Well Design Differentiators for CO2 Sequestration in Depleted Reservoirs

Abstract

Abstract Reducing carbon emissions is a global problem which has become firmly established as a common objective. Sequestration of CO2 into underground oil and gas reservoirs on a large scale has the potential to make significant contribution to solving this problem. The process of carbon dioxide injection has been implemented in many different underground geological formations since the early 1970's as a means of enhancing oil recovery. CO2 injection purely for emissions reduction is however relatively new. This paper aims to identify key differentiators between conventional well design techniques and CO2 injection wells in depleted gas reservoirs. Technical focus is placed upon project management, completion well design and integrity assurance. The information is based on industry practices developed from published and unpublished CO2 sequestration projects and other data sources including input from contracting service companies. The key objective is to support the concept and to demonstrate that CO2 sequestration into depleted reservoirs can be achieved effectively and safely from a well design perspective. The information provided in this paper will technically support feasibility studies, demonstrator schemes and contribute to the successful implementation of future CO2 sequestration projects globally. In summary this paper will review the unique operating environment of a CO2 injection well, identify critical differentiators and evaluate the impact on the well design. Introduction This paper is primarily based on the findings from a feasibility study for a CCS (carbon capture and storage) project in the Southern sector of the North Sea, U.K [1] and examines some of the challenges associated with CO2 injection well design in depleted gas reservoirs and other geological formations. Conventional well design project workflow models fail to facilitate the interdisciplinary requirements of CCS projects. Key areas such as capacity, injectivity and integrity (Figure 1) overlap significantly requiring an integrated team approach. A rigorous and tailored project workflow model is required to ensure the right amount of collaboration is achieved and to develop a common understanding of the CO2 injection environment. Exchanging information between technical workgroups is required to model the CO2 injection process from the supply flowline to the reservoir.