Deepest Deployment Of Riserless Dual Gradient Mud Recovery System In Drilling Operation In The North Sea

Abstract

Riserless Dual Gradient Drilling (DGD) using a specialized subsea pump placed on the seafloor during top hole drilling has been widely used on offshore subsea wells prior to installing the blow out preventer (BOP). Riserless DGD systems, kown as riserless mud recovery (RMR), have been developed to allow riserless sections to be drilled with weighted mud while taking returns back to surface. This allows the operator to set surface casing strings deeper, thereby reducing the total number of liners/casing strings in the well. This paper addresses the deepest RMR operation on the Norwegian Continental Shelf to date. The water depth was 854m and the 26″ hole section was successfully drilled to 1972mMD (1913mTVD). The riserless mud recovery system enabled the 20″ shoe to be set at a sufficient depth to allow elimination of the 16″ liner, thereby reducing casing strings, cost, well complexity and most importantly setting up the 13-5/8″ string cementation for success. This was mission critical from a well integrity perspective in the context of a big bore 9-5/8″ upper completion. Following the successful drilling of the 26″, the 20″ casing was installed and cemented. Foam cement was pumped using the riserless mud recovery system in cuttings transfer mode to prevent accumulation of returned cement at the well head. The 20″ casing was successfully tested after installing the BOP and marine riser. The paper describes the riserless mud recovery equipment and the planning of the well, plus the engineering of a multi-stage subsea pump and the subsequent seabed deployment in order to drill the longest and deepest 26″ section on the field. A 26″ directional BHA with a 1.30sg surface mud weight (1.18sg downhole mud weight) KCL glycol mud at flow rates of up to 4800 lpm was used to drill to TD. At TD the well was circulated at a lower rate to 1.38sg surface mud weight at 3200lpm to provide trip margin over the effective mud density required for wellbore stability.

Study of the Relationships among the Reverse Torque, Vibration, and Input Parameters of Mud Pumps in Riserless Mud Recovery Drilling

“…Sci. 2023, 13, 11878 2 of 20 ECD of an RMR system based on drilling data from a vertical well in the South China Sea. Reynolds et al [11] presented a pioneering case study for the Luiperd Mine and one of the measures for reducing environmental risk was to adopt a new articulation tool to minimize the bending stress applied to the subsea wellhead running tool (WHRT) and landing rope in running through the inflow pipe and surface casing.…”

“…Claudey et al [12] employed a controlled mud level technique in the Barents Sea, which controlled the liquid position within the riser, optimized the downhole pressure, prevented mud leakage, and maintained pressure balance. Claudey et al [13] successfully deployed a riserless mud recovery (RMR) system at a water depth of 854 m, the deepest operation of its kind in the North Sea to date. Mud-lifting circulation was achieved without wellbore stability or shallow hazard issues, and no mud contamination occurred.…”

Quantitative Analysis of the Stability of a Mud-Return Circulation System in a Riserless Mud-Recovery Drilling System

“…RMR can also compensate for the lack of intermediate casing and the absence of a blowout preventer (BOP) when drilling in overpressured zones [25][26][27][28][29]. Thus, it has been successful in various offshore areas with loose formations and losses.…”

Establishment and analysis of temperature field of riserless mud recovery system

“…Compared with the conventional offshore drilling, RMR adopts the dual-gradient control principle to control the annulus pressure more precisely, so as to effectively solve problems such as narrow mud density window, shallow gas and shallow flow that the offshore drilling engineering has always been facing (Michael and Michael, 2001;Myers, 2008;Smith et al, 2010;Stave et al, 2008). Because RMR abandons the riser used in the traditional offshore drilling and uses a seabed pump as a device for lifting drilling fluid, it reduces the cost of drilling and the demand for drilling platform (Claudey et al, 2016;Gao et al, 2009;Hannegan and Stave, 2006;Stave et al, 2014). From the above two points, RMR is suitable for drilling in deep water and ultra-deep water, which is in line with the development trend of the current offshore drilling engineering.…”