Implementation of Rig Simultaneous Operations Over Drill Centers to Improve Deepwater Drilling Performance
Authors: Abuah Aihanuwa , Okenyi Kingsley , Erhunmwunsee Kingsley , Onafeso Olatunde , Abdallah Daniel 
Published: February 2020

In 2017, the business plan set out was to deliver best-in-class wells in an upcoming deepwater drilling campaign offshore West Africa in 28 days (ca. 25 days/10000 ft) which is 10 days shorter than the average performance on the previous campaign, safely and within the budget by leveraging on the capabilities of the new rig.

Historically, the scope of operations in the field cuts across drilling, completions, well intervention, work over and abandonment. These operations have been executed with various rigs over the years. The two types of Mobile Offshore Drilling Units (MODUs), namely drill ships and semi-submersibles, have been used extensively in the field.

The rig planned for the campaign was a newly built, dual activity, seventh-generation drillship. This rig offers numerous offline opportunities and obvious advantages over the rigs used in previous campaigns which had limitations such as limited bulk storage space / tank capacity, limited deck/derrick space, single derrick/rotary, single BOPs, no Active Heave Compensated (AHC) crane etc. The dual activity capability of the rig enables open-water tripping, casing running and surface activities to be moved entirely offline. In addition to the huge savings from dual activity during batch drilling, development work also offers the opportunity to run the subsea Tubing Head Spools/Xmas tree offline using the active heave compensated subsea crane onboard the rig.

However, the governing procedures for the field's Simultaneous Operations (SIMOPS) prohibited heavy lifting over open water at a drill center due to the risk of dropped objects on subsea infrastructure. Through a thorough risk assessment and DROPS assessment, the procedure was challenged, and approval was secured to perform heavy lifting operations at the drill centers.

The scope of this paper is limited to heavy-lifting operations at the drill centres (also referred to as manifolds) which were hitherto impossible in previous campaign.

The following operations have been implemented in the Drilling campaign and Intervention campaign respectively:Running the 20" or 20" x 13-3/8" surface casing offline while drilling the tophole from the main rotary which has significantly improved tophole performance. The average tophole performance has reduced from 5.4 days in the previous campaign to 3.9 days. The best field tophole time of 2.7 days has been recorded in the campaign.Deployment and Installation of the Tubing Head Spool (THS) prior to running the new technology Single Trip Completion. Previously, a Field Service Vessel (FSV) was used for this operation but this has been eliminated. This operation has also been performed more efficiently on the rig saving ca. 0.2 days (5 hours) per well.Recovery and Installation of Christmas trees during the Intervention campaign. This operation was previously performed with the FSV. Consequently, THS recovery for the upcoming Abandonment campaign is now planned to leverage on learnings and experience of the rig thereby reducing the project budget (ABEX) and eliminating the need for the FSV for this operation.Drilling the tophole from the auxillary rotary with the BOP suspended in the main rotary for non-batched single topholes.

The utilization of the rig capabilities to optimize operations has significantly reduced the risk exposure of personnel, reduced well cost due to improved performance and enabled the deployment of new technology in the field.