As discussed in the previous lesson, geologic considerations are vital to drilling operations to prevent or mitigate subsurface integrity problems and ensure successful production. Subsurface integrity is only one part of the subsurface containment equation. Wellbore integrity is the complement to subsurface integrity in assuring subsurface containment. Engineering considerations are important to ensure the well is not leaking. For example, good engineering design in a well environment with corrosive subsurface fluids would include protection against leaks that could occur as a result of casing corrosion. A good engineer designs to prevent problems; but a good engineer also anticipates potential problems and designs to mitigate them. Integrating both geologic and engineering considerations into the operation of a well ensures good containment design and adherence to necessary safety standards. Let’s take a deeper dive into wellbore integrity.
To ensure wellbore integrity, engineers focus on the following aspects of a well:
- Testing (is the design working like we thought)
- Maintenance (if the design is experiencing wear and tear or is not working as anticipated, we need to make repairs or adjustments)
Well design occurs before drilling and construction of the well. Think back to our earlier lesson about the stages that are taken up before drilling and construction even start of an oil and gas well, such as completion design and casing/cementing design. For example, casing must be designed to withstand certain types of forces or loads, for example tensile, burst, and collapse loads.
Part of the design process is to include not only hardware barriers, but human barriers in the systems. Examples of these include:
- Hardware Barriers: leakage detection systems, emergency shutoff valves, blowout preventers, etc.
- Human Barriers: documentation, preparedness plans, communication, etc.
When the geology, geography, human proximity and other factors may contribute to unusual project challenges, extra barriers are needed for prevention.
Testing takes place during construction and continues afterwards during operations. Engineers test for the integrity of the well in an effort to confirm that it can contain hydrocarbons within the well, that fluids are moving where they should and not leaking internally within the well system or external to the well, and to ensure that there is no significant fluid movement into an underground source of drinking water. Through well testing, engineers continually check the integrity of the wellbore to ensure proper construction and that regulations are met. We will examine a few common tests for wellbore integrity on the next page.
Maintenance takes place during construction and continues afterwards during operations. Through regular maintenance, engineers ensure the integrity of the wellbore. Proper maintenance involves implementing and inspecting those hardware and human barriers designed into the project. Those barriers are an important line of defense in preventing failures. Engineers must ensure that operators and management have a good understanding of these barriers. Geologists must also do the same when assessing the integrity of the subsurface.