, Hydraulic Fracturing
This lesson discusses what is fracking, or hydraulic fracturing, used to transform a shale oil and gas reservoir into producing wells; it builds on the Oil 201 “Well Completion” lesson, where we learned the fundamentals of cementing used to isolate productive zones and perforating to connect those zones to the wellbore.
This lesson includes the following topics:
• Shale Reservoir Characteristics
• Global Shale Oil & Gas Developments
• Horizontal Drilling, an important innovation supporting shale development
• The Basic Vocabulary of Sub-Surface Operations, including: – fracturing – proppants – gel fluids – fracturing stages
• The Surface Equipment and Process Flow Used to Frack Wells
Fracking, Hydraulic Fracturing – Introduction
In shale plays, where does hydraulic fracturing, or fracking, fit and why is it so important?
In the last 20 years, large oil and gas reserves, especially in the US, have been developed in what are called shale plays. Shale plays are over 1500 meters below the surface, and are typically 100 to 150 meters thick, with potential hydrocarbons spread over thousands of acres.
The shale potential has been known for decades.
However, with ultra-low permeability in the reservoir shale, hydrocarbons have been inaccessible. Permeability is defined as a measure of the ability of any rock formation to allow a fluid to pass through it.
In shales, the openings called pore throats are too small to allow flow, fracturing is the oilfield operation that uses treated water and proppants injected into a vertical or horizontal wellbore at high pressure, causing the formation to fail or split.
A fracture treatment can extend deep into the formation increasing the drainage area volume.
Hydraulic Fracturing – History
Hydraulic fracturing, or fracking, is the process of injecting water, chemicals, and sand into wells. The resulting fractures in surrounding rock formations allows for hydrocarbons to escape.
In 1997, Mitchell Energy performed the first slickwater frack – a technique that uses mostly water and significantly less chemicals than experts previously thought was necessary.
This method substantially lowered the cost of hydraulically fracturing wells. Coupled with new horizontal drilling techniques, fracking allowed vast shale resources to be developed and the boom in North American oil and gas production began.
The EIA data above depicts how swiftly these technologies are evolving and affecting global oil and gas reserve calculations.
Environment and Politics
Hydraulic fracturing has not been without its controversy in the political and environmental arenas. The process is very water intensive – fracking a single well can take up to 5 million gallons of water.
Some common drilling areas already face localized water supply issues leading to concerns of straining water supplies and necessitating water purchases.
Additionally, the effect of chemicals in fracking fluid on groundwater reserves and the treatment and disposal of used frack water, has been a concern to local communities from an environmental standpoint.
These concerns have led to an uneven use of this technology from state-to-state and country-to-country as politicians weigh conflicting constituencies. These shifting dynamics are still being assessed in the global marketplace.
Global Shale Oil and Gas Developments
Successful shale production rates, from horizontal drilling and fracking, have turned the US into a global energy powerhouse; now a major exporter of natural gas and in 2018, became the world’s largest crude oil producer, at nearly 11 million barrels a day.
Numerous international hydraulic fracturing projects are also underway, including:
• A multi-billion dollar project by BP in the Oman desert.
• Oil majors have moved in to frack Argentina’s massive shale reserves, but high costs have slowed progress.
• Gazprom, in Russia, is experimenting to frack one of the world’s largest shale gas formations.
• Huge shale gas deposits in China are now being developed with “homegrown” technologies.
However, in Europe, environmental regulations have severely limited any fracking initiatives.
Before we discuss fracking and hydraulic fracturing, we need to introduce horizontal oil well drilling – another technology that has made shale oil and gas development so successful.
To start, a vertical well is drilled and cased to about 1,500 meters to what is called the kickoff point.
Then, using specific tools the wellbore is curved to become horizontal. The horizontal portion of the shale well can be either a cased-hole or open-hole completion, as was discussed in Oil 201 Well Completion.
No shale plays are in consistent horizontal layers.
Therefore, to keep the well in the productive zone, the horizontal well must be controlled and deviated, up or down, left or right by drilling motors and real-time measurement technologies. Today, a horizontal leg in a shale play can exceed 3,000 meters.
Fracking, Hydraulic Fracturing – Vocabulary
Now let’s see what’s happening in the sub-surface and introduce some basic fracking vocabulary. As mentioned in our hydraulic fracturing definition, a fracture is formed when treated water is pumped from a horizontal well into a shale formation at a very high rate.
The split looks similar to one in a log caused by severe weather. As the fluid builds up near the wellbore, the pressure increases until it exceeds the strength of the rock – and the formation fails.
The formation fracture gets more pronounced as more fluid is pumped in. The process is helped by additional fractures created along natural zones of weakness in the shale. The geometry of a created fracture is typically 90 to 700 meters long, 15 to 150 meters high and less than 6 mm wide. It all depends on the geology of the rock formation.
However, if the pumping pressure decreases, the fracture would close, eliminating any benefit. To keep the fractures open, proppants are placed in the created fractures.
The most common proppant is sand. Other proppants include proprietary, customized, small-diameter ceramic beads.
There is great pride in the industry in the design of custom proppants! As the fluid leaks off into the formation, the proppant is trapped in the fracture. The proppant then provides a high conductivity flow path, like an eight-lane freeway, for the oil and gas to flow through the wellbore to the surface.
Today, a fracked well can use over 22 million kilograms of sand and other proppants.
Hydraulic Fracturing Gel Fluids
To improve fracking performance, a gel fluid is then used.
So what is gel and why is it important?
Gel chemicals are added to make the water thicker. A common natural chemical is from a bean called Guar, grown in India.
Guar gum powder has unique binding, thickening and emulsifying qualities, which make it suitable for fracking. Other chemical compounds can also be used to customize gel fluid properties.
Gel fluids provide two advantages over treated water: 1. It helps suspend the proppants – allowing optimum placement in the fracture to improve the flow paths.
It also creates a longer fracture with less fluid. When fracking a permeable formation, the treated water frack fluid leaks off.
The longer the fracture – the higher the rate of leak off. A gel fluid will leak off much more slowly helping to extend the fracture.
Today, 95 million liters of fluid can be used in one fractured well!
The first fracture is done by perforating the horizontal leg at the longest point in the lateral. A shale well development plan can call for numerous perforated intervals called stages, spaced approximately 15 to 25 meters apart.
One of the first fracture stages involves treated water and proppant and is called the pad stage. Stages are implemented using a wireline unit.
It lowers isolation plugs and perforating guns into the horizontal lateral, to complete each, next stage of fracturing, in sequence. A bridge plug is placed to isolate a newly fractured zone.
The fracturing process is then repeated over and over, until all of the designed stages are completed.
At the conclusion of the fracturing operation, the isolation plugs are removed from the lateral and production can start.
Again, today some fracked horizontal wells could have as many as 50 stages! They could cost $100-$200,000 per stage…so this is a very expensive operation.
Hydraulic Fracturing Surface Fracturing Equipment
Now let’s see what it takes at the surface to do a frack job.
Remember that a 3,000 meter horizontal frack job could use close to 22 million kilograms of sand and 95 million liters of fluid. Just imagine the logistical nightmare of gathering, delivering, storing and managing all that material at a wellsite!
Once the equipment arrives, you could be surrounded by over $50 million worth of technology, all on wheels. Because, the whole fracking process is done in a couple of weeks, then the equipment moves to another location.
There can be 50 men working around the clock.
One thing is clear, from remotely controlled valves to extra precautions with the workers; safety is the number one concern at the site.
Hydraulic Fracturing Surface Fracturing
After pressure testing all the equipment, water is passed from a storage impoundment or pond into the red working tanks. The water is then pulled into a hydration unit to gel the fluid, as we discussed earlier. A conveyor belt moves the proppant from storage tanks to the blender.
Here it is mixed with frack fluid, and chemicals that aid in the fracturing process are also added.
The blender transfers the fluid and proppant mixture to the pump trucks using the low pressure side of a manifold. The manifold is a series of pipes that connect the pump trucks to the blender and the wellhead.
The pump trucks increase the frack fluid pressure to as much as 9,000 psi, sending it back through the high pressure side of the manifold – where it enters the well through the wellhead.
The entire fracturing process is controlled from the treatment monitoring data vans.
Surface Fracturing Equipment
Let’s now learn more about the importance and specifications of the surface fracking equipment, including:
• The Frack Fluid Tanks
• Sand and Proppant Equipment
• Blenders, and
• Pressure Pump Trucks
Hydraulic Fracturing Frack Fluid Tanks
Numerous frack fluid tanks are needed at the wellsite to manage huge quantities of water and liquid chemicals, and the same tanks can be used for contaminated flowback. Frack fluid tanks therefore represent a significant opportunity for suitable internal linings.
They have a standard 80,000 liter square structure. The fluid tanks have wheels and axles for maximum maneuverability.
A typical dry weight is 12,000 kilos, and the design must fit within the maximum allowed road transport dimensions. A similar square tank design, and size, is used for sand and proppant.
Hydraulic Fracturing Sand & Proppant Management
As we learned earlier, hydraulic fracturing requires millions of kilos of sand and proppant. Many sand management facilities use what are called silos for storage at the wellsite.
There could be three to six silos – each with 180,000 kilos of capacity.
Each silo has a conveyor belt and bucket elevator to load the sand hauled from the quarry. Another portable sand storage equipment option with multiple compartments is called a frack-sander.
Powered by an industrial diesel engine:
• the proppant is discharged from each compartment,
• through a controlled gate,
• onto a conveyor belt that delivers the proppant into the blender.
The delivery rate to the blender can be as much as 9,000 kilos a minute!
Hydraulic Fracturing Blenders
A mobile frack blending unit is designed to turn huge quantities of water, sand, dry and liquid chemicals into what is called a slurry.
The correct slurry ratio is set by the fracturing design engineer.
Blenders are diesel powered to easily manage a variety of both liquid and physical inputs. Most modern blenders are:
• 1,200 to1,500 horsepower,
• fully automated, and can be
• operated from the control van.
The blender’s importance is often understated, because a site has many pump trucks but only one or two blenders.
Once blended, the slurry is discharged into the low pressure side of the manifold, adjacent to the pressure pump trucks.
Slurry management is critical to an effective fracturing operation.
Hydraulic Fracturing Pressure Pump Trucks
The heart of the fracking operation is the pressure pump truck, and there can be as many as 14 on a particular site.
In addition to the high pressure pumps, each truck has a sophisticated communication and control system.
Pump trucks range in size and can be up to 2,500 horsepower.
The engine, transmission and pumps are synchronized and controlled electronically from a data van.
In 2018, a respected industry expert reported that the pressure pump truck market is over 23 million horsepower!
Hydraulic Fracturing Microseismic Survey
So, how do we know what is going on downhole during a fracturing operation?
A technology is used called a microseismic survey. Here, an array of very sensitive microphones is lowered into a monitor well – positioned near the well that will be fractured.
The monitor well tools can pick up the slightest signal created in real time, as the formation fails or cracks.
Using triangulation, multiple microphones can then identify where the crack is occurring in the formation.
This microseismic data can be 3-D mapped to provide a picture of the created fracture geometry to more effectively design the fracture treatments and new well spacing.
Hydraulic Fracturing Frack Water Treatment
Let’s now discuss a very important operational aspect of fracking, called fluid management.
Frack fluids going into the formation are generally non-toxic. However, produced fluids, called flowback, have toxic contaminants that require special handling. So they are diverted through a flowback manifold into separate storage tanks.
Frack fluids can now be filtered and cleaned sufficiently to be reused at the wellsite.
New chemicals are constantly being developed which can do their job even with contaminated flowback fluids.
The cheapest disposal method is to pump flowback down disposal wells approved by government regulators.
In the US, disposal is managed by the individual states.
Hydraulic Fracturing Summary
From our discussion of hydraulic fracturing, you should now understand that:
1. Oil and gas developments in shale reservoirs are underway around the world.
2. Horizontal drilling and hydraulic fracturing are two technologies that have enabled significant production volumes of oil and gas from shale plays.
3. A fracture is formed when treated water is pumped into a shale formation at very high rates.
4. To keep fractures open, sand and ceramic proppants are placed in the created fracture.
5. A gel fluid is more efficient than treated water in improving a fractures flow path
6. A horizontal well plan can call for numerous perforated intervals called stages.
7. A fracturing operation could have over $50 million of equipment – all on wheels to be quickly moved to another location.
8. Microseismic survey tools can manage a fracture operation in real time.
9. Flowback fluids from a fractured well require special handling