- The Role of Natural Fractures in Shale Gas Production
- I. Walton ; J. McLennan
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing - Chpater 16
- Year: 2013
- Mining ; Other Geotechnical
- Keywords: natural fractures ; shale gas production
- Description
- In this paper we investigate the role played by natural fractures in the gas production process. By applying a new model of the production process to data from many shale gas wells across a number of shale plays in North America, we can for the first time begin to sort out assertion from inference in the role that these fractures play. Specifically, we are able to estimate the magnitude of the fracture surface through which gas is actually produced. We are
able to demonstrate that although it may be commensurate with the expected surface area of
open natural fractures for the ultra-low permeability shallow gas shales, it is in fact com‐
mensurate with a very much smaller area for the deeper gas shales such as the Barnett. Furthermore, given a typical value of the matrix permeability, almost all the gas between the
fractures would have been produced in an uncharacteristically short period of time unless
the producing fractures are 100s of feet apart. The implications of these findings for completion and stimulation strategies will be discussed.
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- Do Perforated Completions Have Value for Engineered Geothermal Systems
- W. Glauser ; J. McLennan ; I. Walton
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing - Chapter 17
- Year: 2013
- Mining ; Other Geotechnical ; Geothermal
- Keywords: perforations ; openhole ; multiple fractures
- Description
- A comparative and realistic
analysis is done to assess the impact of perforation skin, tortuosity associated with shear fractures intersecting the wellbore and relative economics associated with perforating and
cementing geothermal wells
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- Initiation and Breakdown of an Axisymmetric Hydraulic Fracture Transverse to a Horizontal Wellbore
- S. Abbas ; B. Lecampion
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing - Chapter 19
- Year: 2013
- Mining ; Other Geotechnical
- Keywords: axisymmetric hydraulic fracture ; hydraulic fracture propagation
- Description
- We investigate the initiation and early-stage propagation of an axi-symmetric hydraulic
fracture from a wellbore drilled in the direction of the minimum principal stress in an elastic
and impermeable formation. Such a configuration is akin to the case of a horizontal well and
a hydraulic fracture transverse to the well axis in an open hole completion. In addition to the
effect of the wellbore on the elasticity equation, the effect of the injection system compressi‐
bility is also taken into account. The formulation accounts for the strong coupling between
the elasticity equation, the flow of the injected fluid within the newly created crack and the
fracture propagation condition. Dimensional analysis of the problem reveals that three di‐
mensionless parameters control the entire problem: the ratio of the initial defect length over
the wellbore radius, the ratio between the wellbore radius and a length-scale associated with
the fluid stored by compressibility in the injection system during the well pressurization,
and finally the ratio of the time-scale of transition from viscosity to toughness dominated
propagation to the time-scale associated with compressibility effects. A fully coupled nu‐
merical solver is presented, and validated against solutions for a radial hydraulic fracture
propagating in an infinite medium. The influence of the different parameters on the transi‐
tion from the near-wellbore to the case of a hydraulic fracture propagating in an infinite me‐
dium is fully discussed.
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- Microseismic Monitoring Developments in Hydraulic Fracture Stimulation
- M. van der Baan ; D. Eaton ; M- Dusseault
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 21
- Instrumentation ; Mining
- Keywords: microseismic monitoring ; hydraulic fracturing
- Description
- The last decade has seen a significantly increased interest in microseismic monitoring by the hydrocarbon industry due to the recent surge in unconventional resources such as shale-gas
and heavy-oil plays. Both hydraulic fracturing and steam injection create changes in local pore pressures and in situ stresses and thereby brittle failure in intact rock plus additional slip/shearing in naturally fractured rock. Local rock failure or slip yields an acoustic emission, which is also known as a microseismic event. The microseismic cloud represents thus a volumetric map of the extent of induced fracture shearing, opening and closing. Microseismic monitoring can provide pertinent information on in situ reservoir deformation due to fluid stimulation, thus ultimately facilitating reservoir drainage. This paper reviews some of the current key questions and research in microseismicity, ranging from acquisition, processing to interpretation.
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- A Numerical Investigation of Fault Slip Triggered by Hydraulic Fracturing
- N. Zangeneh ; E. Eberhardt ; R.M. Bustin ; A. Bustin
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 23
- Numerical & Constitutive Modeling ; Mining
- Keywords: numerical investigation ; hydraulic fracturing ; shale gas reservoirs
- Description
- The study of fault slip in response to fluid injection offers a means to understand the complex hydromechanical behavior of shale gas and oil reservoir systems during hydraulic fracturing operations, together with the induced seismicity, and corresponding mitigation measures, arising from such events. In this paper, a series of numerical simulations are performed to investigate the relationship between hydraulic fracturing (i.e. fluid injection) and the response of a naturally fractured rock mass to transient fluid pressures. The analysis is carried out using the discontinuum-based distinct-element program UDEC assuming a fracture flow system. The conceptual reservoir model consists of a critically stressed fault plane and the surrounding rock mass containing planes of weakness, for which a hydraulic fracture is numerically simulated and the response modeled using a transient, coupled hydro-mechanical solution. The results demonstrate the influence of fluid diffusion generated by the fracing fluid after shut-in on the triggering of fault slip. The simulation is then used to interpret the associated seismic events and their relationship to the injections and shut-in pressures, and to estimate the maximum magnitude of the induced seismic event.
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- Numerical Simulation of Hydraulic Fracturing in Heterogeneous Rock: The Effect of Perforation Angles and Bedding Plane on Hydraulic Fractures Evolutions
- X. Men ; C. Tang ; S. Wang ; Y. Li ; Ta Yang ; Ti Ma
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 24
- Numerical & Constitutive Modeling ; Mining
- Keywords: hydraulic fracturing ; heterogeneity ; numerical simulation ; fracture evolution
- Description
- Considering the heterogeneity of rock, the hydraulic fracturing process of rock specimen
due to internal hydraulic pressure was numerically simulated in a meso-scale by
RFPA2D2.0 (Realistic Failure Process Analysis). The differences of perforation angle, bedding angle and bedding material of rock specimens are considered. The numerical results showed that the initiation and propagation of hydraulic fractures were controlled by both global pore pressure’s distribution gradient and local pore pressure around the crack tip. Both the lateral compressive pressure ratio and the bedding angle could affect the evolution of the hydraulic fractures. The numerically simulated results were in agreement with the experimental results.
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- Quantitative Evaluation of Completion Techniques on Influencing Shale Fracture ‘Complexity’
- N. Nagel ; F. Zhang ; M. Sanchez-Nagel ; D. Walls
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 25
- Discrete Element ; Mining
- Keywords: hydraulic fracturing ; discrete element mode ; shale ; numerical simulation
- Description
- In many of the active shale plays, the extremely low permeability of the shale means simple,
bi-planar hydraulic fractures do not provide enough surface area to make an economic well.
In these cases, the optimal, economic completion requires stimulation of the natural fracture
system - often called increasing the ‘complexity’ of the stimulation. A number of different
multi-well completion techniques have been proposed to enhance shale complexity. The
‘simul-frac’ technique is where companion wells are stimulated at the same location at the
same time, whereas the ‘zipper-frac’ technique employs companion wells that are stimulated
in staggered locations at the same time. The intention with these techniques is to alter either
or both the stress field and the pore pressure field to enhance the shearing of natural fractures.
In this paper, we present the results of a numerical study to quantitatively evaluate the
effectiveness of multi-well completion techniques, particularly the ‘modified zipper-frac’
technique, to optimize shale completions. The study includes a parametric study of the effects
of in-situ stress conditions, natural fracture orientation and fracture friction, and hydraulic
fracture layout on changing near and far-field natural fracture shear (complexity). Changes in
the stress field, particularly shear stress, are considered the primary means of increasing
fracture complexity. The quantitative results of the study provide a means to optimize the
application and design of different multi-well completion techniques as a function of the
presented parameters. Optimized completion designs mean lower well costs, greater produc‐
tion and, ultimately, improved well economics.
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- Hydraulic Fracturing Mine Back Trials — Design Rationale and Project Status
- P.K. Kaiser ; B. Valley ; M.B. Dusseault ; D. Duff
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 44
- Rock Mechanics ; Mining
- Keywords: stress management ; stiffness modification ; shale gas analogue ; mine-back experiments ; naturally fractured rocks
- Description
- Last year, a joint Mining and Oil & Gas industry consortium was established in Canada to
conduct hydraulic fracturing (HF) tests accompanied by a mine-back of fractured regions to assess HF models and microseismic monitoring data during controlled experiments. Details about the displacement field, fracture aperture and extent, and micro-seismic parameters could then be verified and used as calibration data for modeling of HF processes in igneous and dense sedimentary rocks.
Various injection experiments are planned and they will include pre-fracturing rock mass
characterisation using best available current techniques, dense arrays of multi-parameter
wall and borehole-mounted instruments, and the treated volume will be mined through to
assess fracturing effectiveness, existing fractures and new fracture interactions, and to deter‐
mine if pathways can be identified for improving currently available numerical and fracture
network modeling tools.
In this paper we present the results of the experimental design and planning phase, outlin‐
ing objectives and justifications for planned experimental layouts. Preliminary plans for a
first mine-through trial at Newcrest Mining’s Cadia East mine in New South Wales, Austral‐
ia are described. The hypotheses advanced in this experimental design, supported by evi‐
dence from the literature, are that activation and development of a fracture network by
hydraulic stimulation is possible if the injection procedure is designed such that injection
pressures and rates are maintained within an optimal window, thereby producing condi‐
tions under which effective stress management for risk mitigation in deep mining can best be achieved. The evaluation of these hypotheses is the focus of the current high level experi‐
mental plan presented in the paper.
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- Monitoring and Measuring Hydraulic Fracturing Growth During Preconditioning of a Roof Rock over a Coal Longwall Panel
- R.G. Jeffrey ; Z. Chen ; K.W. Mills ; S. Pegg
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 45
- Rock Mechanics ; Mining
- Keywords: hydraulic fracturing
- Description
- Narrabri Coal Operations is longwall mining coal directly below a 15 to 20 m thick conglomerate sequence expected to be capable of producing a windblast upon first caving at longwall startup and producing periodic weighting during regular mining. Site characterisation and field trials were undertaken to evaluate hydraulic fracturing as a method to precondition the conglomerate strata sufficiently to promote normal caving behaviour at longwall startup and reduce the severity of periodic weighting. This paper presents the results of the trials and illustrates the effectiveness of hydraulic fracturing as a preconditioning technique. Initial work was directed at determining if hydraulic fractures were able to be grown with a horizontal orientation, which would allow efficient preconditioning of the rock mass by placing a number of fractures at different depths through the conglomerate from vertical boreholes drilled from the surface. The measurements and trials were designed to determine the in situ principal stresses, the hydraulic fracture orientation and growth rate, and whether the fractures could be extended as essentially parallel fractures to a radius of at least 30 m. Overcore stress measurements were used to determine the orientation and magnitude of the in situ principal stresses, a surface tiltmeter array was used to determine the hydraulic fracture orientation, and stress change monitoring, pressure monitoring and temperature logging in offset boreholes were used to establish the fracture growth rate, lateral extent, and that the fractures maintained their initial spacing to a radial distance of greater than 30 metres. The measurements and trials demonstrated that horizontal fractures could be extended parallel to one another to a distance of 30 to 50 m by injection of 5,000 to 15,000 litres of water at a rate of 400 to 500 L/min. Results from the trial allowed a preconditioning plan to be developed and successfully implemented.
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- Estimation 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 Mine
- S. Sengupta ; D.S. Subrahmanyam ; R.K. Sinha ; G. Shyam
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 46
- Mining
- Keywords: hydro-fracture method ; mining stresses
- Description
- To sustain and increase the productivity in a large underground copper mine in India the
management of the mine decided to design and develop stopes below the mined out area.
For the design of the stopes a detailed stress measurement programme was carried out by
hydrofracture method at different depths from the developments available near the pro‐
posed stope. The result indicated a post mining induced high stress tensor with the direction
of the maximum compression (maximum principal horizontal stress) rotated 70- 750 from
the pre-mining stress tensor and oriented almost transverse to the ore body as against sub
parallel to the orebody during pre-mining stage. A 3-D numerical modeling of the mine
with pre mining stress tensor as input parameter substantiated the field result at the post
mining stage. The generation of post - mining stress helped in understanding the impact of
mining on the stress and was used for design and sequencing of the stoping operation for
the safe and optimum extraction of the ore.
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- Settlement and shear strength of uncemented coal mine overburden materials placed loose under dry and wet conditions
- A.K. Kho ; D.J. Williams
- Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, September 2-6 2013
- Year: 2013
- Settlements ; Shear Strength of Underground Materials ; Mining
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- Prediction of hard rock TBM penetration rate based on Data Mining techniques
- T.F.S. Miranda ; F.F. Martins
- Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, September 2-6 2013
- Year: 2013
- Rock Mechanics ; Mining
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- Physical modeling of arch action in undercut slopes with actual engineering practice to Mae Moh open-pit mine of Thailand
- J. Takemura ; M.H. Khosravi ; T. Pipatpongsa
- Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, September 2-6 2013
- Year: 2013
- Slope Stability ; Numerical & Constitutive Modeling ; Mining
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- Stability and movements of open-pit lignite mines in Northern Greece
- C. Steiakakis ; P. Schilizzi ; Z. Agioutantis ; M. Kavvadas
- Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, September 2-6 2013
- Year: 2013
- Mining ; Slope Stability
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- Fracturing Fluids
- C. Montogomery
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing - Chapter 1
- Year: 2013
- Mining
- Keywords: fracturing fluids ; viscocity ; hydraulic fracturing
- Description
- When fracturing, viscosity play a major role in providing sufficient fracture width to insure
proppant entrance into the fracture, carrying the proppant from the wellbore to the fracture
tip, generating a desired net pressure to control height growth and providing fluid loss con‐
trol. The fluid used to generate the desired viscosity must be safe to handle, environmental‐
ly friendly, non-damaging to the fracture conductivity and to the reservoir permeability,
easy to mix, inexpensive and able to control fluid loss. This is a very demanding list of re‐
quirements that has been recognized since the beginning of Hydraulic fracturing. This paper
describes the history of fracturing fluids, the types of fracturing fluids used, the engineering
requirement of a good fracturing fluid, how viscosity is measured and what the limitations
of the engineering design parameters are.
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