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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.
In 2019, a well operator in North Sea UK executed a conductor batch drilling and cementing campaign consisting of eight 28-in conductor casings. With the aim to further optimize the cementing operation efficiency and reduce wait-on-cement (WOC) time, thus helping the operator to reduce drilling time to complete this batch drilling campaign, the cementing service company used an integrated approach with the application of dual-component cement blend with high compressive strength development and inner string stabbed-in cementing technique in this conductor batch cementing campaign.
The common cementing objective for conductor casing is to provide structural support for the wellhead by having the top of cement in the annulus at the seabed, depending on the well fatigue limit analysis result. With the weak unconsolidated formation at shallow depth and the low seabed temperature, the challenge was to provide an engineered cementing solution with high early compressive strength development rate at low temperature and of lighter density to avoid fracturing the weak formation. The cementing service company formulated a dual component cement blend to provide such a cement slurry by combining the rapid hardening cement and hollow silicate spheres. To further optimize the drilling operation efficiency from cementing perspective, an inner string stabbed-in cementing technique with double float casing shoe was used to eliminate the time to drill out cement left inside the casing shoe track.
The 36-in. open hole section was drilled to 310 m, and 28-in. conductor casing was cemented with a lightweight rapid hardening cement slurry. The cement slurry density was formulated at 1.5-SG with seawater as the base fluid to further accelerate the setting time and compressive strength development of the cement. This paper discusses the risk assessment and safety factors that were considered in the cement job design phase, including the laboratory testing that was carried out according to
The conductor casing batch cementing job successfully met the well timing objective set by the well operator. An estimated 96 hours was saved from the conductor batching campaign with this integrated approach to optimize operational efficiency from cementing perspective. This paper will help to establish a solid case history for well operators to further improve the drilling operational efficiency for conductor drilling.
Rollins, Brandon (Whiting Petroleum Corporation) | Lauer, Travis (Whiting Petroleum Corporation) | Jordan, Andrew (BJ Services) | Albrighton, Lucas (BJ Services) | Spirek, Matthew (BJ Services) | Pernites, Roderick (BJ Services)
Abstract Frequently exposed weak formations require the use of lighter slurries, and with increased wellbore pressures encountered during fracture stimulations, stronger cements are essential. Lighter, stronger cementing technologies are the key to ensuring well integrity and enabling simple, cost-effective well construction designs. This paper describes the benefits and features of newly developed, lightweight cementing materials available for operations in the Williston Basin. Applications of these materials are supported by case histories and extensive laboratory test data. Regionally, materials have been identified that can be used to produce innovative, bulk lightweight cementing systems. These materials can be inter-ground with the cement during manufacturing or blended with bulk cement. Both methods create cost-effective, high-strength cement systems that can easily be formulated into slurries with densities as low as 10.5 ppg. Comprehensive laboratory test data was generated to support well simulations and field trials of the new materials. Field trial data is then analyzed to illustrate the benefits of cement systems. Economical lightweight cements are commonly produced with fly ash extended systems, however, these systems have low strength at low densities. Lightweight, high-strength, fit-for-purpose cement materials are common in southern oil and gas basins, but transporting these materials to northern states is cost prohibitive. Exotic solutions to create lightweight cements (nitrogen foams or hollow glass micro-beads) are available but expensive, adding considerable operational complexity. Laboratory data demonstrates mechanical properties of the cement systems, slurry properties and set characteristics. The new, low-density cement systems show far greater compressive strengths than conventional blends. Conventional slurry provides a compressive strength of 500 psi, whereas the new low-density 12 ppg blends provide compressive strengths greater than 1,000 psi. Additional practical benefits of these systems are illustrated by varying water content to improve slurry density from 11 to 13.5 ppg without additional cementing additives. Multiple case histories illustrate the results of the applications of these materials at downhole temperatures ranging from 140°F to 220°F and well depths up to 11,000 ft TVD in the Dakota, Mowry and Charles Salt formations. The limitations associated with traditional cementing materials will no longer restrict the creation of efficient well designs in northern states with the implementation of new, low-density cement systems necessary to exploit these oil and gas basins. Using lighter, stronger cement technologies will provide simple, cost-effective designs that are needed to ensure wellbore integrity in the Williston Basin.
Lau, Chee Hen (Schlumberger) | Duong, Anh (Schlumberger) | Taoutaou, Salim (Schlumberger) | Kumar, Avinash Kishore (PETRONAS Carigali Sdn. Bhd.) | Ahmad, Khairunnisa Bt (PETRONAS Carigali Sdn. Bhd.) | Jain, Pankaj (PETRONAS Carigali Sdn. Bhd.) | Amin, Remy Azrai (PETRONAS Carigali Sdn. Bhd.) | Toha, Rozaidi (PETRONAS Carigali Sdn. Bhd.)
Abstract In 2018, an operator in Malaysia completed a sidetrack campaign consisting of injector wells. These wells were planned for maximum productivity via sustainable wellbore zonal isolation. The presence of Carbon Dioxide (CO2) in these wells elevated concern about the zonal isolation of cement across the interval. Moreover, for an injector well, the cement must exhibit resilient properties by design of enhanced mechanical properties to provide long-term isolation based on a cyclic wellbore. An advanced slurry system was designed that enabled the set cement to manifest superior properties in three parameters—corrosion resistance against CO2, flexibility against wellbore stress changes, and expansion to mitigate microannuli. The design of the slag-based flexible cement system with expanding additive (slag-flex) considered all three parameters in the fit-for-purpose application of a resilient and flexible expansive cement system in a CO2-rich well. The system’s mechanical properties, such as Young’s Modulus, Poisson’s Ratio, and tensile strength, were verified with laboratory-scale testing and validation against stress analysis software to confirm on the resilient and flexible properties. The laboratory testing result demonstrated the improved properties of the system, including high tensile strength and low Young’s modulus. Furthermore, the reduced water content of the system decreases the permeability of set cement and thus increases resistance towards corrosive substance such as CO2. For certain cases in the past, two separate slurry systems had to be designed—a lead slurry with CO2-resistant properties and a tail slurry with flexible and resilient properties. Often, several issues arose from this practice, including complex logistics due to cement silo blend arrangement and complexity during job execution. Hence, this new system presents a novel idea and methodology that will deliver value to the oilfield industry by integrating CO2 resistance, flexibility and expansion properties in a single slurry system. The system was successfully pumped in wells in Malaysia; no sustained casing pressure has been recorded to date, and wells have been delivered to their intended zonal isolation requirements without compromising well design and overall integrity. This is an innovative application of this type of cement system in the region, and the long-term zonal isolation and well integrity assurance in these and future wells have the potential to save millions of dollars in remedial work. The cement system is currently recognized as the default technology for CO2-rich injector wells in Malaysia.
Abstract Lightweight cements offer significant performance benefits over conventional higher density cement blends, including; improved mechanical properties and stress resilience, lower thermal conductivity, lower ECDs and improved returns to surface and potentially lower risk of casing collapse due to trapped annular pressure. However, a number of challenges exist in developing lightweight blends for thermal applications specifically concerning achieving short wait on cement at low bottom hole static temperature while also ensuring long-term chemical and mechanical stability at high temperatures. Here we report the development of a new lightweight thermal cement by utilizing hollow glass microspheres. Further fine-tuning of the desired slurry properties including controllable thickening times, zero free water, low fluid loss and short WOC was achieved through cost-effective additive adjustment, and the mechanical properties of the cement we validated by long term curing at both ambient and high temperaures (340 °C). To ensure that the high performance achieved in the controlled lab environment was maintained once deployed at full-scale field level an extensive QA/QC program was undertaken. This process involved collecting dry bulk field samples and confirming performance (thickening time, free water, rheology and fluid loss) prior to every job. After initial optimization of the blending process, a 100% success rate was achieved over the course of a more than a twenty jobs. Overall, a high quality lightweight thermal cement with excellent long-term mechanical properties was successfully developed and deployed.
Abstract Cementing across highly depleted zones and weaker formations requires low density cement systems capable of reducing the hydrostatic pressure of the fluid column during cement placement. If wellbores encounter weak or depleted zones, standard cement cannot be used because the bottom-hole pressure will exceed the pressure gradient and cement will be lost to the formation. Service companies offer cement solutions made light enough to circulate in such situations while retaining the ability to withstand down-hole conditions and maintaining adequate compressive strength to meet regulatory guidelines. Lightweight cements can be achieved using water extension, foamed cement or lightweight microspheres. This paper focuses on the use of lightweight microspheres as density reducing agents. Preliminary experimental data comparing different grades of hollow microspheres is discussed. Cement slurries containing hollow glass spheres and other lightweight hollow microspheres were evaluated while still liquid and after cured. While still liquid the cement slurries were characterized in terms of effective density as a function of pressure. After being cured at room conditions, the resulting cement specimens were characterized in terms of compressive strength. Experimental data suggests that cement compressive strength is mostly independent of the lightweight microsphere strength and strongly dependent on the cement load. Guidelines on the selection of the appropriate microsphere grade are also presented.
Putra, T.. (Schlumberger) | Steven, A.. (Schlumberger) | Wedhaswari, V. R. (Schlumberger) | Awalt, M. S. (Schlumberger) | Natanagara, B. B. (Schlumberger) | Pasteris, M.. (Schlumberger) | Jaffery, M. F. (Schlumberger) | Sheikh Veisi, M.. (Schlumberger) | Rudiantoro, A.. (Chevron Indonesia Company)
Abstract Seguni field and Sejadi field are smaller regions of Sepinggan field in offshore of East Kalimantan, Indonesia, which were drilled and developed by the operator since 1977. Seguni-V (redrilled well) was prognosed to encounter several depleted sandstone formations with reduced pore pressure due to produced hydrocarbons. Consequently, the utilized drilling fluid density was set as low as reasonably practical and this methodology had successfully prevented any lost circulation event until the total depth (TD) was reached. Nonetheless, the risk of losses were greater in the cementation phase of the 3 1/2-in tubing due to long column of cement (>7000 ftMD) required. Therefore, the challenge was to reduce the cement slurry density that still can achieve a required compressive strength within timely manner. The reduced slurry density was also predicted to be instable downhole due to the immense bottomhole pressure, which might crush the conventional cenospheres in the slurry as lightweight materials and result in an increase of downhole slurry density. Therefore, to minimize the risk of induced lost circulation caused by slurry density increase, a novel lightweight material with highly-crush resistant property was proposed. The result of the job with this cement system was satisfactory with no losses occurred and the targeted intervals were covered with good cement. Sejadi field, on the other hand, had experienced losses while drilling, from seepage losses which were commonly found, up to 170 bbl/hr of loss rate at one of the wells in the field. A particular lost circulation case with persistent loss rate into depleted formations was observed at Sejadi-X well. 728 bbl of synthetic based mud (SBM) had been lost into the hole when a loss rate of >40 bbl/hr was encountered while drilling 8 1/2-in open hole (OH) section. The loss rate could not be reduced even after spotting three times of 30 bbl conventional lost circulation material (LCM) pill and had cost significant volume of SBM and LCM amount lost to the formation, as well as 2 rig days spent in attempt to cure the loss. The study of the previous failure on similar problems in the neighboring well led to the solution proposal to use engineered, optimized fiber in cement slurry for lost circulation plug. The result was prominently effective and drilling operation could be resumed to total depth. This paper describes the features, case histories, challenges, field applications, as well as the acknowledged results of mentioned technologies. Lastly, this paper also introduces a mutualistic technical feature when the two technologies are combined to both prevent and mitigate lost circulation.
Fortunately, this effect can be prevented, and the set-cement integrity can be preserved. Five solid cement blends were prepared; their compositions are presented in Table 1. The blends were formulated according to the engineered-particle-size concept, wherein the volumes of coarse, medium, and fine particles are optimized to maximize the packing volume fraction (PVF). An increase in the PVF reduces the amount of mix fluid required to prepare a stable and pumpable slurry, and it increases the strength and reduces the permeability of the set cement. The five blends contained 50% by volume of blend (BVOB) silica, which is sufficient to allow formation of the calcium silicate hydrate mineral xonotlite [Ca6Si6O17(OH)2] upon curing at temperatures above approximately 160 C. The weighting-agent concentration was held constant at 15% BVOB. The slurries were prepared according to the recommended American Petroleum Institute (API) procedure.
Ilyas, Muhammad (1Mari Gas Company Limited, Pakistan) | Sadiq, Nauman (2Dowell Schlumberger Western S.A., Pakistan) | Mughal, Muhammad Ali (1Mari Gas Company Limited, Pakistan) | Pardawalla, Hassan (2Dowell Schlumberger Western S.A., Pakistan) | Noor, Sameer Mustafa (2Dowell Schlumberger Western S.A., Pakistan)
ABSTRACT This research work "Improvement of Cementing in Deep Wells" was carried out with the collaboration of Mari Gas Company Limited (MGCL), Pakistan and Schlumberger Pakistan, to recommend the designs and practices by which future cementing operations for zonal isolation in deep Wells may be improved. Mari Gas Company Limited had successfully drilled, tested and completed Halini Well - 1 (Total Depth = 5350 m) in the Karak Block. The Karak Block is located in Northern Region of Pakistan which is known for its challenges, such as high pressure water influxes and weak zones, which led to a number of cementing challenges in this Well. The Cementing related problems that were faced on this Well were: 1-Sustained Casing Annulus Pressure in 13 3/8" × 9 5/8" Casing Annulus 2-Poor CBL-VDL results in 13 3/8" and 9 5/8" Casing The scope of the project was to investigate the root cause of cementing challenges faced at Halini Well-1 and to propose recommendations for improving future cementing in deep Wells. In regards to the above, the cementing of Halini Well- 1 was thoroughly analyzed along with similar case histories and problems in offset fields. On the basis of observations made, various recommendations have been proposed, mostly related to areas of fluid rheology, fluid contamination, fluid channeling, density and friction pressure hierarchy between fluids, fluid loss, temperature differential, and setting of casing slips etc. The idea for this project is to serve as a guideline for cementing the future deep Wells.