scholarly journals Modelling Rock Fracture Induced By Hydraulic Pulses

2021 ◽  
Author(s):  
Xun Xi ◽  
Shangtong Yang ◽  
Christopher I. McDermott ◽  
Zoe K. Shipton ◽  
Andrew Fraser-Harris ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Rock Fracture ◽  
Cohesive Crack ◽  
Constitutive Relationship ◽  
Crack Model ◽  
Hydraulic Pressure ◽  
Breakdown Pressure ◽  
Hydraulic Flow ◽  
Discrete Crack ◽  
Fracturing Process

AbstractSoft cyclic hydraulic fracturing has become an effective technology used in subsurface energy extraction which utilises cyclic hydraulic flow pressure to fracture rock. This new technique induces fatigue of rock to reduce the breakdown pressure and potentially the associated risk of seismicity. To control the fracturing process and achieve desirable fracture networks for enhanced permeability, the rock response under cyclic hydraulic stimulation needs to be understood. However, the mechanism for cyclic stimulation-induced fatigue of rock is rather unclear and to date there is no implementation of fatigue degradation in modelling the rock response under hydraulic cyclic loading. This makes accurate prediction of rock fracture under cyclic hydraulic pressure impossible. This paper develops a numerical method to model rock fracture induced by hydraulic pulses with consideration of rock fatigue. The fatigue degradation is based on S–N curves (S for cyclic stress and N for cycles to failure) and implemented into the constitutive relationship for fracture of rock using in-house FORTRAN scripts and ABAQUS solver. The cohesive crack model is used to simulate discrete crack propagation in the rock which is coupled with hydraulic flow and pore pressure capability. The developed numerical model is validated via experimental results of pulsating hydraulic fracturing of the rock. The effects of flow rate and frequency of cyclic injection on borehole pressure development are investigated. A new loading strategy for pulsating hydraulic fracturing is proposed. It has been found that hydraulic pulses can reduce the breakdown pressure of rock by 10–18% upon 10–4000 cycles. Using the new loading strategy, a slow and steady rock fracture process is obtained while the failure pressure is reduced.

Field Experiments on Hydraulic Fracturing

1972 ◽  
Vol 12 (01) ◽  
pp. 69-77 ◽  
Author(s):  
Hilmar von Schonfeldt ◽  
C. Fairhurst
Keyword(s):  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Compressive Stress ◽  
Rupture Strength ◽  
Breakdown Pressure ◽  
Near Surface ◽  
Fracturing Process ◽  
Fluid Penetration ◽  
Regional Stresses

Abstract Hydraulic fracturing experiments at two underground and one near-surface location in igneous and shale formations were described. The tests were designed to study the feasibility of hydraulic fracturing as a method of determining in-situ stresses. The tests were carried out in open holes of 2-3/8-in. diameter. Fracturing tests on two 5-ft diameter cores were also reported. The test results revealed an increase in the magnitude of the stress as the face of an opening was approached from inside a rock mass. Horizontal fractures also were observed in areas of reportedly high lateral stress, providing some evidence for the validity of the providing some evidence for the validity of the principle of least resistance. The results also principle of least resistance. The results also indicate that caution must be used in using the shut-in pressure as a measure of the least compressive stress. Introduction Hydraulic fracturing is best known as a well stimulation method. There are other important applications, however, for which the process shows great potential. One of these is in the area of in-situ stress determination as suggested by Scheidegger Kehle and Fairhurst. The mechanics of the fracturing process is the same in any application, and improvement of the method may therefore be expected through a mutual exchange of experience in each of these areas. The theory of the hydraulic fracturing technique relates measurable quantities such as the breakdown pressure and the instantaneous shut-in pressure to pressure and the instantaneous shut-in pressure to the tectonic stresses and certain physical rock properties. properties. Assuming negligible pore pressure and fluid penetration, the break-down pressure (pC) at the penetration, the break-down pressure (pC) at the instant of fracture initiation is given by the following expressions....................(1) when the fracture extends in a "radial" direction (in a plane parallel to the axis of the borehole). And...................(2) when the fracture extends in a direction normal to the borehole axis. Corresponding expressions that include the effect of pore pressure and fluid penetration are given in the literature Because our work was done in dry and impermeable formations, Eqs. 1 and 2 are considered adequate. These formulae are based on the assumption that the borehole is drilled parallel to 3 and that the rock behaves as a linearly elastic isotropic material; it also assumes that the fracture is initiated in a direction perpendicular to the least compressive stress, i.e., 2 or 3, respectively, in accordance with the principle of least resistance. The terms "radial" and "normal" fractures are introduced in place of the commonly used terms "vertical" and "horizontal" fractures in order to avoid possible confusion in the event a borehole is drilled in a direction other than the vertical. Eqs. 1 and 2 establish a simple relation between the breakdown pressure and the regional (far-field) stresses. It also has been suggested that the instantaneous shut-in pressure is a measure for the least compressive stress because a fracture will propagate in a direction normal to it. Therefore, propagate in a direction normal to it. Therefore, or ..........................(3) Thus Eqs. 1 and 3 may serve to estimate the regional stresses 1, and 2 provided it is known that a radial fracture was generated, and it is possible to determine the rupture strength (K ). possible to determine the rupture strength (K ). Similarly Eqs. 2 or 3 will give an estimate of the stress 3. Scheidegger and Kehle determined regional stresses through a similar analysis of hydraulic fracturing data. SPEJ P. 69

Chemically-Induced Pressure Pulse: Fracturing Competent Reservoirs

2021 ◽  
Author(s):  
Ayman R. Al-Nakhli ◽  
Zeeshan Tariq ◽  
Mohamed Mahmoud ◽  
Abdulazeez Abdulraheem
Keyword(s):  
Hydraulic Fracturing ◽  
Rock Fracture ◽  
Applied Pressure ◽  
Hydraulic Fractures ◽  
Breakdown Pressure ◽  
Hydrocarbon Production ◽  
Fracture Pressure ◽  
Micro Cracks ◽  
Chemically Induced ◽  
Fracturing Experiments

Abstract Commercial volumes of hydrocarbon production from tight unconventional reservoirs need massive hydraulic fracturing operations. Tight unconventional formations are typically located inside deep and over-pressured formations where the rock fracture pressure with slickwater becomes so high because of huge in situ stresses. Therefore, several lost potentials and failures were recorded because of high pumping pressure requirements and reservoir tightness. In this study, thermochemical fluids are introduced as a replacement for slickwater. These thermochemical fluids are capable of reducing the rock fracture pressure by generating micro-cracks and tiny fractures along with the main hydraulic fractures. Thermochemical upon reaction can generate heat and pressure simultaneously. In this study, several hydraulic fracturing experiments in the laboratory on different synthetic cement samples blocks were carried out. Cement blocks were made up of several combinations of cement and sand ratios to simulate real rock scenarios. Results showed that fracturing with thermochemical fluids can reduce the breakdown pressure of the cement blocks by 30%, while applied pressure was reduced up to 88%, when using thermochemical fluid, compared to slickwater. In basins with excessive tectonic stresses, the current invention can become an enabler to fracture and stimulate well stages which otherwise left untreated. A new methodology is developed to lower the breakdown pressure of such reservoirs, and enable fracturing. Keywords: Unconventional formation; breakdown pressure; thermochemicals; micro fractures.

Discrete crack path prediction by an adaptive cohesive crack model

2010 ◽  
Vol 77 (18) ◽  
pp. 3541-3557 ◽  
Author(s):  
G. Geißler ◽  
C. Netzker ◽  
M. Kaliske
Keyword(s):  
Crack Path ◽  
Cohesive Crack ◽  
Crack Model ◽  
Cohesive Crack Model ◽  
Discrete Crack ◽  
Path Prediction ◽  
Crack Path Prediction

scholarly journals Investigations on the Directional Propagation of Hydraulic Fracture in Hard Roof of Mine: Utilizing a Set of Fractures and the Stress Disturbance of Hydraulic Fracture

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 4) ◽  
Author(s):  
Yuekun Xing ◽  
Bingxiang Huang ◽  
Binghong Li ◽  
Jiangfeng Liu ◽  
Qingwang Cai ◽  
...  
Keyword(s):  
Principal Stress ◽  
Hydraulic Fracture ◽  
Rock Fracture ◽  
Cohesive Crack ◽  
Hydraulic Fractures ◽  
Principal Stresses ◽  
Direction Parallel ◽  
Hard Roof ◽  
Fracturing Process ◽  
Simulation Results

Abstract Directional fracturing is fundamental to weakening the hard roof in the mine. However, due to the significant stress disturbance in the mine, principal stresses present complicated and unmeasurable. Consequently, the designed hydraulic fracture (HF) extension path is always oblique to principal stresses. Then, the HF will present deflecting propagation, which will restrict the weakness of the hard roof. In this work, we proposed an approach to drive the HF to propagate directionally in the hard roof, utilizing a set of hydraulic fractures and their stress disturbance. In this approach, directional fracturing in the hard roof is conducted via the sequential fracturing of three linear distribution slots. The disturbed stresses produced by the first fracturing (in the middle) are utilized to restrict the HF deflecting extension of the subsequent fracturing. Then, the combined hydraulic fractures constitute a roughly directional fracturing trajectory in rock, i.e., the directional fracturing. To validate the directional fracturing approach, the cohesive crack (representing rock fracture process zone (FPZ)) model coupled with the extended finite element method (XFEM) was employed to simulate the 2D hydraulic fracturing process. The benchmark of the above fracturing simulation method was firstly conducted, which presents the high consistency between simulation results and the fracturing experiments. Then, the published geological data of the hard roof in Datong coal mine (in Shanxi, China) was employed in the fracturing simulation model, with various principal stress differences (2~6 MPa) and designed fracturing directions (30°~60°). The simulation results show that the disturbing stress of the first fracturing significantly inhibits the deflecting propagation of the subsequent fractures. More specifically, along the direction parallel to the initial minimum principal stress, the extension distance of the subsequent hydraulic fractures is 2~3 times higher than that of the deflecting HF in the first fracturing. The fracturing trajectory of the proposed direction fracturing method deviates from the designed fracturing path by only 2°~14°, reduced by 76%~93% compared with the traditional fracturing method utilizing a single hydraulic fracture. This newly proposed method can enhance the HF directional propagation ability more effectively and conveniently in the complex and unmeasurable stress field. Besides, this directional fracturing method can also provide references for the directional fracturing in the oil-gas and geothermal reservoir.

ORGANIC COMPOUND CHARACTERIZATION OF HYDRAULIC FRACTURING FLOWBACK WATERS THROUGHOUT THE FRACTURING PROCESS

2016 ◽  
Author(s):  
Karl Oetjen ◽  
◽  
Simon Roberts ◽  
Tzahi Y. Cath ◽  
Chris Higgins
Keyword(s):  
Organic Compound ◽  
Hydraulic Fracturing ◽  
Fracturing Process
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