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Fluid-Loss-Control Additives (FLAs) are used to maintain a consistent fluid volume within a cement slurry to ensure that the slurry performance properties remain within an acceptable range. The variability of each of these parameters (slurry performance properties) is dependent upon the water content of the slurry. If the water content is less than intended, the opposite will normally occur. The magnitude of change is directly related to the amount of fluid lost from the slurry. Because predictability of performance is typically the most important parameter in a cementing operation, considerable attention has been paid to mechanical control of slurry density during the mixing of the slurry to assure reproducibility.
Spacers and flushes are effective displacement aids, because they separate incompatible fluids such as cement and drilling fluid. A spacer is a fluid used to separate drilling fluids and cementing slurries. A spacer can be designed for use with either water-based or oil-based drilling fluids, and prepares both pipe and formation for the cementing operation. Spacers are typically densified with insoluble-solid weighting agents. For example, a spacer is a volume of fluid injected ahead of the cement, but behind the drilling fluid.
Elhassan, Azza (ADNOC Offshore) | Hamidzada, Ahmedagha Eldaniz (ADNOC Offshore) | Takahiro, Toki (ADNOC Offshore) | Motohiro, Toma (ADNOC Offshore) | Orfali, Mohd Waheed (Schlumberger) | Phyoe, Thein Zaw (Schlumberger) | Salazar, Jose (Schlumberger) | Alaleeli, Ahmed Rashed (ADNOC Offshore)
Abstract Good cementing practices are required to achieve effective zonal isolation and provide long-term well integrity for uninterrupted safe production and subsequent abandonment. Zonal isolation can be attained by paying close attention to optimizing the drilling parameters, hole cleaning, fluid design, cement placement, and monitoring. In challenging extended reach wells in the UAE, different methods were employed to deliver progressive improvement in zonal isolation. Cementing the intermediate and production sections in the UAE field is challenging because of the highly deviated, long, open holes; use of nonaqueous fluids (NAFs); and the persistent problem of lost circulation. Compounding the problem are the multiple potential reservoirs; the pressure testing of the casing at high pressures after cement is set; and the change in downhole pressures and temperatures during production phases, which results in additional stresses. Hence, the mechanical properties for cement systems must be customized to withstand the downhole stresses. The requirement of spacer fluids with nonaqueous compatible properties adds complexity. Lessons learned from prior operations were applied sequentially to produce fit-for-purpose solutions in the UAE field. Standard cement practices were taken as a starting point, and subsequent changes were introduced to overcome specific challenges. These challenges included deeper 12 ¼-in. sections, which made it difficult to manage equivalent circulating densities (ECDs), and a stricter requirement of zonal isolation across sublayers in addition to required top of cement at surface. To satisfy these requirements, several measures were taken gradually: applying engineered trimodal blend systems to remain under ECD limits; pumping a lower-viscosity fluid ahead of the spacer; using NAF-compatible spacers for effective mud removal; employing flexible cement systems to withstand downhole stresses; and modeling the cement job with an advanced cement placement software to simulate displacement rates, bottomhole circulating temperatures, centralizer placement, mud removal and comply with a zero discharge policy that restricts the extra slurry volume to reach surface. To enhance conventional chemistry-based mud cleaning, an engineered scrubbing additive was included in the spacers with a microemulsion-based surfactant. The results of cement jobs were analyzed by playback in advanced evaluation software to verify the efficiency of the applied solutions. This continuous improvement response to changes in well design has resulted in a significant positive change in cement bond logs; a flexural attenuation measurement tool has been used to evaluate the lightweight slurry quality behind the casing, which has helped in enhancing the confidence level in well integrity in these challenging wells. The results highlight the benefit of developing engineering solutions that can be adapted to respond to radical changes in conditions or requirements.
Abstract An operator in the Norwegian continental shelf (NCS) required sufficient zonal isolation around a casing shoe to accommodate subsequent targeted injection operations. Located in the Ivar Aasen field, and classified as critical, the well had a 9 ⅝-in. casing shoe set in the depleted Skagerrak 2 reservoir. The lost circulation risk was high during cementing because the Hugin formation, located above the reservoir, contained 40 m [~ 131.2 ft] of highly porous and permeable sandstone. During previous operations in the field, lost circulation was observed before and during the casing running and cementing operations. After unsuccessful attempts to cure the losses with various lost circulation materials, a new solution was proposed to target the specific lost circulation problem by combining two types of reinforced composite mat pill (RCMP) technology. Specifically, the first type of RCMP technology was engineered for use in the viscous preflush spacer, and the second was applied to the cement slurry itself. Working in synergy, the RCMP systems mitigated the risk of incomplete zonal isolation. With no losses observed upon reaching total depth (TD) for the 12 ¼-in. hole, the 9 ⅝-in. casing was run with a reamer shoe and 15 rigid centralizers. Between 2700 and 2728 m [~ 8,858 and 8,950 ft] measured depth (MD), the rig observed constant drag of 30 to 40 MT whilst working the casing down, and circulation was completely lost before partial returns were eventually observed. The rig continued to work the string down to the planned landing depth at 3897 m [~ 12,785 ft] MD. Precementing circulation ensued with staged pump rates increasing at 100-L/min [~ 0.6-bbl/min] intervals up to 1400 L/min [~ 8.8 bbl/min], which induced losses at a rate of 6.5 m/hour [~ 40 bbl/hour]). Subsequently, the flow rate was reduced to 1300 L/min [~ 8.1 bbl/min], and the annular volume was circulated 2.6 times with full returns. Attempts to reduce equivalent circulating density (ECD) ahead of the cementing operation were implemented at 1300 L/min [~ 8.1 bbl/min] using a low-density, low-rheology oil-based drilling fluid pill. However, a significant loss rate of 18.0 m/hour [~113 bbl/hour] was observed. The flow rate was reduced to 950 L/min [~ 6.0 bbl/min], and partial circulation was recovered. After the spacer and cement had reached the annulus, full returns were immediately observed and continued until the top plug was successfully bumped. Acoustic logging determined that the operation had achieved the primary job objective of establishing the required length of hydraulically isolating cement in the annulus. Lost circulation is a costly problem that can be difficult to solve, even with the wide variety of technologies available (Vidick, B., Yearwood, J. A., and Perthuis, H. 1988. How To Solve Lost Circulation Problems. SPE-17811-MS). This case study demonstrates a successful solution. The operator will be able to incorporate lessons learned and best practices into future operations, and these lessons and practices will be useful to other operators with similar circumstances.
Drilling in the Appalachian Basin in Pennsylvania has evolved since its inception. Operators have shifted their focus from mere wellbore delivery to delivering wells in the shortest amount of time to reduce risks and costs and drive efficiency. The complete paper presents a case study in which offline cementing improved operational efficiency by reducing drilling times and provided significant cost savings. For decades, the focus during drilling operations has been on achieving faster rate of penetration (ROP) and drilling time to reduce well costs. Many areas with possible efficiency gains have yet to be explored within the cycle.
Abstract Lightweight or, alternatively, foamed cement slurries for surface casing operations are often necessary during special situations (i.e., low fracture gradients) for the required zone to be isolated. The foamed cement technique reduces the heat of hydration (HoH) of the slurries, reducing potential risk of shallow hydrate flow and losses because of its reduced hydrostatic pressure. This alternative for lightweight slurries has been used globally with successful results. The foamed cement operation was designed and executed considering specific aspects and details, including a combination of factors, such as expected low fracture gradient, mechanical property requirements, logistic constraints in terms of the difficulty managing two types of cement (large tonnage of Blend and G cement vs. rig capacity and safety volume requirements), long sections to be cemented, and the uncertainty of the cement volume excess necessary to achieve return in the seabed. Because this was the first cement operation for the operator at this remote deepwater field, the planning phase required extensive discussions. Rig silo capacities and deck space on the rig were limited, which constrained the possibility of considering backup for all bulks, chemicals, and equipment. Execution of the cement operation was as per the approved program without deviation. The cement volume returned at seabed indicated an openhole diameter with ±100% washout. A tracer additive (fluorescent dye) mixed with the spacer was successfully used to indicate fluid return at seabed (2120-m water depth). As part of the best practices to execute this operation, a liquid additive system was used to provide pump volume flexibility. Foamed cement laboratory tests were performed, considering field samples and the foaming agent (surfactant) were injected straight at the suction of the pump. As expected, the foamed cement operation is an extremely efficient and effective technique to achieve zonal isolation in a surface casing string of a deepwater well. Currently, this procedure is frequently used in fields globally. A case study of the first foamed cement application for surface casing in French Guiana is discussed.
Barros, Adelson (Adnoc Offshore) | Alaleeli, Ahmed Rashed (Adnoc Offshore) | Hamidzada, Ahmedagha (Adnoc Offshore) | El Hassan, Azza (Adnoc Offshore) | Melo, Alexandre (Adnoc Offshore) | Orfali, Mohd Waheed (Schlumberger) | Phyoe, Thein Zaw (Schlumberger) | Salazar, Jose (Schlumberger) | Kapoor, Saurabh (Schlumberger) | Kondo, Kazuyoshi (Schlumberger)
Abstract Lost circulation (LC) is an expensive and time-consuming problem. It's desirable to minimize losses before cement job to ensure good cement coverage and maximize well integrity. But quite commonly, wells experience induced losses just before cementing, during casing running and circulation. In such a scenario, the options to control losses have been few, with limited results. The paper demonstrates a viable solution that can be successfully applied to reduce or eliminate such induced losses during the cement job. To effectively solve lost circulation with the correct technique, it is necessary to know the severity of the losses and the type of lost circulation zone. In UAE fields, the loss rates range from 150 bbl/h to more than 700 bbl/h in the 17½- and 12¼-in open hole sections. During cementing operations, lost circulation causes reduced top of cement, poor zonal isolation, and risks to drill ahead. To solve this problem, a composite fiber-based spacer system based on a novel four-step methodology was designed using advanced software. Before a field trial, rigorous lab-scale and yard-scale testing was conducted to optimize the application. Initially, no losses were witnessed while drilling the 12¼-in section. But during casing running and circulation, severe losses of 150 bbl/hr were induced. To counter these losses, the specially designed fiber-based lost circulation spacer system was pumped ahead of the cement slurry using standard surface equipment. At the beginning of the displacement—while cement and spacer were still in the casing string—the loss rate increased to 700 bbl/hr (total losses). This high loss rate in the crucial intermediate section would normally have resulted in costly remedial operations, loss of mud and cement, and expensive rig time. It was observed that the loss rate remained at 700 bbl/hr until the lost circulation spacer arrived at the loss zone. Subsequently, the loss rate kept on declining finally resulting in full returns during remaining displacement. The designed excess of cement was received as returns, thereby ensuring the desired top of cement at surface. This proved that the fiber-based spacer was effective in curing the losses. An advanced cement bond log showed complete cement coverage over the entire section. This further proved the spacer's effectiveness in achieving all well integrity objectives. The successful application of the engineered fiber-based lost circulation control spacer during primary cementing demonstrates a reliable solution to the challenge posed by losses induced immediately before a cement job. The system is easy to deliver and design and can plug the fracture network in the formation during the cement job. Globally, this engineered composite fiber-blend spacer has proved to improve performance during cementing operations by healing losses to maximize well integrity.
Abstract Over the ages of the well drilling history, primary and remedial cementing remains one of the most challenging activities with direct effect on the well life and well integrity status. This paper is based on the actual lessons learned and latest best practices in zonal isolation of Company fields developed according to business requirements during drilling and workover operations. It covers the aspects of primary cementing in two main types of casing design, and describes major challenges associated. Authors tried to define a clear criteria on what can be considered as the minimum acceptable zonal isolation, what are the issues associated with its evaluation, what needs to be done in order to meet those criteria. Additionally, there is an analysis done on the direct impact of the cementing job on the well life. Particularly, the focus is made on well integrity related issues and remedial solutions to cure them based on successful case histories. The paper answers on many questions related to the consequences of the poor cement isolation (up to well control incidents), as an actual lessons learned collected over the 60 years of operation. The impact of the casing design on the well integrity status is analyzed based on the results of wellhead pressure monitoring of around 4,000 wells. It includes revision and analysis of cement evaluation logs of wells with behind casing communication (sustained pressure in "B" annulus) along with the challenges associated with the diagnostic investigations of the leak source. Various cementing remedial techniques are described with pros and cons analysis and actual case histories including results of post-job wellhead pressure monitoring. The subject of swelling phenomena of soft shale formations and its effect on acoustic based tools for cement bond evaluation is touched as well. Finally, the paper contains interesting results of the recent corrosion logging campaign that reveals a correlation between casing condition and casing design.
Abstract Brazilian pre-salt reservoir is mainly composed of carbonate rocks which are naturally fractured and where severe loss of circulation has often occurred. Loss of circulation during drilling or cementing is a serious issue that usually leads to nonproductive time, increase of well construction costs, and impairment of cement sheath quality, which may lead to deficient zonal isolation in the future and compromise well integrity in long term. Data analysis from studies developed by operators around the world show that approximately 12% of all nonproductive time accumulated in a certain period is due to loss of circulation occurrence. In Brazil, an analysis performed by an operator in 2014, pointed that more than 100 days were lost in pre-salt wells in operations to cure or minimize loss of circulation. This same analysis concluded that more than 170 000 barrels of drilling fluid were consumed due to this scenario of losses. It is also important to emphasize the cases where a remedial cementing job was necessary due to failure of zonal isolation achievement through primary cementing, resulting in additional costs and nonproductive time. Said that, it was important to develop and implement a new technology capable of mitigate losses during cementing operations and minimize the risk of a remedial cementing need. Since January 2017, Fibrous Loss Circulation Material has been used in the cementing jobs for production casings in the pre-salt wells successfully. Up to now, six wells were cemented using this technology; no remedial job necessary and the cementing logging evaluation showed excellent results.
Abstract Drilling in the Appalachian basin in Pennsylvania has evolved since its inception. Operators have shifted their focus from mere wellbore delivery to delivering wells in the shortest amount of time to reduce risks and costs, as well as drive efficiency. This paper presents a case study in which offline cementing helped improve operation efficiency by reducing drilling times and provided significant cost savings. Offline cementing is not a new concept. In Q4 2015, an operator drilling in the Eagle Ford shale began the movement of their program toward offline cementing of both the surface and production casings. The operator determined that reducing flat time was crucial to create a cost savings (Hsieh 2018). When another operator began their 2018 drilling program in northeastern Pennsylvania, improving efficiencies was discussed with the service company. After quantifying the experience obtained during a previous project, the service company proposed offline cementing because of the economic benefits it could provide. The service company was able to cement both the surface and intermediate casing strings offline while the operator skidded to the next well to begin rigging up. All surface casings were drilled and cemented offline and the rig skidded back to drill for the intermediate casings, which were also cemented offline. Approximately 15 hours was saved by skidding between surface strings, and another 16 hours was saved between intermediate casings. This paper discusses the successful use of offline cementing during drilling operations in northeastern Pennsylvania. The flat time reduction achieved during this drilling program can be quantified into a cost savings of approximately USD 80,000 per well.