An Integrated BHA with a Wired Underreamer Enables Exceptional Underreaming While Drilling and Rathole Elimination Performance in a Single Trip for Exploration Offshore Operation in Azerbaijan–A Case Study
Authors: Abdullayev Nurlan , Scalabre Sebastien , Alirzayev Tevekkul , Isayeva Elina , Dairova Bakytgul , Ilett Thomas , Ahsan Adeel , Ungaliyev Gaukharbek 
Published: November 2023

The Shah Deniz field is located in the South Caspian Sea, Azerbaijan. It is a giant high-pressure gascondensate reservoir. The well design of the Shah Deniz exploration well requires a significant borehole enlargement strategy through most of the planned sections. There was a requirement for each hole section to be delivered in a single run to optimize costs and reduce the time impact of the inherent shock and vibrations, wellbore stability, and tight hydraulics margins. An additional vital success factor was minimizing long open hole exposure for the successful 16-in. and 13 5/8-in. casing runs through interbedded lithology and efficient cementing operations.

For the directional drilling service provider, it was critical that the technologies adapt to the anticipated drilling environment over the longest well section intervals. Significant work was invested in planning for this well utilizing a thorough engineering approach. Advanced drilling engineering analysis was performed to select the robust dual hole opening bottomhole assembly (BHA) design to deliver simultaneous directional, logging, and borehole enlargement performance with low shock and vibrations and a high rate of penetration. To enable a single-run strategy, a hydraulic-actuating near-bit underreamer had to be utilized with a real-time BHA connector inside to enable real-time communication with the rotary steerable system critical for geo-stopping with near-bit gamma ray while eliminating a dedicated rathole elimination run at section total depth. This was combined with a ball-drop-actuated hydraulic underreamer above the measurements-while drilling and logging-while-drilling tools for conventional hole-opening operations.

The directional objectives were successfully achieved, delivering a smooth kickoff from 10° up to 22° inclination and maintaining a constant azimuth while simultaneously enlarging the borehole with the upper underreamer. At section total depth, rathole elimination was then effectively conducted with the predefined modeled drilling parameters. Actuated near-bit underreamer enabled for higher bottoms-up circulation rates to achieve efficient hole cleaning in large open holes within surface equipment margins for smooth casing operations.

The implementation of this unique BHA design and real-time downhole drilling dynamics optimization in underreaming-while-drilling consecutive 16 1/2-in. × 19 1/2-in. and 14 3/4-in. × 17-in. sections led to stable drilling performance across geologically challenging and long 2,025-m and 972-m intervals in a deep environment of over 4,900m true vertical depth. Furthermore, the bespoke ruggedization package for the directional equipment enabled effective shoe-to-shoe drilling of interbedded shale and sand structures with intermittent hard formation stringers and resulted in minimal wear.

Recent results of underreaming while drilling and rathole elimination operation with wired underreamer are presented. The operation was performed for the first time in the Caspian region.