EXPERIMENTAL INVESTIGATION ON THE IMPACT OF INITIAL PORE PRESSURE ON BREAKDOWN PRESSURE OF BOREHOLE RADIAL FRACTURE FOR UNSATURATED MORTAR HYDRAULIC FRACTURING UNDER TRUE TRIAXIAL STRESS

2018 ◽  
Vol 21 (11) ◽  
pp. 1041-1057 ◽  
Author(s):  
Bingxiang Huang ◽  
Xinglong Zhao ◽  
Weichao Xue ◽  
Tianyuan Sun
Keyword(s):  
Experimental Investigation ◽  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Triaxial Stress ◽  
Radial Fracture ◽  
Breakdown Pressure ◽  
True Triaxial ◽  
True Triaxial Stress ◽  
The Impact

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

Minerals ◽  
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.

A True Triaxial Stress Cell to simulate deep downhole drilling conditions

2010 ◽  
Vol 50 (1) ◽  
pp. 61 ◽  
Author(s):  
Vamegh Rasouli ◽  
Brian Evans
Keyword(s):  
Stress Field ◽  
Pore Pressure ◽  
Oil And Gas ◽  
Triaxial Stress ◽  
Production Performance ◽  
Small Cells ◽  
Real Field ◽  
Co2 Injection ◽  
True Triaxial ◽  
True Triaxial Stress

Conventional rock mechanics experiments using triaxial cells trying to simulate the true downhole stress field by applying equal horizontal stresses, fundamentally fail to treat real field borehole conditions as three independent stresses. In the real world, the horizontal stress field at shallow depth can have a different direction from that at greater depths, resulting in well failure if the driller is not careful. Core samples used in small cells applying uniaxial stress simply cannot be used to properly simulate these anomalous downhole stress fields. A True Triaxial Stress Cell (TTSC) has been built to overcome this problem by properly simulating the true earth stresses. This technology will mimic stresses in deep oil and gas fields existing in highly anisotropically stressed environments. The TTSC allows vertical and two independent horizontal stresses to be applied up to 50 MPa in each direction on a 30 cm cube of rock and, at the same time, allows pore pressure to be applied up to 21 MPa. Through a hole drilled through the centre of the rock, a fluid can be injected to simulate hydraulic fracturing, or CO2 injection into saline aquifers or coal. Sanding analysis can be performed by increasing pore pressure and producing pore fluid from the borehole. Formations having different geological properties may be simulated, while deviated drilling through the rock simulates the deviated stresses when drilling horizontal wells. Fracture propagation, sanding initiation, and in-flow production performance is monitored in real-time using ultrasonic seismic transducers mounted around the sample.

Sign in / Sign up

Export Citation Format

Share Document