An approach for assessing engineering risk from shale gas wells in the United States

• Published in: International journal of coal geology 2014-06, Vol.126, p.4-19
• Main Authors: Soeder, Daniel J., Sharma, Shikha, Pekney, Natalie, Hopkinson, Leslie, Dilmore, Robert, Kutchko, Barbara, Stewart, Brian, Carter, Kimberly, Hakala, Alexandra, Capo, Rosemary
• Format: Article
• Language: English
• Subjects: Coal; Environmental; Fracture toughness; FRACTURING; HAZARDS; Horizontal wells; Hydraulic fracturing; IAM; Risk; Sand; Shale gas; SHALES; Wells
• ISSN: 0166-5162; 1872-7840
• DOI: 10.1016/j.coal.2014.01.004

In response to a series of “energy crises” in the 1970s, the United States government began investigating the potential of unconventional, domestic sources of energy to offset imported oil. Hydraulic fracturing applied to vertical tight sand and coal bed methane wells achieved some degree of success during a period of high energy prices in the early 1980s, but shale gas remained largely untapped until the late 1990s with the application of directional drilling, a mature technology adapted from deepwater offshore platforms that allowed horizontal wells to penetrate kilometers of organic-rich shale, and staged hydraulic fracturing, which created high permeability flowpaths from the horizontal wells into a much greater volume of the target formations than previous completion methods. These new engineering techniques opened up vast unconventional natural gas and oil reserves, but also raised concerns about potential environmental impacts. These include short-term and long-term impacts to air and water quality from rig operations, potential migration of gas, fluids and chemicals through the ground, and effects on small watersheds and landscapes from roads, pads and other surface structures. Engineering risk assessment commonly uses integrated assessment models (IAMs), which define sources of risk from features, events and processes. The risk from each system element is assessed using high-fidelity models. Output from these is simplified into reduced-order models, so that a large, integrated site performance assessment can be run using the IAM. The technique has been applied to engineered systems in geologic settings for sequestering carbon dioxide, and it is also applicable to shale gas, albeit with some modifications of the various system elements. Preliminary findings indicate that shale gas well drilling and hydraulic fracturing techniques are generally safe when properly applied. Incident reports recorded by state environmental agencies suggest that human error resulting from the disregard of prescribed practices is the greatest cause of environmental incidents. This can only be addressed through education, regulations and enforcement. •New drilling and completion technologies have opened up vast reserves of shale gas.•These technologies have also introduced considerable environmental concerns.•Engineering risk to the environment is being assessed using integrated models.•Human factors appear to be the greatest environmental risk.