Managing Risk and Reaping Reward in a High Temperature, High H2S, Extended Reach Environment: A Case Study of a Coiled Tubing Stimulation Campaign in the UAE

Abstract

Abstract Coiled Tubing (CT) interventions, even in simple environments, carry inherent risk. This risk is further compounded as the intervention envelope is expanded and the environment made more complex. This gas field in the UAE is an example of such a reservoir. The high temperatures and high levels of both H2S and CO2 present in the field make this an unforgiving environment. The drilling strategy dictates a substantial number of long, horizontal, dual lateral wells to target different sections of the reservoir which in turn vary significantly in reservoir quality. Finally, the production strategy stipulates that wells require acid stimulation with CT selected as the preferred placement technique. Meeting all of the above requirements in a single intervention strategy requires extensive and careful pre-planning and hazard analysis and identification at the onset of such a project. The obvious challenges relate to the selection of a suitable CT string for such a job and subsequently protecting it from attack from H2S, complicated by extended exposure to acid. The more subtle challenges lie in the appropriate selection and combination of downhole tools technologies to achieve the multiple objectives of lateral access, extended reach capability and stimulation efficiency in a single bottom-hole assembly (BHA). To achieve all of these multi-level objectives, this paper will review the planning, execution and post-job phases of the CT stimulation campaign completed in this gas field. Focus will be given to the initial Hazard Identification Study (HAZID) carried out and the subsequent actions taken to mitigate the risks identified. These include but are not limited to the design of the CT string, the selection of the stimulation strategy including laboratory testing done for fluid selection and corrosion inhibition, a review of the various yard-testing conducted to select and set-up the required intervention BHAs, and finally the integration of a new, real-time CT pipe monitoring system to affirm the effectiveness of the pipe management and mitigation strategy used. The results reaffirm the value of investing time upfront to conduct a HAZID and then do the necessary due diligence to follow through on action items and implement engineered solutions. Furthermore, the workflows and best practices resulting continue to be used and updated as the project continues.