The subsurface formations and reservoir conditions encountered in certain areas of the Barents Sea offer some unique challenges for the operators and the drilling industry. These areas of the Norwegian Barents Sea consist of naturally fractured and weathered carbonate formations which may incorporate open karsts. Drilling into large open fractures or karsts will result in total losses and mud cap drilling practices must be employed to enable further progress. Such locations may require some unique solutions to drill effectively and safely while conforming to local rules and regulations; including deploying winterized rigs capable of year-round operations in Arctic environment. This paper describes the process of selecting a viable solution for drilling in such an area where potential mud cap drilling practices could be required, the rig integration process, class notation process, development of operational procedures, risk assessment, training and testing of equipment prior to commencing the operation. This was a fast track project which incorporated developing new mud cap drilling procedures and processes when operating the Controlled Mud Level (CML) system. Since mud cap drilling practices from a floater on the Norwegian Continental Shelf (NCS) is a rare occurrence, it required close cooperation between the operator, the drilling contractor and the service provider. To facilitate the process and assure sound practices a third party with experience on mud cap operations was also engaged. The paper will also briefly describe the Controlled Mud Cap Drilling (CMCD) principle and the results from drilling the well.
The objective was to be prepared for a total and sudden loss scenario while drilling and coring a challenging well in the Barents sea. A dual-gradient Controlled Mud Level (CML) system with Controlled Mud Cap Drilling (CMCD) mode was installed on the rig to manage minor and/or total losses. Prior to spud of the section, an advanced dynamic simulator with the actual well configuration loaded was used to conduct offline training, and prepare the drilling team and involved service personnel for the operation. Experience from previous wells in the area identified the risk of drilling into karstified carbonate zones with the potential of leading to total and sudden losses. An advanced dynamic simulator was used to reflect the details of the CML system to be used. The rig crew together with the CML operator and other involved service personnel were trained on how to manage a total loss scenario by switching from CML to CMCD mode. All relevant operational procedures were used as a basis for creating training scenarios and operational preparations for the exercises. This paper will briefly present the simulator set-up, the operation/training procedures and results from the training. Feedback from the operation itself will also be described including lesson-learned from utilizing a full-scale dynamic simulator with the actual well loaded during preparation for operation.
Curing losses during drilling is a widely known and discussed topic. Losses are mainly cured by spotting a lost circulation pill from the mud company or by spotting and squeezing a lost circulation cement plug. Many papers have been published regarding the composition of lost circulation pills, which is considered one of the key success factors. However, the technique used to place these pills in a zone of interest also can be tricky and equally contributes to the success of the job. In most cases, a cement plug is spotted using the traditional balanced plug method. However, in high-pressure/high-temperature (HP/HT) wells having a very narrow margin between pore pressure and fracture gradient, there is very little probability of spotting a balanced cement plug successfully under lost circulation conditions. In the above mentioned situation, spotting any cement plug becomes a critical application. The correct amount of annular pressure required during the spotting of the plug must be calculated precisely, as even minor differences in applied surface pressure can damage the downhole stability of the cement plug. BG Egypt recently experienced complete losses, resulting in a loss of more than 1,000 bbl of oil-based mud (OBM) in the Miocene section while drilling a HP/HT well offshore in the Mediterranean Sea. The immediate loss in hydrostatic pressure reduced the equivalent mud weight (EMW) on bottom and required the response of the managed pressure drilling (MPD) system to apply sufficient annular pressure to control the well by spotting lost circulation material (LCM) pills and a cement plug at desired depths. This paper discusses the novel approach used to successfully spot and squeeze a LCM pill and cement plug in a HP/HT situation with a narrow pressure margin using an MPD system, which resulted in reduced mud losses, increased success of the LCM pill and cement plug setting, and reduced time required to fully manipulate the EMW on bottom.
The adequate cementation of an expandable tubular can be challenging but is essential for long-term casing integrity. Such cementing jobs are especially crucial under high-pressure/high-temperature (HP/ HT) conditions for many reasons, including but not limited to rigorous HP/HT laboratory testing schedules, selection of proper cement volume and fluid density, etc. A failed cement job in expandable casing does not allow for a remedial cement job and thus can jeopardize the entire well.An operator in Egypt required running and cementing a 9 5/8-in. expandable casing at 5625 m inside a 12.25-in. open hole (OH). The length of the expandable tubular was approximately 850 m, which corresponds to an expansion time of 8 1/2 to 9 1/2 hr. Accordingly, an adequate cement slurry would require a minimum of 13 to 14 hr of thickening time, with a very long zero gel time. As no centralizers were run, homogenous slurry distribution was also one of the main concerns for this job. Another potential issue for the slurry design was the presence of a possible gas zone in this section, which could cause flow and create a permanent channel in unset cement during casing expansion.An 18.5-lbm/gal anti-gas-migration slurry was designed and tested under 16,300-psi bottomhole pressure (BHP) and at 315°F bottomhole static temperature (BHST) to meet the job requirements. Various numerical simulators were run to calculate hydraulics and displacement efficiency to achieve the zonal isolation objectives and optimum cement sheath around the casing. A specially designed casing shoe was also used to accommodate a foam ball, which acted as a bottom plug to help minimize cement slurry contamination while pumping.This paper describes the challenges, solutions, and lessons learned during the design and execution phase while cementing the deepest expandable casing in Mediterranean offshore Egypt.
The operation described in this paper is related with an ultra-deep-water exploration well drilled in the Mexican waters of the Gulf of Mexico and the first drilled by the operator in the area. From the onset of planning the base case was to integrate a Managed Pressure system into the drilling program to mitigate prognosed pore pressure uncertainty, pressure ramp increase, and narrow PP/FG window operations including; drilling, tripping, running casing. Although Managed Pressure cementing was not originally in the scope of work, it was required due to the tight drilling window and successfully executed. A narrow pressure window (1.07 sg – 1.13 sg) encountered in the 12-1/4" × 16-1/2" section resulted in the managed pressure system being required to run and cement the 13-3/8" casing string while managing the annular pressure profile. Placement of the cement was critical to isolate a permeable zone below the previous casing shoe and reduce the chances for aremedial cement work. The main objective for using the MP system during cementing was to ensure the EMW at both TD and the previous casing shoe did not fall below the set limits throughout the job. While the secondary objective was to reduce and/or eliminate losses. With the total depth being 4,151m, water depth of 3301m, surface mud weight 1.03 sg with down hole equivalent mud weight of 1.047sg due to compressibility and temperature. The main objective for using the MPD system during cementing was to ensure the EMW at both TD and the previous casing shoe did not fall below the set limits throughout the job. While the secondary objective was to reduce and/or eliminate losses. With the operator depth being 4,151m (13,619 ft), water depth of 3,276m (10,748 ft), surface mud weight 1.03 SG (8.58 ppg) with down hole equivalent mud weight of 1.047SG due to compressibility and temperature Planning for the job required input and collaboration from various personnel from the operator as well as third party services working together to run simulations, calculations, and analyses to create a detailed program. With the casing on bottom, the execution phase of the operation again required significant planning and organization on the rig to successfully implement and execute the step by step instructions for the job. MP cementing was executed as planned, with no losses measured, following the displacement sequence and surface backpressure step down until observing the plugs bump. Zonal isolation was achieved, confirmed through an adequate pressure test of the casing, as well as, a sufficient FIT to drill the subsequent section. The focus of this paper is on the planning and execution of an ultra-deep water managed pressure cement job drilled in the Mexico side of the Gulf of Mexico. Learnings and observations were collected during the planning and execution phases. These learnings may assist other managed pressure operations to successfully implement and execute MP cement on ultra-deep water operations in the future.
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