Old Wells, New Purpose: Key Considerations for Re-Purposing Mature Wells and Fields for Carbon Capture and Storage (CCS)

Abstract

Traditionally, when the production cycle of an oil or gas or oil & gas field reaches its economic end of life, the top side facilities are dismantled, the wellbore is permanently plugged and abandoned, and the surrounding land or seabed is returned to its natural condition. Such a procedure is commonly referred to as decommissioning and it is a complex, multi-step process that is expensive, with costs even higher for offshore and deep-water fields and wells. At the same time as increasing numbers of oil and gas assets are reaching their end-of-life and need to be decommissioned, governments world-wide are committing to reach a net zero target for CO2 emissions in the coming decades. With these two concurrent commitments there is now the opportunity to evaluate the potential for re-use of those to-be-decommissioned wells and fields for the use of CO2 injection and storage, commonly referred to as CCS or carbon capture and storage. Re-using wells and fields for CO2 injection provides not only potential cost saving benefits but also promises to reduce the time required for developing the necessary CCS infrastructure because much of it will already be in place. The process of converting hydrocarbon wells to CO2 storage wells has been considered in several planned projects, including the P18-4 depleted gas field near the coast of Rotterdam, part of the wider Porthos project, and Peterhead project in the North Sea (Arts et al., 2012; Marshal et al., 2018). Other inherent advantages to re-use include the availability of rich datasets of downhole measurements including logs, core samples and any subsequent lab analysis, and also in-depth field understanding based on potentially multiple well operations. The operators also have the possibility of turning decommissioned wells into a source of profits, or at least covering decommissioning costs, by selling CO2 storage capacity to others. However, the process for facilitating re-use of wells for injection of CO2, even into a saline aquifer, is far from a simple process of reverse engineering typical oil and gas production practices because there are a number of factors to consider. These include both geological, including reservoir pressure and seal capacity, and engineering not only from a well construction and integrity process but also reservoir engineering and the feasibility of a reservoir to accept the volume and rates of CO2 required to make economic sense for either a new field CCS site or in a re-use case.