4Drilling and Well Stimulation

How do you get crude oil and natural gas out of the ground?

Background

 

Once geoscientists find potentially productive rock formations, potential risks are assessed and data is compiled regarding the drilling site. Drilling may be one of three types: vertical, directional or horizontal; many wells may also 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 horizontally 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 to prevent it from getting too hot and to help bring rock 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 priority, so casing made of steel is lowered into the hole and cemented into place. At a pre-set depth, drillers are required to place additional cement and casing to add extra protection. 

 

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 drilling crew to calculate the position (x, y, and z coordinates) of the drill bit at all times. Horizontal drilling is expensive, and can cost up to three times as much per foot as drilling a vertical well. The extra cost is usually recovered by increased production from the well. Many profitable wells would be failures without these methods.

 

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 since the 1940’s. However, recent advances allow crude oil and natural 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.

 

DRILLING & WELL STIMULATION: Career Connections & Word Wall