Potential Leak Paths Research Articles

Development of a simplified one-dimensional CDA bubble model

Sodium-cooled fast reactors (SFRs) have high safety with an extremely low probability of a core disruptive accident (CDA). However, from a defense-in-depth perspective, the CDA sequence is still worth studying. Severe accidents in SFRs, such as unprotected loss of flow, might lead to a CDA during which fuel and some fission products could be instantly released from a large CDA bubble through potential leak paths in the top shield structure. Therefore, a reasonable prediction of dynamic behavior of a large-scale bubble within the sodium pool is vital for accurately evaluating the migration of source terms. In this study, we propose a simplified one-dimensional CDA bubble model that can handle heat and mass transfer in two-phase multicomponent materials in different computational domains during the rising of bubbles through the sodium pool toward the cover-gas region. In this model, an entrainment model based on the Rayleigh–Taylor instability and Kelvin–Helmholtz instability was used to explain the coolant entrainment through the gas/liquid boundary and jet fragmentation. The model also addresses the mitigation effect of non-condensable gases on the condensation of fuel, steel and sodium vapor at bubble interface. We evaluated the model using a past experiment on the expansion of a two-phase, large bubble with high pressure in a stagnant liquid pool conducted by Purdue University in the late 1970 s using a 1/7-scale model of Clinch River Breeder Reactor. Good agreement with the experimental data demonstrates that the developed model can reasonably represent the essential characteristics of dynamic behavior of a large, high-pressure bubble with heat and mass transfer in two-phase multicomponent materials. This is valuable for evaluating the migration of the source terms, which will be carried out in future studies.

Quantification of Shrinkage-Induced Cracking in Oilwell Cement Sheaths

Summary Ensuring the zonal isolation of hydrocarbon reservoirs is one of the main tasks of the cement sheath, but the development of cracks and debonding between the interfaces might lead to underground water pollution and leaks of oil and gas to the environment. Restrained shrinkage of the cement sheath is one of the most significant causes of cracking, and an experimental investigation has been conducted to quantify how extensive shrinkage-induced cracking might be due to changes in ambient humidity conditions, confinement levels, and mixture compositions. The presence of lateral confinement due to the presence of shale provided an 80% reduction in the cracked area compared to unconfined specimens, but still radial cracks as wide as 200 µm, microannuli up to 100 µm, and cracked areas of 50 mm2 in a representative well section were observed. Additionally, a reduction in crack widths and potential leak paths was obtained by reinforcing the cement slurry with synthetic fibers. A detailed quantification of shrinkage-induced cracking is reported in this study, providing crack information such as position, width, and orientation as a function of time.

(Invited) Safe Design of GS Yuasa Large Format Lithium Ion Cells for Industrial Applications

Since the 1990’s, GS Yuasa has developed and produced large-format Li ion cells for a variety of applications including satellites, rockets, electrified vehicles, trains, AGVs, energy storage systems, UPS, submarines, and others. Through these activities, safer Lithium-ion cell designs have evolved not only through the careful selection of electrode chemistry, but also cell shape, case materials and cell orientation within the module or battery pack. Lithium iron phosphate, for example, is stable and often considered a “safe” material for use in the positive electrodes of lithium-ion cells; however, there have been many lithium iron phosphate cell fires in the field. Fires may be caused by leakage of a flammable electrolyte in proximity to an ignition source. GS Yuasa considers the combination of using a metal cell case with laser-welded seal and a terminals-up orientation of cells in the module or battery pack to drastically decrease the risk of electrolyte leakage. Figure 1 shows the typical cell design of our large lithium ion cells for electrified vehicles and other industrial applications such as trains, AGVs, energy storage systems and UPS. The metal case with laser-welded seal offers high reliability with respect to the prevention of electrolyte leakage. This approach to cell design and orientation locates the more sensitive potential leak paths such as the rupture disk, terminal seal and case welds in the top of the cell and away from free electrolyte. In this presentation, we will detail GS Yuasa’s cell and battery systems and discuss our field experiences. Figure 1

An experimental study on the depressurization of the containment by water spray in a small scale facility

The containment of a nuclear reactor acts as the ultimate barrier for radionuclides to be leaked in the environment. Severe accidents in nuclear reactors may result in the pressurization of the containment and may provide different potential leak paths. So, to enhance the safety of new designs of Indian pressurized heavy water reactors, an additional safety measure called containment Spray System is introduced. The system is designed to cater/mitigate the conditions after design basis accidents. As a contribution to the safety analysis of condition post severe accident, experiments are carried out to investigate the system performance. The accidental conditions are simulated by injecting the saturated steam into the test vessel filled with air at atmospheric pressure and temperature. The effect of different spray parameters such as nozzle geometry, spray mass flow rate and Sauter mean diameter on vessel pressure and temperature is measured. Three initial vessel pressure 1.5 bar, 2.0 bar, 2.5 bar and five different nozzles with nozzle orifice diameter as 1.65 mm, 2.10 mm, 2.45 mm, 2.75 mm and 3.10 mm are chosen for the experimental investigation. The vessel pressures are chosen based on the post accidental conditions in Indian pressurized heavy water reactor. Experiments are conducted with water at room temperature as the spray medium. The experiments are carried out in a vessel of 500 mm diameter and 1200 mm height. These studies are carried out to optimize the containment spray system configuration for best effectiveness. It is seen that the Sauter mean diameter and nozzle geometry influences the depressurization rate of the vessel. The depressurization rate is inversely proportional to the Sauter mean diameter while it increases with the increase in the spray mass flow rate/ Reynolds Number.

Numerical and Experimental Investigation of Structural Gasketing Approach for Gearbox Flange

Heavily loaded flanged joints should not only carry the mechanical loads that are imposed, but they should also provide a fluid seal. Historically, such heavily stressed flanges were sealed with thin paper composition gaskets so that when flange joint was operated at critical load then high compressive forces were induced within the joints. Over the use of gaskets in the flange,they get deformed and due to this torque capacity, they get reduced hence creating some gaps which are potential leak paths. In recent years, chemical gasketing (liquid “formed in place gaskets”), has begun to surface as a possible solution for these dual function flanges. Hence liquid sealants have been introduced in this flange. In coming days, anaerobic and silicone sealants will be introduced in industry, in contrast with solid gaskets which deteriorate gradually with the atmospheric moisture. Anaerobic and Silicone sealants are mostly used because they are ideally suited to small flange gaps curing them rapidly. This paper focuses on the study of gaskets and liquid sealants effects on gearbox flanges. This work has revealed that structural anaerobic sealants significantly reduced the deformation by 6.7μm, and it improved the structural shear strength and shear modules. This paper also investigates the numerical and experimental analysis of gearbox anaerobic sealant flange assembly and it determines the mode shape frequency.

Investigating the Benefits of Rotating-Liner Cementing and Impact Factors

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 180578, “Investigating the Benefits of Rotating-Liner Cementing and Impact Factors,” by Quek Khang Song, SPE, Hao Wang, and Weicun Dong, Halliburton, and Roger Bradshaw, SPE, Wei Cui, and Johnson Njoku, ConocoPhillips, prepared for the 2016 IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition, Singapore, 22–24 August. The paper has not been peer reviewed. Effective primary cementing in the wellbore is critical to achieving positive wellbore isolation. This paper discusses an expandable-liner-hanger (ELH) system that provides liner rotation during the liner deployment and the cementing operation while providing a hydraulically energized liner-top seal upon setting. The case histories of the wells using the system verify the key consideration factors presented in this paper, which help improve the quality of the liner cementing bond. Liner-Hanger System The ELH system incorporates bonded elastomeric sections. The elastomeric element provides the hanging capacity for the liner and a gas-tight seal. The liner-hanger/packer body contains no setting mechanism or external components, such as slips, hydraulic cylinders, or pistons. The hydraulic setting mechanism is contained in the setting-tool assembly and is retrieved, eliminating potential leak paths in the flow stream. This running/setting-tool-assembly system provides the necessary expansion mechanics, cementing pack-off seals, a collet assembly to carry the liner weight and transfer the liner weight to the drillstring, and an end-of-expansion indicator assembly. As required, the liner system can be rotated and reciprocated when incorporated with an ELH high-torque running/setting tool and high-torque liner connections. The liner system can be rotated and reciprocated while running in the hole or during cementing operations (Fig. 1). Liner-Hanger Operation The key to a successful liner deployment is prejob planning. As part of the preplanning, several iterations of the torque-and-drag analysis are simulated with software to determine the ideal run-in-hole solution. The ELH system is run much like conventional liner-hanger systems, with minimal differences. The key difference is that the liner with the ELH system is cemented before setting the hanger because the hanger provides hydraulic isolation when it is set. Cementing before setting the liner hanger enables rotation and reciprocation, which should improve the cementing. No liner reciprocation during the cementing operation was planned because of rig limitations. In addition, rotation was preferred over reciprocation because the liner must be in the position across the zones of interest at all times and prevent any potential operational risk (e.g., stuck pipe or liner set high). The ELH standard setting/running tool has a torque rating limitation of 15,000 lbf-ft. Consequently, it was deployed as a non-rotational liner hanger. The ELH high-torque running/setting tool, with a torque rating of 39,071 lbf-ft, was used with the rotational liner-hanger system. During the cementing operation, the liner string was rotated at 10 to 20 rev/min. The next step is to set the hanger, which is performed hydraulically after releasing a set-ting ball. After the hanger is set, the liner top can be washed using conventional or reverse-circulation techniques. The tools are then retrieved from the wellbore, and the well is ready for completion.

Metal-Formed Liner Hanger Avoids High-Setting-Pressure Requirements

Seminole Services announced the commercialization of its first product, the Powerscrew Liner System, a new expandable-liner hanger that is set with torsional energy from the topdrive (Fig. 1). The Louisiana-based company began development on the tool and associated equipment in the fall of 2012. Rooted in solid mechanics and material science, the company provides engineered wellbore solutions to exploration and production companies actively engaged in drilling oil and gas wells. In the evolution of liner hangers, mechanically set systems were developed first. While many operators believe mechanical systems are more robust and provide superior sealing integrity when compared with hydraulically set hangers, older mechanical systems typically lack reliability, especially in applications requiring longer liners in deviated wellbores. In large part, this is because of the risks associated with reaming a mechanical hanger to setting depth. Reliability rates were increased with the introduction of hydraulically set hangers, which allowed a greater range of applications. However, the newer setting method suffers from its own limitations, such as flow-area restrictions, compatibility with drilling-fluid additives, and a multitude of potential leak paths. With the advent of expandable-liner hangers, further increases in setting reliability were achieved along with even greater applications. The increase in reliability stemmed, at least in part, from greater success reaming the liner to setting depth. The higher reliability of expandables is perhaps a consequence of greater flow area at the liner top and the lack of external setting devices. This has led to many new developments in drilling with liners (DWL). Nevertheless, expandable-liner hangers continue to suffer from potential leak paths associated with high hydraulic pressure sourced at the mud pumps. The hydraulic pressure provides energy to the running tool necessary in setting the liner top. In most expandable systems, pressure pushes the roller/ expansion cones/sleeve through a metal-formed tubular by use of a multitude of pressurized connections and fluid ports. By contrast, the torsionally set system combines the latest in metal-forming technology along with the best features of mechanically set systems. The result is a setting process that does not require high hydraulic pressures and eliminates the risks associated with reaming the liner to setting depth and DWL.

CO2 Fate Comparison for Depleted Gas Field and Dipping Saline Aquifer

An important metric for CO2 storage is the CO2 fate plot, which displays the partitioning of mobile/capillary trapped/dissolved/mineralised CO2 as a function of time. The archetype version of this plot (Fig. 1, from the IPCC 2005 report [1]) is idealised. While a simplification is a good way to illustrate physical mechanisms, the problem with this plot is that due to its popularity it is now easily misinterpreted to be a universal plot. However, for actual case studies the curves behave quantitatively and sometimes qualitatively differently from the archetype plot. The reason for this is that reservoir settings are different from case to case, having a profound impact on the characteristic times, shapes, and magnitudes of the CO2 fate curves. The objective of this work is to generate a realistic range of CO2 fate plots, derived from reservoir simulations on simple geometries but with realistic input parameters, expressing the impact of key control parameters. This new range of plots can be used for communication purposes to a wider audience, and also as a Quality Control tool for future modelling studies. Our results bring out major differences between a depleted gas field setting (more generally: structurally closed setting) and a dipping saline aquifer setting (more generally: structurally open setting). In a structurally closed setting the CO2 dissolution and/or mineralisation takes orders of magnitude longer than in a structurally open setting. This result is quite robust under variation of other parameters such as vertical to horizontal permeability, reservoir thickness, reservoir dip angle, relative permeabilities and geochemical variations. Moreover, only a small subset of structurally open cases, and none of the structurally closed cases, leads to CO2 fate plots that are similar to the one in the IPCC 2005 report. Therefore the CO2 fate plot from the IPCC 2005 report should not be used for quantitative statements regarding the relative size and timing of the various CO2 fate categories; for most potential CO2 storage sites such statements are likely to be invalid. Another implication is that for a structurally closed setting the CO2 tends to be relatively static: slow transitions between CO2 fate categories, and (due to structural closure) limited lateral migration of mobile gas. For a structurally open setting, however, the CO2 fate (spatial distribution and trapping category) is much more likely to vary significantly over time due to relatively quick CO2 plume migration laterally and relatively quick conversion of CO2 into the less mobile (capillary trapped/dissolved/mineralised) CO2 fate categories. For structurally open cases, the balance between, on the one hand, the lateral CO2 plume migration speed and, on the other hand, the capillary trapping/dissolution/mineralisation rate, determines the spatial distribution of the mobile CO2 in relation to potential leak paths. Therefore for CCS project screening/design in structurally open cases it is more critical to investigate this balance than for CCS in structurally closed reservoirs.

Technology Focus: Well Construction (May 2010)

Technology Focus In 2009, the focus of well-construction technology was primarily in two areas: our ability to drill and reliably complete deepwater and high-pressure/high-temperature projects and exploration of the reliability of carbon-capture and -sequestration (CCS) storage wells. Outside these big focus areas, some papers relating construction practices specific to the shale plays are beginning to come forth. Lost circulation is still one of our biggest obstacles to getting deepwater wells to target depth. Unfortunately, lost-circulation issues are expected to become even more difficult in these fields as pore pressure drops because of production and depletion. In one paper, details are presented of higher-risk squeeze techniques used to shut off high-rate losses, enabling completion of two potentially lost wells. The full paper may be a good read the next time you find yourself in such a situation. As we discussed here last year, CCS is our next big area of activity. Progress and acceptance of CCS depend upon very-long-term isolation of the injected CO2. One of the big questions with CCS-well construction is whether special non-Portland or lean-Portland cements are required to ensure the long-term integrity of CO2-injection wells. If so, what does that imply for all the pre-existing wells in the storage area? Much of the early work on this subject has been contradictory. Another paper here describes the industry’s efforts to establish the potential leak paths and to prescribe appropriate construction techniques. Using simple, tubing-sized monobore completions has proved an effective and efficient development strategy for complex multilayer reservoirs. The simplicity and reliability of the wireline tools we run in these small monobores are critical. John Lofton, one of Chevron’s drilling-engineering advisors, was intrigued by the novel, field-tested design evident in the retrievable lock mandrel described in another paper highlighted here. Retrievable tools embodying such features may provide improved reliability for slim monobore completions in hostile environments. Well Construction additional reading available at OnePetro: www.onepetro.org SPE 125642 • “Optimizing Openhole-Completion Techniques for Horizontal Foam-Drilled Wells” by Dave Allison, SPE, Halliburton, et al. SPE 128226 • “Self-Healing Cement System—A Step Forward in Reducing Long-Term Environmental Impact” by S. Le Roy-Delage, SPE, Schlumberger, et al. SPE 126226 • “Effective Zonal Isolation for CO2-Sequestration Wells” by R.E. Sweatman, SPE, Halliburton, et al.

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Thread Compounds + Environment = Change

Introduction Environmental awareness, concern, and regulation have affected virtually every industry in the last several years, and the oil patch is no exception. Changes in the methods required for storage, use, and disposal of materials ranging from pipe coatings to drilling muds have spawned a flood of new products that are more environmentally acceptable. These new products not only differ in composition but also can exhibit substantially different performance properties. The change in performance properties will require changes in operational practices that have been in place for decades. Nowhere is this more true than for thread compounds. Thread Compound Background Historically, compounds used for both drilling and production applications have consisted of a petroleum lubrication grease containing a substantial percentage of heavy metals (lead, copper, zinc, or a combination of the three).The metals are present in a finely divided form as a powder or flake and may make up as much as 60 wt % of the thread compound. These metals have been used since the early days of the industry because their unique material properties provide two main performance requirements of a thread compound:protection against metal/metal contact and galling at high connection bearing stresses andthe sealing of potential leak paths at high internal pressures. Lead, copper, and zinc are malleable and ductile. These properties allow them to compact and deform without fracturing, thereby forming an effective seal either in the thread form of the casing or tubing or between the shoulders of rotary connections. Their ability to prevent wear and damage of ferrous metal surfacesis evidenced by their wide use in a variety of bearing materials. Environmental Factors Unfortunately, restrictions on the use and disposal of materials containing heavy metals have and will continue to become increasingly severe. U.S. Environmental Protection Agency (EPA) guidelines for determining whether a waste material is hazardous include lead and several other heavy metals on the list of toxic substances. If the defined test procedure (the Toxicity Characteristic Leaching Procedure) indicates that any substance on the toxicity list is present in an extract solution above the stated limits. the material is considered a hazardous waste and must be disposed of according to the appropriate regulations. Zinc currently is not on the list but most likely will be added within the next year. Copper also is not listed and probably will not be for the near future. Both zinc and copper, however, are listed for a similar test procedure required by the State of California. Other areas of concern, besides disposal of waste material residues and contaminated containers, are not covered specifically by EPA regulations. Some examples are contaminated effluent from hydrostatic testers that may be discharged to a sanitary sewer system, rain-water run-off from pipe yards and threading facilities, and contaminated mud pits and surrounding soil in field operations. These situations are, for the most part, subject to state and local regulations that can vary considerably, depending on the location. State and federal regulations based on marine biotoxicity and other environmental-impact properties also restrict discharges from offshore operations. Clearly the composition of thread compounds must and will continue to change as environmental regulation increases and other substances are added to the toxicity lists. Performance Considerations What effect do the changes in thread compound composition have on performance properties and operational practices? The answer is complex. The compounds used for the past 40 or 50 years have been fairly generic with well-defined categories sharing similar performance properties. The tables of recommended torque values and operational practices that the API and pipe manufacturers publish are based on the use of these compounds. The new compounds that have appeared recently are of proprietary formulation and can vary widely in both composition and performance properties. Drilling Compounds. Nonmetal drilling compounds rely on such materials as graphite, nonheavy metal oxides or other solid lubricants, and extreme-pressure additives to provide protection against connection galling. Most nonmetallic solids, however, fracture under applied stresses and do not compact and deform into a continuous gasket-like seal between the shoulders as do powdered metals. Seal failure can result in connection damage from washout caused by high-solids drilling muds under pressures as high as 6,000 psi. Because of the malleability of the metal powder particles, high metal compounds also are more effective than nonmetallics at uniformly distributing bearing stresses (60,000 psi in drillcollars) around the connection shoulders. This is particularly critical if the shoulders are not exactly parallel because of wear or substandard field reworks. Uneven distribution of shoulder bearing stresses can cause pin fatigue failures and reduce drillstring life. JPT P. 614^