In the last decade, the global Oil & Gas industry has witnessed a dramatic turn of events in the energy supply equation. Because of renewed efforts and successful adoption of technologies like horizontal drilling and hydraulic fracturing, the U.S has become a major producer of hydrocarbons, ending many decades of dependency on foreign oil.
With these new technologies, operators can unlock vast amounts of resources from hard-to-reach, low-permeability source rocks.
Before we continue with our discourse, let’s find out what the terms conventional and unconventional gas and oil mean.
What Is Conventional Oil and Gas?
Conventional oil and gas are hydrocarbons that have been accumulated in reservoirs with good oil-water or gas-water contact. These resources are relatively easy to obtain by utilizing the natural pressure from the well and pumping operations.
Conventional sources of oil and gas are normally vertical and deviated wells with high-permeability source rocks.
To obtain hydrocarbons from conventional reservoirs, conventional drilling methods (vertical or directional drilling) and multi-zone perforations are carried out.
What Is Unconventional Oil and Gas?
Unconventional oil and gas are hydrocarbons trapped in low-permeability source rock with minimal oil-water or gas-water contact. As a result, they cannot be obtained using simple drilling and perforation operations.
Some unconventional sources of oil and gas include:
- Coal seam gas wells
- Tight-gas sandstone
- Deviated wells
- High temperature/pressure reservoirs
To obtain hydrocarbons from these hard-to-reach sources, a combination of horizontal drilling and hydraulic fracturing is done.
Conventional and Unconventional Oil and Gas in The U.S
The main reason for developing advanced technologies to explore and extract hydrocarbons in the U.S. is the disparity between conventional and unconventional oil and gas reservoirs. This also applies to conventional and unconventional natural gas.
The geological nature of underground formations in North America is vastly low-permeability source rocks. (e.g., tight-gas sandstone and shale) The implication is that conventional oil drilling methods are not viable for producing hydrocarbons. The depth of these formations is up to two miles below the surface.
Some important shale plays in the U.S. include:
- Permian (Texas)
- Eagle Ford (Texas)
- Haynesville (Texas & parts of Louisiana)
- Bakken (North Dakota)
- Niobrara (Colorado & parts of Wyoming)
- Utica (Ohio, New York, and Pennsylvania)
- Marcellus (West Virginia, Pennsylvania, and New York)
What Is Conventional Drilling and Completions?
In conventional drilling operations, a drill bit attached to a series of pipes (called a drill string) is rotated at high speed into the earth surface and underlying rock formations. As the bit rotates, it bores a hole in the ground.
Drilling mud of a specific density is circulated into the hole to counter subsurface pressure conditions as well as cleanse the wellbore of rock fragments from drill action.
After drilling is done, a steel casing is inserted into the wellbore and sections of the pipe (called pay zones) are perforated to allow the flow of oil and natural gas to the surface by utilizing the natural pressure from the well and pumping operations. This is considered the completion operation for the well.
What Are Unconventional Methods?
In the unconventional hydraulic fracturing procedure, fracturing fluid at a high pressure is injected into an underground rock formation to fracture or ‘crack open’ existing fissures which unlocks hard-to-reach hydrocarbon resources. Frac fluid is typically a mix of water, sand, and certain chemical additives.
In 2012, it was reported that at least 2.5 million frac jobs had been done on oil and gas wells around the world, with a million of those carried out in the U.S. alone. Hydraulic fracturing is a precise technique performed using sophisticated tools and equipment.
Hydraulic Fracturing vs. Drilling
The main difference in hydraulic fracturing vs. other methods are the tools and equipment required to carry them out. This also ties up nicely with another important consideration – the cost of carrying out both procedures.
Common Hydraulic Fracturing Methods
Two common hydraulic fracturing methods employed in the industry today are:
- Plug and perf fracturing
- Pinpoint entry fracturing
Plug and Perf Fracturing
The most dominate method, Plug and perf fracturing, is a flexible, multi-stage operation done inside cased holes. It involves pumping a frac plug and perforating guns into the wellbore to a specified depth. After installing the plug, a section of the casing is perforated, and tools are removed from the well via wireline. Then a ball is pumped into the well to land on the frac plug- this creates zonal isolation to enable hydraulic operations to take place within the desired zone.
As the frac fluid is pumped in, the plug works to divert the fluid through the perforations, and into the formation. The process is repeated several times going up the casing to fracture multiple zones.
Pinpoint Entry Fracturing
Pinpoint entry or single-point fracturing, is done using multiple methods of coiled tubing or ball drop activated sliding sleeve systems that are placed in predetermined locations throughout the lateral section of the production casing string. These systems are installed with the help of the drilling rig unlike plug and perf operations that take place after the rig has been moved off location. Once the systems have been installed, the rig is removed and the hydraulic fracturing equipment moves into position.
A ball or Coiled Tubing shifting device deployed from surface, is used to open a single sleeve. Once the sleeve is open, fracturing operations begin to stimulate the individual entry point that was opened. . This technique enables operators to speed up the multi-stage fracturing operation, optimize their simulation designs and more accurately predict the amount of fluid needed to frac the well. Because there is little downtime between stages, this method also reduces the completion time need to bring the well onto production.
Equipment Required for Hydraulic Fracturing Operations
Some equipment required for hydraulic fracturing a well include:
- Hydraulic fracturing fluids
- Hydraulic horsepower (pumps)
- Containment tanks and units
- Completion tools (g., frac plugs and frac sleeves).
Let’s delve a bit into the last two completion tools:
Ball activated Frac plugs work to divert fracturing fluids through the perforations and into the formation during wellbore fracturing operations. Although composite frac plugs remain the most dominate type used in plug and perf operations, dissolvable frac plugs are quickly becoming a viable alternative. Dissolvable plugs eliminate the need for CT millout operations post frac, reducing the completions cost and time needed to bring the well onto production.
Frac sleeves are tools which are installed into the well as part of the production casing string, before multi-stage fracturing operation being. . There are two traditional types of frac sleeve systems: ball drop activated frac sleeves and coil tubing actuated frac sleeves. Both types can be used in open-hole and cased-hole completions.
Cost of Hydraulic Fracturing vs. Drilling
When it comes to the cost of conventional vs. unconventional natural gas and oil extraction methods, hydraulic fracturing is a more expensive process due to the additional equipment and technologies involved.
However, hydraulic fracturing is ultimately lucrative because the technique can be repeated several times – unlike conventional wells which have to be plugged and abandoned when production levels fall to critical levels and artificial lift/EOR procedures no longer cover operational costs.
Gryphon is an industry-leading oilfield service company providing cutting-edge oil and gas completions tools, casing equipment, and remedial solutions with a keen expertise in unconventional downhole technologies. Gryphon tools ensure operational efficiency, minimized costs, and optimized recovery of hydrocarbons in the most challenging oil and gas fields.
Contact us today for more information about our downhole completion tools for unconventional oil and gas.