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

The effect of stress on the primary permeability of rock cores—a facet of hydraulic fracturing

1981 ◽  
Vol 18 (2) ◽  
pp. 195-204 ◽  
Author(s):  
R. Heystee ◽  
J.-C. Roegiers
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
The State ◽  
Stress Conditions ◽  
Breakdown Pressure ◽  
Rock Types ◽  
State Of Stress ◽  
Pressurization Rate ◽  
Fluid Penetration ◽  
Fracturing Experiments

Recent laboratory hydraulic fracturing experiments have shown that fluid penetration into the rock mass adjacent to the borehole being pressurized has a significant influence on the magnitude of the breakdown pressure. One factor affecting the degree of penetration of the pressurizing fluid is the permeability of the rock mass, which in turn is a function of the state of stress present in the rock mass. To study this permeability–stress relationship, a radial permeameter was constructed and three rock types tested. Derived expressions show that during radially divergent and convergent flow in the permeameter, the state of stress in the rock specimen is tensile and compressive respectively. The radial permeameter test results show that the permeability of rock increases significantly under tensile stress conditions and reduces under compressive stress conditions. The results from this study were used to develop a conceptual model which explains the dependency of breakdown pressure levels on the pressurization rate.

Simulation of Hydraulic Fracturing Processes

1980 ◽  
Vol 20 (06) ◽  
pp. 487-500 ◽  
Author(s):  
A. Settari
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Hydraulic Fracturing ◽  
Fracture Propagation ◽  
Thermal Recovery ◽  
Reservoir Rock ◽  
Flow And Heat Transfer ◽  
Fracture Closure ◽  
Fracturing Process

Abstract A mathematical model of the fracturing process, coupling the fracture mechanics and fracture propagation with reservoir flow and heat transfer, has been formulated. The model is applicable to fracturing treatments as well as to high leakoff applications such as fractured waterfloods and thermal fractures. The numerical technique developed is capable of simulating fracture extension for reasonably coarse grids, with truncation error being minimized for high leakoff applications when the grid next to the fracture is approximately square. With the aid of the model, a generalization of Carter's propagation formula has been developed that is also valid for high fluid-loss conditions. The capabilities of the model are illustrated by examples of heat transfer and massive-hydraulic-fracturing (MHF) treatment calculation. Introduction Induced fracturing of reservoir rock occurs under many different circumstances. Controlled hydraulic fracturing is an established method for increasing productivity of wells in low-permeability reservoirs. The technology of fracturing and the earlier design methods are reviewed by Howard and Fast.1 In waterflooding, injection pressures also often exceed fracturing pressures. This may result from poor operational practices, but it also could be intended to increase injectivity.2 In heavy oils, such as Alberta oil sands, most in-situ thermal recovery techniques rely on creating injectivity by fracturing the formation with steam.3 Fracturing also is being used as a method for deterining in-situ stresses4 and for establishing communication between wells for extraction of geothermal energy.5,6 Finally, fractures may be produced by explosive treatment or induced thermal stresses (such as in radioactive waste disposal). To date, most of the research has been directed toward the understanding and design of fracture stimulation treatments, with emphasis on predicting fracture geometry.7–11 The influence of fluid flow and heat transfer in the reservoir has been neglected or accounted for by various approximations in these methods. On the other hand, the need for reservoir engineering analysis of fractured wells led to the development of analytical techniques and numerical models for predicting postfracture performance.1 A common feature of all these methods is that they treat only stationary fractures, which therefore must be computed using some of the methods of the first category mentioned earlier. With the high costs associated with MHF,17–19 and with increasing complexity of the treatments, it is becoming important to be able to understand the interaction of the physical mechanisms involved and to improve the designs. This paper presents a numerical model of the fracturing process that simultaneously accounts for the rock mechanics, two-phase fluid flow, and heat transfer, both in the fracture and in the reservoir. The model is capable of predicting fracture propagation, fluid leakoff and heat transfer, fracture closure, cleanup, and postfracture performance. Although the detailed calculations of geometry, proppant transport, etc., have not been included, they can be integrated in a natural way within the present model. Because vertical fractures are prevalent except for very shallow depths, the discussion is limited to vertical fracturing. The paper focuses attention on the formulation of the basic model and the numerical techniques in general. Applications to fracturing treatments and the specific enhancements of the model are described in a more recent paper.20

Some Effects of Stress, Friction, and Fluid Flow on Hydraulic Fracturing

1982 ◽  
Vol 22 (03) ◽  
pp. 321-332 ◽  
Author(s):  
M.E. Hanson ◽  
G.D. Anderson ◽  
R.J. Shaffer ◽  
L.D. Thorson
Keyword(s):  
Fluid Flow ◽  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Research Program ◽  
In Situ Stress ◽  
Material Interfaces ◽  
Fracture Geometry ◽  
Funded Research ◽  
Fracturing Process

Abstract We are conducting a U.S. DOE-funded research program aimed at understanding the hydraulic fracturing process, especially those phenomena and parameters that strongly affect or control fracture geometry. Our theoretical and experimental studies consistently confirm the well-known fact that in-situ stress has a primary effect on fracture geometry, and that fractures propagate perpendicular to the least principal stress. In addition, we find that frictional interfaces in reservoirs can affect fracturing. We also have quantified some effects on fracture geometry caused by frictional slippage along interfaces. We found that variation of friction along an interface can result in abrupt steps in the fracture path. These effects have been seen in the mineback of emplaced fractures and are demonstrated both theoretically and in the laboratory. Further experiments and calculations indicate possible control of fracture height by vertical change in horizontal stresses. Preliminary results from an analysis of fluid flow in small apertures are discussed also. Introduction Hydraulic fracturing and massive hydraulic fracturing (MHF) are the primary candidates for stimulating production from tight gas reservoirs. MHF can provide large drainage surfaces to produce gas from the low- permeability formation if the fracture surfaces remain in the productive parts of the reservoir. To determine whether it is possibleto contain these fractures in the productive formations andto design the treatment to accomplish this requires a much broader knowledge of the hydraulic fracturing process. Identification of the parameters controlling fracture geometry and the application of this information in designing and performing the hydraulic stimulation treatment is a principal technical problem. Additionally, current measurement technology may not be adequate to provide the required data. and new techniques may have to be devised. Lawrence Livermore Natl. Laboratory has been conducting a DOE-funded research program whose ultimate goal is to develop models that predict created hydraulic fracture geometry within the reservoir. Our approach has been to analyze the phenomenology of the fracturing process to son out and identify those parameters influencing hydraulic fracture geometry. Subsequent model development will incorporate this information. Current theoretical and stimulation design models are based primarily on conservation of mass and provide little insight into the fracturing process. Fracture geometry is implied in the application of these models. Additionally, pressure and flow initiation in the fractures and their interjection with the fracturing process is not predicted adequately with these models. We have reported previously on some rock-mechanics aspects of the fracturing process. For example, we have studied, theoretically and experimentally, pressurized fracture propagation in the neighborhood of material interfaces. Results of interface studies showed that natural fractures in the interfacial region negate any barrier effect when the fracture is propagating from a lower modulus material toward a higher modulus material. On the other hand, some fracture containment could occur when the fracture is propagating from a higher modulus into a lower modulus material. Effect of moduli changes on the in-situ stress field have to be taken into consideration to evaluate fracture containment by material interfaces. Some preliminary analyses have been performed to evaluate how stress changes when material properties change, but we have not evaluated this problem fully. SPEJ P. 321^

scholarly journals Numerical Investigation of the Impacts of Borehole Breakouts on Breakdown Pressure

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 888 ◽  
Author(s):  
Hua Zhang ◽  
Shunde Yin ◽  
Bernt Aadnoy
Keyword(s):  
Hydraulic Fracturing ◽  
Shear Failure ◽  
In Situ Stress ◽  
Test Results ◽  
Breakdown Pressure ◽  
Borehole Breakout ◽  
Borehole Breakouts ◽  
The Difference ◽  
Mud Pressure

Borehole breakouts appear in drilling and production operations when rock subjected to in situ stress experiences shear failure. However, if a borehole breakout occurs, the boundary of the borehole is no longer circular and the stress distribution around it is different. So, the interpretation of the hydraulic fracturing test results based on the Kirsch solution may not be valid. Therefore, it is important to investigate the factors that may affect the correct interpretation of the breakdown pressure in a hydraulic fracturing test for a borehole that had breakouts. In this paper, two steps are taken to implement this investigation. First, sets of finite element modeling provide sets of data on borehole breakout measures. Second, for a given measure of borehole breakouts, according to the linear relation between the mud pressure and the stress on the borehole wall, the breakdown pressure considering the borehole breakouts is acquired by applying different mud pressure in the model. Results show the difference between the breakdown pressure of a circular borehole and that of borehole that had breakouts could be as large as 82% in some situations.

A Data-Driven Approach to Predict the Breakdown Pressure of the Tight and Unconventional Formation

2021 ◽  
Author(s):  
Zeeshan Tariq ◽  
Murtada Saleh Aljawad ◽  
Mobeen Murtaza ◽  
Mohamed Mahmoud ◽  
Dhafer Al-Shehri ◽  
...  
Keyword(s):  
Neural Network ◽  
Hydraulic Fracturing ◽  
Rock Properties ◽  
Breakdown Pressure ◽  
Rock Samples ◽  
In Situ Stresses ◽  
Fracturing Fluids ◽  
The Neural Network ◽  
Different Types

Abstract Unconventional reservoirs are characterized by their extremely low permeabilities surrounded by huge in-situ stresses. Hydraulic fracturing is a most commonly used stimulation technique to produce from such reservoirs. Due to high in situ stresses, breakdown pressure of the rock can be too difficult to achieve despite of reaching maximum pumping capacity. In this study, a new model is proposed to predict the breakdown pressures of the rock. An extensive experimental study was carried out on different cylindrical specimens and the hydraulic fracturing stimulation was performed with different fracturing fluids. Stimulation was carried out to record the rock breakdown pressure. Different types of fracturing fluids such as slick water, linear gel, cross-linked gels, guar gum, and heavy oil were tested. The experiments were carried out on different types of rock samples such as shales, sandstone, and tight carbonates. An extensive rock mechanical study was conducted to measure the elastic and failure parameters of the rock samples tested. An artificial neural network was used to correlate the breakdown pressure of the rock as a function of fracturing fluids, experimental conditions, and rock properties. Fracturing fluid properties included injection rate and fluid viscosity. Rock properties included were tensile strength, unconfined compressive strength, Young's Modulus, Poisson's ratio, porosity, permeability, and bulk density. In the process of data training, we analyzed and optimized the parameters of the neural network, including activation function, number of hidden layers, number of neurons in each layer, training times, data set division, and obtained the optimal model suitable for prediction of breakdown pressure. With the optimal setting of the neural network, we were successfully able to predict the breakdown pressure of the unconventional formation with an accuracy of 95%. The proposed method can greatly reduce the prediction cost of rock breakdown pressure before the fracturing operation of new wells and provides an optional method for the evaluation of tight oil reservoirs.

Hydraulic Fracturing Process: Roles of In Situ Stress and Rock Strength

2012 ◽  
Vol 616-618 ◽  
pp. 435-440
Author(s):  
Yan Jun Feng ◽  
Xiu Wei Shi
Keyword(s):  
Hydraulic Fracturing ◽  
Analytical Model ◽  
Field Experiments ◽  
Rock Strength ◽  
Fracture Initiation ◽  
In Situ Stress ◽  
Experimental Investigations ◽  
Propagation Process ◽  
Fracturing Process

This paper presents results of a comprehensive study involving analytical and field experimental investigations into the factors controlling the hydraulic fracturing process. Analytical theories for fracture initiation of vertical and horizontal borehole are reviewed. The initiation and propagation process of hydraulic fracturing is performed in the field by means of hydraulic fracturing and stepwise hydraulic fracturing, the effect of factors such as in-situ stress and rock strength on fracture propagation process is studied and discussed. The fracture initiation pressures estimated from the analytical model and field experiments are compared as well as the fracturing process during case 1and case 2. Results from the analytical model and field experiments conducted in this study are interpreted with a particular effort to enlighten the factors controlling the hydraulic fracturing process.

scholarly journals Fracture Propagation and Morphology Due to Non-Aqueous Fracturing: Competing Roles between Fluid Characteristics and In Situ Stress State

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 428
Author(s):  
Yunzhong Jia ◽  
Zhaohui Lu ◽  
Hong Liu ◽  
Jiehao Wang ◽  
Yugang Cheng ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Hydraulic Fracturing ◽  
Fracture Propagation ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Fluid Viscosity ◽  
Low Viscosity ◽  
Fracturing Process ◽  
Fluid Characteristics

Non-aqueous or gaseous stimulants are alternative working fluids to water for hydraulic fracturing in shale reservoirs, which offer advantages including conserving water, avoiding clay swelling and decreasing formation damage. Hence, it is crucial to understand fluid-driven fracture propagation and morphology in shale formations. In this research, we conduct fracturing experiments on shale samples with water, liquid carbon dioxide, and supercritical carbon dioxide to explore the effect of fluid characteristics and in situ stress on fracture propagation and morphology. Moreover, a numerical model that couples rock property heterogeneity, micro-scale damage and fluid flow was built to compare with experimental observations. Our results indicate that the competing roles between fluid viscosity and in situ stress determine fluid-driven fracture propagation and morphology during the fracturing process. From the macroscopic aspect, fluid-driven fractures propagate to the direction of maximum horizontal stress direction. From the microscopic aspect, low viscosity fluid easily penetrates into pore throats and creates branches and secondary fractures, which may deflect the main fracture and eventually form the fracture networks. Our results provide a new understanding of fluid-driven fracture propagation, which is beneficial to fracturing fluid selection and fracturing strategy optimization for shale gas hydraulic fracturing operations.

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.

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