Premium Connections Fatigue Assessment Methodology Fit for Multi-stage Hydraulic Fracturing Operations

Objectives/Scope During casing installation and drilling operations, Oil Country Tubular Goods (OCTG) strings are often rotated inside deviated wellbores, generating cyclic bending loading that could lead to fatigue damage. This phenomenon has been previously studied and understood. The completion of multistage fractured horizontal wells (MFHW) involves tens of fracture operations (an ever growing number) as part of the stimulation program in order to maximize production. These fracture operations involve a combination of cyclic pressures and tension loading in the production casing, through which they are conducted, with maximum loads often repeatedly reaching the upper limit of the pipe body performance ratings. This process of cyclic pressure and tension loading near the upper limit of the pipe body performance is the subject of this work. In unconventional plays, where MFHW are the standard approach, both cyclic bending due to rotation and cyclic burst and tension due to multiple fracturing operations are applied on OCTG strings. This combination may lead to a failure mode in which a crack opens due to material fatigue during rotation or fracturing cycles, and subsequently propagates (to failure) during the demanding fracturing stages. Methods, Procedures, Process As it would be expected during any technological evolution, the industry has seen an increase in casing failures during hydraulic fracturing, often not explainable by the current understanding of loads scenarios present in wellbores. Some of these events could be associated to the failure mode described above. Despite the potential risk introduced by this failure mode, to date, there is no standardized testing methodology available to evaluate the resistance of pipes and connections to this loading sequence. Results, Observations, Conclusions In order to cover this gap, a testing sequence aimed at replicating actual operating conditions was developed and deployed by the authors. This includes evaluating the resistance of a premium connection to rotation through a curved hole, and subsequent burst and tension cycles. The methodology and results are presented in this paper. Novel/Additive Information Through this testing approach, operators, manufacturers, and laboratories alike, can ensure the performance and reliability of OCTG, which are key elements in the well construction process. As main observations, all tested specimens successfully passed this very demanding testing sequence, aimed to replicate operative conditions during installation and subsequent stimulation operation.

Research of technology of manufacturing of steeply curved bends

Purpose of work. Investigation of the features of the technological process of manufacturing curvilinear sections of the pipeline – steeply curved bends. Research methods. Three-dimensional modeling of a design of equipment and a finished product; experimental studies of the technology of manufacturing steeply curved bends by pushing through a curved hole of the assembly matrix without using fillers; estimation of deformation by the method of dividing grids. Obtained results. Literary sources are analyzed and the main problems arising in the manufacture of steeply curved bends for each method are identified. To study the features of the manufacturing technology, a three-dimen­sional model of the assembly matrix was modeled using the investigated method, the design, dimensions and material of the tooling were selected. Equipment was made. Sizes and material of pipe billets were selected. The operations of the technology for the manufacture of steeply curved bends by pushing through a curved hole of the assembly matrix without the use of fillers were determined. Experimental studies of the technology have been carried out. For this, the manufactured stamp was installed on a PG-100A hydraulic press. Pipe billets were placed in a guide sleeve, which was screwed to the assembly die when the press rod was placed in the upper position. The punch pushed the pipe billet along the curved hole of the assembly matrix while moving the rod down. Upon completion of the pushing process, the press rod was in the upper position. For unimpeded removal of the finished product, the guide sleeve was removed, the matrix was unscrewed and removed from the clamps. Several samples were obtained, the presence of defects and problems that arose during the formation of steeply curved bends were revealed. To assess the deformation, the method of dividing grids was used. Scientific novelty. The method of manufacturing steeply curved bends by pushing an assembly matrix through a curved hole was further developed. The peculiarity of the investigated technology - rejection of the use of expensive filler or rigid mandrels, reduction of technological operations and time for manufacturing a unit of a finished product. As a result of the study, dangerous zones of pipe billets in the process of manufacturing steeply curved bends were identified: the place of bending (crushing, corrugation, rupture) and the ends of the finished product at the exit (ovalization, distortion, breaks). Practical value. To prevent the occurrence of dangerous zones during deformation of pipe billets and improve the quality of the finished products obtained, requirements were formulated for the design of the working elements of the developed stamp, the choice of optimal modes of the shaping process, the material and the optimal shape of the pipe billet.

Background-Grid Based Mapping Approach to Film Cooling Meshing: Part I — Strategies and Test Cases

Film cooling technique is commonly adopted in modern gas turbine engines to protect high-temperature components from erosion and damage caused by thermal stress. To improve film cooling effectiveness, many efficient prediction tools have been developed and have shown promising results, which are helpful for turbine aero-thermal design. For film cooling, evidence has shown that it is strongly affected by the momentum and heat transport in the boundary layer when hot gas and coolant are mixed downstream of the ejection. From the view of resolution accuracy in the boundary layer, structured grids will be the primary choice in fluid domain. However, the high-pressure gas turbine blades usually have several hundreds of cooling holes with different configurations and arrangements. Numerical simulations often face a big challenge in multi-block structured-grid generations when a large number of cooling holes are involved on curved hole-to-mainstream interfaces. Conventional block-splitting and mesh-generation for all holes are quite time-consuming and cumbersome, because the copying, translating and rotating manipulations cannot be applied on curved hole-to-mainstream interfaces directly. To solve these difficulties, this paper presents a novel mesh-generation strategy, which is a background-grid based mapping (BGBM) method, to generate multi-block structured grids for film-cooled blade efficiently without modifying the existing meshing tools and solvers, which is convenient for CFD users. It consists of three main steps: At first, the correspondence between physical space and computational space is established by two sets of background grids. Then, the sectional curves of geometry features in physical space are projected to the computational space. With these treatments, the curved hole-to-mainstream interfaces are flattened in computational space, where grids can be quickly generated with block copying, translating, rotating and merging manipulations. Thereafter, meshes in computational space are mapped back to the physical space based on the correspondence between physical and computational spaces, and high-quality structured-meshes can be obtained for numerical simulations. To demonstrate the presented meshing strategy, several typical cases with film cooling are selected for testing, including single cooling hole on curved surface, multiple rows of cooling holes on curved surface and NASA C3X vane with multiple hole arrays. In these cases, different holes, including the cylindrical holes and shaped holes with different ejection angles and arrangements, on curved interfaces are taken into consideration. The quality of generated structured grids for each test case is illustrated, which is able to meet the requirement of CFD solver. With the generated meshes, conjugate heat transfer performance in the turbine vane with different cooling arrangements is investigated and also validated with the existing experimental data.

Development of Curved Hole Electrical Discharge Machining Method: Automatic Generation of Device Operating Command in Consideration of Realizing the Machining

Aiming to enhance the degree of freedom of hole shapes which can be realized by machining methods, our research group has developed a new device that can fabricate curved holes by means of electrical discharge machining. The previous studies have shown that the device has the ability of fabricating curved holes and have developed the manner for fabricating curved holes with desired shapes by use of the device. This manner is built on the basis of the teaching playback method. So, the manner contains the teaching process for generating the operating commands that can make the device fabricate desired curved holes. However, the teaching process just built needed troublesome manual works. Not to need such works, the last study has devised the manner for automatizing the teaching process. Contrary to our expectation, however, the operating command generated by the automatized teaching process could not fabricate a desired curved hole due to the lack of the consideration to the motion capacity of the device and so on. To overcome this problem, this study has improved the algorithm to generate the operation command. The machining experiment employing the operating command generated by using the improved algorithm can fabricate the desired curved hole. This proves that the improved algorithm is effective to the fabrication of desired curved holes by means of the device.

Enhancement of Film Cooling Effectiveness Using Dean Vortices

Film cooling technology is widely used in gas turbines. With the additive manufacturing anticipated in the future, there will be more freedom in film cooling hole design. Exploiting this freedom, the present authors tried using curved holes to generate Dean vortices within the delivery line. These vortices have opposite direction of rotation to the vorticity of the kidney vortices and, thus, there is interaction between these vortices in the mixing region. It is shown that as a result of the inclusion of Dean vortices, the curved hole delivery leads to enhanced film cooling effectiveness. Numerical results, including film cooling effectiveness values, tracking of vortices in the flow field, heat transfer coefficients, and net heat flux reduction (NHFR), are compared between the curved hole, round hole, and a laidback, fan-shaped hole with blowing ratios, M, of 0.5, 1.0, 1.5, 2.0, and 2.5. The comparison shows that film cooling effectiveness values with the curved hole are higher than those with cylindrical film cooling holes at every blowing ratio studied. The curved hole has lower film cooling effectiveness values than the laidback, fan-shaped holes when M = 0.5 and 1.0, but shows advantages when the blowing ratio is higher than 1.0. There is heat transfer enhancement for the curved hole case due to a higher kinetic energy transferred to the near-wall region, however. Nevertheless, the curved hole still displays a higher NHFR when the blowing ratio is high.

Enhancement of Film Cooling Effectiveness Using Dean Vortices

Film cooling technology is widely used in gas turbines. Improvement of gas turbine thermal efficiency, specific power and specific thrust can be achieved by reducing the use of cooling air by improvements on film cooling technology. Experimental and numerical efforts have demonstrated that cooling effectiveness is reduced when kidney vortices created as the emerging film cooling jet flow interacts with the passage flow resulting in coolant lift-off and mixing. With higher blowing ratios, M, these kidney vortices become stronger and effectiveness worsens. Different technologies have been developed to enhance film cooling effectiveness by manipulating the kidney vortices. Some reduce local blowing ratios and local injection angles with expanded hole exits, called shaped holes. Others are employing hole geometries in an attempt to establish anti-kidney vortices in the flow field to weaken the effects of kidney vortices. Most of these film cooling technologies focus on methods that are within the present limits of manufacturing technology. However, with the additive manufacturing anticipated in the future, there will be more freedom in film cooling hole design. Exploiting this freedom, the present authors tried using curved holes to generate Dean vortices within the delivery line. These vortices have opposite direction of rotation to the vorticity of the kidney vortices and, thus, there is interaction between these vortices in the mixing region. It is shown that as a result of the inclusion of Dean vortices, the curved hole delivery leads to enhanced film cooling effectiveness. Numerical results, including film cooling effectiveness values, tracking of vortices in the flow field, heat transfer coefficients, and net heat flux reduction are compared between the curved hole (CH), round hole (RH) and a laidback, fan-shaped hole (SH) with blowing ratios, M, of 0.5, 1.0, 1.5, 2.0 and 2.5. The laidback, fan-shaped hole represents the state of the art in film cooling hole design. Another curved hole (RCH) with the opposite (to the CH hole) curvature of delivery line is checked for comparison, with M = 1.5. The comparison shows that film cooling effectiveness values with the CH curved hole are higher than those with cylindrical film cooling holes at every blowing ratio studied. The curved hole has lower film cooling effectiveness values than the laidback, fan-shaped holes when M = 0.5 and 1.0, but shows advantages when the blowing ratio is higher than 1.0. With the interaction between Dean vortices and kidney vortices when using curved holes, a large amount of coolant re-attaches to the wall after moving streamwise for some distance, providing improved downstream film cooling performance. There is heat transfer enhancement for the curved hole case due to a higher kinetic energy transferred to the near-wall region, however. Nevertheless, the curved hole still displays a higher net heat flux reduction (NHFR) when the blowing ratio is high.