Good cement bond at the casing-cement and cement-formation interfaces is essential for effective zonal isolation. Poor bonding can lead to underground fluids and gases to enter the annulus and create sustained casing pressure (SCP), jeopardising the working envelope of the well and limiting its production. One of the causes of a poor cement-formation bonding is attributed to a cement shrinkage. Cement systems that expand after setting can help improve primary cementing job results by sealing microannulus. The enhanced bonding is the result of enhanced shear bond and adhesion of the cement against the pipe and formation. Cement expansion is achieved by addition of the expanding additives into cement system. The mechanism of expansion is based on set cement volume growth over initial volume post setting. This is driven either by gas bubbles created during chemical reaction or by crystal growth within set cement matrix. Careful optimization of the cement slurry designs with an addition of the expansion additives to conventional and complex blend systems allowed greatly improving the cement bond evaluation log results without compromising other mechanical properties of cement. This paper outlines the successful application of expanding cement to seal different sizes of wellbore; the study evaluates the effect of the expansion by comparing the cement evaluation log from numerous cementing jobs. Examples included in the comparison are cemented production strings (casings and liners) with different types of cement systems used across 9 5/8-in. production casings and 7-in. and 4 1/2-in. production liners.
Long-term well integrity and zonal isolation are the ultimate objectives for cementing in the well construction process. Effective mud removal plays an essential role in obtaining competent zonal isolation and hence should not be overlooked and underestimated. The negative consequences of poor mud removal can lead to microannulus, channeling, or gas migration, which might require costly time-consuming remediation. The conventional approach of optimizing spacers based on chemical interactions with the mud layer does not always yield desired results and, thus, demanding further improvement. In this paper we discuss the approach taken to boost the mud removal efficiency by implementing an innovative engineered scrubbing spacer containing fibers in a challenging environment, resulting in notable improvement in long-term cement sheath integrity. The engineered scrubbing fibers were thoroughly tested in the laboratory to ensure spacer stability and efficiency. The new spacer with an additional scrubbing capability was introduced to one of the major operators on the Caspian shelf and after successful implementation, it has now been used on more than 20 cementing operations. Scrubbing fibers concentration was optimized through thorough laboratory testing covering flowability, dispersibility, and mud removal efficiency; later, it was applied on most of the cement operations, including 4½-in. liners characterized by a very narrow annular gap across the hanger sections. Cement evaluation log results from those cementing operations demonstrated an improvement in mud removal efficiency, suggesting no issues associated with microannulus, channeling, or gas migration, thus confirming the effectiveness of the newly implemented engineered scrubbing spacer. The typical challenges associated with meeting the zonal isolation requirement on one of the offshore fields of the Caspian shelf, and the success of the approach taken to overcome those challenges by implementing the new engineered scrubbing spacer are discussed. The comparison of cement bond evaluation log results of the jobs where conventional spacer systems were used vs. those where the spacer with scrubbing capability was used are also presented, demonstrating the clear difference and improvement.
Lost circulation in depleted sands during a primary cementing job is a serious problem in Turkmenistan. The uncertainty in formation pressure across these sands increases the risk of losses during drilling and cementing, which results in remedial operations and nonproductive time. The need to find a fit-for-purpose lost circulation solution becomes even more critical in an environment with narrow pore pressure-to-fracture gradient, where each cement job with losses compromises the downhole well integrity. An engineered lost circulation solution using innovative materials in the cement slurry was carefully assessed and qualified in the laboratory for each case to optimize the formulation. The lost circulation control treatment combines specialized engineered fibers with sized bridging materials to increase the effectiveness of treatment, formulated and added to the cement slurries based on the slurry solids volume fraction (SVF). Cement slurries with low SVF were treated with higher concentrations of the product and slurries with high SVF used lower concentrations. More than 50 jobs were performed with cement slurries designed at various densities and SVF up to 58% and using this advanced lost circulation material (LCM) to mitigate losses during cementing. Field experience showed positive results, where the differential pressure up to 2,800 psi was expected during cementing operation. A local database, generated based on the design and development work performed, enabled improved decision-making for selection and LCM application requirements for subsequent jobs and development of a lost circulation strategy. The mitigation plan was put in place against losses in critical sections and depleted sand formations in Turkmenistan. It assisted in meeting the cement coverage requirements on numerous occasions, improving overall the integrity of the wells and thus, was considered to be a success. This paper provides insight of this advanced LCM, its application in cement slurries, the logic behind the developed loss circulation strategy, and the high success rate of its implementation. Three case histories are presented to demonstrate the strategy and results.
Complete and durable zonal isolation is the foremost goal of the cement job. In the deep and high-pressure environment, obtaining such goal is particularly critical, but also challenging due to the additional factors associated with the high drilling fluid densities that limit mud removal efficiency, narrow margins between fracture and pore pressures that cause loss circulation and differential sticking, and cement sheath exposure to downhole stresses during construction and production phases that compromises its integrity. Careful planning is required to ensure all risks are captured and mitigated during the design stage, taking into consideration not only the construction phase, but also post-placement downhole conditions changes caused by temperature, pressure fluctuations, and mechanical shocks during perforation and stimulation operations. Data analysis of the offset wells located in the eastern section of the Caspian shelf showed that conventional cement systems and previously applied cement job designs had limited success in addressing those challenging complex requirements. Thus, a new approach was required. This approach was used in 20 wells in the field with excellent results. Two wells were used to demonstrate the improvements obtained in zonal isolation behind production liners upon implementation of new engineered methodology. The innovative complex approach involved not only the revision of the previously used cement and spacer fluid designs, but also required revisiting and evaluating every aspect of cementing practices to achieve the desired results. Fiber-based spacer technology was introduced to enhance mud displacement and an engineered flexible and expanding cement system to achieve and maintain well integrity. Numerical analysis modelling was used to simulate the stresses that the cement sheath will experience over the well's life and calculate the minimum required mechanical properties of cement to be able to withstand these stresses. The set cement mechanical properties were then customized using a proprietary trimodal particle-size distribution technology to accommodate the expected downhole stresses. Hydraulic isolation improvement was achieved and confirmed by downhole logs.
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.
customersupport@researchsolutions.com
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.