Fracturing Chronology: Milestones of the Hydraulic Fracturing Process

The mechanism of how hydraulic fracturing influences gas drainage in coal-rock mass is still not clear due to its complex mechanism. In this work, statistical distributions are firstly introduced to describe heterogeneity of coal-rock mass; a novel simultaneously coupled mathematical model, which can describe the fully coupled process including seepage-damage coupling during hydraulic fracturing process and subsequent gas flow during gas drainage process, is established; its numerical implementation procedure is coded into a Matlab program to calculate the damage variables, and it partly uses COMSOL solver to obtain numerical solutions of governing equations with damage-flow coupling; the mathematical model and its implementation are validated for initial damage pressure and mode of a single solid model without considering flow-damage coupling, as well as fracture initiation pressure and influence of heterogeneity on damage evolution of hydraulic fracturing considering flow-damage coupling; and finally, based on an engineering practice of hydraulic fracturing with two boreholes, the mechanism of how hydraulic fracturing influences gas drainage is investigated, numerical simulation results indicate that coal-rock mass pore-fissure structure has been improved, and there would exist a gas migration channel with characteristics of higher porosity and lower stresses, which demonstrates significant effects and mechanism of hydraulic fracturing on improving coal-rock permeability and enhancing gas drainage. The research results provide a guide for operation of hydraulic fracturing and optimal layout of gas drainage boreholes.

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Effects of pulse wave on the variation of coal pore structure in pulsating hydraulic fracturing process of coal seam

Fuel ◽

10.1016/j.fuel.2019.116906 ◽

2020 ◽

Vol 264 ◽

pp. 116906 ◽

Cited By ~ 9

Author(s):

Xie Jingna ◽

Xie Jun ◽

Ni Guanhua ◽

Sheik Rahman ◽

Sun Qian ◽

...

Keyword(s):

Coal Seam ◽

Hydraulic Fracturing ◽

Pore Structure ◽

Pulse Wave ◽

Fracturing Process

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Simulation of Hydraulic Fracturing Processes

Society of Petroleum Engineers Journal ◽

10.2118/7693-pa ◽

1980 ◽

Vol 20 (06) ◽

pp. 487-500 ◽

Cited By ~ 18

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

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Numerical Simulation on Propagation Mechanism of Hydraulic Fracture in Fractured Rockmass

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.488-489.417 ◽

2014 ◽

Vol 488-489 ◽

pp. 417-420 ◽

Cited By ~ 1

Author(s):

Xiao Xi Men ◽

C.A. Tang ◽

Zhi Hui Han

Keyword(s):

Hydraulic Fracturing ◽

Fracture Initiation ◽

Coupling Model ◽

Natural Fracture ◽

Tensile Fracture ◽

Propagation Mechanism ◽

Initiation And Propagation ◽

Fracturing Process ◽

Two Factors ◽

Seepage Characteristics

Hydraulic fracturing process in fractured rockmass which with an existing single natural fracture at its various conditions: its different angles and different lengths was simulated by using RFPA2D(2.0)-Flow version which adopts the finite element method and considers the heterogeneous characteristics of rock in meso-scale, creates seepage-stress-failure coupling model. The effect tendency of natural fractures angle and length on the seepage characteristics of fractured rockmass was given through the description of tensile fracture initiation and propagation in the rock specimens. The simulation results show that the effect of these two factors on fractures initiation, propagation and rockmass stability under the hydraulic fracturing could be remarkable.

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

Society of Petroleum Engineers Journal ◽

10.2118/9831-pa ◽

1982 ◽

Vol 22 (03) ◽

pp. 321-332 ◽

Cited By ~ 15

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^

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Microseismic search engine for real-time estimation of source location and focal mechanism

Geophysics ◽

10.1190/geo2015-0695.1 ◽

2016 ◽

Vol 81 (5) ◽

pp. KS169-KS182 ◽

Cited By ~ 6

Author(s):

Xiong Zhang ◽

Jie Zhang

Keyword(s):

Hydraulic Fracturing ◽

Real Time ◽

Search Engine ◽

Focal Mechanism ◽

Input Data ◽

Web Search ◽

Solution Space ◽

Web Search Engine ◽

Fracturing Process ◽

Microseismic Events

Similar to a web search engine, we have developed a microseismic search engine that can estimate an event location and the focal mechanism in less than a second to monitor the hydraulic fracturing process. The method was extended from a real-time earthquake monitoring approach for seismological applications. We first calculate the full waveforms of all possible microseismic events over a 3D grid with a known velocity model for a given acquisition geometry to create a database. We then index and rank all of the seismic waveforms in the database by following the characteristics of the phase and amplitude of the waveform through a computer fast search technology, specifically, the multiple randomized k-dimensional tree method. When a microseismic event occurs, the approximate best matches to the entry waveform are found immediately by comparing the characteristic features between the input data and the database. The method returns not just one but a series of solutions, similar to a web search engine. Thus, we can obtain a solution space that delineates the resolution and confidence level of the results. Also similar to a web search engine, the microseismic search engine does not require any input parameter or processing experience; thus, the solutions are the same for any user. Numerical tests suggest that the waveform search approach is insensitive to random and correlated noises. However, if the correlation values between the input data and best matches in the database are too low, suggesting unreliable results, the solution may be rejected automatically by applying a preset threshold. We have applied the method to real data, and found great potential for the routine real-time monitoring of microseismic events during hydraulic fracturing.

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