Non-Productive Time (NPT) is a key measure of cost-effective and successful drilling operations. NPT may be caused by various reasons, such as unpredictable weather or technical issues. Some of those cannot be reduced or controlled (weather), while others can be counteracted by proper preparation and careful planning. Industry experience shows that time lost due to well stability issues accounts, on average, for 10% of all NPT. This can be eventually reduced by appropriate measures and/or procedures.

Offshore drilling operators are collecting and analyzing large amounts of data but it is very rare to perform analysis on unstructured drilling reports like the ones produced and possessed by drilling contractors. This project's aim was to analyze the NPT of drilling operations from the perspective of a contractor. Data from 93 wells drilled by Maersk Drilling from 2006 to 2019 in the North Sea was used to classify, compare and analyze the causes of NPT, as registered in the daily reports, with a focus on well stability issues by the means of text mining and statistical tools. The analysis had shown that the average cost of wellbore stability NPT was in the order of 2,000,000 USD per well and losses were the most common cause of wellbore instability among the wells in the database.

This project was, to the best of our knowledge, the first attempt to extract and analyze information from unstructured daily operation reports collected by a drilling company. The analysis had shown that the contractor's reports very often do not contain the same degree of detail on the causes of NPT in general, and wellbore stability issues in particular, as the ones produced by the operator. The results of our analysis can be used as a framework for improvement of current practices for registration and categorization of NPT causes in the drilling contractor's reports. In future, these reports should be structured in a way that allows to record both the symptoms of wellbore stability issues as well as the issues themselves. A well-structured report will not only allow to analyze easier historical data but also may be used to facilitate the automatization of the drilling process. Based on experiences from previous wells, specific NPT symptoms and scenarios could be identified and compared with current situations therefore allowing to promptly forecast and counteract possible issues.

The ultimate goal of such structured reports is to create an efficient database and provide guidelines to the drilling crew on how to recognize and minimize NPT related to wellbore stability problem. Suc h database can help make drilling more predictable by providing field-specific wellbore related problem data, which can be used to ensure the planning of effective mitigating measures. The method used for this analysis can also be extended to other problematic areas.

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