Long-Term Well Cement Integrity for wells in CO2 environments
Research output: Research › Master's Thesis
Is zonal isolation provided by the cement sheath? Cementing is central to the discussion of zonal isolation and well integrity, because cement typically provides at least one barrier in a well and is a component of the barrier envelope or barrier system during well construction and the operational phases of the well. Cement parameters are typically included in regulations and included as part of the permanent-abandonment requirements for oil and gas wells (NORSOK D-010 Rev.4, 2013). The task of the cement will be to be able to maintain its physical strength and low permeability over lengthy exposure time to CO2 – saturated brine and supercritical CO2 in carbon sequestration reservoirs. Currently, the mechanisms how cement corrosion and carbonation works is well known and can be predicted within a reasonable range of uncertainty. On the other hand, the interface between cement/ rock and cement/casing is still a poorly defined science and rarely tested satisfactorily. As an industry, installing and maintaining the cement barrier and well integrity are part of our license to operate. In the last several years, regulations have been updated and rewritten worldwide. In every jurisdiction, we can point to a regulation or industry standard that affects drilling and cementing operations. This regulatory attention compels us to double-check our practices, continue effective techniques, and develop technology where improvements are needed. Technology is also focused on improving verification of cement placement and barrier achievement. Cement evaluation, including wellsite observations during cement placement, pressure tests, and logging techniques, are part of the well integrity equation. These enhanced evaluation methods provide confidence that zonal isolation and well integrity are achieved. Up to now, there is still no API or ISO standard in place that gives you kind of guidance on how to deal with wells in CO2 environments upfront and during a cement job. The scope of this work was to set up a workflow on well cement integrity that deals with operations for existing and future wells in CO2 environments. What can be done to extend the lifetime of standard Portland cements to seal up those wells? Is there a deliberate need for new cement systems or are we going to tackle this issue by combining our skillsets and knowledge with bioengineering? Should we challenge our perception by testing out cement scenarios in the manner that civil engineers have done continue to do.