Offshore cementing poses many challenges across the world as drilling oper ations move towards deep-water and ultra -deep-water. As a new initiative of continuous improvement, a deep-water cementing peer review process was started early 2011. To this date, th is team has reviewed more than 12 00 deep-water cementing jobs in more than 30 countries worldwide.
Well barriers are an important factor during the life of a well. As cementing is involved in many of those well barriers, there is considerable focus in the oil field on the design, execution, and validation of the cement as a well barrier. It is important that the cement job design begins at the same time as the basic well design, especially in deepwater operations. Decisions made early in the well design can have a tremendous effect on the cement job execution. Early in the well design, the cement job objectives are set, and through simulations, the cement job placement, slurry design, and, in some cases, well design, are optimized to overcome any identified challenges and minimize risks during cement placement. Cement equipment is becoming increasingly more sophisticated and cement job designs more critical; additional attention needs to be placed on the cementing job preparation on location prior to the actual cement job. By using the latest advances in communications, it is easier for the offshore cementing specialists to stay in contact with the shore-based staff; not only with the design engineer, but also the maintenance manager or operation support staff. Improved monitoring and automation during the job execution enhances the process control. Advances in real-time capabilities enable the onshore experts to monitor the offshore operations and provide advice during the execution of the cement job itself. The final step of a cement job is the evaluation phase. A cement job evaluation is more than just a pressure leak-off test or running a cement evaluation log. The evaluation procedure of a cement job ties together all the parameters of the job, including the job objectives, drilling parameters, job execution, and post-job test results. Looking at one parameter only will often not provide a complete analysis and evaluation. Because cementing provides critically needed well barriers, it becomes a very important aspect in well integrity management during the life of the well.
When wells have come to the end of their lives, it becomes necessary to plug and abandon them and return the seabed to its original condition. In the UK sector of the Central North Sea (CNS), an operator managed 6 fields comprising a total of 30 subsea wells in 7 clusters, required to be plugged and abandoned. These fields are among many that are coming to the decommission stage, with the over-riding requirement from the UK government being that of no leakage of hydrocarbons to the environment or between separate permeable geological zones. The operator standards required the placement of two cement barriers of a minimum of 100-ft each for zonal isolation. The preferred route was to find the annular portion of the barrier by interpretation of ultrasonic imaging tool in combination with the cement bond (CBL) wireline logs used for cement evaluation service, then to set a 500-ft plug inside the casing opposite that zone. In the case that no barrier quality cement was identified in the annulus, section milling of the casing was undertaken to expose 100-ft of formation over which cement was placed. A number of challenges were faced to design the cement slurry prior to the logging results. The setting depth may only have been confirmed a few hours before the cement job. To cover the possible setting depths and temperature ranges, laboratory testing consisted of performing temperature sensitivity tests on base slurries designed with a wide temperature range retarder, but still optimizing the system to minimize wait on cement (WOC) time. A specialized high magnesium resistance (HMR) cement system that provides long-term zonal isolation and protects against cement degradation was identified as being best solution. The HMR cement is a blend of blast furnace cement and fly-ash, which reduces the cement permeability and limits the effect of alkaline brine corrosion. Optimal plug placement was also required for long-term isolation. Specialized plug placement software that accounts for in-pipe and annular contamination, and fluid interface matching during pulling out of the plug was utilised. The slurry design and emplacement best practices will be summarized in this paper. These subsea wells have been successfully plugged and abandoned by laying temporary, primary, secondary and environmental cement barriers by several different methods: inside casing, across section-milled windows, multi-annular, through scaled production tubing and through coiled tubing according to each particular well's condition. Success ratio was exceptionally high with all the long term barrier themselves being flawlessly placed and verified without any repeat job being required.
The drive to recover hydrocarbons from difficult to reach reservoirs and optimize production is taking center stage in the Exploration and Production industry. Complex wells are being planned which push the existing technology to limits. The success and longevity of such wells depends upon providing good zonal isolation and sound well integrity for the complete life cycle of the projects. Cementing the wells in a narrow pressure regime without losses and overcoming challenges for optimum zonal isolation presents a unique test to the industry. The Extended-Reach-Drilling (ERD) wells drilled in the Caspian Sea prior to 2011 have historically seen inadequate zonal isolation in the long intermediate section due to channeling of cement during placement; consistent with directional profile of the wells. Remedial cementing was needed in some cases before the next phase of the well. As the acceptance criteria for well integrity becomes more stringent, the onus lies on achieving zonal isolation during primary cementing through a combination of optimized cement placement and mechanical barriers. This paper presents the investigative approach towards earlier jobs and the recommended suggestions which led to improvement that was confirmed by cement evaluation logs. The authors present case histories with lessons learnt during the course of implementing the new approach to cementing design and the success of achieving adequate cement coverage across potential flow zones.
The cementation of tophole sections in deepwater operations is very challenging due to the conditions in which those jobs take place. Tophole sections in deepwater operations often have a narrow margin between the pore and fracture gradients and shallow hazards, such as gas or water flow, associated with them. The low temperature found at seabed results in high fluid viscosities, slow gel strength development, and delayed early compressive strength development of the slurry. To optimize the low-temperature slurries currently used, a novel low-temperature dispersant was developed that enables designing the slurry to meet the required properties. The new dispersant has several main benefits in slurry design and properties. The dispersant enables the slurry to develop faster gel strength and has no retarding effect compared to conventional dispersants. The new dispersant will provide a flat rheology over time, allowing better control of the circulating pressures during placement. Laboratory tests show less gelation and an improvement in static gel strength development as compared to current dispersants. The dispersant also provides better rheological properties, often at lower concentrations, thereby facilitating a simplified slurry design. Following laboratory testing, the low-temperature dispersant was introduced in Gulf of Mexico operations with very good results. Operationally, the dispersant is easy to handle. It is compatible with all typical cementing additives and can be used with conventional cementing equipment and liquid additive systems. The low-temperature dispersant has been used in various types of deepwater slurries such as lightweight, conventional, and foamed slurry system, using drill water or seawater as the base fluid, often requiring less concentration and improving key slurry properties to achieve successful cementing operations in challenging low-temperature conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.