Ending With a High Note: Striving for Safe and Resilient Well Abandonment Through Geomechanics-Driven Cap Rock Restoration Study

Abstract Well abandonment is the last stage of well management life cycle post production cease and well shut in. Estimating field potential during the early appraisal stage, sustaining and enhancing the well productivity throughout the active producing years become the critical agenda to meet production target. Well healthiness and performance issues are easily identified through surveillance and well diagnostics surveys which continue till the end of well life including during well abandonment campaign if required. Reservoir pressure is one of the critical parameters monitored during this period to indicate production drive. The importance of pressure data will be emphasized during well abandonment stage together with cap rock evaluation for well barrier assessment. Pressure survey during drilling execution and throughout production period till abandonment is used as critical input to evaluate the cap rock strength. Initial reservoir pressure with full gas evacuation from the reservoir are assumed to happen to determine the minimum setting depth for the cement plug where the gas line intersects with fracture gradient line. Competent cap rock interval must be identified below this threshold depth to allow for safe and adequate natural barrier in case of pressure increase. Pressure depletion element is also factored in the assessment of reservoir rock to further sensitive the depth range to set the cement plug. Results indicate that out of 12 wells evaluated only one well requires cement squeeze directly into the existing perforation following the conventional well abandonment approach while the rest of wells are assured through the cap rock restoration assessment without any completion string below top packer removal required. This has translated to project cost optimization of USD 8 million. Systematic workflow process honouring the cap rock and geomechanics concepts are formulated as best practices for future project replication. In addition, systematic tabulation of pressure record, legacy cement bond log profile and well intervention history provide an elusive overview if any cement remedial job is required to re-establish the well barrier. A comprehensive track record allows few millions dollars of cost savings by eliminating additional cement bond log run and any new data acquisition run. In conclusion, cap rock restoration technique backed with geomechanics-driven pressure analysis is able to provide for safe and reliable well abandonment portfolio. Doing the right analysis using the right data for the right application will help to strengthen technical integrity of subsurface evaluation work and ensure a more responsible way of abandoning the well for good.