The Marcellus shale is a rock formation that lies more than a mile beneath the earth’s surface. The formation is special because it contains a significant volume of natural gas trapped inside tiny spaces within the rock. It is estimated that the gas within the rock could supply the United States for the next decade – this is a result of the newer technologies used to drill below the earth’s surface.
The term “fracking” is a one that you probably have heard. Whether it is on the local news channel, online in an article, or in the newspaper – the word is closely associated with the Marcellus shale drilling. But what exactly is fracking?
“Fracking” – or hydraulic fracturing is the process in which oil and gas companies drill into the ground to extract natural gas from the shale rock that lays thousands of feet under the ground. Extracting the gas involves drilling down to the depth of the formation using new horizontal drilling technology that exposes more of the shale. Once the formation is reached, gallons of water, sand, and an extensive list of manmade chemicals are injected into the well under high pressure. This combination inserted in the well, will fracture the rock and release gas.
The fracking process is very technical and very intensive. Through the drilling process, each well can require up to 6 million gallons of water to reach desired completion. Drilling companies typically pipe the water they use from nearby rivers and streams.
Below is a step by step process of fracking and the steps it takes to extract natural gas from Marcellus Shale.
Once a drilling location is established, the drilling can begin. A drill bit is then mounted on the end of a drill pipe. As the bit continues to grind its way down, air is pumped down the pipe to flush rock cuttings from the hole and lift them to the surface.
The hole is drilled to just underneath the first amount of fresh water underneath the surface. Then the drill pipe and bit are now removed.
Next, surface casing is inserted into the hole to isolate the fresh water zone. And, also serves as a foundation for the blowout preventer – a safety device that connects the rig to the wellbore. Then, cement is pumped through the casing and out through the opening of the shoe at the bottom of the casing.
The cement is then forced up between the casing and the hole sealing off the wellbore from the fresh water. The cementing process prevents any contamination of the fresh water aquifers.
The pipe and bit are lowered back down the hole to drill through the plug and the cement and continue the vertical section of the well to approximately 500 feet above the plant horizontal leg. This depth is called the kick off point – where the curve will begin so that the horizontal section can be drilled.
Again, the pipe and bit are pulled out of the hole. A down hole drilling motor is inserted in the hole to begin horizontal drilling. Horizontal drilling is the most efficient type of drilling technique. Horizontal drilling begins as a typical vertical well, but when the desired distance is reached, it makes a 90 degree turn so that the well can run along the length of the seam.
The distance is under a quarter of the mile. It takes over 350 pieces of pipe to drill a 10,500 foot well. While drilling, the drill and drill bit usually require maintenance. This maintenance is also referred to as “tripping pipe.”
When target distance is reached, the drill and pipe are removed once again. Production casing is inserted into the full length of the wellbore. Cement is pumped down the casing and out through the hole, forcing the cement up between the casing and the wall of the hole, filling the open space. Casing the well is a very important process because it permantaly secures the wellbore and it prevents hydrocarbons from seeping out as they are brought to the surface. At this point, the drilling rig is no longer needed and a temporary well head is installed.
STEP TWO – Perfing and Fracking
Once step one is complete, it is now time to perf and frack the area.
Perfing – a perforating gun is lowered by wire line into the casing. An electrical current is sent down and sets off a charge that shoots small holes through the casing and cement. The perf gun in then pulled out of the hole.
Next, the well will have to be fracked. Water, sand, and lube are sent into the wellbore under high pressure. As the mixture is forced through, the shale is pressured to fracture. This creates a fairway connecting the reservoir to the well and allows the released gas to flow to the wellbore.
A temp plug is placed at the end of the first frack. The second stage section can then be perfed and fracked. With advancements in technology, multi stage fracking has become the norm. Fracking is completed several times to cover the horizontal distance of the wellbore.
Once fracking is complete, the plugs are pulled and gas flows up the wellbore. A permanent wellhead is installed – which is also called a “Christmas tree.” A pipeline is built to transport the gas to the pipeline network.
Diagram of a Typical Hydraulic Fracturing Operation