OPEX Reduction Through De-Risked Multi-Zone Gravel Pack De-Completion/Workover - An OML 54 Case

Abstract The cardinal objective of working over an oil or gas well is to increase the well’s production performance. It involves stimulating existing production zone(s) with impaired production due to skin or other near-wellbore damage situations, pulling an existing completion, accessing new zones behind the casing, and installing a new completion. A direct option to work over is a side-track from the existing wellbore after partial or complete removal of the previously installed completions depending on depths of behind-casing opportunities. Workover is preferred to side-track due to cost. However, to achieve the cost reduction benefit of workover, the operational steps involved must be fully de-risked. Risk, especially that seen with de-completing dual completions to fishing of single or dual gravel packs, is the primary driver behind most operators undertaking side-track over traditional workover options. This paper shares experience from working over a dual-string multi-zone gravel pack well located in OML 54, onshore Niger Delta. The overall cost of de-completing and completing the well was compared with a side-track option, the result was 30% savings. The project team zeroed in and scrutinized operational cost drivers and concluded that de-risking each of the de-completion operational stages was key. The candidate well was completed as a two-zone gravel pack and produced via two production strings. In de-risking the operations, the project team considered the following: Age of the existing dual completionSize of the production strings and the gravel packs.Complexity of the completionWell budget (AFE – authorization for expenditure)Expected recovery from each of the new zones. The well was successfully de-completed and completed by adhering to an operational flowchart. The chart provided a step-by-step roadmap from retrieving the upper dual completions, the upper gravel pack screen, the lower gravel pack screens, and installing a new two-string multi-zone completion.