Repurposing Depleted Gas Fields into Potential Carbon Storage Sites - Case Study of Assessment and Screening Methodology

Abstract

As the world is moving towards low carbon future, it is vital to explore ways to reduce carbon emission and one of the way is carbon capture and storage. This paper discusses on the criteria and methods used in screening depleted gas fields in Peninsular Malaysia to be repurposed into potential carbon storage sites. There are three main aspects to be considered for carbon storage sites which are containment, storage capacity and well integrity. Depleted gas fields are selected for potential carbon storage sites assessment due to its proven petroleum system which can retain hydrocarbon in its structure. This will reduce the uncertainty in terms of geological structure to store carbon downhole. Besides containment, storage capacity is another important aspect in screening for storage sites. After excluding fields with lower Gas Initially in Place (GIIP) which has lower potential storage capacity, screened fields are assessed for storage capacity by having high case and low case with different assumptions on percentage of gas Estimated Ultimate Recovery (EUR) replacement by carbon dioxide (CO2) and coupled with injectivity assessment via well model. The aspect of well integrity is also important when screening depleted gas fields as they could pose risks in terms of leak paths towards the surface. Both abandoned and producing wells are assessed in terms of cement integrity and material used in well construction. A total of 151 Non-Associated Gas (NAG) in Peninsular Malaysia (PM) fields went through the first pass filters which includes removing fields with <500 BSCF of GIIP to exclude fields with low storage capacity. Then pre-development fields are removed due to uncertainty on depletion timing. Further filter includes fields with significant EUR loss due to specified injection date because they are less likely to be commercial. From the first pass screening, 13 fields remained, and they are further assessed and ranked in terms of containment risks via geological complexity scoring, storage capacity and well integrity analysis. This paper will provide valuable insights for operators looking to repurpose and retool depleted gas fields into potential carbon storage sites as the demand for low carbon future is increasing.