In the late twentieth century, going into the 2000’s, hydraulic fracturing and the process of horizontal drilling contributed to dramatic increases in oil and gas production from shale basins in areas such as Texas, Eastern Ohio, and Pennsylvania.1Anderson, J. (2018, January 11). API Report: Amidst Shale Revolution, Industry Safer Than It’s Ever Been. Energy In Depth. https://www.energyindepth.org/api-report-amidst-shale-revolution-industry-safer-than-its-ever-been/. This boom in production was referred to as the “Shale Revolution.” The revolution eventually contributed to the United States becoming a world leader in oil and gas production, with natural gas growing exponentially in the early 2000’s along with increases in crude oil production.2Horsley, S. (2019, August 13). Energy Boom That Trump Celebrates Began Years Before He Took Office. NPR. https://www.npr.org/2019/08/13/750528826/energy-boom-that-trump-celebrates-began-years-before-he-took-office.
Hydraulic fracturing is the process in which water and chemicals are injected into the underlying low permeability formation, such as shale, to stimulate fractures or cracks within the rock. This stimulation creates a flow path for hydrocarbons, trapped in low permeability rock, to migrate to the wellbore. Once water is injected for stimulation, sand or other material referred to as proppant is pumped down to allow the new fractures and flow paths to remain open.
Horizontal drilling greatly increases the contact area between the wellbore and the formation relative to vertical drilling. Once fracturing has sufficiently been accomplished, fluid pressure is reduced and hydrocarbon production can occur. The type of fracturing fluid, how much fluid is needed to meet pressure requirements, and which proppant to use must be determined in the planning and designing phase for hydraulic fracturing.
However, hydraulic fracturing isn’t done proficiently by just pumping fluids into the ground to stimulate and open fractures. Engineers and geologists must be able to assess in what direction the opening of fractures needs to occur and mitigate risks, such as induced seismicity and groundwater contamination. For example, the size and length of fractures can be predicted through various measurements such as Young’s Modulus, and Poisson’s Ratio, which predicts stiffness of the rock and how the rock may deform when pressure is applied. Using principles of how faults form in the Earth and an understanding of stress regimes, geologists can predict the direction in which fractures will occur. Geologists must also be aware of the distance of the target formation from any underground sources of drinking water.