Flow-induced microfracturing of granite in superhot geothermal environments

2021 ◽  
Author(s):  
Ryota Goto ◽  
Noriaki Watanabe ◽  
Kiyotoshi Sakaguchi ◽  
Youqing Chen ◽  
Takuya Ishibashi ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Working Fluid ◽  
Fracture System ◽  
Geothermal Resources ◽  
Rock Body ◽  
True Triaxial ◽  
Low Viscosity ◽  
Fracture Systems ◽  
Geothermal Environments ◽  
Fracturing Experiments

<p>Superhot geothermal environments with temperatures of approximately 400-500<sup>︒</sup>C at depth of approximately 2-4 km are expected as a new geothermal energy frontier. In order to efficiently exploit the superhot geothermal resources, fracture systems are necessary as flow path of working fluid. Hydraulic fracturing is a promising technique because it is able to create a new fracture system or enhance the permeability of preexisting fracture system. Laboratory-scale hydraulic fracturing experiments of granite have demonstrated the formation of densely distributed network of permeable fractures throughout the entire rock body at or near the supercritical temperature for water. Though the process has been presumed to involve continuous infiltration of low-viscosity water into preexisting microfractures followed by creation and merger of the subsequent fractures, plausible criterion for the fracturing is yet to be clarified. The possibility that the Griffith failure criterion is available to predict the occurrence of fracturing was shown by hydraulic fracturing experiments with acoustic emission measurements of granite at 400<sup>︒</sup>C under true triaxial stress. The present study provides a theoretical basis required to establish the procedure for hydraulic fracturing in superhot geothermal environment.</p>

scholarly journals Interaction Law between Natural Fractures-Vugs and Acid-Etched Fracture during Steering Acid Fracturing in Carbonate Reservoirs

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Yifan Dai ◽  
Bing Hou ◽  
Changlin Zhou ◽  
Kunpeng Zhang ◽  
Fei Liu
Keyword(s):  
Fracture Surface ◽  
Physical Simulation ◽  
Carbonate Reservoir ◽  
Natural Fracture ◽  
Simulation Experiments ◽  
True Triaxial ◽  
Acid Fracturing ◽  
Low Viscosity ◽  
Fracturing Experiments ◽  
Interaction Law

Steering acid fracturing is a technique that improves the conductivity of carbonate reservoir. It is widely used in a carbonate reservoir. However, due to the lack of comparative experiments, the application of steering acid to improve the fracturing results is still unknown. Therefore, a series of true triaxial acid fracturing experiments were conducted to study steering acid fracturing in carbonate reservoir. The carbonate specimens used in the experiment were from the Qixia group and Dengsi Member in Sichuan, China. In this study, slick water, cross-linked gel, and self-generating acid were used as ahead fluid to cooperate with steering acid. Experimental results show that (1) the low-viscosity ahead fluid with steering acid can result in more complex fractures; (2) the complexity of fractures is influenced by natural fracture and the viscosity of the ahead fluid; and (3) based on the 3D scanning results of the fracture surface, different ahead fluids will lead to different corrosion results. This study provides useful suggestions on steering acid fracturing design and physical simulation experiments.

Increasing the Productivity of Horizontal Wells Through Multistage Hydraulic Fracturing Using a Working Fluid Based on a New Biopolymer System

2021 ◽  
Author(s):  
Nikolay Mikhaylovich Migunov ◽  
Aleksey Dmitrievich Alekseev ◽  
Dinar Farvarovich Bukharov ◽  
Vadim Alexeevich Kuznetsov ◽  
Aleksandr Yuryevich Milkov ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Russian Federation ◽  
Oil Production ◽  
Horizontal Wells ◽  
Working Fluid ◽  
High Tech ◽  
Executive Order ◽  
Bazhenov Formation ◽  
Multistage Hydraulic Fracturing ◽  
The Russian Federation

Abstract According to the US Energy Agency (EIA), Russia is the world leader in terms of the volume of technically recoverable "tight oil" resources (U.S. Department of Energy, 2013). To convert them into commercial production, it is necessary to create cost-effective development technologies. For this purpose, a strategy has been adopted, which is implemented at the state level and one of the key elements of which is the development of the high-tech service market. In 2017, the Minister of Energy of the Russian Federation, in accordance with a government executive order (Government Executive Order of the Russian Federation, 2014), awarded the Gazprom Neft project on the creation of a complex of domestic technologies and high-tech equipment for developing the Bazhenov formation with the national status. It is implemented in several directions and covers a wide range of technologies required for the horizontal wells drilling and stimulating flows from them using multi-stage hydraulic fracturing (MS HF) methods. Within the framework of the technological experiment implemented at the Palyanovskaya area at the Krasnoleninskoye field by the Industrial Integration Center "Gazpromneft - Technological Partnerships" (a subsidiary of Gazprom Neft), from 2015 to 2020, 29 high-tech wells with different lengths of horizontal wellbore were constructed, and multistage hydraulic fracturing operations were performed with various designs. Upon results of 2020, it became possible to increase annual oil production from the Bazhenov formation by 78 % in comparison with up to 100,000 tons in 2019. The advancing of development technologies allowed the enterprise to decrease for more than twice the cost of the Bazhenov oil production from 30 thousand rubles per ton (69$/bbl) at the start of the project in 2015 to 13 thousand rubles (24$/bbl) in 2020. A significant contribution to the increase in production in 2020 was made by horizontal wells, where MS HF operations were carried out using an experimental process fluid, which is based on the modified Si Bioxan biopolymer. This article is devoted to the background of this experiment and the analysis of its results.

scholarly journals Hydromechanical-Coupled Cohesive Interface Simulation of Complex Fracture Network Induced by Hydrofracturing with Low-Viscosity Supercritical CO2

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 1) ◽  
Author(s):  
Xin Cai ◽  
Wei Liu
Keyword(s):  
Hydraulic Fracturing ◽  
Supercritical Co2 ◽  
Fracture Propagation ◽  
Zone Model ◽  
Hydraulic Pressure ◽  
Small Aperture ◽  
Complex Fracture ◽  
Low Viscosity ◽  
Fracturing Fluids ◽  
Low Viscosity Fluids

Abstract Hydraulic fracturing experiments with low-viscosity fluids, such as supercritical CO2, demonstrate the formation of complex fracture networks spread throughout the rocks. To study the influence of viscosity of the fracturing fluids on hydraulic fracture propagation, a hydromechanical-coupled cohesive zone model is proposed for the simulation of mechanical response of rock grains boundary separation. This simulation methodology considers the synergistic effects of unsteady flow in fracture and rock grain deformation induced by hydraulic pressure. The simulation results indicate a tendency of complex fracture propagation with more branches as the viscosity of fracturing fluids decrease, which is in accord with experimental results. The low-viscosity fluid can flow into the microfractures with extremely small aperture and create more shear failed fracture. This study confirms the possibility of effective well stimulations by hydraulic fracturing with low-viscosity fluids.

Optimized Clay Control Fracturing Fluid Used in a Highly Water-Sensitive Tight Oil Reservoir Hydraulic Fracturing Application in Xinjiang Oil Field: Case Study

2021 ◽  
Author(s):  
Xinjun Mao ◽  
Chaofeng Chen ◽  
Renzhong Gan ◽  
Shubo Zhou ◽  
Zichao Wang ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Recovery Rate ◽  
Oil Field ◽  
National Standard ◽  
Working Fluid ◽  
Tight Oil ◽  
Fracturing Fluid ◽  
Core Flow ◽  
Velocity Sensitivity ◽  
Highly Sensitive

Abstract The candidate wells are tight oil wells and most of the wells in the area have a low recovery rate of fracturing fluid after fracturing treatment. The lithology is glutenite with weak cementation and a high sensitivity tendency. This paper presents the process of sensitivity evaluation and fracturing fluid evaluation. Also, this paper introduces a customized and optimized clay control fracturing fluid wells in a highly sensitive reservoir. Per local national standard, traditional methods of swelling test (ST) and x-ray diffraction (XRD) were employed for qualitative formation cutting analysis. An innovative trial was then developed to evaluate cores quantitatively by water sensitivity. A clay stabilizer was then chosen to be used for the highly sensitive cores and regain permeability testing of the broken fracturing fluid was performed. Based on the analysis and evaluation, a customized treatment design was initiated for the hydraulic fracturing treatment. The qualitative evaluation showed the rock is highly water sensitive and the cores easily collapse because of weak cementation. No flow could be established during traditional core flow tests with brine. The newly developed method used kerosene as the working fluid to prevent the cores from contact with water or brine. The core flow tests resulted in a velocity sensitivity damage rate of 92%, which is considered as highly velocity sensitive. Accordingly, a special clay stabilizer was chosen to be used in the fracturing fluid and the permeability damage of the broken fracturing fluid is only 26.9%(Table 16). Field results have shown that the fracturing fluid recovery rate in treated wells is higher than the area average level and treated wells have significant oil production increase. The innovative clay control fracturing fluid and its field application reduces the influence of water and velocity sensitivity. The customized treatment with special clay stabilizer helps increase the recovery rate of fracturing fluid in reservoirs with severe clay stability and weak cementation issues.

scholarly journals Study on Fracture Morphological Characteristics of Refracturing for Longmaxi Shale Formation

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-13 ◽  
Author(s):  
Yintong Guo ◽  
Lei Wang ◽  
Xin Chang ◽  
Jun Zhou ◽  
Xiaoyu Zhang
Keyword(s):  
Hydraulic Fracturing ◽  
Morphological Characteristics ◽  
Test Method ◽  
Pressure Curve ◽  
Natural Fractures ◽  
True Triaxial ◽  
Bedding Planes ◽  
Initiation And Propagation ◽  
Longmaxi Shale ◽  
Shale Formation

Refracturing technology has become an important means for the regeneration of old wells reconstruction. It is of great significance to understand the formation mechanism of hydraulic fracturing fracture for the design of hydraulic fracturing. In order to accurately evaluate and improve fracturing volume after refracturing, it is necessary to understand the mechanism of refracturing fracture in shale formation. In this paper, a true triaxial refracturing test method was established. A series of large-scale true triaxial fracturing experiments were carried out to characterize the refracturing fracture initiation and propagation. The results show that for shale reservoirs with weak bedding planes and natural fractures, hydraulic fracturing can not only form the main fracturing fracture, which is perpendicular to horizontal minimum principal stress, but it can also open weak bedding plane or natural fractures. The characteristics of fracturing pump curve indicated that the evolution of fracturing fractures, including initiation and propagation and communication of multiple fractures. The violent fluctuation of fracturing pump pressure curve indicates that the sample has undergone multiple fracturing fractures. The result of refracturing shows that initial fracturing fracture channels can be effectively closed by temporary plugging. The refracturing breakdown pressure is generally slightly higher than that of initial fracturing. After temporary plugging, under the influence of stress induced by the initial fracturing fracture, the propagation path of the refracturing fracture is deviated. When the new fracturing fracture communicates with the initial fracturing fracture, the original fracturing fracture can continue to expand and extend, increasing the range of the fracturing modifications. The refracturing test results was shown that for shale reservoir with simple initial fracturing fractures, the complexity fracturing fracture can be increased by refracturing after temporary plugging initial fractures. The effect of refracturing is not obvious for the reservoir with complex initial fracturing fractures. This research results can provide a reliable basis for optimizing refracturing design in shale gas reservoir.

scholarly journals Full-waveform-based characterization of acoustic emission activity in a mine-scale experiment: a comparison of conventional and advanced hydraulic fracturing schemes

2020 ◽  
Vol 222 (1) ◽  
pp. 189-206 ◽  
Author(s):  
Peter Niemz ◽  
Simone Cesca ◽  
Sebastian Heimann ◽  
Francesco Grigoli ◽  
Sebastian von Specht ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Hydraulic Fracturing ◽  
Induced Seismicity ◽  
Large Scale ◽  
Sampling Rate ◽  
Fracture Plane ◽  
B Values ◽  
Full Waveform ◽  
Scale Experiment ◽  
Fracturing Experiments

SUMMARY Understanding fracturing processes and the hydromechanical relation to induced seismicity is a key question for enhanced geothermal systems (EGS). Commonly massive fluid injection, predominately causing hydroshearing, are used in large-scale EGS but also hydraulic fracturing approaches were discussed. To evaluate the applicability of hydraulic fracturing techniques in EGS, six in situ, multistage hydraulic fracturing experiments with three different injection schemes were performed under controlled conditions in crystalline rock at the Äspö Hard Rock Laboratory (Sweden). During the experiments the near-field ground motion was continuously recorded by 11 piezoelectric borehole sensors with a sampling rate of 1 MHz. The sensor network covered a volume of 30×30×30 m around a horizontal, 28-m-long injection borehole at a depth of 410 m. To extract and characterize massive, induced, high-frequency acoustic emission (AE) activity from continuous recordings, a semi-automated workflow was developed relying on full waveform based detection, classification and location procedures. The approach extended the AE catalogue from 196 triggered events in previous studies to more than 19 600 located AEs. The enhanced catalogue, for the first time, allows a detailed analysis of induced seismicity during single hydraulic fracturing experiments, including the individual fracturing stages and the comparison between injection schemes. Beside the detailed study of the spatio-temporal patterns, event clusters and the growth of seismic clouds, we estimate relative magnitudes and b-values of AEs for conventional, cyclic progressive and dynamic pulse injection schemes, the latter two being fatigue hydraulic fracturing techniques. While the conventional fracturing leads to AE patterns clustered in planar regions, indicating the generation of a single main fracture plane, the cyclic progressive injection scheme results in a more diffuse, cloud-like AE distribution, indicating the activation of a more complex fracture network. For a given amount of hydraulic energy (pressure multiplied by injected volume) pumped into the system, the cyclic progressive scheme is characterized by a lower rate of seismicity, lower maximum magnitudes and significantly larger b-values, implying an increased number of small events relative to the large ones. To our knowledge, this is the first direct comparison of high resolution seismicity in a mine-scale experiment induced by different hydraulic fracturing schemes.

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