Abstract
Development of the Kashagan field is very complicated and encounters many challenges, such as a harsh offshore environment with an ice season, highly pressurized wells and a high H2S concentration (sour). All these challenges were known during the field construction phase, but after one year of production, another unforeseen challenge emerged– severe downhole scaling in certain oil producers, flowing at very low water cuts (<0.5% water).
Scaling is a widespread and well-known phenomenon in many, often mature fields around the world, but it was not expected to occur in Kashagan in the early stage of field life. Well scaling developed very fast, leading to almost 50% productivity reduction on several wells in a few weeks time. Wellbore scaling put Kashagan production plans at risk, so it was critical to remediate the affected wells as soon as possible. A multi-disciplinary team started work to address the issue.
For most "brown" fields, remediation of wells affected by scaling is a routine job. In the case of Kashagan, which had just started production, downhole scaling was a big challenge for various reasons. Firstly, when rapid productivity decline was observed on some wells, it was not clear what caused the impairment, and a lot of investigative work was done to identify the nature of impairment and root cause (mechanism) behind it. Secondly, scaling badly affected D-island wells, where SIMOPS well intervention capability is highly restricted. D-island is a hub for offshore processing and gas reinjection facilities, located just few hundred meters away from wells, and any well intervention requires the creation of a "yellow zone" and causes significant production deferment. Thirdly, it was clear from the beginning that remediation is a temporary measure, and that it was important to progress from "firefighting" mode to impairment prevention mode, for all wells. Despite all complexities of the task all affected wells were successfully brought back to production and, after various successful anti-scale treatments, fine-tuning of the scaling prevention process is currently ongoing.
Due to the scaling, multiple processes had to be improved, such as metering, wells testing, wells surveillance and well interventions. In the design phase of the project, a well intervention was considered as something extraordinary, and expected to happen rarely, primarily for well integrity issues, not for scaling issues. Well intervention operations became a more routine operations and have started to play a critical role in the integrated activity planning process.
This paper describes how Kashagan wells were affected by wellbore impairment and what actions were made to remediate wells and to return wells to its original productivity.
