Seismic exploration and fracking

Author: Eng. Alejandro Levy - QA/QC
Marine/Land Supervisor
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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.

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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 INTRODUCTION

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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
drilling targets.

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GEOLOGY BASICS

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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

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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.

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• 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.

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• 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.

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• 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.

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• 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.

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OIL & GAS FORMATION AND TRAPS
2D – 3D & 4D SEISMIC PURPOSE

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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.
2D Seismic 3D Seismic

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SEISMIC DATA
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.

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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

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• 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

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LAND SEISMIC SOURCES
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.

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• 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

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• 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

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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.

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• 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
• EMULSION HIGH EXPLOSIVE

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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

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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

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• 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%

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• 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

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VIBS OPERATION
VIBS OPERATION

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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.

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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

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• 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.

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• 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

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• 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.

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• 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”

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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.

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• 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.
GEOPHONE AND GEOPHONE STRING

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THE SEISMIC LINE
SERCEL AREAL NETWORK

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• 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 or more FDU-428.
FDU: FIELD DIGITIZER UNIT

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LAUL: LINE ACQUISITION UNIT LINE
LAUX: LINE ACQUISITION UNIT

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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.

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THE RECORDING TRUCK
“WHITE HOUSE”
CONFIGURATION TOPOLOGY

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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

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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

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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.

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• 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

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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.

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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.

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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.

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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 assist developers in
siting project facilities in order to avoid or minimize impacts to these resources
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.

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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.

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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.
• Exploration activities are unlikely to affect mining activities, military
operations, or aviation.
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.

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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.

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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.

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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.

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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’

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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.

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• 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

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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.

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• 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).

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• 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).

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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.

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• 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.

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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 ground could then
lead to ground water contamination.
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.

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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.

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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.

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• 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 .

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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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