Plug and abandonment (P&A) of subsea wells is very costly and usually requires semi-submersible drilling rigs (SSR). To reduce total costs of the subsea P&A campaigns, it is beneficial to perform P&A operations with riserless light well intervention (RLWI) vessels instead of rigs. Currently, a drilling rig is required for performing P&A operations in the reservoir section and overburden, whereas intervention vessels can be used for preparatory work and wellhead removal.
This paper discusses how it can be technologically feasible to perform full P&A of subsea wells with RLWI vessels. It is shown that, for wells of simple and medium complexity, innovate approaches with use of existing technologies can enable full P&A of the entire well with RLWI vessels. This is demonstrated by thorough analyses of operational procedures using available technologies, where RLWI operations are compared to rig operations for different well scenarios. Furthermore, to quantify the cost benefits of the innovative approaches, a cost-optimization tool has been used to estimate the resulting cost and time durations of the different approaches and scenarios.