TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAfter most operators quit using Pin connector, Riser and Diverter for safety reasons, when drilling the tophole section of subsea wells, the use of seawater and sacrificial mud with return to seafloor has to date been the only available practical method.The RMR spread was run through the moon pool on a single derrick rig, and guided and stabilized by a heave compensated guide wire extending to a subsea anchor. Ref. System Schematic, Fig 1. The equipment was engineered and manufactured within an 8month period, and the field trial took place in December 2004.The paper also discusses the fluid system used, the operational benefits and limitations by applying the RMR technology.At the same time as the RMR Demo 2000 project was initiated, AGR was requested to design and build a Riserless Mud Recovery System for BP to be tested on the West Azeri field in The Caspian Sea. During 2004 the AGR Dual Gradient RMR system has been used to successfully drill the unstable 26" tophole using weighted inhibited silicate-based mud at approximate 120 -160 meter water depth (reference 1 and 2). This is a somewhat lighter version, which is suspended over the rig side by a winch and using a hose for the returns. Equipment Specification and EngineeringThe design basis and scope of work was based on the results from the Pre-Engineering phase. Further design detailing was developed with input from Hydro and Statoil, and was verified by the Project Steering Committee. The main design and operating requirements were:• The RMR System to be designed for 450 m water depth. • Offshore test to be performed in 330 m water depth.
This article presents results from the Controlled Mud Pressure (CMP) field trial that encompassed well control on a rig equipped for dual gradient drilling. The tests were carried out after successfully drilling three laterals with a partly evacuated riser with a controlled mud level. The paper focus on analysis of the results to quantify the ability to: detect in-/out-fluxes of gas and liquid; circulate out gas with both an open and closed annular preventer; suppress migration of drilled gas into the evacuated part of the riser during drilling.The CMP test objective is to verify the ability of the CMP equipment to detect and controllably circulate out simulated influxes. Five tests are documented: one with liquid in-and out-fluxes introduced through the choke line using the cement pump, and four with gas introduced through the drill string. Nitrogen was used to emulate gas kicks, which were circulated out of the well with both an open riser and with a closed annular preventer and a dedicated return line, connected to the subsea pump module and a topside-mounted choke. To address the challenge with drilled gas accumulating in the evacuated part of the riser, small portions of Methane were injected into the drill string while circulating. Gas sensor readings at the shakers and in the flow-line were used to monitor gas concentration in the mud and above the mud mirror, respectively.The main findings from the field trial are: volume imbalances due to abrupt changes in flow rate into the well are quickly detected; it is possible to circulate small gas kicks out of the well through the subsea pump module and dedicated well control equipment when closing in the well with the annular preventer, given that the pump handles a mixture of mud and gas, and can withstand a high differential pressure to sea; it is not advisable to vent large gas kicks into the evacuated part of the riser without closing the blowout preventer (BOP). In addition, gas migration velocities in water-based mud with varying flow rates and gas content are reported.The article directs attention to deep water well control using specialized equipment for dual gradient drilling. It also contains valuable analysis of field trial results, which contribute to the understanding of gas migration, and the possibilities and restrictions, introduced with dual gradient drilling.
This paper presents ongoing work as well as plans and ideas for future development of a toolbox of managed pressure drilling systems that solves major challenges when drilling in both mid-and deep waters. The toolbox contains three applications based on field proven Controlled Mud Level (CML) technology. Additional benefits can be achieved by combining controlled mud level technology with other technology elements such as a fast closing annular or a sealing element in the riser, usually referred to as a rotating control device (RCD).The first application is called CML. A subsea pump module (SPM) is used to pump the mud returns to surface in a separate mud return line (MRL). The SPM is used to regulate and manage the bottomhole pressure by adjusting the mud level in the riser. High bottomhole pressure or Equivalent Circulating Density (ECD) due to friction and other effects can be avoided by reducing the mud level in the riser accordingly. One of the objectives with this technology is to avoid or reduce losses both during drilling and other operations such as cementing.In the second application called ECD-Management, CML is combined with a fast closing annular installed in the riser just above the SPM. This enables extending the operating envelope of the technology to a point where loss of circulating capability could potentially cause an underbalance scenario in the well. The hydrostatic pressure from the drill string or MRL can be trapped within a few seconds by closing the fast closing annular element, e.g. on unplanned rig pump stops or formation pack off situations. A second annular will also be installed to be used during connections in order to save time filling up the riser to compensate for the ECD effect (friction losses in the annulus).The third application in the toolbox is called ECD-Control. Here a subsea RCD or a sealing element is installed in the riser and the SPM can then be used to manipulate the pressure below the RCD to compensate for ECD variations. The riser is always topped up with mud and hydrostatic overbalance is maintained.The paper will present simulation results comparing the different technologies and address benefits and challenges with the different methods.
Well control has been a major obstacle for introducing dual gradient systems for deep water drilling, involving both new and more complex procedures and equipment. Here test results using a new dual gradient drilling (DGD) system to control simulated well control events are presented. After successfully drilling a Statoil well with Enhanced Drilling's dual gradient solution (EC-Drill) at the Troll (Kjøsnes et al. 2014) field on the Norwegian continental shelf, the well was plugged and made ready for 48 hours of controlled testing. Several tests were run, each designed to determine the functionality of the system; to detect and handle liquid loss, gas and liquid influx, gas migration in the riser, and circulation of gas through the subsea pump module. The detection tests were carried out with a reduced riser level and an open annular, to quantify the capability of the system to detect volume imbalances while drilling. Three circulation tests with increasing amount of gas injected through the drillstring were performed. After the influx was detected, the annular was closed, and the flow was routed from the well through a bypass line to the subsea pump module. A topside choke in the mud return line was actively used to apply backpressure with the objective to control bottom-hole pressure, while circulating the gas from the well. In the last test gas was allowed to migrate into the marine drilling riser with a reduced riser level and open annular. The paper will present the planning and preparations as well as the results.
A world first "Controlled Annular Mud Level" type Dual Gradient Drilling (DGD) system was successfully applied on an ultra-deepwater well drilled in May -July 2012. Water depth was 2260m and the formation was generally carbonates with potential for severe or total losses. DGD was applied to prevent losses from occurring. Dynamic circulation pressure effects were eliminated. The DGD topside system was rigged up offline and when running the riser, the DGD pump was launched and attached to the riser for the last 400m. During drilling of the 17 ½" hole section, a Dual Gradient mud weight was selected and the riser level was maintained between 150 and 200m below flow line most of the time. On connections the riser level was kept unchanged. The level was decided according to PWD Readings. On several occasions it was demonstrated that lowering the riser level increased ROP whilst raising it again decreased ROP in hard rock. In the 12 ¼" hole section, drilled to well TD, the same approach was taken, but here the riser level was raised 50 m (approximately 75 psi) on connections to account for some of the reduced bottom hole pressure when shutting down the rig mud pumps. In this section some gas bearing formations were penetrated with a reduced riser level. No gas at all was seen in the riser top. During drilling of the reservoir and surrounding formations, no losses were seen and the hole was in good condition with no indication of fill or drag. The paper will present the technology applied and analyze the results achieved on this well.
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