The duration spent on drilling is an essential element to be taken into account when exploring any hydrocarbon field as it is a direct reflection of the money spent. This article looks into Non-Performing Time events by discussing it from the sub-surface and surface scenarios, based on the analysis performed in 5 wells of the Volve Oilfield.
Data Source
The content refers to description in the End of Well Reports, Drilling Plan reports and the Daily Drilling Progress reports (DDPR). We are thankful to AUI SYSTEMS for automated analyses of the DDPR of the Volve Oilfield wells.
Major categories of NPT events:
Stuck Pipe (STK)
The drill string becomes stuck and cannot be easily retrieved. This can be attributed to various reasons, such as differential pressure, wellbore geometry, or formation characteristic.
Mud Loss (MLO)
It refers to the unintentional flow of drilling fluid into the formation, leading to a decrease in the mud volume circulating in the wellbore. Mud loss can be caused by fractures, highly permeable zones, or other passageways in the formation. It can also cause wellbore instability along with inadequate drilling performance.
Tight spots (TSO)
These are narrow sections within the wellbore that pose challenges during drilling. These tight spots can be caused by various factors, including wellbore geometry, formation heterogeneity, or wellbore collapse.
Repair (RPR)
Unexpected equipment failures or malfunctions can result in downtime and the need for repairs. In order to reduce the effects of such issues on drilling operations, efficient repair processes and well-equipped maintenance teams are important.
Wait on Cement (WOC)
The time required for the cement slurry to set and form a proper seal in the wellbore. Drilling operations shall not commence after the cement has attained the desired strength during this waiting period.
Wait on Weather (WOW)
Adverse weather conditions can also lead to delays, as it may be unsafe to continue drilling operations during severe weather events. Waiting on weather ensures the safety of personnel and equipment, but it adds to the overall drilling time.
Non Productive Time
Wells 15-9-F-1, 15-9-F-15, 15-9-F-14, 15-9-F-5 and 15-9-F-4 have been selected to ensure that major regions of the field are considered in the analysis. Repair is seen to be the most prominent reason for NPT, followed by Wait on Weather.
Fig: Distribution of drilling events indicating Repair of equipment being a major contributor to NPT. (Ref: auisys.com)
Fig: Drilling Performance Curves indicating the NPT Events which have occurred generally at TD. The red dot indicates NPT events. [Well timeline is compressed for wells [15-9-F-1, 15-9-F-5, 15-9-F-15] for better viewing.] (Ref: auisys.com)
Sand formations contributing to NPT
Lost circulation issues
The Balder Formation is associated with a loose friable tuff that can act as a loss zone (15/9-F-10) and has also been found to be vulnerable to washouts. Losses were experienced in wells 15/9-F-15 and 15/9-F-10 in the Ty Formation with fractures opening up at 1.48-1.50 sg. Mud loss is also expected in the Utsira formation. The figure below is the borehole stability analysis for well 15/9-F-14.
Fig: Note the change in formation pressure gradient at depths 2240 m (Balder formation) and 2520 m (Ty Formation)
Hole Instability
Claystones are present in the Nordland, the Hordaland, the Rogaland Group and Viking Group. Tight hole situations have been experienced, but there is no definite evidence for significant unstable conditions when drilled at high inclinations and when the wellbore is left open for prolonged periods of time.
Conclusion
This paper provides the results from an automated NPT insights obtained using a cognitive engine driven by knowledge-based A.I. These insights also identify the zones that are contributing towards the NPT. The Volve dataset includes a detailed analysis of these NPT events in the End of Well Reports (EOWR).
The article is published only for educational purposes.
