a numerical investigation of fault slip triggered by hydraulic … · 2013. 5. 28. · a numerical...

Chapter 23

A Numerical Investigation of Fault Slip Triggered byHydraulic Fracturing

Neda Zangeneh, Erik Eberhardt, R. Marc Bustin andAmanda Bustin

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/56191

Abstract

The study of fault slip in response to fluid injection offers a means to understand the complexhydromechanical behavior of shale gas and oil reservoir systems during hydraulic fracturingoperations, together with the induced seismicity, and corresponding mitigation measures,arising from such events. In this paper, a series of numerical simulations are performed toinvestigate the relationship between hydraulic fracturing (i.e. fluid injection) and the responseof a naturally fractured rock mass to transient fluid pressures. The analysis is carried out usingthe discontinuum-based distinct-element program UDEC assuming a fracture flow system.The conceptual reservoir model consists of a critically stressed fault plane and the surroundingrock mass containing planes of weakness, for which a hydraulic fracture is numericallysimulated and the response modeled using a transient, coupled hydro-mechanical solution.The results demonstrate the influence of fluid diffusion generated by the fracing fluid aftershut-in on the triggering of fault slip. The simulation is then used to interpret the associatedseismic events and their relationship to the injections and shut-in pressures, and to estimatethe maximum magnitude of the induced seismic event.

1. Introduction

Hydraulic fracture operations involve the injection of fluids from a wellbore into a formationto maximize the extraction of oil and gas resources from the reservoir. These stimulations allowthe development of previously uneconomical reserves, for example shales gas. However, ithas been well established that these fluid injections also induce seismicity (e.g., Hollister and

© 2013 Zangeneh et al.; licensee InTech. This is an open access article distributed under the terms of theCreative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permitsunrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Weimer [1], Ohtake [2], Fletcher and Sykes [3], Pearson, [4], Talwani and Acree, [5], Simpsonet al. [6], Zoback and Harjes [7]).

The occurrence of induced seismicity, whether through hydraulic fracturing, enhancedgeothermal systems, or carbon dioxide (CO2) sequestration, represents an important consid‐eration in the risk profile of an injection well. Zoback [8] suggested that because of the criticallystressed nature of the crust, fluid injection in deep wells can trigger earthquakes throughincreases in pore pressure (and decreases in effective stress) in the vicinity of the pre-existingfaults. The increased pore pressure reduces the shear resistance to fault slip, allowing elasticenergy already stored in the surrounding rocks to be released (Healy et al. [9]).

This paper describes a numerical experiment investigating the influence of pore pressurediffusion on the modeling of seismicity after a hydraulic fracture treatment. One objective isto evaluate the utility of 2-D distinct element techniques to model both pore pressure build-up and diffusion along existing rock weakness planes in response to fluid injection andsubsequent changes to the effective stress field. A second objective is to estimate the corre‐sponding maximum seismic magnitude that is likely to occur in response to the hydraulicfracture treatment.

2. Effect of fluid injection on induced seismicity

The occurrence of injection-induced seismicity is usually confined in both space and time, withpressure build-up and diffusion controlling the spatial and temporal pattern of the seismicityafter a hydrofrac treatment. Spatially, the problem can be conceptualized as a scenario in whicha wellbore in the vicinity of a critically-stressed fault is pressurized and the injected fluidsdiffuse towards the fault, increasing pore pressures and reducing the effective normal stressuntil slip is triggered along a portion of the fault. The transient nature of the fluid front as itradiates outward from the injection well allows for the triggering of events after injection andshut-in, referred to here as post-injection seismicity.

The importance of fluid pressure in generating induced seismicity was demonstrated in 1962in Denver, Colorado, when it was observed that a series of seismic events were being generatedshortly after a chemical weapons plant had begun injecting contaminated wastewater downa deep well. Detailed studies by Hollister and Weimer [1] and Healy et al. [9] confirmed thecausal observations of Evans [10] that the seismic events were induced by the waste fluidinjection. Similar relations between local seismicity and fluid injection were likewise observedat the Rangely Oil Field, Colorado by Pakiser et al. [11], Healy et al. [12] and Gibbs et al. [13],and in the Los Angeles basin by Teng et al. [14].

More recently, post-injection seismicity associated with gas shale and geothermal projects haveentered the public spotlight with heightened sensitivity directed towards hydraulic fracturingpractices and induced seismicity. Between 2000 and 2005, numerous seismic events wererecorded at the European geothermal project in Soultz-sous-Forêts, France, with events as largeas M=2.5 being recorded during injection and M=2.6 several days after shut-in (Charlety et al.

Effective and Sustainable Hydraulic Fracturing478

[15]). For stimulations carried out in 2000, 2003 and 2004 the largest seismic events occurredjust after or after shut-in. Similar experiences were encountered at Basel, Switzerland whereinduced seismicity reached a Richter Magnitude of 3.4 despite precautionary reductions of theinjection rate, leading to suspension of its hot dry rock enhanced geothermal systems project(Haring et al. [16]).

Experiences with hydraulic fracturing treatments in gas shales have generated similarseismicity, generally viewed as low risk due to the remote nature of the locations. In theBowland shale, Lancashire, UK, two notable events were recorded with Richter Magnitudesof 1.5 and 2.3. These occurred almost 10 hours after shut-in (de Pater and Baisch [17]). de Paterand Baisch [17] suggested that reducing the treatment volume is one means to mitigate inducedseismicity. In a detailed study in the Horn River Basin in northeastern British Columbia,Canada, approximately 38 events ranging between Richter Magnitudes 2.2 and 3.8 wererecorded between 2009 and 201l, with only one being felt on surface in this remote region(BCOG, [18]). In their 2012 report of the findings from this investigation, the B.C. Oil and GasCommission found that several of the Horn River events greater than M 2.0 were located alongfaults intersecting the wellbores. They also note that there were other instances where faultsintersected wellbores without anomalous events being detected (BCOG, [18]).

3. Methodology

The Distinct Element Method (DEM) applies a Lagrangian formulation to compute the motionand interaction between a series of discrete deformable blocks, representing the problemdomain, via compliant contacts and Newton’s equation of motion (Cundall and Hart, [19]).This enables the problem domain to be divided through by one or more discontinuity sets ofvariable orientation, spacing and persistence. One fundamental advantage of the DEM is thatpre-existing (natural) joints in the rock mass can be modeled explicitly and allow for joints toundergo large deformations in shear (slip) or opening (dilation). The 2-D commercial codeUDEC (Universal Distinct Element Code; Itasca Consulting Group, 1999) is used here to modelthe response of a jointed rock mass subjected to static loading and hydraulic injection.

UDEC is capable of modeling the behavior of weak jointed rock masses in which both thedeformation and yielding of weak rock and slip along pre-existing discontinuities are impor‐tant controlling factors. Progressive failure associated with crack propagation and fault slipcan be simulated by the breaking of pre-existing contacts between the pre-defined jointbounded blocks, which although deformable, remain intact.

Key for simulating hydrofracturing, UDEC has the capability to model fluid flow through thedefined fracture network. A fully coupled hydro-mechanical analysis can be performed, inwhich fracture conductivity is dependent on mechanical deformation of joint apertures and,conversely, joint water pressures can affect the mechanical computations of joint aperture. Theblocks in this assemblage are treated as being impermeable, and fracture flow is calculatedusing a cubic law relationship for joint aperture:

A Numerical Investigation of Fault Slip Triggered by Hydraulic Fracturinghttp://dx.doi.org/10.5772/56191

479

3 Pq kalD

= (1)

where, k is a joint conductivity factor (dependent on the fluid dynamic viscosity), a is the contacthydraulic aperture, ΔP is the pressure difference between the two adjacent domains, and l isthe length assigned to the contact between the domains. Since the UDEC formulation isrestricted to the modeling of fracture flow, it should be noted that leak-off along the fracturesdiffusing into the rock matrix is assumed to be negligible (only leak-off into other fractures isconsidered). Furthermore, the cubic law flow assumption limits tortuosity. When a jointcontact is broken, the fluid flows into the joint.

4. Simulation setup and input parameters

The rock mass modeled in this study is represented by two persistent orthogonal planes ofweakness (Figure 1). These serve as incipient planes along which hydrofrac propagation isrestricted. The simulation of induced seismicity is executed through the inclusion of a fault,which extends across the model. An injection well is located such that a significant portion ofthe fluid injected diffuses towards the fault and eventually penetrates the fault following shut-in. The fluid pressure decays slowly after the injection and the disturbed pressure front diffusesthrough the surrounding rock mass. Although the fluid pressures decrease with time anddistance, there is still sufficient pressure to trigger fault slip. The fault model is based oninteractions between neighboring fault segments allowing the model to simulate slippage ona single contact together with the subsequent interactions and responses of its neighboringcontacts.

The input material parameters include both those for the rock matrix and incipient planes ofweakness and fault. The rock matrix was modeled as being elastic, assuming typical valuesfor shale (density=2500 kg/m3, Young’s modulus=30 GPa, Poisson’s ratio=0.25). The incipientplanes of weakness and fault were modeled assuming a Coulomb-slip constitutive model withboth peak and post-peak properties. These are given in Table 1. The depth of the injection andhorizontal plane represented by the model is 1000 m. The maximum and minimum horizontalstresses were assumed to be 30 and 20 MPa, respectively.

Discontinuity property Incipient fractures Fault Units

Friction angle 30 20 degrees

Residual friction angle 25 20 MPa

Cohesion 1.0 0.0 MPa

Residual cohesion 0.0 0.0 MPa/m

Tensile strength 0.5 0.0 MPa/m


Discontinuity property Incipient fractures Fault Units

Residual tensile strength 0.0 0.0 degrees

Normal stiffness 1e4 10 MPa

Shear stiffness 1e3 1 MPa

Table 1. Properties assigned to the modeled planes of weakness and fault.

Figure 1. Rock mass model with two sets of weakness planes and a fault.

5. Post-injection seismicity simulations

Numerical simulations were performed using the model developed to investigate the influenceof hydraulic fracturing on fluid pressure changes around the neighboring fault and anysubsequent shear slippage along the fault. Both fluid pressure build-up during the injectionuntil the time of shut-in as well as fluid pressure diffusion after the shut-in were considered.

5.1. Fluid pressure build-up during injection and diffusion after shut-in

Experience gained from mapping hundreds of hydraulic fracturing treatments with downholegeophones has shown that the occurrence of seismic event induced during a treatment isgreatly influenced by the injection volume and rate used. Here, the hydraulic fracturingsimulation was conducted by pressurizing the wellbore in the vicinity of a critically stressed


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fault (Figure 1). Figure 2 shows the joint fluid pressure distribution in the rock mass at the timethat fluid injection is stopped (i.e., shut-in). It can be seen that the fluid pressure has not reachedthe fault at the end of the hydraulic fracture treatment and shut-in. Here the fluid pressuretreatment was applied for a period of 50 minutes.

After shut-in, the injected fluids continue to diffuse and radiate towards the fault, eventuallypenetrating it (Figure 3). The response of the fault to the elevated fluid pressures then dependson the spatial and temporal characteristics of the diffusion pulse, with a series of slip eventsbeing produced as opposed to a single event. The strongest slip event was typically observedlate in the sequence, sometimes long after injection had stopped (up to 150 minutes for themodel simulations performed here).

Figure 2. Pore pressure distribution at the time of shut-in.

5.2. Shear slip of critically stressed fault

The shear slip distribution along the fault, after 50 minutes of injection and 150 additionalminutes of shut-in, is presented in Figures 4. The figure shows a distribution of slip magnitudesalong the length of the fault, with a maximum fault slip of approximately 10 mm. Displace‐ments between 5 and 10 mm were observed along 680 meters of the total 800 meter fault length,with an average fault slip of 8 mm. This average slip magnitude was then used to calculate themaximum earthquake magnitude, as presented in the following section.


Figure 4. Fault shear displacement 2 ½ hours after shut-in.

Figure 3. Pore pressure distribution 2 ½ hours after shut-in.


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6. Seismic moment and moment magnitude calculations

The seismic moment is a direct measurement of the energy released by a seismic event and isrelated to the strength characteristics of the fault. It can be calculated as follows (Kramer, [20]):

oM ADm= (2)

Where:

Mo is the seismic moment (dyne∙cm),

μ is the rupture strength of the rock along the fault (dyne/cm2),

A is the rupture area (cm2), and

D̄ is the average amount of slip (cm).

Here, the rupture strength of the fault is equal to 1e10 dyne/cm2, the length of the fault thatslipped is equal to 6.8e4 cm (680 m), and the average amount of slip is equal to 0.8 cm. Assuminga unit depth of fault slip due to the 2-D nature of the model (i.e., rupture area = 6.8e9 cm2), theresulting seismic moment is equal to 5.4e19 dyne.cm.

Figure 5. Saturation of various magnitude scales: Mw (moment magnitude), ML (Richter local magnitude), Ms (surfacewave magnitude), mb (short-period body wave magnitude), mB (long-period body wave magnitude), and MJMA (Japa‐nese Metrological Agency magnitude). After Idriss [22] and Kramer [20].


Seismic moment can be converted into a moment magnitude using the following relationship(Hanks and Kanomori [21]):

2 / 3log 10.7w oM M= - (3)

Where:

Mw is moment magnitude (dyne.cm), and

Mo is seismic moment (dyne.cm).

The moment magnitude calculated from equation 3 is 2.45. Figure 5 is used to convert thecalculated moment magnitude to the Richter local magnitude. As seen in Figure 5, forearthquake magnitudes smaller than 6, the moment and local magnitudes are near equal; thelocal magnitude for the calculated moment magnitude is equal to 2.45.

Figure 6 uses a well-established seismological relationship that correlates earthquake magni‐tude to the size of the fault that slipped and seismic moment (Stein and Wysession [23]). Thissuggests that only faults that are at least tens of kilometers long are capable of producing largeseismic events with magnitudes exceeding 6 (Zoback and Gorelick [8]). Zoback and Gorelick[8] note here that the fault size in Figure 6 is a lower bound value that refers to the size of thefault segment that slips in a given earthquake. As a geological feature, the total fault length isgenerally much longer than the part (segment) that slips during an individual event. As shownin Figure 6, an active fault slip segment of 680 meters, as produced in the UDEC model, iscapable of producing an earthquake with a magnitude between 2.3 and 3.8 for a fault slipdisplacement between 1mm and 1 cm, depending on the magnitude of stress released by the

Figure 6. Relationship among various scaling parameters for earthquakes. The larger the earthquake, the larger thefault and amount of slip, depending on the stress drop in a particular earthquake. Observational data indicate thatearthquake stress drops range between 0.1 and 10 MPa (modified after Zoback and Gorelick, [8]).


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event, or stress drop. For the case modeled here, the 0.8 mm of average slip produced corre‐sponds to an event with a magnitude equal to 2.45, which is in the range shown in Figure 6.

7. Discussion and conclusions

A numerical modeling study has been carried out to investigate the application of the distinctelement technique to the simulation of fault slip and induced seismicity resulting from ahydraulic fracture treatment via a wellbore in the vicinity of a natural fault. The model wasable to predict the occurrence of post-injection seismicity in response to diffusion of the injectedfluids, in a system governed by fracture permeability, long after the hydraulic fracturingtreatment is finished and shut-in is initiated.

In most areas, regional-scale faults should be easily identified during geological site charac‐terization studies. Smaller-scale faults or those that are shallow dipping (i.e., that do notdaylight on surface and therefore would not be detected through surface mapping) may bemore difficult to locate a priori. Experience gained from monitoring hundreds of hydraulicfracturing treatments with downhole geophones has shown that the occurrence of seismicevents induced by the treatments is greatly influenced by the injection volume used duringthe operation. Improved understanding of this condition will allow designers and operatorsto control the amount of injection during a hydraulic fracturing treatment to minimize fluidpressure diffusion and subsequent slip of a neighboring fault.

The simulations presented here show great potential in providing a deeper understanding ofthe effect of natural fracture systems and pressure diffusion of fracing fluids into a neighboringfault causing shear slip and induced seismicity after a hydraulic fracture treatment. Futurework will include modeling of hydrofrac fluid diffusion into a fault in the vicinity of thehydrofrac treatment site in a three-dimensional model.

Author details

Neda Zangeneh*, Erik Eberhardt, R. Marc Bustin and Amanda Bustin

*Address all correspondence to: [email protected]

University of British Columbia, Vancouver, British Columbia, Canada

References

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[2] Ohtake, M. Seismic Activity Induced by Water Injection at Matsushiro, Japan. Jour‐nal of Physics of the Earth (1974). , 22, 163-176.

[3] Fletcher, J. B, & Sykes, L. R. Earthquakes Related to Hydraulic Mining and NaturalSeismic Activity in Western New York State. Journal of Geophysical Research(1977). , 82(26), 13767-3780.

[4] Pearson, C. The Relationship Between Microseismicty and High Pore Pressures Dur‐ing Hydraulic Stimulation Experiments in Low Permeability Granitic Rocks. Journalof Geophysical Research (1981). , 86, 7855-7864.

[5] Talwani, P, & Acree, S. Pore Pressure Diffusion and the Mechanism of Reservoir-in‐duced Seismicity, Pageoph (1985). , 122, 947-965.

[6] Simpson, D. W, Leith, W. S, & Scholz, C. H. Two Types of Reservoir Induced Seis‐micity, Bulletin of the Seismological Society of America (1988). , 78, 2025-2040.

[7] Zoeback, M, & Harjes, H. P. Injection Induced Earthquakes and the Crustal Stress at9 km Depth at the KTB Deep Drilling Site, Germany. Journal of Geophysical Re‐search (1997). B8): 18477-18491.

[8] Zoback, M. D, & Gorelick, S. M. Earthquake Triggering and Large-scale GeologicStorage of Carbon Dioxide. Proceeding of the National Academy of Science of theUnited States of America (PNAS) (2012). , 109(26), 10164-10168.

[9] Healy, J. H, Rubey, W. W, Griggs, D. T, & Raleigh, C. B. The Denver Earthquakes,Science (1968). , 161, 1301-1310.

[10] Evans, D. M. The Denver Area Earthquakes and the Rocky Mountain Arsenal Dis‐posal Well, Mountain Geologist (1966). , 3, 23-36.

[11] Pakiser, L. C, Eaton, J. P, Healy, J. H, & Releigh, C. B. Earthquake Prediction andControl, Science (1969). , 166, 1467-1474.

[12] Healy, J. H, Lee, W. H. K, Pakiser, L. C, Raleigh, C. B, & Wood, M. D. Prospects forEarthquake Prediction and Control, Techtonophys (1972). , 319-332.

[13] Gibbs, J. F, Healy, J. H, Raleigh, C. B, & Coakley, J. Seismicity in the Rangely, Colora‐do Area: 1962-1970. Bulletin of Seismological Society of America (1973). , 63,1557-1570.

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[15] Charlety, J, Cuenot, N, Dorbath, L, Dorbath, C, Haessler, H, & Frogneux, M. LargeEarthquakes During Hydraulic Stimulations at the Geothermal Site of Soultz-sous-Forets. International Journal of Rock Mechanics and Mining Sciences (2007). , 44,1091-1105.


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[16] Haring, M. O, Schanz, U, Ladner, F, & Dyer, B. C. Characterisation of the Basel 1 En‐hanced Geothermal System. Geothermics (2008). , 31, 469-495.

[17] De Pater, C. J, & Baisch, S. Geomechanical Study of Bowland Shale Seismicity, Syn‐thesis Report (2011).

[18] BCOGInvestigation of Observed Seismicity in the Horn River Basin. British Colum‐bia Oil and Gas Commission Report (2012).

[19] Cundall, P. A, & Hart, R. D. Numerical Modeling of Discontinua. ComprehensiveRock Engineering (1993). A. Hudson, ed. Oxford: Pergamon Press Ltd., 2, 231-243.

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[22] Idriss, I. M. Evaluating Seismic Risk in Engineering Practice. Conference Proceeding,11th International Conference on Soil Mechanics and Foundation Engineering,(1985). , 1

[23] Stein, S, & Wysession, M. An Introduction to Seismology, Earthquakes and EarthStructure. Blackwell, Oxford; (2002).


Section 1 Keynote LecturesChapter 1Fracturing FluidsAbstract1. Introduction2. History3. Types of fracturing fluids4. Chacterization of fracturing fluids5. Rheological models6. Shear history simulation7. Slurry viscosity8. Proppant fall rates9. Viscosity and fracture treating pressureAuthor detailsReferences

Chapter 2Fracturing Fluid Components1. Introduction1.1. Water

2. Clay control agents3. Friction Reducers (FR)3.1. Polyacrylic Acid (PAAc)3.2. Polyacrylamide (PAAm)3.3. Partially Hydrolyzed Polyacylamide (PHPA)3.4. AcrylamidoMethylPropane Sulfonate (AMPS)

4. Gelling agents4.1. Guar4.2. HydroxyEthyl Cellulose (HEC)4.3. ViscoElastic Surfactant (VES)4.4. Foam/PolyEmulsions4.5. Oil based fluids

5. Crosslinkers5.1. Borate5.2. Titanium and zirconium

6. Breakers6.1. Oxidizer6.2. Acids6.3. Enzymes6.4. Viscosity stabilizers

7. Buffers8. Surfactants/Mutual solvents9. Biocides/BactericidesAuthor detailsReferences

Chapter 3Fractures and Fracturing:Hydraulic Fracturing in Jointed Rock1. Introduction2. Hydraulic fracturing3. Influence of fractures and discontinuities on the strength of brittle materials4. Theorem of minimum potential energy5. Mechanics of hydraulic fracturing6. Hydroshear7. Deformation and failure of rock in situ8. Microseismicity as an indicator of slip on fractures9. In-situ stress10. ‘Critical stress state’ in the Earth’s crust11. Hydraulic fracturing in tight shales12. Fracture network engineering13. ConclusionsAppendix 1Earth resources engineeringAppendix 2Effect of coring in pre-stressed rockAuthor detailsReferences

Chapter 4Five Things You Didn’t Want to Know about Hydraulic Fractures1. Introduction2. Complex flow regimes3. Conductivity degrades4. Heterogeneous reservoirs5. Complex frac geometry6. Non-unique interpretations7. Discussion of five deficiencies8. Removing the uncertainty9. Opportunities to improve fracture performanceAuthor detailsReferences

Chapter 5EGS — Goodbye or Back to the Future1. Introduction2. Characteristics of key projects2.1. Los Alamos2.2. Camborne2.3. Soultz-sous-Forêts

3. Observations and results of stimulation and circulation tests3.1. General observations3.2. Size of the stimulated region3.3. Characteristics and internal structure of the stimulated region3.4. Number of stimulated fractures3.5. Aperture of stimulated fractures3.6. Heat exchanging area3.7. Hydraulic properties

References4. Interpretation and discussion5. Summary and way forwardAuthor detailsReferences

Chapter 6Understanding Hydraulic Fracture Growth, Effectiveness, and Safety Through Microseismic Monitoring1. Introduction2. Microseismic applications3. Beyond dots, or beyond verification4. Environmental aspects5. SummaryAuthor detailsReferences

Section 2 Naturally Fractured Reservoirs 1Chapter 7Development of Fracture Networks Through Hydraulic Fracture Growth in Naturally Fractured ReservoirsAbstract1. Introduction2. The model3. A simple test problem4. Random fracture geometry5. Discussion5.1. Fluid-driven fracture nucleation, growth and connection5.2. Implications for fracture-controlled flow system

Author detailsReferences

Chapter 8Hydraulic Fracture Propagation Across a Weak Discontinuity Controlled by Fluid InjectionAbstract1. Introduction2. Problem statement3. Parameterization of HF-NF problem4. Results of parametric study4.1. Dimensionless toughness κIC vs. angle β diagram4.2. κIC vs.ΔΣ diagram4.3. λ vs. κIC(NF) / κIC diagram

5. Effect of NF permeability5.1. Analytical model5.2. Numerical simulations

6. ConclusionsAuthor detailsReferences

Chapter 9Effect of Flow Rate and Viscosity on Complex Fracture Development in UFM Model1. Introduction2. UFM model specifics3. New crossing model in UFM4. Comparison of hydraulic fracturing simulations with OpenT versus eRP4.1. Influence of viscosity4.2. Influence of pumping rates4.3. Barnett example

5. Possible impact on production forecast6. ConclusionsAuthor detailsReferences

Section 3 Regulations, Risks, and CommunitiesChapter 10Hydrochemical and Hydrogeological Impact of Hydraulic Fracturing in the Karoo, South Africa1. Introduction1.1. Development of shale gas in South Africa1.2. Geology and gas plays in South Africa

2. Problem formulation3. Results and discussion3.1. Hydraulic fracturing process3.2. Backflow event after hydraulic fracturing3.3. Environmental impacts of hydraulic fracturing


Chapter 11Regulatory Nirvana for Hydraulic Fracture Stimulation1. Introduction2. The Roadmap3. Regulation to enable hydraulic fracture stimulation in the public’s interest — The South Australian approach4. Principles for best practice regulation5. Environmental assessment and approval6. Activity notification and application for approval7. Notice of entry8. Compliance and enforcement9. ConclusionsAuthor detailsReferences

Chapter 12How Can Understanding Community Concerns About Hydraulic Fracturing Help to Address Them?1. Introduction2. Public concern about CSG extraction and hydraulic fracturing3. The role of attitudes and risk perception4. The role of trust5. The role of a trusted advisor6. Concluding remarksAuthor detailsReferences

Section 4 Naturally Fractured Reservoirs 2Chapter 13Numerical Study of Interaction Between Hydraulic Fracture and Discrete Fracture Network1. Introduction2. Representation of the discrete fracture network3. Numerical approach4. Results4.1. Effect of DFN connectivity4.2. Effect of fracture size distribution

5. Effect of injection rate6. ConclusionsAuthor detailsReferences

Chapter 14Hydraulic Fracturing in Formations with Permeable Natural Fractures1. Introduction2. UFM model specifics3. Modeling leakoff into permeable NF in UFM4. Basic governing equations4.1. Continuity of fluid volume (mass)4.2. Pressure drop along closed NF4.3. Change of NF permeability due to stress and pressure changes4.4. The width of closed invaded NF4.5. Shear failure4.6. Fluid density as function of pressure and temperature4.7. Fluid flow in opened NF

5. Combined fluid flow into the opened and closed parts of invaded NF5.1. Opened part of NF5.2. Filtration zone (closed part of NF invaded by fracturing fluid)5.3. Closed pressurized part of NF (filled with reservoir fluid).

6. Numerical approach description6.1. Decoupled numerical approach6.2. Fully coupled numerical approach


Chapter 15Injection Modeling and Shear Failure Predictions in Tight Gas Sands — A Coupled Geomechanical Simulation ApproachAbstract1. Introduction2. Theory of fracture propagation modelling3. The field study4. History matching of field injection pressure — Uncoupled geomechanical injection models4.1. Effects of fracture permeability reduction factor (Rfa)4.2. Effects of limiting length of fracture propagation

5. History matching of field injection pressure — Coupled geomechanical injection models5.1. Effects of limiting length of fracture propagation5.1.1. Discussion on the late time history matching (Well A)

5.2. Effects of stress factor (S)

6. Failure predictions — Tensile and shear failure6.1. Base case — High cohesion6.2. Case with low cohesion

7. ConclusionsNomenclatureAuthor detailsReferences

Chapter 16The Role of Natural Fractures in Shale Gas Production1. Introduction1.1. Coal bed methane1.2. Devonian shales of the appalachian basin1.3. Devonian Antrim Shale of the Michigan basin1.4. Deeper gas shales

2. Production mechanisms, production modeling techniques and simulators2.1. Discrete fracture network models2.2. Dual porosity/dual permeability models2.3. Development of new semi-analytic solution

3. Production data interpretation4. Identification of production drivers: Nature versus nurture4.1. Example: Barnett shale production data analysis

5. Implications and deductions5.1. Productive fracture surface area5.2. Productive fracture spacing

6. ConclusionsNomenclatureAuthor detailsReferences

Section 5 Well Completions and Fracture Initiation 1Chapter 17Do Perforated Completions Have Value for Engineered Geothermal SystemsAbstract1. Introduction2. Requirements for a Successful Geothermal Well (EGS)3. Cemented versus barefoot completions4. Using diversion in openhole situations5. How to develop multiple fracture systems6. Perforation skin — Pressure loss during injection7. Perforation skin — Pressure loss during production8. Relative order of magnitude calculations — Pressure losses9. Modeling pressure drop due to perforations in a fractured reservoir10. Relative order of magnitude calculations — Supplemental power11. Erosion of perforations12. SummaryAppendix I — Pressure losses during production (Literature survey)Author detailsReferences

Chapter 18Differentiating Applications of Hydraulic FracturingAbstract1. Introduction2. Hydraulic fracturing applications2.1. Water well production enhancement2.2. Block cave mining (Hydraulic pre-conditioning)2.3. Rock stress determination for geotechnical design (Mines, tunnels, dams, foundations)2.4. Conventional oil and gas production2.5. Geothermal (Hot dry rock, or “enhanced” geothermal)2.6. Carbon sequestration (Carbon capture and storage)2.7. Coalbed Methane (CBM) development2.8. Coal Mine Methane (CMM) drainage2.9. Rock burst mitigation

3. Characterization4. Terminology to differentiate hydraulic fracturing5. ConclusionsAuthor detailsReferences

Chapter 19Initiation and Breakdown of an Axisymmetric Hydraulic Fracture Transverse to a Horizontal Wellbore1. Introduction2. Problem statement2.1. Elasticity2.2. Fluid flow2.3. Boundary conditions2.4. Initiation and fracture propagation condition

3. Scaling3.1. Field and laboratory conditions: Scaling

4. Numerical algorithm5. Results and discussion6. ConclusionsAppendix AAppendix BAppendix CAuthor detailsReferences

Chapter 20Hydraulic and Sleeve Fracturing Laboratory Experiments on 6 Rock Types1. Introduction1.1. Theory of hydraulic and sleeve fracturing on hollow cylinders

2. Sample preparation and rock testing2.1. Stress field and injection2.2. Acoustic emission monitoring

3. Results3.1. Petrophysical and mechanical parameters3.2. MF and SMF experiments

4. ConclusionAppendixAuthor detailsReferences

Section 6 Induced Seismicity and SlipChapter 21Microseismic Monitoring Developments in Hydraulic Fracture Stimulation1. Introduction2. Background3. Acquisition4. Microseismic data processing4.1. Analysis and attenuation of coherent noise4.2. Traveltime picking4.3. Locations

5. Better understanding of physical processes associated with microseismicity5.1. Advanced microseismic source analysis5.2. Geomechanical response and reservoir analysis5.3. Relating geomechanical properties to microseismic observables5.4. Analogues5.5. Geomechanical modelling5.6. Physical modelling


Chapter 22Blue Shift in the Spectrum of Arrival Times of Acoustic Signals Emitted during Laboratory Hydraulic FracturingAbstract1. Introduction2. Blue shift indicator3. Laboratory tests4. Blue shift indicator for the experimental data5. ConclusionsAuthor detailsReferences

Chapter 23A Numerical Investigation of Fault Slip Triggered by Hydraulic Fracturing1. Introduction2. Effect of fluid injection on induced seismicity3. Methodology4. Simulation setup and input parameters5. Post-injection seismicity simulations5.1. Fluid pressure build-up during injection and diffusion after shut-in5.2. Shear slip of critically stressed fault

6. Seismic moment and moment magnitude calculations7. Discussion and conclusionsAuthor detailsReferences

Section 7 Well Completions and Fracture Initiation 2Chapter 24Numerical Simulation of Hydraulic Fracturing in Heterogeneous Rock: The Effect of Perforation Angles and Bedding Plane on Hydraulic Fractures Evolutions1. Introduction2. Introduction of RFPA2D2.0-Flow3. Model set4. Simulation results4.1. The effect of perforation angles4.2. The effect of bedding angles4.3. The effect of bedding materials

5. Discussions6. ConclusionsAuthor detailsReferences

Chapter 25Quantitative Evaluation of Completion Techniques on Influencing Shale Fracture ‘Complexity’Abstract1. Introduction1.1. Natural fracture behavior1.2. Hydraulic fracturing and stress shadows1.3. Natural fracture behavior and stress shadows: Implications for completion strategies1.4. Numerical simulation of completion strategies: Modified zipper-frac

2. Model setup and simulation matrix2.2. Model setup2.3. Modeling assumptions2.4. Simulation matrix

3. Quantitative numerical evaluation of modified zipper-fracs3.1. Natural fracture shear from a single hydraulic fracture3.2. Natural fracture shear superimposing two hydraulic fractures3.3. Natural fracture shear from dual, competing hydraulic fractures3.3.1. Shear results for the ‘145°’ DFN and 20m hydraulic fracture separation3.3.2. Observations for the ‘145°’ DFN and 20m separation simulations3.3.3. Shear results for the ‘145°’ DFN and other hydraulic fracture separations3.3.4. Observations for the ‘145°’ DFN dual hydraulic fracture simulations3.3.5. Shear results for the ‘180°’ DFN and 20m hydraulic fracture separation3.3.6. Observations for the ‘180°’ DFN dual hydraulic fracture simulations3.3.7. Shear results for the ‘180°’ DFN and altered in-situ stress3.3.8. Observations for the ‘180°’ DFN dual fracture simulations with revised in-situ stress

4. Discussion4.1. Observations on the influence of fracture network4.2. Observations on the influence of natural fracture friction4.3. Observations on the influence of hydraulic fracture separation distance4.4. Observations on the influence of hydraulic fracture Xf2 half-length


Section 8 Flow Paths and Flow NetworksChapter 26Modeling of Proppant Permeability and Inertial Factor for Fluid Flow Through Packed ColumnsAbstract1. Introduction2. Pressure loss equations for flow through packed columns3. Proppant permeability formulation4. ConclusionNomenclatureGreekSubscriptsAppendix A: Flow through packed columnsAuthor detailsReferences

Chapter 27A New Approach to Hydraulic Stimulation of Geothermal Reservoirs by Roughness Induced Fracture OpeningAbstract1. Introduction1.1. Reservoir stimulation by induced fluid pressure

2. Simulation of fluid flow and heat transfer2.1. Hybrid of single continuum and discrete fracture2.2. Domain discretization using the hybrid methodology2.3. REV discretization for permeability tensor calculation2.4. Reservoir scale fluid flow simulation

3. Fracture network generation4. Results and discussions5. ConclusionsAuthor detailsReferences

Chapter 28Fracture Network Connectivity — A Key To Hydraulic Fracturing Effectiveness and Microseismicity GenerationAbstract1. Introduction2. Fracture network connectivity and DFN realization3. Numerical simulations3.3. Simulation results


Section 9 Multiscale ModelingChapter 29Fluid-Driven Fracture in a Poroelastic RockChapter 30Pressurization of a PKN Fracture in a Permeable Rock During Injection of a Low Viscosity FluidChapter 31Modified Formulation, ε-Regularization and the Efficient Solution of Hydraulic Fracture Problems1. Introduction2. Modified formulation of hydraulic fracture problem3. Analytical solutions4. Increasing efficiency of numerical simulations5. Extension to P3D models6. ConclusionsAuthor detailsReferences

Section 10 Mulitiple Hydraulic Fracture GrowthChapter 32The Geomechanical Interaction of Multiple Hydraulic Fractures in Horizontal Wells1. Introduction2. Analytical model3. Non-planar 3D model of hydraulic fractures3.1. Non-planar fracture propagation3.2. Wellbore hydraulic model

4. Comparing simulation results with analytical solution and experiment5. Frac fluid viscosity and fractures height growth6. DiscussionAuthor detailsReferences

Chapter 33Numerical Simulation of Sequential and Simultaneous Hydraulic Fracturing1. Introduction2. Model development3. Displacement discontinuity method4. Joint model5. Fracture propagation6. Fluid flow7. Simulation examples8. ConclusionsAuthor detailsReferences

Chapter 34Three Dimensional Forms ofClosely-Spaced Hydraulic FracturesAbstract1. Introduction2. Experimental method3. Results3.1. Case 1 (Block 3) un-notched zero vertical stress3.2. Case 2 (Block 4) notched no vertical stress3.3. Case 3 (Block 6) notched with substantial vertical stress

4. Experimental practicalities and future work5. ConclusionAuthor detailsReferences

Section 11 Numerical Modeling 1Chapter 35The XFEM with an Explicit-Implicit Crack Description for Hydraulic Fracture Problems1. Introduction2. Laboratory experiments for model verification and optimization2.1. Large-scale2.2. Small-scale

3. Governing equations3.1. Deformation3.2. Fluid flow3.3. Propagation condition3.4. Asymptotic behavior

4. XFEM approximation4.1. Standard formulation4.2. Numerical integration4.3. Explicit-implicit interface description4.4. Discretization of governing equations

5. Hydraulic fracture propagation5.1. Numerical algorithm5.2. Numerical results


Chapter 36An ABAQUS Implementation of the XFEM for Hydraulic Fracture Problems1. Introduction2. Problem formulation2.1. Problem definition2.2. Governing equations

3. Weak form and FEM discretization4. The extended finite elemet method and element implementation4.1. Extended finite element approximation4.2. Element implementation

5. Numerical examples6. SummaryApendix: Analytical solutions for plane strain Kristianovic-Geertsma-de Klerk (KGD) hydraulic fracturesAuthor detailsReferences

Chapter 37Stress Intensity Factor Determination for Three-Dimensional Crack Using the Displacement Discontinuity Method with Applications to Hydraulic Fracture Height Growth and Non-Planar Propagation Paths1. Introduction2. Numerical procedure2.1. Displacement discontinuity method2.2. Stress intensity factor computation

3. Validation of numerical model3.1. Rectangular crack3.2. Elliptical crack3.3. Penny-shaped crack

4. Fracture propagation5. Application: Fracture misalignment and height growth6. ConclusionAuthor detailsReferences

Section 12 Injection and EfficiencyChapter 38Secondary Fractures and Their Potential Impacts on Hydraulic Fractures Efficiency1. Introduction2. Natural facture distribution3. Elastoplastic effect in fracturing4. Initiation and propagation of cracks5. Results and discussion6. ConclusionAuthor detailsReferences

Chapter 39Importance of Fracture Closure to Cuttings Injection Efficiency1. Introduction2. Quality of pressure maintenance in CI operations3. Fracture closure analysis4. Implications of fracture behavior from G function superposition derivative5. ConclusionsAuthor detailsReferences

Chapter 40The Fate of Injected Water in Shale Formations1. Introduction2. Technical approach3. ConclusionsAuthor detailsReferences

Section 13 Numerical Modeling 2Chapter 41Three-Dimensional Numerical Model of Hydraulic Fracturing in Fractured Rock Masses1. Introduction2. Model description2.1. Background: Synthetic rock mass approach2.2. Lattice2.3. Fluid flow2.4. Hydro-mechanical coupling

3. Verification test: Penny-shaped crack propagation in medium with zero toughness4. Example application5. ConclusionAuthor detailsReferences

Chapter 42Testing and Review of Various Displacement Discontinuity Elements for LEFM Crack Problems1. Introduction2. Displacement discontinuity method3. Higher-order elements of displacement discontinuity method4. Crack tip elements of displacement discontinuity method4.1. Quarter element method4.2. Square root element method

5. Comparison5.1. Single pressurized crack in an infinite elastic domain5.2. A slanted straight crack5.3. A circular arc crack5.4. Computational efficiency

6. ConclusionNomenclatureAuthor detailsReferences

Chapter 43The Impact of the Near-Tip Logic on the Accuracy and Convergence Rate of Hydraulic Fracture Simulators Compared to Reference Solutions

Section 14 Mining and MeasurementChapter 44Hydraulic Fracturing Mine Back Trials — Design Rationale and Project Status1. Introduction2. Project objectives2.1. Mining perspective2.2. O&G perspective

3. Review of injection practices and their effect on the rock mass4. Planned experimental approach4.1. Site conditions summary4.2. High level experimental design

5. ConclusionAuthor detailsReferences

Chapter 45Monitoring and Measuring Hydraulic Fracturing Growth During Preconditioning of a Roof Rock over a Coal Longwall Panel1. Introduction1.1. Design approach

2. Preconditioning plan3. Test sites and measurements3.1. Stress measurements3.2. Fracture asymmetry measurement3.2.1. Asymmetry from analysis of tilt data

3.3. Fracture growth measurement3.4. Fracture vertical spacing measurement

4. Caving behaviour5. ConclusionsAuthor detailsReferences

Chapter 46Estimation of the Impact of Mining on Stresses by Actual Measurements in Pre and Post Mining Stages by Hydrofracture Method–A Case Study in a Copper Mine1. Introduction2. Background3. Geology and tectonics3.1. Geology3.2. Tectonics

4. Mining status5. Methodology6. Stress evaluation procedures and results7. Numerical modeling8. Discussion and conclusionAuthor detailsReferences

Section 15 Thermo-Hydro-Mechanical SystemsChapter 47An Efficient and Accurate Approach for Studying the Heat Extraction from Multiple Recharge and Discharge Wells1. Introduction2. Problem description3. Governing equations3.1. Pressure diffusion in planar fractures3.2. Heat transport in closed fractures3.3. Initial and boundary condition

4. Dimensionless formulation5. Velocity potential and stream function6. Methodology, verification and numerical results6.1. Cases with one single well and dipole wells6.2. Cases with two injection wells or multiple wells


Chapter 48Thermal Effects on Shear Fracturing and Injectivity During CO2 StorageAbstract1. Introduction2. Construction of the flow, thermal and geomechanical model3. Thermal fracturing in the reservoir below isothermal fracture pressure4. Thermally induced shear failure in the caprock5. ConclusionsAuthor detailsReferences

Chapter 49Scale Model Simulation of Hydraulic Fracturing for EGS Reservoir Creation Using a Heated True-Triaxial ApparatusAbstract1. Introduction2. Equipment design and specifications2.1. Heated true triaxial cell2.2. High pressure hydraulic injection system2.3. Multi-component data acquisition system2.4. Test materials

3. Test results and observations3.1. Sample preparation3.2. Primary hydraulic fracturing3.3. Drilling the fracture intercept production borehole3.4. Fracture reopening and circulation flow


Section 16 Experimental GeomechanicsChapter 50Comparison of Hydraulic and Conventional Tensile Strength Tests1. Introduction2. Materials and methods2.1. Sample material2.2. Petrophysical characterization2.3. Testing procedure of the tensile strength tests2.3.1. Hydraulic fracturing core experiments (MF) procedure2.3.2. Brazilian Disc Tests (BDT) procedure2.3.3. Modified Tension Test (MTT) procedure

3. Experimental results3.1. Brazilian disc test size dependency3.2. MF, BDT and MTT tensile strength results3.3. Acoustic Emissions results

4. Numerical model5. DiscussionAuthor detailsReferences

Chapter 51Formation Fracturing by Pore Pressure Drop (Laboratory Study)1. Introduction2. Experimental procedure3. Results4. Discussion5. ConclusionsAuthor detailsReferences

Section 17 Optimizing Stimulation of Fractured ReservoirsChapter 52Optimizing Hydraulic Fracturing Treatment Integrating Geomechanical Analysis and Reservoir Simulation for a Fractured Tight Gas Reservoir, Tarim Basin, China1. Introduction2. Project background3. Geomechanical model4. Natural fractures characterization and stimulation modeling5. Predicting the shape of the stimulated reservoir volume6. Hydraulic fracturing design and reservoir simulation7. Injectivity test and stage 1 treatment8. Discussion and conclusionAuthor detailsReferences

Chapter 53Investigation of Hydraulic and Natural Fracture Interaction: Numerical Modeling or Artificial Intelligence?1. Introduction2. Interaction between hydraulic and natural fractures3. Numerical modeling: Extended Finite Element Method (XFEM)4. Artificial intelligence: Artificial Neural Network (ANN)4.1. Feed-forward network with back-propagation4.2. ANN performance criteria

5. Results and discussions6. ConclusionsAuthor detailsReferences

a numerical investigation of fault slip triggered by hydraulic … · 2013. 5. 28. · a numerical...

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