scholarly journals Numerical simulation of hydraulic fracturing in enhanced geothermal systems considering thermal stress cracks

2021 ◽  
Author(s):  
Ziyang Zhou ◽  
Hitoshi MIKADA ◽  
Junichi TAKEKAWA ◽  
Shibo Xu
Keyword(s):  
Thermal Stress ◽  
High Temperature ◽  
Hydraulic Fracturing ◽  
Geothermal Energy ◽  
Confining Pressure ◽  
Numerical Results ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Compression Tests ◽  
High Confining Pressure

Abstract With the increasing attention to clean and economical energy resources, geothermal energy and enhanced geothermal systems (EGS) have gained much importance. For the efficient development of deep geothermal reservoirs, it is crucial to understand the mechanical behavior of reservoir rock and its interaction with injected fluid under high temperature and high confining pressure environments. In the present study, we develop a novel numerical scheme based on the distinct element method (DEM) to simulate the failure behavior of rock by considering the influence of thermal stress cracks and high confining pressure for EGS. We validated the proposing method by comparing our numerical results with experimental laboratory results of uniaxial compression tests under various temperatures and biaxial compression tests under different confining pressure regarding failure patterns and stress-strain curves. We then apply the developed scheme to the hydraulic fracturing simulations under various temperatures, confining pressure, and injection fluid conditions. Our numerical results indicate that the number of hydraulic cracks is proportional to the temperature. At a high temperature and low confining pressure environment, a complex crack network with large crack width can be observed, whereas the generation of the micro cracks is suppressed in high confining pressure conditions. In addition, high-viscosity injection fluid tends to induce more hydraulic fractures. Since the fracture network in the geothermal reservoir is an essential factor for the efficient production of geothermal energy, the combination of the above factors should be considered in hydraulic fracturing treatment in EGS.

scholarly journals Experimental and Numerical Evaluation of Hydraulic Fracturing under High Temperature and Embedded Fractures in Large Concrete Samples

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3171
Author(s):  
Liangliang Guo ◽  
Zihong Wang ◽  
Yanjun Zhang ◽  
Zhichao Wang ◽  
Haiyang Jiang
Keyword(s):  
Numerical Simulation ◽  
High Temperature ◽  
Hydraulic Fracturing ◽  
Laboratory Test ◽  
High Temperatures ◽  
Large Scale ◽  
Hydraulic Fractures ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Fracture Density

In order to study the mechanism of hydraulic fracturing in enhanced geothermal systems, we analyzed the influence of high temperatures and embedded fractures on the initiation and propagation of hydraulic fractures using a laboratory test and numerical simulation. The analysis was conducted via large-scale true triaxial hydraulic fracturing tests with acoustic emission monitoring. Moreover, we discussed and established the elastic-plastic criterion of hydraulic fracturing initiation. The corresponding fracturing procedure was designed and embedded into the FLAC3D software. Then, a numerical simulation was conducted and compared with the laboratory test to verify the accuracy of the fracturing procedure. The influence of high temperatures on hydraulic fracturing presented the following features. First, multi-fractures were created, especially in the near-well region. Second, fracturing pressure, extension pressure, and fracture flow resistance became larger than those at room temperature. 3D acoustic fracturing emission results indicated that the influence of the spatial distribution pattern of embedded fractures on hydraulic fracturing direction was larger than that of triaxial stress. Furthermore, the fracturing and extension pressures decreased with the increase of embedded fracture density. For hydraulic fracturing in a high temperature reservoir, a plastic zone was generated near the borehole, and this zone increased as the injection pressure increased until the well wall failed.

scholarly journals Environmentally friendly, rheoreversible, hydraulic-fracturing fluids for enhanced geothermal systems

Geothermics ◽  
2015 ◽  
Vol 58 ◽  
pp. 22-31 ◽  
Author(s):  
Hongbo Shao ◽  
Senthil Kabilan ◽  
Sean Stephens ◽  
Niraj Suresh ◽  
Anthon N. Beck ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Environmentally Friendly ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Fracturing Fluids

230°C Accelerometer with Digitized Output for Directional Drilling

2014 ◽  
Vol 2014 (HITEC) ◽  
pp. 000298-000304
Author(s):  
Douglas C. MacGugan ◽  
Eric C. Abbott ◽  
J. Chris Milne
Keyword(s):  
High Temperature ◽  
Oil And Gas ◽  
Elevated Temperatures ◽  
Digital Signal ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Directional Drilling ◽  
Orientation Measurement ◽  
Acceleration Signal ◽  
Vibrating Beams

Measurement-While-Drilling (MWD) technology for oil and gas, and geothermal directional drilling exploration is pushing into ever higher temperature environments - beyond 200°C. Orientation sensors supporting these high temperature environments need to provide highly accurate elevation and tool face measurements on the order of 0.1°. Honeywell has developed a new digital high temperature down-hole accelerometer, DHTA230, capable of providing the required accuracy at the elevated temperatures of 230°C, in the rugged MWD shock and vibration environment, with expected excellent reliability and life. The DHTA230 is designed for use in the downhole environment, but is based upon a mature Honeywell accelerometer using dual vibrating beam sensing elements. These sensing elements are configured as double-ended-tuning-forks in a push-pull orientation attached onto a pendulous proof mass. This push-pull configuration provides an acceleration signal proportional to the frequency difference of the vibrating beams, an easily captured digital signal through measurement of the two vibrating beam phases. The digitized accelerometer eliminates the need for A/D electronics in the high temperature drilling environment. The DHTA230 is 0.79” in diameter with a depth of .393” at the mount flange. The ruggedized configuration of the DHTA230 is expected to provide reliable orientation measurement in high temperature direction drilling applications up to 1000h. The DHTA230 electronics incorporate ceramic hybrids with chip and wire construction. Active die are based upon proven 300°C chips developed previously for the Enhanced Geothermal Systems OM300, fabricated using Honeywell HTSOI4 process. The electronics include power conditioning providing reliable operation using a single power supply between 7V and 15V. Dual oscillator electronic circuits provide the necessary function to drive and sense the dual vibrating beams, while providing a CMOS logic level signal of the frequency pulse train. The accelerometer provides precision output up to 15g acceleration inputs, and allows sensing of higher-g vibration levels. This paper contains information on the target application, electrical and mechanical component requirements, design, fabrication approach, and initial prototype testing. The DHTA230 is expected to enter production transition in 2015.

scholarly journals Triaxial Testing of Geosynthetics Reinforced Tailings with Different Reinforced Layers

Materials ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1943
Author(s):  
Fu Yi ◽  
Changbo Du
Keyword(s):  
Triaxial Compression ◽  
Friction Angle ◽  
Confining Pressure ◽  
Test Results ◽  
Compression Tests ◽  
Strength Index ◽  
Stress Strain ◽  
High Confining Pressure ◽  
Zhang Model ◽  
Triaxial Compression Tests

To evaluate the shear properties of geotextile-reinforced tailings, triaxial compression tests were performed on geogrids and geotextiles with zero, one, two, and four reinforced layers. The stress–strain characteristics and reinforcement effects of the reinforced tailings with different layers were analyzed. According to the test results, the geogrid stress–strain curves show hardening characteristics, whereas the geotextile stress–strain curves have strain-softening properties. With more reinforced layers, the hardening or softening characteristics become more prominent. We demonstrate that the stress–strain curves of geogrids and geotextile reinforced tailings under different reinforced layers can be fitted by the Duncan–Zhang model, which indicates that the pseudo-cohesion of shear strength index increases linearly whereas the friction angle remains primarily unchanged with the increase in reinforced layers. In addition, we observed that, although the strength of the reinforced tailings increases substantially, the reinforcement effect is more significant at a low confining pressure than at a high confining pressure. On the contrary, the triaxial specimen strength decreases with the increase in the number of reinforced layers. Our findings can provide valuable input toward the design and application of reinforced engineering.

scholarly journals Mechanical behavior investigation of Longmaxi shale under high temperature and high confining pressure

2019 ◽  
Vol 23 (3 Part A) ◽  
pp. 1521-1527
Author(s):  
Hui-Jun Lu ◽  
Dong-Feng Hu ◽  
Ru Zhang ◽  
Cun-Bao Li ◽  
Jun Wang ◽  
...  
Keyword(s):  
High Temperature ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Bedding Plane ◽  
Brittleness Index ◽  
Tensile Fracture ◽  
Pressure Condition ◽  
Failure Patterns ◽  
Longmaxi Shale ◽  
High Confining Pressure

Triaxial compression tests are conducted on Longmaxi shale under high temperature and high confining pressure condition corresponding to a depth of 3000 m for two typical bedding plane orientations (0? and 90?). It is found that the crack initiation stresses and crack damage stresses of the Longmaxi shale specimens with different vein orientations are different, reflecting that the inclination of the bedding plane has a non-negligible influence on the microcrack initiation and propagation. In addition, the brittleness index of the Longmaxi shale with a bedding plane orientation of 90? is greater than that with an orientation of 0?, which confirmed that the brittleness index is related to the structural orientation under a high temperature and high confining pressure condition. Concerning the failure patterns, both the shear and tensile fracture modes has been observed.

Analog Component Development for 300°C Sensor Interface Applications

2012 ◽  
Vol 2012 (HITEC) ◽  
pp. 000199-000206 ◽  
Author(s):  
Bruce W. Ohme ◽  
Mark R. Larson
Keyword(s):  
High Temperature ◽  
Oil And Gas ◽  
Frequency Converter ◽  
Electrical Power ◽  
Low Noise ◽  
Silicon On Insulator ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Oil And Gas Development ◽  
Sensor Interface

The development of Enhanced Geothermal Systems (EGS) for base-load electrical power generation will require electronics for sensing and control during exploration and drilling and also during production. The operating temperature environments for these applications will generally be more extreme than those encountered by electronics currently deployed for oil and gas development and production monitoring. To address this requirement, electronic components have been designed and fabricated for operation at temperatures of 300°C. These integrated circuits use silicon-on-insulator (SOI) fabrication processes to achieve high temperature operation. High-fidelity simulation models have been developed by characterization of SOI devices at 300°C. These device models were employed to design components required for the development of a down-hole orientation module. A wide-bandwidth, low-noise operational amplifier has been developed for use with MEMS accelerometer sensors. A multi-channel synchronous voltage-to-frequency converter with built-in reference and oscillators has also been developed for use with 3-axis flux-gate magnetometers. The components themselves are general purpose and could easily be used for other high-temperature sensor-interface applications. .

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