Managing Shallow Water Flow During Tophole Drilling Operations in the Southern North Sea – A Case Study

Solarin, Adebowale (Maersk Drilling)



With a shallow water flow-back in excess of 200 bbl/hr from the Top Chalk formation during the 17½" section, the deviated exploration / development well "Well #4" was planned and drilled successfully with a jackup rig. The well was planned from a platform in the Southern North Sea.

The primary goal for the 17½" section was to safely drill to section TD, set casing and cement same with zero incident in a minimum amount of time while encountering shallow water flow.

The key challenges for this well were:

Flowing Top Chalk Formation: The Top chalk formation flowed at all three previously drilled offset wells with 12.0 ppg EMW and approximately 200 bbl/hr. Several attempts to shut in the well and stop the flowing Top Chalk on the offset well "Well #1" failed.

Obtaining regulatory approval from authorities, and commitment and acceptance by all involved parties to drill the well under flowing conditions.

Hole cleaning and hole stability considerations when drilling with seawater

Permanently shutting off the shallow water flow with a two-stage cementation.

Rig uncertainty and general service market (in 2017): A new drilling contractor and drilling services not familiar with the peculiarities of operations in this area

Safety, communication and human factor considerations for a potentially hazardous non-routine operation.

A collaborative well-planning and preparation process involving the operator drilling team, the drilling contractor and key service providers was critical to the success of the overall operation.

The team worked together to ensure all requirements, risk mitigating measures, lessons learned from previous operations and offset wells, and human factor considerations were incorporated in the execution program.

The well was successfully drilled to TD, evaluated, completed and flowed. The notable highlights from the top-hole drilling operation include:

Fastest 17-1/2" phase compared to offset wells: drilling and casing operations completed in 94.25 hrs with the well flowing.

Zero NPT in the 17-1/2" drilling phase: drilled 654 m in 37.5 hrs with an average ROP of 17.5 m/hr without any complications.

Continuous monitoring and fingerprinting of the shallow water flow

This paper describes the key planning considerations, preparations and creative solutions deployed to deliver the well. The lessons learnt will serve as a resource for planning future wells with similar challenges.