Basic Observations of Permeability Evolution – EGS and SGRs Key Issues in EGS and SGRs

[email protected] 1

Effects of Solid-State and Pore-Fluid Chemistry and Stress on Permeability Evolution

Derek Elsworth (Penn State) and Josh Taron (USGS)

Basic Observations of Permeability Evolution – EGS and SGRsKey Issues in EGS and SGRs

Spectrum of Behaviors EGS to SGRHomogeneous Permeability Flow Modes

Diagenesis Permeability Evolution

Basin EvolutionStimulation and Production

Scaling Relations in Rocks and ProppantsReinforcing Feedbacks

Induced SeismicityMineralogical Transformations – Seismic -vs- AseismicFirst- and Second-Order Frictional Effects

Key Issues

[email protected] 2

Basic Observations of Permeability Evolution

Challenges• Prospecting (characterization) • Accessing (drilling)• Creating reservoir• Sustaining reservoir• Environmental issues

Observation• Stress-sensitive reservoirs• T H M C all influence via effective stress• Effective stresses influence

• Permeability• Reactive surface area• Induced seismicity

Understanding T H M C is key:• Size of relative effects of THMC(B)• Timing of effects• Migration within reservoir• Using them to engineer the reservoir

Permeability

Reactive surface area

Induced seismicity

Resource• Hydrothermal (US:104 EJ) • EGS (US:107 EJ; 100 GW in 50y)

[email protected] 3

Key Questions in EGS and SGRs

Needs• Fluid availability

• Native or introduced• H20/CO2 working fluids?

• Fluid transmission • Permeability microD to mD?• Distributed permeability

• Thermal efficiency• Large heat transfer area• Small conduction length

• Long-lived• Maintain mD and HT-area• Chemistry

• Environment• Induced seismicity• Fugitive fluids

• Ubiquitous

[Ingebritsen and Manning, various, in Manga et al., 2012]

[email protected] 4

Contrasts Between EGS & SGRs

EGS (Order of Mag.)

Property ESRs (Order of Mag)

Fractured-non-porous General Porous-fractured

<<1%,<1% Porosity, n0 -> nstim ~10-30%, ~same

microD -> mD Permeability, k0 -> kstim

>mD -> >mD

106 Kf/kmatrix 106 ->1

10-100m Heat transfer length, s

1m -> 1cm

>>100/1. >100/1 *Heatsolid/Heatfluid ~10/1-2/1, same

? Chemistry ?

V. Strong TM Perm. Feedbacks Less strong

Moderate, late time TC Perm. Feedbacks Strong?

[email protected] 5

Thermal Drawdown EGS –vs- SGRs

Wate

r Tem

p

(at

outl

et)

Rock

Tem

p

(in r

ese

rvoir

)

Thermal Output:

In-Reservoir Water Temperature Distributions:

[email protected] 6

Thermal Recovery at Field ScaleParallel Flow Model Spherical Reservoir

Model

Tinjection

Dim

ensi

onle

ss

tem

pera

ture

Dimensionless time Dimensionless time

Trock

[Elsworth, JVGR, 1990]

[Gringarten and Witherspoon, Geothermics,1974] [Elsworth, JGR, 1989]

[Note: not linear in log-time]

Spacing, s, is small

Spacing, s, is large

[email protected] 7

What Does This Mean?

This makes the case that:

Permeability needs to be large enough to allow Mdot_sufficient without:

1. Fracturing reservoir during production

2. Large pump costs

Beyond that – issues of heterogeneity are imp:

1. No feedbacks (Rick)

2. Reinforcing feedbacks (Kate/Paul/Golder/Gringarten)

Diagenesis contributes to this:

1. Initial basin evolution [k0,n0]

2. Reservoir stimulation/development [k,n=f(t)]

3. Reinforcing feedbacks [k,n=f(x,t)] for THMC

[email protected] 8









Key Issues

[email protected] 9

Controls on Reservoir Evolution

Many processes of vital importance to EGS/SGR are defined by coupled THMC processes.Thermal sweep/fluid residence timeShort circuitingInduced seismicityProlonged sustainability of fluid transmission

Fractures dominate the fluid transfer systemTransmission characterized by:

History of mineral depositionChemo-mechanical creep at contacting asperitiesMechanical compactionShear dilation and the reactivation of relic fractures

[email protected] 10

Typical Response of Fractures (Dissolution)

[Polak et al., GRL, 2003]

m


Typical Response of Fractures (Precipitation)

[Dobson et al., 2001]

Experimental arrangement

Precipitation

Thermal gradient along fracture

Dissolution Processes Approaches to Determine k or b

Time

b

precipitation

diffusion

dissolution

grain

grain

Time

b

precipitation

diffusion

dissolution

precipitation

diffusion

dissolution

grain

grain

Time

Component Model

•Interface Dissolution

•Interface Diffusion

•Pore Precipitation eqporeporeprec

CCkM

AV

dt

dM

dx

dCDJ b 2

c

m br d

dCJ r D

dr

porec

bdiffm CC

ad

D

dt

dMJ

int

2ln

2

TR

dkV

dd

dt

dM

cgeffm

cgdissdiss

4

3

422

2

TR

dkV

dt

dM cgcamdiss

4

3 22

1

4

mm

cm

TE T

V

[Yasuhara et al., JGR, 2003]

Matching Compaction Data

[Experimental data from Elias and Hajash, 1992]

System Evolution at 35-70 MPa and 150°C

Observation Extension

70 MPa and 150°C 35 MPa and 150°C

[Experimental data from Elias and Hajash, 1992]


Timescales of Evolution of Granular Systems at 35 MPa and 75-150°C

75°C 150°C


Permeability Evolution in Granular Systems at 35 MPa and 75-300°C

150°C

300°C

75°C

2

Capillary Model :96

nk

20Pore Evolution: ( / 4)pV d

0

Linked Permeability: ~24

pnVk

d[Yasuhara et al., JGR, 2003]


Fracture/Proppant Diagenesis

Do we understand the mechanisms?

Various mechanisms – appear complex but include:• Dissolution/precipitation • Solid and aqueous chemical transformations• Fluid/chemical assisted strength loss of proppant

and proppant collapse

2 4 6 8 10 12 140.000

0.005

0.010

0.015

0.020

0.025

0.030

L (

inch

es)

Time (days)

250F 275F 325F 350F

Experiment

Observation

Characterization

Analysis

[Dae Sung Lee et al., 2009]

g3.ems.psu.edu 20

THMC/HPHT Continuum Models

THMC-S – Linked codes Spatial Permeability Evolution

Temporal Permeability Evolution

g3.ems.psu.edu 21

Constraint on Fracture Apertures and Fluid Concentrations

(a)

(b)

(c)

max 0[( ) / ]r c cb b b Exp R R a

maxb

rb

Asperity contacts

Local contact

area, Alc

dc

Incre

asin

g f

ractu

re

clo

su

re

g3.ems.psu.edu 22

Modeling Results - Novaculite


K+~x300

g3.ems.psu.edu 23 [Yasuhara et al., JGR, 2004]

Projected Response of Fracture

Define projected behavior for varied temperatures

….and mean stress magnitudes

Reactive - Hydrodynamic ControlsPeclet No. (Pe)

0Advective flux

Dispersive flux m m

q vbPe

D D

Damkohler No. (Da)

Pe < 1 Dispersion dominated – Perturbations damped

Pe > 1 Advection dominated – Perturbations enhanced

0

2 2Reactive flux

Advective flux

k L k LDa

q vb

Da << 1 Reaction slow - Undersaturated along fracture – Perturbations damped

Da larger << 1 – Reaction fasterSaturated along fracture – Perturbations enhanced

2Reactive flux.

Dispersive flux m

k LPe Da

D

PeDa No. (Removes <q>)

[Sherwood No.]

Reactive Hydrodynamics: Role of Damkohler Number (PeDa)

[Detwiler and Rajaram, WRR, 2007]

15 cm x 10cmVoxel = 1 mmAperture:Black (0)-White(0.25mm) Time

High PeDa

Low PeDa










Key Issues


Triggered Seismicity – Key Questions

Principal trigger - change in (effective) stress regime:Fluid pressureThermal stress Chemical creep

How do these processes contribute to:Rates and event size (frequency-magnitude)Spatial distributionTime history (migration)

How can this information be used to: Evaluate seismicityManage/manipulate seismicityLink seismicity to permeability evolution

Reservoir Conditions:

THMC Model:


Observations of Induced Seismicity (Basel)

[Goertz-Allmann et al, 2011] [Shapiro and Dinske, 2009]


r-t Plot - Fluid and Thermal Fronts and Induced Seismicity

Parameters utilized in simulation

k0 Permeability[m2] 10-17

Pp Pore Pressure[Mpa] 14.8

Pinj Fluid Pressure[Mpa] 17.8

Tres Reservoir Temperature[°c]

250

Tinj Fluid Temperature[°c] 70

S Fracture Spacing[m] 10 to 500

3

0

2,

12

Qt br k

h S

Q: Flow rate

t : Time

h: Thickness

ϕ: Porosity

b: Aperture

[Izadi and Elsworth, in review, 2013]

g3.ems.psu.edu 30

Fault Reactivation (and Control)

FaultInjection well

Controls on Magnitude and Timing:kfault & kmedium

[10-16 – 10-12 m2]Injection temperature dT [50C – 250C]Stress field obliquity [45-60 degrees]

Permeability & Magnitude Timin

g

[Gan and Elsworth, in review, 2013]


Seismic –vs- Aseismic Events

[Peng and Gomberg, Nature Geosc., 2010]Seismic Moment (N.m) [Magnitude]

Dura

tion (

s) [

secs

->

years

]


Approaches – Rate-State versus Brittle Behavior

Rate-State Brittle

µ0

(a-b)ln(v/v0)

a ln(v/v0)

DC

Low velocity

High velocity

Low velocity

Displacement

Coe

ffici

ent o

f fric

tion

Syste

m S

tiffn

ess

(Sto

red E

nerg

y)

Failu

re C

riterio

n

(Trig

ger)

-b ln(v/v0)


Seismic –vs- Aseismic Events

[Ikari et al., Geology, 2011]

Friction

Stability (a-b)

Velocity Weakening (unstable slip)

Velocity Strengthening (stable slip)

Scale Effects in Hydrology – Space and Time

[Elkhoury et al., Nature, 2006]

• Remote earthquakes trigger dynamic changes in permeability

• Unusual record transits ~8y• Sharp rise in permeability followed

by slow “healing” to background• Scales of observations:

– Field scale

– Laboratory scale

– Missing intermediate scale with control

Per

mea

bilit

y

Pe

rme

ab

ilit

y


Role of Wear ProductsSample Holder

Sample

Shear-Permeability Evolution

Dissolution Products

[Faoro et al., JGR, 2009]


Key Questions in EGS and SGRs Needs• Fluid availability

• Native or introduced – fluid/geochemical compatibility• H20/CO2 working fluids? – arid envts.

• Fluid transmission • Permeability microD to milliD? – high enough?• Distributed permeability

• Characterizing location and magnitude• Defining mechanisms of perm evolution (chem/mech/thermal)• Well configurations for sweep efficiency and isolating short-circuits

• Thermal efficiency• Large heat transfer area – better for SGRs than EGS?• Small conduction length – better for SGRs than EGS?

• Long-lived• Maintain mD and HT-area – better understanding diagenetic effects?• Chemistry - complex

• Environment• Induced seismicity - Event size (max)/timing/processes (THMCB)• Fugitive fluids – Fluid loss on production and environment – seal integrity

• Ubiquitous

Documents

Basic Observations of Permeability Evolution – EGS and SGRs Key Issues in EGS and SGRs