Chapter 7 Numerical estimation of upper bound of injection pressure window with casing integrity under hydraulic fracturing

Hydraulic fracturing can improve the permeability of composite thin coal seam. Recently, characterizing hydraulic fracture (HF) propagation inside the coal seam and evaluating the permeability enhancement with HF extension remain challenging and crucial. In this work, based on the geological characteristics of the coal seam in a coal mine of the southwest China, the RFPA2D-Flow software is employed to simulate the HF propagation and its permeability-increasing effect in the composite thin coal seam, and a couple of outcomes were obtained. (1) Continuous propagation of the hydraulic microcrack-band is the prominent characteristic of HF propagation. With the increment of the injection-water pressure, HF generation in the composite thin coal seam can be divided into three stages: stress accumulation, stable fracture propagation, and unstable fracture propagation. (2) The hydraulic microcrack-band propagates continuously driven by the fluid-injection pressure. The microcrack-band not only cracks the coal seam but also fractures the gangue sandwiched between the coal seams. (3) The permeability in the composite thin coal seam increases significantly with the propagation of hydraulic microcrack-band. The permeability increases by 1~2 magnitudes after hydraulic fracturing. This study provides references to the field applications of hydraulic fracturing in the composite thin coal seam, such as optimizing hydraulic fracturing parameters, improving gas drainage, and safe-efficient mining.

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Discrete Element Simulation of Interaction between Hydraulic Fracturing and a Single Natural Fracture

Fluids ◽

10.3390/fluids4020076 ◽

2019 ◽

Vol 4 (2) ◽

pp. 76

Author(s):

Basirat ◽

Goshtasbi ◽

Ahmadi

Keyword(s):

Hydraulic Fracturing ◽

Fractured Reservoirs ◽

Critical Role ◽

Injection Pressure ◽

Discrete Element ◽

Natural Fracture ◽

Effective Parameters ◽

Fracture Geometry ◽

Interaction Mode ◽

Element Simulation

Hydraulic fracturing (HF) treatment is performed to enhance the productivity in the fractured reservoirs. During this process, the interaction between HF and natural fracture (NF) plays a critical role by making it possible to predict fracture geometry and reservoir production. In this paper, interaction modes between HF and NF are simulated using the discrete element method (DEM) and effective parameters on the interaction mechanisms are investigated. The numerical results also are compared with different analytical methods and experimental results. The results showed that HF generally tends to cross the NF at an angle of more than 45° and a moderate differential stress (greater than 5 MPa), and the opening mode is dominated at an angle of fewer than 45°. Two effects of changing in the interaction mode and NF opening were also found by changing the strength parameters of NF. Interaction mode was changed by increasing the friction coefficient, while by increasing the cohesion of NF it was less opened under a constant injection pressure.

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A field demonstration of hydraulic fracturing for solids waste disposal — Injection pressure analysis

International Journal of Rock Mechanics and Mining Sciences ◽

10.1016/s1365-1609(97)00212-8 ◽

1997 ◽

Vol 34 (3-4) ◽

pp. 331.e1-331.e17 ◽

Cited By ~ 3

Author(s):

X. Weng ◽

A. Settari ◽

R.G. Keck

Keyword(s):

Hydraulic Fracturing ◽

Waste Disposal ◽

Injection Pressure ◽

Pressure Analysis

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Characteristics of Acoustic Emission Waveforms Induced by Hydraulic Fracturing of Coal under True Triaxial Stress in a Laboratory-Scale Experiment

Minerals ◽

10.3390/min12010104 ◽

2022 ◽

Vol 12 (1) ◽

pp. 104

Author(s):

Nan Li ◽

Liulin Fang ◽

Bingxiang Huang ◽

Peng Chen ◽

Chao Cai ◽

...

Keyword(s):

Acoustic Emission ◽

Hydraulic Fracturing ◽

Coal Sample ◽

Injection Pressure ◽

Triaxial Stress ◽

Pressure Curve ◽

Secondary Fracture ◽

True Triaxial ◽

True Triaxial Stress ◽

Study Laboratory

Hydraulic fracturing (HF) is an effective technology to prevent and control coal dynamic disaster. The process of coal hydraulic fracturing (HF) induces a large number of microseismic/acoustic emission (MS/AE) waveforms. Understanding the characteristic of AE waveforms’ parameters is essential for evaluating the fracturing effect and optimizing the HF strategy in coal formation. In this study, laboratory hydraulic fracturing under true triaxial stress was performed on a cubic coal sample combined with AE monitoring. The injection pressure curve and temporal variation of AE waveforms’ parameters in different stages were analyzed in detail. The experimental results show that the characteristics of the AE waveforms’ parameters well reflect the HF growth behavior in coal. The majority of AE waveforms’ dominant frequency is distributed between 145 and 160 kHz during HF. The sharp decrease of the injection pressure curve and the sharp increase of the AE waveforms’ amplitude show that the fracture already runs through the coal sample during the initial fracture stage. The “trapezoidal” rise pattern of cumulative energy and most AE waveforms with low amplitude may indicate the stage of liquid storage space expansion. The largest proportion of AE waveforms’ energy and higher overall level of AE waveforms’ amplitude occur during the secondary fracture stage, which indicates the most severe degree of coal fracture and complex activity of internal fracture. The phenomenon shows the difference in fracture mechanism between the initial and secondary fracture stage. We propose a window-number index of AE waveforms for better response to hydraulic fracture, which can improve the accuracy of the HF process division.

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Response Characteristics of Coal-Like Material Subjected to Repeated Hydraulic Fracturing: An Evaluation Based on Real-Time Monitoring of Water Injection Pressure and Roof Stress Distribution

Shock and Vibration ◽

10.1155/2021/9931137 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Yongjiang Zhang ◽

Benqing Yuan ◽

Xingang Niu

Keyword(s):

Stress Distribution ◽

Coal Seam ◽

Hydraulic Fracturing ◽

Water Pressure ◽

Water Injection ◽

Injection Pressure ◽

Research Results ◽

Term Extraction ◽

Radius Of Influence ◽

The Impact

Conventional hydraulic fracturing has several disadvantages, including a short effective extraction time and low fracture conductivity during long-term extraction. Aiming at overcoming these shortcomings, a similar simulation test of repeated hydraulic fracturing was conducted in this study, and the evolutionary rules regarding the injection water pressure and stress distribution of the coal seam roof during this repeated hydraulic fracturing were revealed. The research results show that after multiple hydraulic fracturing, the number of cracks in the coal seam and the range of fracturing influence have increased significantly. As the number of fracturing increases, the initial pressure required for cracking decreases. The highest water injection pressure of the first fracturing was 2.8 MPa, while the highest water injection pressures of the second and third fracturing were 2.7 MPa and 2.4 MPa, respectively. As the number of fracturing increases, the area of increased stress will continue to expand. After the first fracturing, the impact radius of fracturing is 100 cm. After the second fracturing, the radius of influence of fracturing expanded to 150 cm. When the third fracturing was over, the radius of influence of the fracturing expanded to approximately 250 cm. It can be seen that, compared with conventional hydraulic fracturing, repeated hydraulic fracturing shows better fracturing effect. The research results can be used as a basis for repeated hydraulic fracturing field tests to increase coal seam permeability.

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A Numerical Investigation of the Hazardous Injection Area of Induced Earthquake during Hydraulic Fracturing

Shock and Vibration ◽

10.1155/2021/9997597 ◽

2021 ◽

Vol 2021 ◽

pp. 1-21

Author(s):

Zhiyong Niu ◽

Shiquan Wang ◽

Hongrui Ma ◽

Songbao Feng ◽

Hengjie Luan ◽

...

Keyword(s):

Hydraulic Fracturing ◽

Geothermal Energy ◽

Hanging Wall ◽

Injection Pressure ◽

Geothermal Field ◽

Fault Slip ◽

Rock Fracturing ◽

Induced Earthquakes ◽

Induced Earthquake ◽

The Stability

Hot dry rock (HDR) geothermal energy has many advantages, such as being renewable, clean, widely distributed, and without time and weather limitations. Hydraulic fracturing is usually needed for the exploitation of HDR geothermal energy. It has many hidden faults in the reservoir/caprock sequences. Injecting fluid into underground formations during hydraulic fracturing often induces fault slip and leads to earthquakes. Therefore, to well understand the induced fault slip and earthquakes is important for the applications and development of HDR geothermal exploitation. In this study, we investigated the hazardous injection area of the induced earthquakes during hydraulic fracturing. The study was based on a hydraulic fracturing test in Qiabuqia geothermal field in China. According to the field, a fault-surrounding rock-fracturing region system was developed to study the influences of fluid injection on the stability of the specific fault. A total of 60 hydraulic fracturing regions and 180 numerical experiments were designed. The results revealed that the hazardous injection regions that threaten the fault’s stability were near to the fault and concentrated on the following four areas: (a) above the top of the fault in underlying strata; (b) above the top of the hanging wall of the fault in underlying strata; (c) near to the fault planes in both footwall and hanging wall; (d) at the bottom of the footwall of the fault in underlying strata. The hazardous injection area can be controlled effectively by adjusting the injection pressure.

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Dynamics of hydraulic fracture development according to acoustic transmission data

10.5194/egusphere-egu21-8858 ◽

2021 ◽

Author(s):

Sergey Turuntaev ◽

Evgeny Zenchenko ◽

Petr Zenchenko ◽

Maria Trimonova ◽

Nikolai Baryshnikov

Keyword(s):

Hydraulic Fracturing ◽

Hydraulic Fracture ◽

Injection Pressure ◽

Ultrasonic Pulse ◽

Theoretical Research ◽

Fracture Rate ◽

Acoustic Transmission ◽

Fracturing Fluid ◽

Fracture Closure ◽

Transmission Data

Acoustic transmission data obtained in laboratory experiment were used to estimate main stages of hydraulic fracture onset, growth and filling by fracturing fluid. Laboratory setup consists of two horizontal disks with a diameter of 750 mm, and a sidewall with an internal diameter of 430 mm. The disks and the sidewall form a pressure chamber with a diameter of 430 mm at a height of 70 mm. There are a number of holes in the disks and the sidewall that are used for mounting ultrasonic transducers, pressure sensors, as well as for fluid injections. As a model material, a mixture of gypsum with cement was used, which was poured into the chamber. The sample was saturated with water gypsum solution and loaded with vertical and two horizontal stresses using special chambers. The fracture was created by viscous fluid (mineral oil with viscosity 0.1 Pa*s) injection with a constant rate 0.2 cm3/s through a cased borehole (diameter 12 mm) with a horizontal slot, which was preliminary located in the center of the sample. Hydraulic fracturing monitoring was carried out by recording of ultrasonic pulses passing through the sample during fracturing. To separate the ultrasonic pulses, the frequency of their sending was used. After that, the envelope of each record fragment was constructed using the Hilbert transformation and its maximum was found. Comparison of the ultrasonic pulse amplitude variations and injection pressure led to the following observations. Initial decrease in the pulse amplitudes began before the maximum pressure was reached, which may indicate the hydraulic fracturing onset at a pressure less than the maximum. The amplitude decline occurs smoothly, so it is difficult to identify any characteristic point on these curves and, accordingly, it is difficult to establish an accurate time of the fracturing onset and the fracture rate. The fracture rate was estimated by different methods previously as &#8776;130 mm/s. After the decline, the pulse amplitudes started to increase, that was related with the injection fluid front propagation in the fracture. In contrast to the decline, the beginning of the amplitude growth was clearly detected. Taking into account the spatial locations of the ultrasonic pulse source, receivers, and fracture, it is possible to estimate the propagation velocity of the fracturing fluid front as &#8776;35 mm/s. After the increase, the ultrasonic pulse amplitudes started to decrease significantly (up to 3 times), which is probably due to the further expansion of the fracture aperture. On the transducers located closer to the well, this decline is maximum. When the injection is stopped, the ultrasonic pulse amplitudes began to grow again, which indicates the fracture closure as the injection pressure decrease. In the experiments on the fracture re-opening under various stress applied to the sample, a linear relationship between the fracture re-opening pressure and applied vertical stress was found. This type of relationship should be expected, but values of the relation parameters declined from the values suggested in theoretical research, which was explained by taken into account back-stresses and non-linear behavior of the sample material.

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A 3D numerical model of hydraulic fracturing, injection pressure and microseismicity in anisotropic stress fields

10.5194/egusphere-egu2020-5006 ◽

2020 ◽

Author(s):

Magnus Wangen

Keyword(s):

Numerical Model ◽

Bond Strength ◽

Hydraulic Fracturing ◽

Fluid Pressure ◽

Injection Pressure ◽

B Value ◽

Invasion Percolation ◽

Event Distribution ◽

3D Numerical Model ◽

Microseismic Event

We present a 3D numerical model for hydraulic fracturing and damage of low permeable rock in an anisotropic stress field. The 3D numerical model computes the intermittent damage propagation, microseismic event-locations, microseismic event-distribution, damaged rock volume, and injection pressure. The model builds on concepts from invasion percolation theory, where cells in a regular grid are connected by transmissibilities, also called bonds. A numerical pressure solution provides the pressure in each cell at each time step during the hydraulic fracturing operation. The numerical solution is based on a cell-centered finite volume scheme. A fast version of the numerical scheme is suggested by restricting fluid flow to the damaged rock volume. The hydraulic fracture and the damaged rock volume propagate by one cell when a bond breaks. An intact bond breaks when the fluid pressure exceeds the least compressive stress and a random uniformly distributed bond strength. The model is different from a pure invasion percolation model by using the fluid pressure in combination with a random bond strength to decide which bond to break, instead of only the random strength. The volume of damaged rock is estimated with a simple expression for cases with high permeability of the damaged rock volume. The model is tested with a published case from the Barnett Shale. It reproduces the observed main features of the Barnett case, such as the spatial and temporal distribution of the events, the magnitude &#8211; frequency distribution and the injection pressure. It is found that the microseismic event-distribution and the b-value depend on the permeability of the damaged rock volume. The b-value increases with decreasing permeability from 0.6 to a value above 2 for the maximum possible permeabilities. The damaged rock volume is non-compact and similar to a percolation cluster for &#8216;&#8216;high&#8217;&#8217; damaged rock permeabilities, and it becomes increasingly compact with decreasing permeabilities. The resulting loop-less fracture network is found to have similar characteristics for different damaged rock permeabilities.

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Analysis of the laboratory hydraulic fracturing curves.

10.5194/egusphere-egu2020-9960 ◽

2020 ◽

Author(s):

Helen Novikova ◽

Mariia Trimonova

Keyword(s):

Hydraulic Fracturing ◽

Laboratory Experiment ◽

Logarithmic Derivative ◽

Injection Pressure ◽

Technical Conference ◽

Function Technique ◽

Experimental Conditions ◽

Laboratory Setup ◽

Fracture Closure ◽

Reported Study

In this study, the data obtained during a series of laboratory experiments on hydraulic fracturing were analyzed. The main goal was to determine the time of the fracture closure, the pressure of the fracture closure, and the permeability of the sample, where the fracture was formed and propagated.A special laboratory setup was used to conduct the experiments. The design of this setup allows to provide a three-axis load on the model sample, which makes the conditions of the laboratory experiment on hydraulic fracturing closer to the real conditions in the field. To produce the fracture, viscous fluid was injected under constant rate through the preliminary created cased borehole with perforations.As results of the experiments, the curves of the fluid injection pressure variations with time were obtained. Their analysis was carried out using the G-function technique developed by Nordgren [1] and Nolte [2]. It is based on the plotting and analyzing of the behavior of the following dependencies: the injection pressure, first derivative of the pressure and the semi-logarithmic derivative of the pressure with respect to G-function. The curves processing allows to estimate the time of the fractures closure, with the help of which the fracture closure pressure was determined. The obtained pressure values were compared with the minimum stresses known from the experimental conditions.Additionally, the permeability of the model reservoir sample was calculated using a technique developed by Horner [3] and improved by Nolte et al. [4]. The approach is based on an assumption that the fracture in the formation has been already closed, and a radial regime of fluid flow has been established. The obtained results were compared with the actual permeability, which was determined in the preliminary laboratory experiment.AcknowledgementsThe reported study was funded by RFBR, project number 20-35-80018, and state task 0146-2019-0007.References<ol><li>Nordgren, R. P. [1972] Propagation of a vertical Hydraulic Fracture. SPE 45th Annual Fall Meeting, Houston, SPE-3009-PA.</li> <li>Nolte, K. G. [1979] Determination of Fracture Parameters from Fracturing Pressure Decline. The 54th Annual Fall Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME, Las Vegas, SPE-8341-MS.</li> <li>Horner, D. R. [1951] Pressure Build-Up in Wells. 3rd World Petroleum Congress, Netherlands, WPC-4135.</li> <li>Nolte, K. G., Maniere, J. L., Owens, K. A. [1997] After-Closure Analysis of Fracture Calibration Tests. SPE Annual Technical Conference and Exhibition, San Antonio, Texas, SPE-38676-MS.</li> </ol>

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