- Fractures and Fracturing: Hydraulic Fracturing in Jointed Rock
- C. Fairhurst
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing - Chapter 3
- Year: 2013
- Rock Engineering
- Keywords: hydraulic fracturing ; fractures ; jointed rock
- Description
- Rock in situ is arguably the most complex material encountered in any engineering disci‐
pline. Deformed and fractured over many millions of years and different tectonic stress re‐
gimes, it contains fractures on a wide variety of length scales from microscopic to tectonic
plate boundaries.
Hydraulic fractures, sometimes on the scale of hundreds of meters, may encounter such dis‐
continuities on several scales. Developed initially as a technology to enhance recovery from
petroleum reservoirs, hydraulic fracturing is now applied in a variety of subsurface engineering applications. Often carried out at depths of kilometers, the fracturing process cannot
be observed directly.
Early analyses of the hydraulic fracturing process assumed that a single fracture developed
symmetrically from the packed off-pressurized interval of a borehole in a stressed elastic
continuum. It is now recognized that this is often not the case. Pre-existing fractures can and
do have a significant influence on fracture development, and on the associated distributions
of increased fluid pressure and stresses in the rock.
Given the usual lack of information and/or uncertainties concerning important variables
such as the disposition and mechanical properties of pre-existing fracture systems and properties, rock mass permeabilities, in-situ stress state at the depths of interest, fundamental questions as to how a propagating fracture is affected by encounters with pre-existing faults, etc., it is clear that design of hydraulic fracturing treatments is not an exact science.
Fractures in fabricated materials tend to occur on a length of scale that is small; of the order
of the ‘grain size’ of the material. Increase in the size of the structure does not introduce new
fracture sets.
Numerical modeling of fracture systems has made significant advances and is being applied
to attempt to assess the extent of these uncertainties and how they may affect the outcome of practical fracturing programs. Geophysical observations including both micro-seismic activity and P- and S-wave velocity changes during and after stimulation are valuable tools to assist in verifying model predictions and development of a better overall understanding of
the process of hydraulic fracturing on the field scale. Fundamental studies supported by lab‐
oratory investigations can also contribute significantly to improved understanding.
Given the widening application of hydraulic fracturing to situations where there is little pri‐
or experience (e.g., Enhanced Geothermal Systems (EGS), gas extraction from ‘tight shales’ by fracturing in essentially horizontal wellbores, etc.) development of a greater understanding of the mechanics of hydraulic fracturing in naturally fractured rock masses should be an industry-wide imperative. HF 2013 International Conference for Effective and Sustainable Hydraulic Fracturing is very timely!
This lecture will describe examples of some current attempts to address these uncertainties
and gaps in understanding. And, it is hoped, it will stimulate discussion of how to achieve
more effective practical design of hydraulic fracturing treatments.
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- Fracturing Fluid Components
- C. Montgomery
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing - Chapter 2
- Year: 2013
- Mining
- Keywords: hydraulic fracturing ; fracturing fluids
- Description
- The materials and chemistry used to manufacture hydraulic fracture fluids are often confusing and difficult for the practicing hydraulic fracturing engineer to understand and optimize. Many times the failure of a particular fracturing treatment is blamed on the fluid because that is a major unknown from the design engineer's viewpoint. Many of the components and processes used to manufacture the fluid are held proprietary by the service company which adds to the confusion and misunderstanding. This paper makes an attempt to describe the components used in fracturing fluids at a level that the practicing frac-engineer can understand and use. The paper is intended as a companion paper to the Fracturing Fluids design paper which describes how to use the fluids and viscosity generated by the fluids
to design a fracturing treatment.
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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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- Special Issue: Geomechanics of Hydraulic Fracturing in Shale Formations
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- Book Title / Journal: e-newsletter
- Year: 2014
- Other Geotechnical
- Keywords: hydraulic fracturing ; shale formation ; oil ; oil extraction
- Description
- The Spring 2014 Special Issue of the ARMA e-newsletter is dedicated to geomechanics in petroleum extraction with particular interest to
hydraulic fracturing of shale formations and contains four technical notes.
The lead article, by Paul La Pointe, introduces us to the general field of oil extraction, emphasizing the importance of combining geology and geomechanics in that pursuit. The other three technical notes address different aspects of producing oil from shale formations.
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