Seismic exploration and fracking

LAND SEISMIC OIL
EXPLORATION
&
HYDRAULIC FRACTURE
TECHNIQUE
AUTHOR:
ENG. ALEJANDRO LEVY – QA/QC SESIMIC SUPERVISOR
SEIS.ENG01@GMAIL.COM
BOLIVIA 2015

ABSTRACT
• We are walking trough an “hyper-information” age. At the same time
we hear, so many things that are said which some of them are and
not are true.
The oil and gas, we liked or not, have been with us for more than 50
years in more products that we can imagine.
The meaning of this lecture is to present the operations carried out in
one of the first steps to the oil and gas production. Explain why is
done, in which way, their environmental impact, and risks to human
health.
Finally the much controversial technique, hydraulics or stimulation
fracturing of wells, with the aim of giving the participant of this
course a technical understanding of how it's done and their risks.

TABLE OF CONTENTS
• SEISMIC INTRODUCTION
• GEOLOGY BASICS
• 2D – 3D & 4D SEISMIC PURPOSE
• SEISMIC DATA
• LAND SEISMIC SOURCES
• SEISMIC LAND SENSORS “THE GEOPHONE”
• THE SEISMIC LINE
• THE RECORDING TRUCK “WHITE HOUSE”
• SEISMIC DATA PROCESSING & INTERPRETATION
• ENVIRONMENTAL CONCERNS FOR ONSHORE OIL & GAS EXPLORATION
• FRACKING

SEISMIC HISTORY
• The first use of explosive to delineate structures under the
earth was in the 1920’s and 1930’s in the Southern U.S. and
South America
• Digital processing and tape recording made a great
improvement in the seismic techniques in the 50’s

WHY, SEISMIC EXPLORATION
• Seismic exploration is the search for commercially economic
subsurface deposits of crude oil, natural gas, and minerals by the
recording, processing, and interpretation of artificially induced shock
waves in the earth.
• Artificial seismic energy is generated on land by shallow borehole
explosives such as dynamite, or surficial vibratory mechanisms
known as vibrators.
• Seismic waves reflect and refract off subsurface rock formations and
travel back to acoustic receivers called geophones (on land).
• The travel times (measured in milliseconds) of the returned seismic
energy, integrated with existing borehole well information, aid
geoscientists in estimating the structure (folding and faulting)and
stratigraphy (rock type, depositional environment, and fluid content)
of subsurface formations, and facilitate the location of prospective

ROCK TYPES
• Rocks can be classified into three main types, depending on the chemistry
of their formation
a. Igneous Rocks:
These rocks were formed by the cooling and
subsequent solidification of a molten mass of rock material, know as
magma.
b. Metamorphic Rocks:
Are those whose composition and texture has been
altered by heat and pressure deep within the Earth’s crust.
c. Sedimentary Rocks:
Sedimentary rocks are the weathered debris
derived by the slow processes of erosion of upland regions containing
other rock types.

ROCKS
IGNEOUS METAMORPHICS
SEDIMENTARY

SEDIMENTARY BASINS
• Sedimentary basins were formed over hundreds of millions of
year by the action of the deposition of eroded material and the
precipitation of chemicals and organic matter in the sea water.
• External geological forces then distort and modify the layered
strata.

• The following sequences of pictures show (exaggerated) the formation of
a typical basin.
• Sediment collects on the sea-bed, the weight causing subsidence.
• Different materials collected at the different times, so producing the
regular “layering” of strata in the basin.

• Volcanic action, or the movement of land masses, causes faults to
appear in the basin.

• These same forces cause rotation of the overall basin forming a
new mount range

• Erosion of the highlands, and additional subsidence forms yet another
area of low-lying land that is filled with water forming another ancient
sea.
• Additional sedimentation takes place, causing an “unconformity” in the
underlying strata.

• Finally, land mass movement causes folding and distortion of the
basin

OIL AND GAS FORMATION
• The temperature increases with depth within the Earth’s crust, so that
sediments, and the organic material they contain, heat up as they become
buried under younger sediments.
• As the heat and pressure increase, the natural fats and oils present in buried
algae, bacteria and other material link and form kerogen, an hydrocarbon that is
the precursor of petroleum
• As this source rock becomes hotter, chains of hydrogen and carbon atoms break
away and form heavy oil.
• At higher temperatures the chains become shorter and light oil or gas is formed.
• Gas may also be directly formed from the decomposition of kerogen produced
from the woody parts of plants
• This woody material also generates coals seams within the strata
• If the temperature and pressure gets too high, the kerogen becomes carbonized
and dose not produce hydrocarbons.

• The oil and gas produced by these processes may be in any
combination and are almost always mixed with water
• The minute particles of hydrocarbon are produced within the pores
of PERMEABLE ROCKS (i.e.: sandstone) and, being lighter than the
surroding material, move up through the rock until prevented from
doing so by an IMPERMEABLE ROCK.
• Although the initial source rock may only contain minute amount of
hydrocarbon, as the particles of oil, gas and water move or
MIGRATE, through the pore space within younger permeable rocks,
they coalesce into large volumes

• By the time this movement is stopped by the presence of a cap of
impermeable rock (or when they reach the surface) the total
hydrocarbon volume may be large enough to be a produce an oil or
gas field that will be profitable to develop.
• The ultimate profitability of such a field depends, of course, on
external economic forces and world demand as much as on ease of
extraction
• As seismic exploration is concerned with the imaging of sub-surface
structures, it is those structures that may indicate a potential
hydrocarbon trap that are of most interest to the explorationist.

2D – 3D & 4D SEISMIC PURPOSE

2D – 3D & 4D SEISMIC
• 2D Seismic shows a single slice of the earth.
• 3D Seismic Shows a volume of earth.
• 4D Seismic shows a 3D volume at different times in the life of
an oil and/or gas field.
• Seismic is the primary choice of data collection today for oil
and gas exploration.

WHAT IS THE SEISMIC DATA?
• Seismic data is an image of the earth below the surface of the
ground.
• Seismic data shows different rock formations as layers of
reflectors.
• Different rock types, and the fluids in the rocks, cause seismic
reflection events.
• Seismic data is collected in the field, processed in a computer
center, and interpreted by a geophysicist.

SEISMIC TRACE
• The data recorded from one “shot” (one detonation of an
explosive or implosive energy source) at one receive position is
referred to as a seismic trace

HOW THE SEISMIC DATA LOOKS LIKE

• This seismic Trace is recorded as a function of time measured
in milliseconds (the time since the shot was fired).
• As this time represents the time taken for the energy to travel
into the earth, reflect, and then return back to the surface.
• During the processing sequence these traces are combined
together in various ways, and modified by some fairly complex
mathematical operation.

SEISMIC PROFILE
• The display of many traces side-by-side in their correct spatial
positions produces the final “seismic section” or “seismic profile”
• The seismic profile provides the geologist with a structural picture
of the subsurface

THE IDEAL SEISMIC SOURCE
• Changes in the speed (velocity) of sound and the density within
particular rocks causes reflection and refraction of the sound
wave produced by a seismic source.
• Specifically, variation of these parameters at an interface
between two different rock types causes a reflection of some of
the seismic energy back towards the surface.
• It is the record of these reflections against time that produce
our seismic section.

• A seismic reflector can only reflect back to the surface an image of
the energy pulse it receives.
• If we send a complex pulse into the ground, that pulse will be
superimposed on every reflector we record.

• For this reason we wish to make the actual seismic source as
close as possible to a single pulse of energy - a spike.
• A spike of energy sent into the earth produces a set of clear
reflections.
• A more complex energy pule produces confused reflections

• In practice and ideal spike is impossible to achieve.
• As spike implies that an infinitely wide range of frequencies need
to be present in the source, all released over an infinitesimally
small time range.
• The earliest seismic surveys used explosives as a seismic source
with, for offshore exploration, up to 50 pounds (23 kg) of dynamite
being exploded just below the surface of the water.
• This is a very effective source, still used for onshore surveys, and
for offshore the source use is the ‘airgun’.

EXPLOSIVES
• The Explosive source develop
its power in a very short time
(theoretically “cero”)
VIBRATORS
• Vibrational Sources (vibrators)
distribute their power for a
sustained period of time,
usually several seconds

EXPLOSIVES
ADVANTAGES
Dynamite is a high –power source
of short duration
As such, it creates a compact
wavelet with a wide bandwidth
Other advantages over vibrator
trucks are its light weight, low cost,
lack of required maintenance and
capacity for deployment in rugged
terrain unreachable by vehicles
DISADVANTAGES
 The process of drilling shot holes, burying the
dynamite and cleaning up after the operation is
labor intensive, and with this option the survey
geometry cannot be changed without drilling
new shot holes.
 The input signal can be neither measured nor
reliably repeated.
 Explosive sources are subject to strict security
regulations and permission for use and
transportation may be difficult to obtain in
some places.
 The potential for causing damage prevents their
use in populated areas.

CHARACTERISTIC OF SEISMIC DYNAMITE
• Explosive developed for seismic work use nitroglycerin and/or
nitrocellulose as active ingredients.
• The substances in their pure state are extremely dangerous and
highly volatile.
• However, when these highly explosive substances are absorbed by a
pores material such as wood pulp, kieselguhr, powdered chalk, or
roasted flour they are quite safe to transport, to store and use.
• Currently the gelatin dynamites are the most widely used in seismic
work world wide.

• Some of the most important characteristics that seismic dynamite must
possess are:
High explosive power
High detonation rate
Great water resistance
Effective detonation under great water pressure
High density
Freezing resistance
Safety in handling

SEISMIC EXPLOSIVES
• WesternGeco and Dyno Nobel developed dBX purpose-built seismic
explosive, the first explosive specifically designed for seismic use.
• The formulation offers significant geophysical benefits over
conventional explosive, optimizing energy transfer to the earth and
delivering higher S/N and greater bandwidth than dynamite.
• A comparison test in Canada demonstrated the capability of the
dBX source to improve imaging of deep reflectors

VIBROSEIS
• Vibrators are a Surface source
• In a Vibroseis survey, specially designed vehicles lift their weight
onto a large plate, in contact with the ground, which is then
vibrated over a period of time (typically 8-20 seconds), with a
sweep of frequencies.

• Seismic vibrators are the predominant source used in land seismic
exploration today
• The performance of a seismic vibrator is dictated by its actuator,
which is composed of a driven and a driving structure.
• The main element of the driven structure is the baseplate which is
pressed to the ground by weight of the truck
• The main element of the driving structure is the heavy reaction mass.
A piston inside the reaction mass is mounted above the baseplate
with a hydraulic system to drive the mass up and down

• During operation the vibrator moves into position and lowers the
baseplate to the ground, where it applies a compression to the
earth. By controlling hydraulic fluid flow around the piston inside
the mass, the vehicle operator can make the piston and base plate
assembly move up and down at specific frequencies, transmitting
energy through the baseplate and into the ground.
• The base plate is often coupled with a large fixed weight known as
the hold-down weight
• During those parts of the cycle in which the reaction mass is
moving down and the base plate is moving up, the hold-down
weight applies a compressive force to keep the base plate in
contact with the ground
HOW THE VIBRATOR WORKS

HOW THE VIBRATOR WORKS (CONT.)
• Harmonic distortions, or resonances, both in the vibrator and at
the earth/baseplate interface, can have the effect of additional
upward-directed force and must be considered in the selection
of the desired vibrator output.
• Increasing the hold-down weight on the vibrator adds stability
to the system and helps establish optimal operating conditions.
• For coupling (base plate/ground) stability the hold down weight
limit should be between the 70-85%

• The energy developed in a sweep may or may not be sufficient to
meet the proposed requirement (target depth), and therefore must
be issued other sweeps (acting the vibrators in "fleet" or groups).
• The fleet’s energy will be added in the Seismograph.

VIBRATORS
ADVANTAGES
The energy spectrum can be
controlled easily.
The force applied to the ground can
be monitors and adjusted in real
time.
Can be used in urban areas and can
be equipped with special tires or
track for deployment in
environmentally sensitive areas,
such as sand dunes or arctic
snowpack.
DISADVANTAGES
The restriction of access in difficult
terrains like swamps, mountains
and coastal areas.
Fleets of vibs are expensive and
their maintenance as well.
The input signal is not impulsive,
so additional processing is required
to extract interpretable data. A
recorded trace is correlated with a
reference trace to extract the
reflected signal

THE VIBROSEIS CONCEPT - SIGNALS USED
IN VIBROSEIS OPERATIONS
• One of the most important characteristic of the Vibroseis
method is the limitation of the bandwidth of the source.
• By this way, the Vibroseis technique allows us to generate only
those frequencies we actually need whereas with an impulsive
source like dynamite, some of the frequencies generated by the
blast are ignored during the seismic acquisition.

VIBROSEIS SYSTEM DESCRIPTION
• The Sercel Vibroseis System is composed of :
• A sweep generator,
• A vibrator to emit the sweep into the earth,
• A correlator to compress the long sweep into a short reflection
pulse,
• The correlator consists of a correlation process stage (FTP
board in the Central Control Unit) that detects the reflected
sweeps.

HOW TO GENERATE A VIBROSEIS BAND-
LIMITED SIGNAL
• The signal that makes it possible to have a band-limited component
amplitude spectrum, through Fourier Transform, is represented in
time like that shown in Fig. 1 - c.
• Unfortunately, the shape of that signal is not suited for the Vibroseis
technique that requires a long, low-power rather than short, high-
power signal.
• To describe the signal used in the Vibroseis technique, we have to
change the short, high-power signal (c) into a long, low-power signal
while preserving the limited bandwidth of the component amplitude
spectrum.
• This signal is virtually a sine wave, called sweep in the Vibroseis
terminology

• To expand a short pulse of high peak amplitude into a long sweep
of low peak amplitude you need to apply some frequency-
dependent delays. The energy in both forms of the signal (i. e.
pulse or sweep form) is the same. That’s why Vibroseis is not a low
energy system but a low power system.

• Naturally, in real-world situations we have to deal with multiple
reflectors, hence multiple reflections. If the reflection time is
shorter than the duration of the sweep, this causes the signals
picked up by the geophones to overlap:

• Where
• Trace (a) shows the sweep reflected from the first reflector,
• Trace (b) shows the same from the second reflector,
• Trace (c) is the signal detected by the geophone, i. e. the sum of traces (a),
and (b).
• Trace (c) is passed through the correlator to generate trace (d).
• The correlator boosts the signal and leaves the noise unchanged

• It should also be noted that for a given sweep amplitude in
Vibroseis the way of increasing the energy in the sweep is to
increase its duration or/and to increase the number of vibrators.
The fact is, it is the long duration of the sweep that allows us to get
the necessary energy into the ground. So, the peak amplitude of the
correlator output improves with the duration of the sweep.

• The side lobes of the auto-correlation function of a sweep can
be reduced by tapering the start/ends of the sweep.
• It is important to consider that the ground can be
mathematically consider as a “Low Pass Filter” since attenuation
is greater at higher sweep frequencies.

• In the Figure, an 8 seconds sweep length is plotted (Sweep Length: 8 sec) where the
time Seismic Data Acquisition is "12-second" (Record Length: 12 sec).
• The final registration Correlated possess the length of time called "listening time"
which is equivalent to the time required for the last component of the original sweep
to travel to the deeper reflector horizon, chosen as a target, and return to the
surface (in dynamite, because the duration of the event is infinitesimal, then
"listening time" is the "total time of acquisition)

SEISMIC LAND SENSOR
“THE GEOPHONE”

GEOPHONE BASICS
• A geophone consist in an element of a coil of wire wound on a
former and mounted on springs.
• The idea is that inertia will, in principle, keep the coil fixed
in space while a magnet firmly attached to the case moves
around it (above natural frequency).
• When a conductor breaks the magnetic flux lines produced by
the magnet a current is generated and a voltage is induced
(Faraday's Law)

• In our case these current and voltage are the very first stage in
my recording system.
• The current produced and the induced voltage are very small so
we need to boost the signal.

• The voltage that the geophone produces is proportional to the
velocity of the ground it is couple to (above natural frequency)
• Just as we need to perform instrument test on recording system
we need to perform test on the geophones.
• This ensures the signal that we record on tape is an accurate
representation of the ground respon to an energy release.

• This section presents the organization of all the network of the field
equipment as well as its hardware description.
• The acquisition system is made of a central unit (LCI), boxes (LAUX-
428, LAUL-428), and of cables (including FDU-428s).
• The LAUX428s are connected to the control modules through the
transverse cables or Fiber Optic ; they manage the link between the
transverses and the lines and generate the power supply and the
control of the links on each side of it.
• Inside the lines, the LAUL-428s are regularly connected to power and
control the segment (several links between LAUL-428s). A LAUL-428
can be replaced by a LAUX-428. A link is made of one cable and one

LAUL: LINE ACQUISITION UNIT LINE

ACQUISITION CHANNEL CIRCUITRY -
STAGES
• ADC Analog to Digital Converter, a device that will convert an
analog signal into a digital one.
• DSP Digital Signal Processor, a device that will convert the data
to 24 bits and in so doing, apply either a linear or a minimum
phase response characteristic.

ACQUISITION CHANNEL CIRCUITRY -
DESCRIPTION
• The signal acquisition circuitry is composed of the following four circuits :
• Input filter (FDU-428) : performing initial high-cut filtering.
• Modulators (FDU-428) : consisting of a Delta Sigma analogue-to-digital
converter ( ADC).
• Delay Memory (used in LAU Slave) :consisting of a RAM used to provide
temporary storage for signal processing and remove the sample skew by
synchronizing the start of acquisition.
• Digital Signal Processors (FDU-428 and used in LAU Slave) : removing all that
is of no use in the signal (including the quantization noise and high frequency
components.

THE RECORDING TRUCK
“WHITE HOUSE”

LCI – DPG – NAS - DSD
• LCI(Line Control Interface): Interface between the spread and the e-
428 client/server architecture
• DPG (Digital Pilot Generator): A control unit for the vibrator
electronics (DSD). Connects to the LCI-428.
• NAS (Network Attached Storage system): Large-capacity, removable
disks to record your SEGD files, allowing zero-dead-time shooting.
• DSD (Digital Servo Drive): Digital Servo Drive. Performs real-time
control of the energy imparted into the earth by a vibrator.
Communicates with a DPG via a radio link.

SEISMIC DATA PROCESSING &
INTERPRETATION

OBJECTIVES
• Using computer software's to reconstruct the process of wave
propagation from the recorded data.
• Based on the established links between wave anomalies and
geological features, interpret the reconstruct wave fields in
terms of subsurface structures and rock formation properties

ENVIRONMENTAL CONCERNS
FOR ONSHORE OIL AND GAS
EXPLORATION

ONSHORE SEISMIC SOURCES
• There are enormous logistical problems associated with
Onshore Seismic Exploration. (i.e.: Lakes, cities, mountains, etc.
)
• The seismic "line" must first be accurately marked out by
surveyors.

• This may mean painting marks on roads through residential
areas for example or cutting through dense jungle to mark shot
and receiver positions.
• In either case modern GPS equipment has simplified the
positioning

• Oil & Gas deposits tend to be in some of the more inhospitable
regions of the Earth, so the actual terrain conditions may limit the
available shooting/recording positions as well as define the costs of
the acquisition.
• Innovative seismic techniques are energizing exploration and
development activities in onshore areas, many of which have proved
difficult to image in the past.
• New seismic sources, acquisition methods and processing
approaches help illuminate reservoir hidden beneath complex near-
surface layers

SOURCES OF SEISMIC ENERGY
• Recent advances in source technology are further improving
data quality by putting more seismic energy into the earth at a
wider range of frequencies
• The ideal source for seismic exploration is an impulsive source
that concentrates its energy at a point in space and release it
instantaneously.
• In practice, sources have finite spatial size and emit signals
over a finite period, producing broadened wavelets that add
complexity to processing

• Where better surface conditions exist, or access is difficult, a
portable form of drilling rig may be used.
• Water & mud pumps, compressed air, emulsion and foam have all
been used to improve the circulation of the drill bit in different
conditions. The types of drill used extends from hand-held augers
to large truck-mounted hammer drills.
• Production rates for "conventional" (dynamite) exploration depend
almost entirely on the rate at which holes can be drilled.

EXPLORATION IMPACTS
• Potential environmental impacts from exploration activities (including
seismic surveys and exploratory drilling) are generally temporary and
of relatively small magnitude.
• Activities during the exploration phase (including seismic surveys,
testing, and exploratory drilling) are temporary and are conducted at
a smaller scale than those at the drilling/development, production,
and decommissioning/reclamation phases.
• The impacts described for each resource would occur from typical
exploration activities, such as localized ground clearing, vehicular
traffic, seismic testing, positioning of equipment, and exploratory
drilling.
• Most impacts during the exploration phase would be associated with
the development of access roads and exploratory wells.

NOISE
• Primary sources of noise associated with exploration are:
• Earth-moving equipment,
• vehicle traffic,
• seismic surveys,
• blasting,
• vibrators and drilling operations.

AIR QUALITY
• Impacts on air quality during exploration activities would include emissions
and dust from earth-moving equipment, vehicles, seismic surveys, well
completion and testing, and drill rig exhaust.
• Pollutants would include , particulates, oxides of nitrogen, carbon
monoxide, sulfur dioxide, and volatile organic compounds (VOCs). Nitrogen
oxides and VOCs may combine to form ground-level ozone.
• Impacts would depend upon the amount, duration, location, and
characteristics of the emissions and the meteorological conditions (e.g.,
wind speed and direction, precipitation, and relative humidity). Emissions
during this phase would not have a measurable impact on climate change .

CULTURAL RESOURCES
• The amount of surface and subsurface disturbance is minimal during
the exploration phase.
• Cultural resources buried below the surface are unlikely to be
affected; while material present on the surface could be disturbed by
vehicular traffic, ground clearing, and pedestrian activity (including
collection of artifacts).
• Exploration activities could affect areas of interest depending on the
placement of equipment and/or level of visual intrusion.
• Surveys conducted during this phase to evaluate the presence and/or
significance of cultural resources in the area would assist developers
in siting project facilities in order to avoid or minimize impacts to
these resources.

ECOLOGICAL RESOURCES
• Impacts to ecological resources (vegetation, wildlife, aquatic
biota, special status species, and their habitats) would be
minimal and localized during exploration because of the
limited nature of the activities.
• The introduction or spread of some nonnative invasive
vegetation could occur as a result of vehicular traffic, but this
would be relatively limited in extent. Seismic surveys could
disturb wildlife.
• Exploratory well establishment would destroy vegetation and
impact wildlife.
• Surveys conducted during this phase to evaluate the presence
and/or significance of ecological resources in the area would

ENVIRONMENTAL JUSTICE
• Exploration activities are limited and would not result in
significant adverse impacts in any resource area; therefore,
environmental justice is not expected to be an issue during this
phase.

HAZARDOUS MATERIALS AND WASTE
MANAGEMENT
• Seismic and exploratory well crews may generate waste (plastic,
paper, containers, fuel leaks/spills, food and human waste).
Wastes produced by exploratory drilling would be similar, but
occur to a lesser extent than those produced during drilling
and operation of production wells.
• They would include drilling fluid and muds, used and filters,
spilled fuel, drill cutting, spent and unused solvents, scrap
metal, solid waste and garbage.

HEALTH AND SAFETY
• The potential impacts on human health and safety resulting from
exploration activities could include:
• Occupational accidents and injuries;
• Vehicle or aircraft accidents,
• Exposure to weather extremes,
• Wildlife encounters,
• Trips and falls on uneven terrain,
• Adverse health effects from dust generation and emissions, and
contact with hazardous materials (e.g., from spills).
• The potential for these impacts to occur would be low because of the
limited range of activities and number of workers required during
exploration.

LAND USE
• Temporary and localized impacts to would result from
exploration activities.
• These activities could create a temporary disturbance in the
immediate vicinity of a surveying or monitoring site or an
exploratory well (e.g., disturb recreational activities or livestock
grazing).
• Wire pin flags used for surveying could be shredded in the
making of hay.
• The leftover metal bits can kill livestock that eat the feed.
• Livestock and wildlife can also die after eating ribbons attached
to the flags.

PALEONTOLOGICAL RESOURCES
• Paleontological resources are nonrenewable resources.
Disturbance to such resources, whether it is through
mechanical surface
• Disturbance, erosion, or paleontological excavation, irrevocably
alters or destroys them.
• Direct impacts to paleontological resources would include
surface disturbance during seismic surveys and the drilling of
exploratory wells and the construction of access roads and
other ancillary facilities.

PALEONTOLOGICAL RESOURCES
• The amount of subsurface disturbance is minimal during the
exploration phase and paleontological resources buried below the
surface are unlikely to be affected.
• Fossil material present on the surface could be disturbed by
vehicular traffic, ground clearing, and pedestrian activities (including
collection of fossils).
• Surveys conducted during this phase to evaluate the presence and/or
significance of paleontological resources in the area would assist
developers in siting project facilities in order to avoid or minimize
impacts to these resources

SOCIOECONOMICS
• As the activities conducted during the exploration phase are
temporary and limited in scope, they would not result in
significant socioeconomic impacts on employment, local
services, or property values.

SOILS AND GEOLOGIC RESOURCES
• Surface effects from vehicular traffic could occur in areas that
contain special (e.g., crypto biotic) soils.
• The loss of biological crusts can substantially increase water
and wind erosion.
• Also, soil compaction due to development activities at the
exploratory and along access roads would reduce aeration,
permeability, and water-holding capacity of the soils and cause
an increase in surface runoff, potentially causing increased
sheet, rill, and gully erosion.

• The excavation and reapplication of surface soils could cause the
mixing of shallow , resulting in a blending of soil characteristics and
types.
• This blending would modify physical characteristics of the soils
including structure, texture, and rock content, which could lead to
reduced permeability and increased runoff from these areas.
• Potential impacts to geologic and mineral resources would include
depletion of hydrocarbons and sand and gravel resources.
• It is unlikely that exploration activities would activate geologic
hazards.
• Impacts to soils and geologic resources would be proportional to the
amount of disturbance.
• The amount of surface disturbance and use of geologic materials
during exploration would be minimal.

TRANSPORTATION
• No impacts on transportation are anticipated during the
exploration phase.
• Transportation activities would be temporary and intermittent
and limited to low volumes of light utility trucks and personal
vehicles

VISUAL RESOURCES
• Impacts to visual resources would be considered adverse if the
landscape were substantially degraded or modified.
• Exploration activities would have only temporary and minor
visual effects, resulting from the presence of drill rigs, workers,
vehicles, and other equipment.

WATER RESOURCES (SURFACE WATER AND
GROUNDWATER)
• Minimal impact to water resources (water quality, water flows, and
surface water/ groundwater interactions) would be anticipated from
exploration activities.
• Exploratory wellbores may provide a path for surface contaminants
to come into contact with groundwater or for waters from subsurface
formations to commingle. They may also decrease pressure in water
wells and affect their quality. Very little produced water would likely
be generated during the exploration phase.
• Most water needed to support drilling operations could be trucked in
from off-site.

HYDRAULIC FRACTURING OR
‘FRACKING’

WHAT IS FRACKING
• Hydraulic fracturing, or ‘fracking’, is a method used by drilling engineers to
stimulate or improve fluid flow from rocks in the subsurface. In brief, the
technique involves pumping a water-rich fluid into a borehole until the fluid
pressure at depth causes the rock to fracture.
• The pumped fluid contains small particles known as proppant (often quartz-
rich sand) which serve to prop open the fractures.
• After the fracking job, the pressure in the well is dropped and the water
containing released natural gas flows back to the well head at the surface.
• The boreholes themselves are often deviated away from the vertical, into
sub-horizontal orientations, to ensure better and more efficient coverage of
the targeted shale gas reservoir.

• The fracking fluid also contains small amounts (typically < 2%
in total by volume) of chemical additives such as acid to help
initiate fractures, corrosion and scale inhibitors to protect the
borehole lining and gelling agents to alter the fluid viscosity.

POTENTIAL RISKS
• Injecting large volumes of fluid into the subsurface is not without
risk.
• Here are highlighted the potential for the following:
A. Earthquakes induced by slip on nearby faults;
B. Contamination of ground water, and possibly even drinking water,
with natural gas and other chemicals;
C. Emissions of volatile components, such as CO2 or methane, into
the atmosphere;
D. The leakage of contaminated drilling waste fluid from storage
ponds

GEOLOGICAL PRINCIPLES OF FRACKING &
SHALE GAS EXTRACTION
• Some of the key geological issues with relevance to the potential
environmental impacts of fracking are:
• The relatively limited understanding of rock fracture patterns and
processes in shales;
• The ability to predict and quantify permeable fracture networks in the
subsurface before drilling;
• The accuracy and precision with which the geometry (size or extent,
position, thickness) of shale formations and aquifers in the
subsurface can be determined, especially in areas with complex
geological histories.

• The ability of fluids to flow through rock is controlled by a
property called permeability, itself a function of porosity. The
pore space in rocks is made up of a diverse range of voids in
the solid rock matrix and includes cracks induced by stresses.
• The aim of fracking is to massively improve permeability by
creating (or reopening) a locally dense network of open and
connected – i.e. hydraulically conductive – fractures.

• It is important to recognize that the fracking process of pumping
large volumes of water into a borehole at a certain depth cannot
control the type of fractures that are created or reactivated.
• This could have implications for the risk of ground water
contamination by fracking operations, as the fracture network
generated by the fracking fluid could be complex and difficult to
predict in detail.
• The orientations, sizes and apertures of permeable rock fractures
created by a fracking operation ultimately control the fate of the
fracking fluid and the released shale gas, at least in the deep
subsurface.

GEOLOGICAL RISKS
• Fracking inherently involves geomechanical risks – i.e. the
injection of large volumes of pressurized water at depth will, by
design, alter the in situ stress state and change the propensity
of existing fractures to open or faults to slip, and possibly
result in seismic activity (i.e. earthquakes).

• Fracking also entails geochemical or hydrogeological risks. The key
issue is the fate of the water (plus additives) after the fracking has
occurred. As discussed above, during fracking there is little direct
control on the nature of the permeable fracture network created, and
how this new network might then connect to any pre-existing (and
potentially undetected) fracture network.
• Whilst potential contamination of ground water with the injected
fracking fluid is therefore an important concern, another issue is the
fate of the initial drilling fluid (or ‘mud’) used to lubricate the
borehole during drilling.
• An additional risk is that of the natural gas released by the fracking
process entering the ground water, however there has only been one
confirmed case of this kind of contamination to date, with natural
gas released from a fracking operation

POTENTIAL ENVIRONMENTAL IMPACTS
• The number of proven environmental impacts demonstrated to
have been caused by fracking remains small in relation to the
volume of fracking activity.
• One estimate is that approximately one million oil and gas
wells have been drilled and fracked (University of Texas, 2012).

GROUND WATER CONTAMINATION
• The potential risk to ground water comes from two sources: the
injected fluid (water + chemical additives) and the released
natural gas.
• There are alleged cases of both types (University of Texas,
2012;
• The current opinion shared by several agencies is that all
scientifically documented cases of ground water contamination
associated with fracking are related to poor well casings and
their cements, or from leakages of fluid at the surface.

• The potential risks identified from alleged incidents of ground
water contamination so far include:
• Overweight (or ‘overbalanced’) drilling mud causing leakage of
drilling fluids from the well bore into near surface aquifers;
• Contamination from solid components in the shale entering the
flow back fluid;
• Poor cement jobs on well bore casing, especially at shallow
depths.

• Many shales contain quantities of potentially harmful chemical
elements and compounds that could be dissolved into the fracking
fluid, and then return towards the surface during flow back.
• These include methane (i.e. the target natural gas to be released),
carbon dioxide, hydrogen sulphide, nitrogen and helium; trace
elements such as mercury, arsenic and lead; naturally occurring
radioactive material (radium, thorium, uranium); and “volatile organic
compounds” (VOCs) that easily vaporize into the air, such as benzene
(House of Commons Energy & Climate Change Committee, 2011).
• The amount of material dissolved also varies widely, with estimates
of between 13,000 and 120,000 ppm for shale gas plays in the USA
(University of Texas, 2012). Careful chemical monitoring of fracking
fluids, including the flow back fluid and produced water, is required
to mitigate the risks of contamination from this source.

CHEMICAL ADDITIVES
• Defining the toxicity level of additives used in the fracking
phase should be a relatively simple and quantifiable scientific
task, however in some countries fracking companies are under
no legal obligation to declare the exact composition of this
mixture.
• In fact, for companies operating in deregulated market
economies there is a clear vested interest in keeping the fluid
formula secret for competitive advantage.

BLOW OUTS
• If the fluid injected into the well head does not fracture the
rock volume around the bottom of the well as intended, then
the elevated fluid pressure will drive the fluid into other open
and permeable pathways.
• These pathways can include the injecting well bore, but also
any other boreholes in the vicinity that are not capped for these
high pressures (e.g. other oil and gas wells or artesian wells
used for drinking water).
• Explosive eruptions of drilling fluid and/or oil and gas from
neighboring wells are a direct consequence of pre-existing
permeable connectivity at depth.
• Seepage of any surface spillage from a blow out into the

WATER SOURCES
• Sourcing the vast volumes of water required for an extended fracking
programme can be challenging, especially in arid or depleted areas.
Estimates of water volume required vary widely, with between 90,000
and 13,500,000 litres per well (MIT, 2011).
• Local extraction of water from small catchments could have an
impact on the ecology and hydrology of rivers in these areas.
• Related environmental impacts may also develop from transporting
water in to the drilling site from further afield: construction of new
roads to remote drilling sites and increased heavy road traffic and
pollution.

FATE OF THE FRACKING FLUID
• Some operators have chosen to pond this flow back fluid in man-
made pools and then allow it to either evaporate, or be transported
away at a later date. Evaporation leads to concentration of the
chemical additives, increasing the potential for environmental impact
if a leak develops.
• At least one operator in the US has successfully reused the flow back
fluid in the subsequent fracking operations at the same well head,
with no loss in efficiency. However, the costs involved in processing
the flow back fluid to remove any contaminants collected during the
first cycle may deter wider application.

EMISSIONS TO THE ATMOSPHERE FROM
FRACKING
• An issue related to the fracking fluid is the emission of gas
and/or vapour to the atmosphere from the fluid, either of
original additive chemicals, entrained contaminants from the
shale formation or the methane released by the fracking
process.
• Fracking operators should therefore seek to minimize all
emissions to the atmosphere, and monitoring processes need
to be actively enforced.

ADVANTAGES
• Unlike coal, natural gas does not release sulfur dioxide,
mercury and other particles when burned; ashes, and emits
only half the carbon dioxide.
• The inventory of greenhouse gases produced by the Agency for
Environmental Protection (EPA) shows that CO2 emissions
across the country were 7% lower in 2010 than in 2005,
representing just over 400 million tons. (Preliminary data for
2011 indicate that the decline continues).
• Reduced emissions from power plants, especially by switching
from coal to gas, account for a little over a third of the decline.

• The new legislation developed in 2012 by the EPA require the
gas industry to measure their missions and the reduced. A
major leak occurs when the opening of a well finished and
hydraulic fracturing fluids that are at high pressure, returning
the well dragging methane. The new rules prescribe that from
2015 companies start to capture that gas.

• Some experts believe the capture of methane as a great
opportunity, it is much easier to control the CO2 to slow global
warming, at least in the short term, since small amounts of
methane have considerable effects and also is a valuable fuel .

REFERENCES
• References:
 Seismic Course – Robertson Research International Limited – U.S. 1998
 Training Course – Sercel – France 2008
 Land Seismic Techniques for High Quality Data – Schlumberger – Norwa
 Hydraulic Fracturing by Dr Dave Healy
 SMT-400 Operator’s Manual - ION Sensor Nederland
 NATIONAL GEOGRAPHIC – Los pros y los contras del fracking
 Amos B. Batto – El riesgo del fracking en Bolivia

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