A major challenge that is being occasionally faced during the well construction phase is to cement the formations holding narrow pressure margins between the pore and fracture gradients without inducing losses. Losses can commonly occur in these cases, compromising the integrity of the cement barrier. Designed slurry densities generally lead to high equivalent circulating density (ECD) levels during the cementing operations. This condition, combined with mud weights conventionally designed to be above pore pressure, usually results in downhole pressures which approach or exceed the fracture limit. Commonly, operators implement strategies to mitigate losses during the cementing phase, however, in most cases the losses are unavoidable using a conventional cementing approach. Managed pressure cementing (MPC) is an important technique for primary cementing operations in wells with such narrow pressure margins. This paper presents the design considerations, methodology and results of a land well where high-pressure influx was encountered while drilling an 8-3/8-in hole across a water-bearing formation. Narrow pressure gradient persuaded to utilize managed pressure drilling (MPD) to continue the drilling. The well was drilled to the target depth using 138-lbm/ft3 oil-based drilling fluid while maintaining the ECD from 146.5 to 149.5 lbm/ft3. Careful attention was paid to estimate the bottom hole circulating temperature, using the temperature modeling simulator. A 150-lbm/ft3 slurry was designed to keep the ECD intact. The slurry was batch-mixed to ensure the homogeneity of the final slurry mixture. A special spacer system was designed to reduce the losses while cementing. Additionally, the spacer was loaded with optimum amounts of surfactant package to serve as an aid to remove the mud and to water-wet the formation and pipe for better cement bonding. The centralizers placement plan was optimized, and additionally the liner was rotated during the cement job to achieve the required displacement efficiency yet staying within the torque and drag (T&D) limits. The cement treatment was performed as designed and met all zonal isolation objectives. The managed pressure cementing (MPC) system provides safe isolation of problematic zones in cost effective manner even in challenging narrow pressure window scenarios. The system provides precise control of the pressure and flow during and after the cement job. Constant pressure can be achieved at weak zones, preventing losses to the formation. This case study presents an overview of the engineering process used to plan and design the MPC operations and the results obtained. This paper reviews a successful MPC operation and presents findings and lessons learnt. After the successful results on this job and subsequent operations, this technique is now being adopted to optimize cementing, where losses during cementing operations in the past had forced to modify the well construction.
A good primary cementing job governs in a great part the producing performance of a well. Successful zonal isolation, which is the main objective of any cementing job, primarily depends on the right cement design. The resin-based cement system, which is a relatively new technology within the oil industry has the potential to replace conventional cement in critical primary cementing applications. This paper describes the lab-testing and field deployment of the resin-based cement systems. The resin-based cement systems were deployed in those well sections where a potential high-pressure influx was expected. The resin-based cement system, which was placed as a tail slurry was designed to have better mechanical properties as compared to the conventional cement systems. The paper describes the process used to get the right resin-based cement slurry design and how its application was important to the success of the cementing jobs. The cement job was executed successfully and met all the zonal-isolation objectives. The resin-based cement's increased shear bond strength and better mechanical properties were deemed to be instrumental in providing a reliable barrier that would thwart any future issues arising due to sustained casing pressure (SCP). This paper describes the required lab-testing, lab-evaluation, and the successful field deployment of the resin-based cement systems.
This paper addresses some challenges concerning cement slurry designs, focused on thickening time, requiring careful engineering practices, and proper cementing operational considerations. It presents a series of thickening time test studies compared to "conventional testing practice" versus "field simulated testing" to illustrate the differences between results. Many aspects of oilfield cementing are sufficiently important to warrant study. One area that requires attention is the procedures used to design the cement slurry in the well. The batch-mix and static conditions influence the physical attributes of oilfield cement, including thickening time. Conventional laboratory testing invariably follows the API procedure for thickening time. Although this might be adequate in most cases, it may only precisely predict field behavior (at actual conditions) in some cases. Conventional thickening time tests may not necessarily indicate the true responsiveness of cement slurry. Traditional thickening time waiting periods do not relate directly to how long a slurry can remain static and still be moveable after an inadvertent or intentional shutdown during placement. Mixing, pumping, and displacing the cement (including any shutdown) affect the hydration and thickening behavior. Therefore, it is imperative to understand the relative contributions from each part of the process toward the thickening time to help prevent failures. These contributions might not significantly impact slurry properties but should be quantified and understood. The reliable prediction of cement thickening time can be vital to the success of oilfield cementing operations. Because cement placement techniques have become complex, delivering slurry with accurate thickening time can be crucial to the job's success. This paper presents a modified testing protocol to evaluate the effects of batch-mixing and static-period on cement slurry's thickening time to minimize the incidents related to the premature setting of cement slurry.
A significant challenge occasionally faced during the well's lifecycle is the pressure buildup between the cemented annuli, also known as sustained casing pressure (SCP). The presence of SCP indicates a path of flow of formation fluids to the surface. Compromise of cement sheath integrity is one of the primary reasons for such a pressure buildup. This challenge prompted the development of such an isolation material that should enhance the mechanical properties of cement to prevent the SCP. In parallel, another isolation material was required to remediate the wells suffering from SCP. After some research, a specialized resin system was developed that could be deployed to prevent and eliminate the SCP in the situations mentioned above. This paper presents the lab testing and application of the innovative resin system. This system can be used as a standalone product and blended with cement, depending upon the nature of the application and zonal isolation objective. While using the resin as a standalone product, its solids-free nature and low yield point enable it to flow freely into micron-sized leaks or channels. Pure resin is mainly used for remedial applications. When the resin is added to the cement during primary cementing operations, it forms a dense and highly cross-linked matrix with improved mechanical properties that helps to provide a dependable barrier to maintain long-term zonal isolation. Engineered solutions ultimately deliver the optimal asset value of the reservoir. During the last few decades, several laboratory investigations and field studies have been conducted to find answers to the problem of SCP, which appears after primary or remedial cement jobs. Almost all these studies unanimously conclude that conventional cement does not always endure the mechanical stresses imposed by the wellbore conditions, and it often falls short in providing permanent isolation beyond the well's production life. This paper illustrates two case studies to validate this. The first case study is related to primary cementing, where the resin-cement blend was successfully utilized to prevent the expected high-pressure influx across a water-bearing formation. The resin-cement system was designed to be placed as a tail slurry to provide enhanced mechanical properties compared to a conventional slurry. The combined mixture of resin and cement slurry provided the desired product's necessary properties. The cement treatment was performed as designed and met all zonal isolation objectives. The second case study relates to remedial cementing, where the resin system was utilized to remediate the three annuli on an offshore oil well. Reliable and effective annular barriers are critical to well management for safety and performance. Conventional Cement slurries have been the industry's typical means of creating these barriers. However, the cement alone is inadequate to meet the industry needs; hence, combined solutions deliver improved well integrity.
Maintaining zonal isolation is vital to well economics and productive life. Well integrity is becoming more challenging with the drilling of deeper, highly deviated, and horizontal wells worldwide. Oil companies are focused on to enhance the well productivity during drilling long horizontal wells in a harsh environment by achieving maximum accessible reservoir contact. These wellbore geometries incorporate additional challenges to design and deliver a dependable barrier. In this paper, a case study about cementing the longest liner across Khuff-C reservoir has been presented discussing the main challenges, engineering considerations, field implementation, results, and conclusions. The well was drilled horizontally across Khuff-C carbonates using oil-based drilling fluid. The 5-7/8-in open hole section was planned to be cemented in single stage, utilizing 8370 ft of a 4-1/2-in liner. Careful attention was paid to estimate the bottom hole circulating temperature, using the temperature modeling simulator. A 118-lbm/ft3 slurry was designed to keep the equivalent circulation density intact. Gas migration control additives were included in the slurry design to lower the slurry's transition time, in order to reduce the chances of gas migration through the cement slurry. The slurry was batch-mixed to ensure the homogeneity of the final slurry mixture. A reactive spacer was designed to improve the cement bonding from long term zonal isolation perspective. Additionally, the spacer was loaded with optimum amounts of surfactant package to serve as an aid to remove the mud and to water-wet the formation and pipe for better cement bonding. Centralizers placement plan was optimized to allow around 63% average standoff around the pipe, staying within the torque and drag (T&D) limits. The cement treatment was performed as designed and met all zonal isolation objectives. The process of cementing horizontal liners comes with unique procedures. There are several challenges associated with carrying out wellbore zonal isolation for primary cementing of horizontal liners, therefore, a unique level of attention is required during the design and execution stages. The slurry design requires careful formulation to achieve the desired specifications while ensuring its easy deployment and placement in the liner annulus. By planning in advance and following proven techniques, many of the problems associated with the running and cementing of deep and long horizontal liners can be alleviated. This paper highlights the necessary laboratory testing, field execution procedures, and treatment evaluation methods so that this technique can be a key resource for such operations in the future. The paper describes the process used to design the liner cement job and how its application was significant to the success of the job.
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