oa Legacy Well Leak Rate Evaluation in Mature Fields using Flow Simulator and Decision Tree Analysis

A recent major shift in Indonesia oil and gas industry is its interest to implement geological carbon storage. Many of the projects are considering depleted reservoir due to its well proven seal and intention to bring additional value to the mature fields. Despite those advantages, repurposing mature oil and gas fields come with a challenge from containment perspective. The seal to the depleted reservoir is littered with legacy well (drilled prior to the CCS project) that are commonly not built to withstand sour condition. Thus, those well becomes potential conduit for leakage that might compromise the CO2 storage.

Risk analysis workflow has been developed to quantify potential leakage from legacy well and its probability to occur. The well along with its detail completion and P&A barriers is modelled in PETEX GAP. Sensitivity analysis that evaluates the possible scenarios of barrier breach are done using decision tree analysis. Industry statistics are utilized to evaluate the probability. Lastly, based on the result of the uncertainty analysis, a cumulative distribution function is created to understand whether it falls under IPCC recommendation of maximum 1% loss for the entire injection and post injection site care duration of >100 years