scholarly journals Cryogenic Fracturing of Wellbores Under True Triaxial-Confining Stresses: Experimental Investigation

SPE Journal ◽  
2018 ◽  
Vol 23 (04) ◽  
pp. 1271-1289 ◽  
Author(s):  
Minsu Cha ◽  
Naif B. Alqahtani ◽  
Bowen Yao ◽  
Xiaolong Yin ◽  
Timothy J. Kneafsey ◽  
...  
Keyword(s):  
High Pressure ◽  
Thermal Shock ◽  
Principal Stress ◽  
Breakdown Pressure ◽  
True Triaxial ◽  
Pressure Decay ◽  
Stress Levels ◽  
Cryogenic Fracturing ◽  
Flow Through ◽  
Thermal Shocks

Summary A laboratory study of cryogenic fracturing was performed to test its ability to improve oil/gas recovery from low-permeability reservoirs. Our objective is to develop well-stimulation technologies using cryogenic fluids [e.g., liquid nitrogen (LN)] to increase permeability in a large reservoir volume surrounding wells. The new technology has the potential to reduce formation damage caused by current stimulation methods and minimize or eliminate water usage. The concept of cryogenic fracturing is that a sharp thermal gradient (thermal shock) created at the surfaces of formation rocks by applying cryogenic fluid can cause strong local tensile stress and start fractures. We developed a laboratory system for cryogenic fracturing under true-triaxial loading, with LN-delivery/control and -measurement systems. The loading system simulates confining stresses by independently loading each axis up to approximately 5,000 psi on 8×8×8-in. cubes. Temperature in boreholes and at block surfaces and fluid pressure in boreholes were continuously monitored. Acoustic and pressure-decay measurements were obtained before and at various stages of stimulations. Cubic blocks (8 × 8×8-in.) of Niobrara shale, concrete, and sandstones were tested, and stress levels and anisotropies varied. Three schemes were considered: gas fracturing without cryo-stimulation, gas fracturing after low-pressure cryogen flow-through, and gas fracturing after high-pressure cryogen flow-through. Results from pressure-decay tests show that LN stimulation clearly increases permeability, and repeated stimulations further increase the permeability. Acoustic velocities and amplitudes decreased significantly after cryo-stimulation, indicating fracture creation. In the gas fracturing without the stimulation, breakdown (complete fracturing) occurs suddenly without any initial leaking, and major fracture planes form along the plane containing principal-stress and intermediate-stress directions, as expected theoretically. However, in the gas fracturing after cryogenic stimulations, breakdown occurred gradually and with massive leaking because of thermal fractures created during stimulation. In addition, the major fracture direction does not necessarily follow the plane containing the principal-stress direction, especially at low confining-stress levels. In tests, we observed that cryogenic stimulation seems to disrupt the internal stress field. The increase in borehole temperature after stimulation affects the permeability of the specimen. When a stimulated specimen is still cold, it maintains high permeability because fractures remain open and local thermal tension is maintained near the borehole. When the rock warms back, fractures close and permeability decreases. In these tests, we have not used proppants. Overall, fractures are clearly generated by low- and high-pressure thermal shocks. The added pressure of the high-pressure thermal shocks helps to further propagate cryogenic fractures generated by thermal shock. Breakdown pressure is significantly lowered by LN stimulation, with observed breakdown-pressure reductions up to approximately 40%.

INVESTIGATION OF THE TIME OF GAS FLOW THROUGH A HOLE IN LONG PIPELINES UNDER HIGH PRESSURE

2020 ◽  
Vol 58 (1) ◽  
pp. 30-43
Author(s):  
N.D. Yakimov ◽  
◽  
A.I. Khafizova ◽  
N.D. Chichirova ◽  
O.S. Dmitrieva ◽  
...  
Keyword(s):  
High Pressure ◽  
Gas Flow ◽  
Flow Through

Board-Level Reliability of Pb-Free Surface Mounted Assemblies during Thermal Shock Testing

2006 ◽  
Vol 15-17 ◽  
pp. 633-638 ◽  
Author(s):  
Jong Woong Kim ◽  
Hyun Suk Chun ◽  
Sang Su Ha ◽  
Jong Hyuck Chae ◽  
Jin Ho Joo ◽  
...  
Keyword(s):  
Thermal Shock ◽  
Solder Joints ◽  
Lead Frame ◽  
Shear Forces ◽  
Microstructural Investigation ◽  
Shock Testing ◽  
Ceramic Capacitor ◽  
Board Level ◽  
Board Level Reliability ◽  
Thermal Shocks

Board-level reliability of conventional Sn-37Pb and Pb-free Sn-3.0Ag-0.5Cu solder joints was evaluated using thermal shock testing. In the microstructural investigation of the solder joints, the formation of Cu6Sn5 intermetallic compound (IMC) layer was observed between both solders and Cu lead frame, but any crack or newly introduced defect cannot be found even after 2000 cycles of thermal shocks. Shear test of the multi layer ceramic capacitor (MLCC) joints were also conducted to investigate the effect of microstructural variations on the bonding strength of the solder joints. Shear forces of the both solder joints decreased with increasing thermal shock cycles. The reason to the decrease in shear force was discussed with fracture surfaces of the shear tested solder joints.

scholarly journals Simulation of the Residual Stress of the Y2O3/Al2O3 Composite Deuterium Permeation Barrier under Thermal Shock

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Kezhi Huang ◽  
Weijing Wang ◽  
Qinghe Yu ◽  
Lei Hao ◽  
Jing Mi ◽  
...  
Keyword(s):  
Residual Stress ◽  
Thermal Stress ◽  
Thermal Shock ◽  
Principal Stress ◽  
Stress Singularity ◽  
Residual Thermal Stress ◽  
Al2o3 Coating ◽  
Element Analysis ◽  
Al2o3 Layer ◽  
Y2o3 Coating

A deuterium permeation barrier is an essential part in the core component of nuclear reactors. It can protect the structure made of steel from being penetrated by deuterium in a fusion reactor. However, residual stress induced in the operation would dramatically influence the mechanical endurance of the coating, threatening the safety of the facilities. In this paper, finite element analysis was conducted to investigate the residual stress in nanoscale Al2O3 and Y2O3 coatings and their composites under thermal shock, from 700°C to 25°C. The max principal stress is assumed as the cause of crack initiation in the coating, because ceramics are brittle and fragile under tensile stress. Max shear stress and max Mises stress in the systems are also analyzed, and the effect of thickness in the range 100 nm to 1000 nm was investigated. The max principal stress in Al2O3 coating reaches its maximum value, 1.33 GPa, when the thickness of coating reaches 450 nm. And the max principal stress decreases at a very low rate as the thickness increases exceeding 450 nm. The max principal stress in Y2O3 coating increases rapidly as the thickness increases when the thickness of the coating is below 250 nm, and the max principal stress is at about 0.9 GPa when the thickness exceeds 500 nm. The max principal stress in the Y2O3/Al2O3 (150 nm) composite coating occurs in the Al2O3 layer and shows no difference from the single layer of 150 nm thick Al2O3 coating. The max principal stress site of all three kinds of coating is located at the edge of the coating 25 nm away from the interface. The result shows that residual thermal stress in the coating increases as the thickness increases when the thickness of the coating is below 200 nm due to the stress singularity of the interface. And as the thickness exceeds 500 nm, the increase in thickness has little impact on the residual thermal stress in the coating. Coating an Y2O3 top layer will not introduce any more residual thermal stress under the thermal shock condition. The Y2O3 coating causes much less residual stress under thermal shock compared with Al2O3 owing to its much lower Young’s modulus. The max principal stress in the 300 nm thick Y2O3 coating is 0.85 GPa while that of the Al2O3 coating is 1.16 GPa. The max residual stress of the composite Y2O3/Al2O3 (150 nm) coating is determined by the Al2O3 layer.

Influence of Backward- and Forward-Facing Steps on the Flow Through a Turning Mid Turbine Frame

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Sabine Bauinger ◽  
Emil Goettlich ◽  
Franz Heitmeir ◽  
Franz Malzacher
Keyword(s):  
High Pressure ◽  
Total Pressure ◽  
Test Rig ◽  
Test Setup ◽  
Aero Engine ◽  
Total Temperature ◽  
Flow Through ◽  
Run Up ◽  
Compact Design ◽  
Probe Measurements

For this work, reality effects, more precisely backward-facing steps (BFSs) and forward-facing steps (FFSs), and their influence on the flow through a two-stage two-spool turbine rig under engine-relevant conditions were experimentally investigated. The test rig consists of an high pressure (HP) and an low pressure (LP) stage, with the two rotors rotating in opposite direction with two different rotational speeds. An S-shaped transition duct, which is equipped with turning struts (so-called turning mid turbine frame (TMTF)) and making therefore a LP stator redundant, connects both stages and leads the flow from a smaller to a larger diameter. This test setup allows the investigation of a TMTF deformation, which occurs in a real aero-engine due to non-uniform warming of the duct during operation—especially during run up—and causes BFSs and FFSs in the flow path. This happens for nonsegmented ducts, which are predominantly part of smaller engines. In the case of the test rig, steps were not generated by varying temperature but by shifting the TMTF in horizontal direction while the rotor and its casing were kept in the same position. In this way, both BFSs and FFSs between duct endwalls and rotor casing could be created. In order to avoid steps further downstream of the interface between HP rotor and TMTF, the complete aft rig was moved laterally too. In this case, the aft rig incorporates among others the LP rotor, the LP rotor casing, and the deswirler downstream of the LP stage. In order to catch the influence of the steps on the whole flow field, 360 deg rake traverses were performed downstream of the HP rotor, downstream of the duct, and downstream of the LP rotor with newly designed, laser-sintered combi-rakes for the measurement of total pressure and total temperature. Only the compact design of the rakes, which can be easily realized by additive manufacturing, makes the aforementioned 360 deg traverses in this test rig possible and allows a number of radial measurements positions, which is comparable to those of a five-hole probe. To get a more detailed information about the flow, also five-hole probe measurements were carried out in three measurement planes and compared to the results of the combi-rakes.

Influence of a Shroud Axisymmetric Slot Injection on a High Pressure Turbine Flow

2016 ◽  
Author(s):  
Etienne Tang ◽  
Mickaël Philit ◽  
Gilles Leroy ◽  
Isabelle Trebinjac ◽  
Ghislaine Ngo Boum
Keyword(s):  
High Pressure ◽  
Incidence Angle ◽  
Main Stream ◽  
High Pressure Turbine ◽  
Unsteady Rans ◽  
Flow Through ◽  
Definition Of ◽  
Cooling Air ◽  
Ideal Process ◽  
Mixing Losses

This paper focuses on an axisymmetric slot injecting cooling air at the casing between the stator and the rotor in a one-stage unshrouded transonic high pressure turbine. This configuration has been studied with the help of unsteady RANS computations with and without the slot. Special care has been taken to model and describe the interaction induced unsteady mechanisms. It has been found that the cooling air is ejected from the axisymmetric slot at a fixed position with respect to the stator vanes, with a much lower incidence angle than the main stream. The flow through the rotor passage is highly modified and reveals an unsteady behaviour which highlights the necessity of using unsteady simulations in order to accurately model such a configuration. The effect on the efficiency and on the repartition of loss generation has been determined. As several different definitions of the efficiency can be used for cooled turbine cases, this choice is discussed. In particular, Young & Horlock’s “Weighted Pressure” definition, which takes into account some unavoidable mixing losses in the definition of the ideal process, is evaluated. With this definition, the slot does not yield any significant decrease in overall efficiency.

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