4 Drilling & well stimulation
How do you get crude oil and natural gas out of the ground?
Once geoscientists find potentially productive rock layers, risks are assessed, environmental studies are carried out and data is compiled regarding the drilling site. Drilling may be of three types: vertical, directional or horizontal; many wells will have a combination of these. Vertical drilling goes down to the depth where the crude oil and/or natural gas formation is believed to be. Directional drilling allows deposits to be reached without disturbing the land directly above the deposit. Horizontal drilling is a technique where the drilling can take a gradual 90-degree turn from the vertical and extend through a formation for a mile or more.
A derrick typically stands more than 100 feet in height and uses a drill string (many joints of steel alloy drill pipe with drill collars) and the drill bit which is capable of drilling through the earth. It is cooled with a constant slurry of mud or air to prevent it from getting too hot and to bring cuttings back to the surface. A drill bit grinds into the rock layers creating rice-sized particles. The entire drill string is rotated at the surface.
Protecting the aquifer is a major concern, so casing made of steel is lowered into the hole and cemented into place. At a pre-set depth, drillers place and cement additional casing adding extra protection to create a seal. Most wells in Ohio are vertical wells approximately 3,000–5,000 feet deep.
For horizontal wells, downhole instruments that transmit various sensor readings to operators at the surface are included in the drill string near the bit. Modern downhole instrumentation allows the directional drilling crew to calculate the position (x, y, and z coordinates) of the drill bit at all times. Additional downhole sensors can be, and often are, included in the drill string. Producers use multilateral drilling to branch out from a main well to tap reserves at different depths, reducing the number of wells drilled on the surface.
After the well is completed, it is necessary to stimulate the flow of crude oil and natural gas into the well. Hydraulic fracturing is used to enhance the permeability and allow more flow of crude oil and natural gas into the well. This is not a new technology; it has been around more than 60 years. However, recent advances allow oil and gas operators to render low-permeability shale reservoirs more permeable by injecting fracturing fluids, consisting primarily of water and sand, under high pressure into the formation. This creates tiny fissures that allow for fluid and gases to flow to the well bore.
Use a Venn Diagram to compare and contrast vertical, directional and horizontal drilling. Ideas to include: depth of wells, protection of the aquifer, environmental impacts, possible production, and number of well holes needed.