00-ags_b1_microseismicity monitoring in oil or gas reservoir

7/28/2019 00-AGS_B1_Microseismicity Monitoring in Oil or Gas Reservoir

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Microseismicity monitoring in oil

or gas reservoir

MSc. Leo Eisner, Ph.D.,

Purkyn Fellow at the

Institute of Rock Mechanics and Structure,

Academy of Sciences of the Czech Republic,

Prague, Czech Republic


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Instructors Background Born in 1970, Prague, Czech Republic (CR), married, 1 child

1994: MSc. in Ray theory at Charles University, Prague, CR

2001: Ph.D. at Caltech on finite difference modeling of

earthquakes in L.A. Basin, Pasadena, USA

2001-2007: Senior scientist in Schlumberger Cambridge,

Cambridge, UK: Borehole monitoring, EU project IMAGES

2008-2010: Microseismic Inc, Houston, USA: Chief

Geophysicist from 2009, surface monitoring

2010-present: Purkyn Fellow at IRSM of ASCR, President ofSeismik Lim, geophysical advisor for MSI, Prague, CR

17 peer-reviewed papers, 11 on MEQs, 23 EAGE/SEG/SPE

abstracts, 10+ patents, AE for Geophysical Prospecting, 2

special issues on MEQs 2010, 2011


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Outline

1. Microseismicity/Seismicity, induced, history,

fracking

2. Location techniques for earthquakes

3. Source mechanisms of microseismic event

4. Anisotropy and microseismicity


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Outline of the 1st lecture

Definition of microseismicity, dictionary

Induced/triggered/tectonic earthquake

Microseismicity outside of oil or gas industry: water

reservoirs, mining, geothermal

Historical review of oil or gas: M-site, Cotton Valley,

Barnett,

Brief intro into hydraulic fracturing


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Definitions Microseismic event = Microearthquake =

Microtremor (= Microseism) Microearthquake an earthquake with magnitude

smaller than 3 or more commonly used withmagnitude smaller than 0

Microseism background elevated noise (or signal)at 0.3-10 Hz due to ocean waves

Earthquake (also known as a quake, tremor ortemblor) is the result of a sudden release of energy

in the Earth's crust that creates seismic waves. Seismicity or seismic activity of an area refers to the

frequency, type and size of earthquakes experiencedover a period of time.


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Definitions cont. Induced (microseismic event) an event caused by a

human activity that would not otherwise happen Triggered (microseismic event) an event initiated by

human activity that would happen later in the time

without human activity

Tectonic event an event that has happened due to

natural processes independent of human activityInduced:

breaking of a wood by bending,

Rangeley (Rocky Mountains Arsenal, Colorado), 1966Triggered:

Basil earthquake 2009,

energy released>energy input

Tectonic:

San Andreas earthquake, 1906


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Reservoir induced seismicity

ISS international


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ReservoirRiver

River


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Acu lake in Brazil

J. Tomic, et al. 2009, Geophys. J. Int.

Magnitudes of the largest

events ~2, ~1012 Nm.

Activity started several

months after filling up of the

reservoir.


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Mining induced seismicity

Shallow (coal/tunnels) mine explosive environment

due to methane

Deep mine cavity closing, large events

Block caving a very large fracturing Nuclear waste storage monitoring of rock mass

integrity

Dam walls

ISS international

ISS international


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Mining: deep/shallow mines

Mine (cross section)

Mine creates zone of weakness as overburden weight is not balanced by in the cavity.

This zone can activate pre-existing faults or eventually create new fractures mainly

above the mined area. Similar problem in tunneling industry. magnitudes < 3-5.


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Mining: block caving, nuclear waste

Block caving: used for low concentration

ore mining where whole block crashed and

loaded.

Microseismicity precedes block failure and

is used to indicate when a block will

collapse.

Magnitudes: 3-4

Nuclear depository is usually made in an

extremely stable rock and objective of the

monitoring is to detect any fracture

propagation that might have been

induced by creating the depository.

Very small magnitudes < -2,-1http://www.seismology.org/

http://www.seismology.org/

http://www.infomine.com/


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Geothermal The most similar to oil and gas industry

Not using any proppant, instead the traditionalstimulation is shear stimulation that is aimed at

creating hydraulic connection between injector and

producer, illustration bellow shows connection

between blue and red injector and producer:

side view

Inline view

L. Dorbath, also in Dorbath et al, JGI, 2009


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Geothermal

Started in early 80-ies (LANL)

HRD evolved into EGS (i.e., HotDry Rock to Enhanced

Geothermal System) Magnitudes similar to Oil and

Gas, but some are much larger

Basel, Switzerland, max

magnitude 3.4 The Geysers, United States,

max magnitude 4.6Dyer et al, 2008, TLE


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Geothermal: Basel shear stim

Dyer et al, 2008, TLE

Induced seismicity,

events are induced

by injection and

their magnitude

and rate seems to

be proportional to

well head pressure

Well head pressure

Pump rate


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Oil and Gas historical review

M-site, western Colorado

M stands for Multi: inclinometers in nearby borehole andtwo deviated wells intersecting the fracture

1992-1996: GRI and the U.S. DOE

Piceance basin of western Colorado near the town ofRifle

The first downhole monitoring with single array ofgeophones deployed in a vertical monitoring borehole

Microseismic height was confirmed by tiltmeters andagreed to a few feet

Microseismic locations were confirmed by deviatedwells.


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Historical review: M-site

Warpinski et.al., 1998, SPE proceedings,

Vertical containment of seismic events confirmed by tiltmeters

Temporal evolution of microseismic events confirmed by intersected well

sampling 1/8 of millisecond, recording 200 - 2000 Hz


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Historical review: Cotton Valley, East

Texas

Following success of microseismic monitoring at the M-site in summer 1997 a dual

microseismic monitoring array was deployed, cemented at wells 21-09 and 22-09,

sampling at 1 ms. Deployment at well 21-09 did not succeeded and majority of thereceivers were dead.

sand

sand

shale

shale

Rutledge and Phillips, 2003, Geophysics.


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Historical review: Cotton Valley


Relationship between number of induced events

and borehole pressure is not that similar to the

EGS Basil stimulation differences are much

shorter time, gels in fluids and proppant


Data were however sampled at 1 ms

resulting in rather coarse sampling of

the high frequency data. Hence data

were resampled in frequency domain to0.2 ms, which allowed highly accurate

picks at peak without the need to

sample at high rate.


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Rutledge

and

Phillip

s,2003,Geophysics.

The only difference between figures above is picking of P and S-waves, no difference in

model or location technique. While initial locations show rather large scatter and only

cloud of microseismic events the repicked location show narrow fairway with less than

10 m width. This was a new understanding on the nature induced events left figure is

diffused cloud around the fracture, right figure suggest direct connection with fracture.Conclusions: location accuracy drives the scatter in initial locations

Initial picks and locations Relocated after resampling


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Historical review: Cotton ValleyRutledg

eand

Phillips,2003

,Geophysics.

The relocated events also allowed comparison of vertical containment as measured from

radioactive proppant tag and event count in vertical bins. However, proppant tag

measures distribution of radioactive material (injected fluid) at most about 1 m from the

treatment well, while event count counts events 100s of meters away. This impacts

discrepancy in perforation A at 2620 m depth, where probably a flow behind casing

occurred. Also microseismic events were shifted several (2 and 4 m) to fit the tracer data

as these shifts are easily explained by velocity model and receiver statics.

Conclusions: microseismicity can reliably measure vertical containment of the hydraulicfracture in the formation, velocity error at least several meters.

Vertical cross-section

Radio-activity benchmark Perforations A-F


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eand

Phillips,2003

,Geophysics.

The growth of microseismic events from injection well to distances of 300-400 m. note

that microseismic events form a cloud of a certain width that is growing at variable rates

without direct connection to treatment pressure or pump rates. The width of the moving

cloud is more than 100 m. Note that some late events still occur close to injection

interval.Conclusions: microseismic events do not occur only around fracture tip.

Injection point Injection point


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Rutledge et al., 2004, BSSA.

Cumulative moment (and energy) released in

seismic events is approximately proportional

to cumulative injected volume (McGarr,

1976). For injections without encountering

pre-existing tectonic stress the

proportionality is constant (treatments A,

C+D, and perhaps B),while when

encountering pre-existing faults the seismic

moment release is much higher as shown in

treatment E. Dashed lines show theoretical

expectation for average media parameters

indicating the real release is much smaller

unless tectonically enhanced.

Conclusions: energy release is much smaller

than energy injected and linearly dependent

on the total volume unless pre-existing

tectonic stress is encountered.


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eand

Phillips,2003

,Geophysics.

The microseismic events exhibited remarkable consistency from event to event as shown

in the display of waveforms above, both in P-waves as well as in S-waves.

Conclusions: microseismic events have probably very similar mechanisms.


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eand

Phillips,2003

,Geophysics.

Source mechanisms were constrained to be shear

only and assumed to have the same mechanisms

in two distinct groups: left-lateral and right-

lateral strike slip. In addition they are shear.

Problem: There is no shear stress on a plane

oriented along SHmax, hence we need small

deviation in strike from SHmax orientation.

Conclusions: microseismic events are likely

occurring on vertical planes aligned closely with

SHmax. The mechanisms are consistent withshear failure.


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Small events can be detected only when near

monitoring well, hence detection threshold

probably cuts off western events except themost energetic ones. Most energetic events

seems to be more favorable oriented to have

shear failure.

Conclusions: detection threshold strongly affects

detection of events and may create artificial frac

assymetry

Rutledgean

dPhillips,2003,Geo

physics.


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Resolution for events with fault planes close to SHmax: hydraulic fractures are alignedwith SHmax but shear planes are not and they create a mesh as proposed in figure on

right. Hydraulic fractures as small, hence undetectable by seismic but they load shear

stress on shear planes of microseismic events.

Conclusions: Event planes are slightly deviated from SHmax and create mesh

connecting silent hydraulic fractures


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Barnett production was steadily declining in 1990ies, however with the

combination of cheaper horizontal drilling and hydraulic fracturing the

declining trend was reversed and today Barnett is the 3rd largest gas field

of the USA.

Since then every major oil player has to have some stake in a shale play,

even if they are not quite shales: Woodford (OK), Haynesville (TX-LA),

Eagle Ford (TX), Marcellus (eastern USA),

Historical review: Barnett shale

The main problem in Barnett

was fracturing into underlying

Ellenberger formation. Hence

microseismic monitoring was

mainly used to control verticalcontainment of the fracs.

26 28 34 4179

135221

304380

503

716

1104

1612

1776

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

year

Productio

ninBCF

Texas Gas Well Gas Production in the Newark, East (Barnett Shale) Field


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Historical review: Barnett

Fischeretal.,2

004,SPE90051

Vertical containment in the stimulated lower Barnett shale is illustrated in left Figure

showing mapped microseismic events induced by the horizontal well stimulation. The

lower layer is Elenberger. Right Figure shows famous case where hydraulic stimulation

of the well in the center (black dot) killed FIVE nearby wells on the edges of the

mapped cloud indicating that microseismicity maps lower volume (subject to detectionthreshold).

Map viewVertical crossection


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Historical review: Cross-stage detection

Vertical containment of the stimulated canyon sand formation can be detected by

using the previously discussed feature of microseismic events: their similarity. Measure

of similarity if crosscorrelation shown in right plot illustrating the overlap between

stages 1, 2 and 3.

Eisner et al. 2006


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Historical review: Canyon sand

Fischeretal.2

008

New location technique based on S-wave allows location 10000+ events. The upper

row shows vertical vs time evolution of event locations induced in 4 stimulations. Note

the stair-case character due to seismicity being held by shale barriers.

Lower plots show horizontal evolution of event locations with asymmetric growth to

east, The speed of fracture growth is also asymetric 5 m/min to NE, 2.5 m/min to SW.


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Historical review: surface monitoring

Since 2003 deployment of 1000+ surface geophones allows mapping of microseismic

events with homogeneous detection threshold across several treatment wells. This

mapping confirmed with definite asymmetry of the hydraulic fractures as illustrated in

Figure on right side where some events occur 2000+ ft from the injection interval.

Duncan

and

Eisne

r,2010

Figures provided by Microseismic Inc

i i l i f i i


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Historical review: surface monitoring

Surface monitoring also allows

determination of source mechanisms by

mapping of the polarity of P-waves andinverting shear only and general (including

tensile) source mechanisms. In this case a

vertical fault plane is again aligned with

SHmax as in the Cotton Valley case.

Tim

e(s)

Line 1 Line 2 Line 9Line 8Lines 3-7

Line 2

Line 3Line 7

Line 8

Line 9

North

Line 1

Figures provided by Microseismic Inc


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Future (?) review: Buried arrays

5 miles

5 miles

Deployment of geophone

arrays to depths of ~100 mreduces the surface noise

and allows consistent

imaging of very large area

with homogeneous

coverage of all wells.

Hence strategies can becompared between wells

and stimulation programs

etc.

Figure provided by Microseismic Inc


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Hydraulic fracturing

Water storage

Pumps

Pond for

produced water



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Hydraulic fracturingHydraulic fracturing - (called "frac jobs," "frac'ing, "fracking, fraccing, or

hydrofracking") is a process that results in the creation of fractures in rocks. The

fracturing is done from a wellbore drilled into reservoir rock formations to increase therate and ultimate recovery of oil and natural gas.

first used in oil and gas industry in 1947

first commercial use of hydraulic fracturing by Halliborton in 1949

Leakoff

Loss of fracturing fluid from the fracture channel into the surrounding permeable

rock.

Fracturing fluid

The fluid used during a hydraulic fracture treatment of oil, gas or water wells. The

fracturing fluid has two major functions 1) Open and extend the fracture; 2)

Transport the proppant along the fracture length.

Proppant

Suspended particles in the fracturing fluid that are used to hold fractures open

after a hydraulic fracturing treatment, thus producing a conductive pathway that

fluids can easily flow along. Naturally occurring sand grains or artificial ceramic

material are common proppants used.


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Hydraulic fracture design

Usually the fluids are

pumped to create pad thatopens the formation.

Formation test to

find out leak-off

Fracking starts.

Strategy of constant

flow rate in this

case results in

decreasing pressure

after the initial frac

End of pad, start

injecting proppant to

keep fracture open after

the pressure is released



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Hydraulic fracturingGeophysicist view

Impermeable layer (cap rock)Impermeable layer (cap rock)

Well

Well


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Mineback test in ash fall tuff at the NevadaTest Site, depth 1500 ft, side of mesa

Real Fracture

Real hydraulic fractures seems tobe mostly planar features. Picture

shows a horizontal well that is

cased and

cemented, perforated, and

fractured with dyed water.

Although the mine back studiesindicate rather complex surfaces

interacting with pre-existing

natural faults and fractures.

Perhaps most surprising feature

of this image are parallel

fractures.The question remains if the

hydraulic fracturing in greater

depths and shales is as complex

as this image in soft shallow

sediments.


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Net pressure

Pressure difference between closure pressure and pressure that keeps thefracture open

Fracture Gradient

The pressure to fracture the formation at a particular depth divided by

the depth. A fracture gradient of 18 kPa/m (0.8 psi/foot) implies that at a

depth of 3 km (10,000 feet) a pressure of 54 MPa (8,000 psi) will extend a

hydraulic fracture. ISIP - Instantaneous Shut In Pressure

The pressure measured immediately after injection stops. The ISIP

provides a measure of the pressure in the fracture at the wellbore by

removing contributions from fluid friction.

p

Net pressure = p - pc

pc

pc time

p

ISIP (frac closure)

Leak off

Net pressure

ghp

il/


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General

First hydraulic fracture 1947

Rangley, 1966

1950

1960

1970

Barnett, horizontal drilling and

hydraulic fracturing, ~ 1997-Cotton Valley experiment, 1997

M-site experiment, 1992-1996

Surface monitoring, 2003

Buried arrays, 2008

1980

1990

2000

2010

Los Alamos NL, Hot Dry Rocks

Fenton hill, 1975-1990

Haynesville, Marcellus, Woodford

Oil/Gasmonitoring

00-ags_b1_microseismicity monitoring in oil or gas reservoir

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