Experience Using Managed Pressure Cementing Techniques with Riserless Mud Recovery and Controlled Mud Level in the Barents Sea

Abstract

The Barents Sea offers unique drilling challenges related to issues such as biogenetic gas in shallow formations, thermogenic gas seeps up to the seabed from underlying formations, shallow formations with abnormal pressure, shallow reservoirs, low-fracture-pressure formations in part of the overburden, and naturally fractured/karstified carbonate reservoirs. This paper discusses cementing challenges when drilling wells in the Barents Sea and the experience gained using managed pressure cementing (MPC) practices. When drilling the surface hole in potentially slightly overpressured formations, the riserless mud recovery (RMR) technique was used. For the first time on the Norwegian Continental Shelf (NCS), MPC was used when cementing the surface casing. RMR compensates for drilling the overpressurized zones without a riser and blowout preventer (BOP), and MPC allows for pressurization and monitoring of the pressure on the subsea wellhead toward the formation during the cement curing stage. Once the marine riser and BOP were installed, controlled mud level (CML) technology was used during drilling, running casing/liners, cementing operations, and other activities. CML enables manipulation of the fluid level in the riser and therefore helps optimize downhole pressure to avoid losses and maintain an overbalance. CML has proven to be particularly useful during cementing of liners in naturally fractured reservoirs and during setting of balanced cement plugs in an open hole. As a result, high circulation rates can be achieved and conventional high-density cement slurries can be used. MPC using either RMR or CML was employed for the first time in the Barents Sea. Examples of how cementing operations were planned and executed are described and results are presented.

Real-Time Detection of Karstification Hazards While Drilling in Carbonates

“…For example, Shell reported that total losses were observed in each of the six wells when drilling in carbonates in Sarawak (Peninsular Malaysia) [30]. Similar problems exist on the Norwegian Continental Shelf when drilling into open fractures or karsts resulted in total losses during a week [20,31,32]. Two to four weeks of non-productive time were reported by an operator company in Qatar when a large volume of cement was pumped to plug intervals of mud losses in carbonates [33].…”

“…It has been shown that caves less than λ 4 (40 m (131 ft)) cannot be separated due to wave interference [19]. In certain regions in the Barents Sea, encountered caves were less than a meter and they were very dangerous for drilling [20].…”

Prediction and Early Detection of Karsts—An Overview of Methods and Technologies for Safer Drilling in Carbonates

“…As reported in [26], the exact geometrical size of the karst is unknown. However, its interpretation from the borehole image defined the geometrical size as more than 50 cm in length with a circumference of 21.6 cm (8.5 section of the well).…”

“…For a better understanding of karst objects and their effects on drilling, we refer interested readers to the studies in [24][25][26] on drilling in karstified carbonates in the Loppa High region in the Barents Sea which classify karstification objects into dangerous and not dangerous for drilling.…”

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

“…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.…”