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Nafikova, Svetlana (Schlumberger) | Bugrayev, Amanmmamet (Schlumberger) | Taoutaou, Salim (Schlumberger) | Baygeldiyev, Gaygysyz (Schlumberger) | Akhmetzianov, Ilshat (Schlumberger) | Gurbanov, Guvanch (Schlumberger) | Eliwa, Ihab (Dragon Oil)
Abstract A major operator on the Caspian Turkmen shelf has started to encounter sustained casing pressures (SCP) attributable to insufficient isolation across a hydrocarbon gas zone, due to downhole stresses and other contributing factors. Enhanced placement techniques of conventional cements failed to prevent SCP, confirming the requirement for an alternative cement system that can withstand anticipated stresses and resolve this challenge. An innovative and cost-effective solution was applied and successfully solved the SCP challenge due to its unique self-healing properties. If cracks or microannuli occur and hydrocarbons reach the cement, the system has the capability to repair itself, restoring integrity of the cement sheath without external intervention. The cement system is placed conventionally in the annulus across or above the hydrocarbon-bearing formation. It then acts as a pressure seal, expanding to accommodate downhole changes and healing if any hydrocarbon reaches it. This technology has been used in four wells in the field with excellent results. Two wells were used to demonstrate the capabilities of the self-healing cement as a lead cement slurry, which created a cap over the pay zones. The self-healing cement was designed with low Young's modulus for optimum flexibility. To minimize the risk of set cement integrity failure due to microannuli or microdebonding from chemical shrinkage after setting, linear expansion up to 1.2% was incorporated into the design. After cementing, the wells were intentionally exposed to a sequence of high-pressure tests, which induced annular pressures in the wells. However, because of the self-repair capability of this cement, isolation and integrity were effectively restored in the two wells within 1 to 2 weeks without external intervention. As a result, the self-healing cement technology has become the standard for the field for all future wells, and the operator plans to extend the self-healing cement technology to other fields with similar challenges. This paper clearly demonstrates successful casing pressure remediation without intervention by engineering a flexible, self-healing cement system. The design strategy, execution, evaluation, and results for two wells are discussed in detail and will help to guide future engineering and operations around the world.
Johnson, Carl (Schlumberger) | Gai, Alessio (Schlumberger) | Ioan, Tiberiu (Schlumberger) | Landa, Julian (Schlumberger) | Gervasi, Giuseppe (Ital Gas Storage S.p.A.) | Bourgeois, Benjamin (Geostock) | Bouteldja, Mohammed (Geostock)
Abstract With today's low energy prices and with the increasing drive towards sustainability, it is essential to develop more economically efficient and ecofriendly technologies in oil and gas field development. Such a technology is self-healing cement, which was successfully applied in a large project in northern Italy in the conversion of a gas field to a gas storage field. During the construction phase of gas production and storage wells, one of the critical goals is to achieve competent hydraulic isolation between the surface and the casing to reach the reservoir. There are several cases documented in the literature where poor isolation has resulted in gas flow to surface, thereby polluting water reserves, greenbelts, and populated areas. Improper isolation can also result in interzonal communication, production of unwanted fluids, gas migration, casing corrosion, and sustained casing pressure. These can have significant health, environmental, and economic impact. Additionally, the impending need for well intervention, along with high re-entry costs, will further weaken revenue margins. Breaking through conventional cementing solutions, a global oilfield service company had established an active cement technology to improve annular isolation in gas wells. This technology is capable of self-healing when exposed to hydrocarbons of any type, unlike other self-healing systems that are limited by the level of methane (CH4) in the gas reservoir. The new system allows universal coverage for any concentration of CH4. Because the concentration of CH4 in different gas reservoirs can vary significantly, the self-healing "protection" against different levels of CH4 is tailored to suit different reservoirs. This field-proven technology, in use for more than 10 years, stemmed from the original self-healing technology commercialized more than a decade ago. Subsequently, an opportunity arose to apply this technology in a large project in the north of Italy. The project would exploit a depleted gas field by conversion to a gas storage field with the drilling of 14 wells from two clusters above the reservoir. The product testing and implementation, job execution, and results evaluation brought several benefits with positive impact to the service company and the owner/operator of the field. A higher level of isolation significantly decreases the need for future well integrity and repair, which provides medium- to long-term benefit for the operator—an added value that is sometimes omitted in well construction design. Using a zonal isolation technology, such as the self-healing cement system described here, inherently places the service company and operator in a much more secure position for the future. Furthermore, in the current industry climate, saving 30 to 40 days of rig time and the cost of remedial operations and achieving important mitigation against health and environmental impact pose a significant economic advantage.
Bugrayev, Amanmammet (Schlumberger) | Nafikova, Svetlana (Schlumberger) | Taoutaou, Salim (Schlumberger) | Timonin, Andrey (Schlumberger) | Gurbanov, Guvanch (Schlumberger) | Rovshenov, Gadam (Schlumberger) | El Sayed, Mohamed (Dragon Oil) | Hay, Kevin (Dragon Oil)
Abstract 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.
Bermea, J.A. Vargas (Schlumberger) | Taoutaou, S.. (Schlumberger) | Olutimehin, K.. (Schlumberger) | Vinaipanit, M.. (Schlumberger) | Ashraf, S.. (Schlumberger) | Segret, G.. (PTTEP) | Asawakowitkorn, J.. (PTTEP) | Kongpat, N.. (PTTEP)
Abstract Cementing design and execution is key to achieving zonal isolation for safe and economic well production. The critical goal of long-term well integrity is a fundamental element of any well construction strategy especially when the well will be subject to cyclic loads and changing downhole stresses e.g from stimulations operations. Exploration and appraisal wells pose an additional challenge because many formation-specific parameters relating to the field may not be fully understood. This case describes the use of self-healing cement and flexible and expandable cement to optimize isolation and ultimately, well delivery on a critical exploration well project for a National Oil Company. Globally, self-healing cements have been increasing used in the last decade and this was the first application for this operator onshore Thailand. The self-healing cement system was used as a secondary barrier in the well in the case of cracks or deformation within the primary cement matrix. The combination would serve as a more robust solution to mitigate the impact of stresses generated during different well lifecycle phases. The design principle of self-healing cement is the ability to swell upon contact with hydrocarbons to restore well integrity. Upon installation in the well, cement evaluation logs and the physical indications showed that zonal isolation had been completely achieved for the entire production interval. In addition, no sustained casing pressure was experienced after the hydraulic fracturing operations were performed. Health, Safety & Environment (HSE) concerns were addressed ensuring no hydrocarbon gas leak to surface and no contamination of underground water zones.
Al-Thuwaini, J.. (Lukoil Saudi Arabia Energy Limited) | Emad, M.. (Lukoil Saudi Arabia Energy Limited) | Ekpe, J.. (Lukoil Saudi Arabia Energy Limited) | Jaffery, M.. (Schlumberger) | Ong, D.. (Schlumberger) | Taoutaou, S.. (Schlumberger) | Ahmad, B.. (Schlumberger)
Abstract Zonal isolation has extreme significance in the construction quality and life of a well. Achieving zonal isolation in deep high- pressure, high-temperature (HPHT) gas wells is a challenging task, and these wells need more attention to achieve zonal isolation than conventional oil or gas wells. In addition to following primary industry best practices, the selection of a cement system appropriate for the environment of the well is very significant. Trapped gas and oil between production and intermediate casing (abnormal annulus wellhead pressure) has been globally recognized as one of the serious challenges facing drilling and production operations. The issue is becoming even more serious since wells are aging and the integrity of the casing portion below the well head is increasingly affected by the shallow-water corrosive environment. The potential safety and environmental hazards of the abnormal annulus pressure, have encouraged LUKSAR (Lukoil Saudi Arabia Energy Limited) to review the current drilling and cementing practices, with the goal of minimizing the impact of the problem, thus improving well life cycle and reducing the frequent work-over interventions. The general guidelines set to resolve the problem focused on eliminating potential leakage paths in the completion and casing strings and emphasized the quality of the primary cementing, especially for casings set on the aquifer zones and production casings. This paper discusses case histories and selection criteria for the different cement systems. It shows how high-performance lightweight sealant across weak zones, fiber-based sealant technology when lost circulation prevails, self healing sealant system where zonal isolation is extremely important, and flexible and expanding sealant for frac candidates are chosen for providing and maintaining well integrity in these extremely remote and challenging HPHT wells.