Reservoir Engineering Aspects of Unconventional · PDF fileSchlumberger CONDENFEST Webinar |...

Schlumberger CONDENFEST Webinar | 03 September 2013Reservoir Engineering Aspects of Unconventional Reservoirs

T.A. Blasingame | Texas A&M University

Schlumberger CONDENFEST Webinar — 03 September 2013Analysis of Reservoir Performance for

Unconventional Gas Condensate Reservoirs

Tom BLASINGAMEPetroleum Engineering — Texas A&M University

College Station, TX 77843-3116 (USA)+1.979.255.8808 — [email protected]

Reservoir Engineering Aspects of Unconventional Reservoirs

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Brief Biography: Tom Blasingame●Role:

■ Professor, Texas A&M U.■ Holder of the Robert L. Whiting Professorship ■ B.S., M.S., and Ph.D. degrees from Texas A&M U. (PETE)

●Counts: (Sep 2013):■ 51 M.S. (thesis) Graduates and 30 M.Eng. (report, non-thesis) Graduates ■ 10 Ph.D. Graduates■Over 120 Technical Articles

●Recognition:■ Distinguished Member of the Society of Petroleum Engineers (2000)■ SPE Distinguished Service Award (2005)■ SPE Distinguished Lecturer (2005-2006)■ SPE Uren Award (2006)■ SPE Lucas Medal (2012)■ SPE DeGolyer Distinguished Service Medal (2013)

●Current Research Activities:■ Nano-Scale Flow Phenomena■ Reservoir Engineering of Near-Critical, "Liquids-Rich" Shale Systems■ Evaluation of Well Performance Data for Shale/Liquids-Rich Systems■ Numerical Modeling of Ultra-Low Permeability Reservoir Systems

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Orientation



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●Liquids-Rich Systems?■ Fluid-Flow Mechanisms (what is really flowing where?)■ PVT (near-critical fluids are not trivial)■ Improved Recovery (we all know this is coming…)■ Fit-for-Purpose Stimulation (higher FcD, more complexity)■ Artificial Lift (fact of life…)

●Never-Ending Arguments…■ SRV (... what is it, really?)■ Desorption (... significance? timing? relevance?)■ Stimulation Fluids (... where does it go? does it matter?)■ Microseismic (... crystal ball, roulette wheel, or roadmap?)■ Pressure-Dependent Whatever (... so what?)■ Natural Fractures (... if/when/why/what?)■ Dual Porosity/Dual Permeability (... what about the physics?)■ Well Placement (vertically) (... when does it matter?)

Orientation: (Focus on Liquids-Rich Systems)

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How Small is Small?(nano-scale pores)



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Pore-Scale: Nelson Pore/Molecule Size ChartQuestion(s):●How small are pores in shale gas? Note

that the size of the pores is on the order of 5-10 times the size of the fluid molecule.

AAPG Bulletin, v. 93, no. 3 (March 2009)Pore-throat Sizes In Sandstones, Tight Sandstones, and ShalesP.H. Nelson, USGS

Perspective:●The concept of pores and

pore throats begins to break down at these scales.

●The flow path can be as small as 10-20 molecular diameters (or less).

Issues:●How do the fluids move?— Darcy flow?— Dispersion (gases)?— Knudsen flow?

●How are the fluids stored?— In the organic matter?— Adsorbed?— Another mechanism?

← Each green line is x10 SMALLER scale.

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Pore-Scale: Shale Pore Space (Barnett Example)Question(s):●Where is/are the gas/liquid stored? There

is porosity, often in the organic materials.●Why is the phase behavior of many

shales "near critical"? Nanopores?

J. Sedimentary Research, v. 79/12 (2009)Morphology, Genesis, and Distribution of Nanometer-scale Pores in Siliceous Mudstones of the Mississippian Barnett ShaleLoucks, R.G., R.M. Reed, S.C. Ruppel, and D.M. Jarvie

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a. Gas Slippage — Kundt, A. and Warburg, E.: "Über Reibung und Wärmeleitung verdünnter Gase, " Poggendorfs Annalen der Physik und Che-mie (1875), 155, 337.

Pore-Scale: Petrophysics/Permeability

c. Microflow model and correlation, "fully implicit" formulation.b. Knudsen "microflow" model (Modified from Karniadakis and Beskok, 2002).

SPE 107954Improved Permeability-Prediction Relations for in Low Permeability SandsF.A. Florence, Occidental Petroleum Corp., J.A. Rushing, Anadarko Petroleum Corp., K.E. Newsham, Apache Corp., and T.A. Blasingame, Texas A&M U.

vx

vy

Gas Flow

1 /11

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21

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0

0

4.0

01-

2

aa

m

aa

m

aa

m

a

kp

ak

pak

pa

kk

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● Knudsen number is typically used to classify fluid flow regimes.

Pore-Scale: Continuum vs. Molecular (Knudsen Number)

→Representative physical length scale.→Mean free path — average distance

travelled by a fluid particle.

0.01 0.1 10 1000 Kn 0.001

CONTINUUM SLIP FLOW TRANSITION MOLECULAR

NON-DARCY FLOW

DARCY FLOW

From: Gonzalez, K.: Current and Evolving Practices for Simulation of Compositional Flow in Nano-Systems, Petroleum Engineering 631 Assigned Report, Texas A&M University (Spring 2013).

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Pore-Scale: Phase Behavior at the Nano-Scale

From: Zarragoicoechea, G.J. and Kuz, V.A. 2002. Van Der Waals Equation of State for a Fluid in a Nanopore. Physical Review E 65 (2): 021110.Zarragoicoechea, G.J. and Kuz, V.A. 2004. Critical Shift of a Confined Fluid in a Nanopore. Fluid Phase Equilibria 220 (1): 7-9.

Intuitive, but Zarragoicoechea and Kuz show by derivation and data that there is a shift in critical temperature due to pore

size, they also postulate a similar relation for critical pressure but note that no data existed (at that time) to

validate the pressure relation.

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Schematic Time-Rate Analysis



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Time-Rate: Schematic Production Performance Plot

●Discussion: Schematic Production Performance Plot■ The schematic represents the most common approach to EUR.■ Used CAREFULLY, this should be valid.

Loga

rithm

of R

ate

Production Time

Hyperbolic Rate

Exponential Rate

"Switch Point"from Hyperbolicto Exponential Economic Limit (in rate — qlimit)

= Estimated Ultimate Recovery (EUR)[The area under the hybrid (hyperbolic-exponential rate curves]

Economic Limit (in time — tlimit)

(tlimit)

(qlimit)

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Time-Rate: Schematic — Multi-Fracture Horizontal Well"Plug and Perf" System: Each STAGE has a certain number of perforation "clusters" (typically 4)

Cluster Cluster Cluster Cluster1 2 3 4

Stage 2


Stage n


Stage 1

"FracPoint" (and other such) Systems: Each STAGE is isolated and stimulated

Stage 1 Stage 2 Stage n

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1:4 Slope (low FcD)

1:2 Slope (high FcD)

1:1 SlopeDepletion

(SRV?)

Compound Linear Flow Regime

Formation Linear Flow Regime

TransitionRegime

Bilinear FlowRegime

EllipticalFlow Regime

Logarithm of Production Time

Loga

rithm

of P

rodu

ctio

n R

ate

])(1[/)( )/1( bii tbDqtq

Early-Time Regimes are HYPERBOLIC?

Discussion:●1:2 Slope → b=2 (HIGH fracture conductivity) .●1:4 Slope → b=4 (LOW fracture conductivity).●This is a schematic, it overly simplifies the system.

][1/ )( tatq LFLF

Time-Rate: Flow Regimes — Multi-Fracture Horizontal Well

][1/ )( 4 tatq BLFBLF

For Shales: | days | weeks | months | years | decades | … |

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Discussion — Reserves for Shale Gas



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Comment:Left plot yields time required to estimate EUR (~12-32 months).The "hyperbolic" (or "constant b") flow regime is required to estimate EUR.

[all data obtained from publicly available sources — Dry Horizontal Shale Gas Wells ONLY]

Modern Decline Analysis: Statistical Analysis

From

:H

eckm

an, T

.L.,

et a

l (20

13):

Bes

t Pra

ctic

es fo

r Res

erve

s Es

timat

ion

in

Unc

onve

ntio

nal R

eser

voirs

—Pr

esen

t and

Fut

ure

Con

side

ratio

ns,

Key

note

pre

sent

atio

n pr

esen

ted

at th

e 20

13 S

PE U

ncon

vent

iona

l R

esou

rces

Con

fere

nce,

The

Woo

dlan

ds, T

X (U

SA),

10-1

2 A

pril

2013

.Sl

ide

—16

/28



Comment:Results vary when segregated by geological area, completions, spacing, etc. Analyses represent an attempt to quantify the RANGE of values.

Modern Decline Analysis: Statistical Analysis

From

:H

eckm

an, T

.L.,

et a

l (20

13):

Bes

t Pra

ctic

es fo

r Res

erve

s Es

timat

ion

in

Unc

onve

ntio

nal R

eser

voirs

—Pr

esen

t and

Fut

ure

Con

side

ratio

ns,

Key

note

pre

sent

atio

n pr

esen

ted

at th

e 20

13 S

PE U

ncon

vent

iona

l R

esou

rces

Con

fere

nce,

The

Woo

dlan

ds, T

X (U

SA),

10-1

2 A

pril

2013

.

[all data obtained from publicly available sources — Dry Horizontal Shale Gas Wells ONLY][P90/P50/P10 EUR Comparisons (Modified Hyperbolic Model with 30 year max life)]

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"Unconventional" Time-Rate Analysis



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Modified Hyperbolic Rate Relation:

Decline Function: D(t)

Hyperbolic Function: b(t)

Function: (t)

Time-Rate: Modified Hyperbolic Rate Relation

)( ]exp[

)( )1()(

limexp,

/1hyp,

t*ttDq

t*ttbD

qtq

i

bi

i

dtdq

qtD 1)(

constant )(

1 )(

tDdtdtb

Discussion:●qDb functions are DIAGNOSTIC.●D(t), b(t), and (t) are evaluated continuously (at all points).●This shale gas case exhibits b=2 behavior → q = a√t (Linear Flow).●Appears to be "hyperbolic," but this is just the Linear Flow portion.

)( 1)( tDtdtdq

qtt

Logarithm of Production Time

Loga

rithm

of P

rodu

ctio

n R

ate,

q(t)

Loga

rithm

ofD

(t)an

d b(

t)

q(t)

D(t)

b(t)

1:2 slope

b(t) ≈ 2

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Discussion:●qDb functions are DIAGNOSTIC.●Power-law exponential relation is derived from:●No direct analog to hyperbolic case.●This is a "tight gas" reservoir case.

PLE Rate Relation:

Decline Function: D(t)

Hyperbolic Function: b(t)

b Function: b(t)

Time-Rate: Power-Law Exponential Rate Relation

]ˆexp[ˆ)( nii tDtDqtq

)1(ˆ

1)(

nitDnD

dtdq

qtD

nn

i

i ttDDn

nDn

tDdtdtb

2)1( ] ˆ[

)1(ˆ

)(1 )(

)1(ˆ nitDnD

)( 1)( tDtdtdq

qtt

Logarithm of Production TimeLo

garit

hm o

fD(t)

and

b(t)

q(t)

D(t)

b(t)

Loga

rithm

of P

rodu

ctio

n R

ate,

q(t)

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Reservoir Modeling —Eagle Ford Case History



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Analysis: ■Model: Horizontal well with multiple fractures, non-linear analysis.■ Input PVT lab data in the model (volatile oil).■Recommend tuning an EOS based on laboratory PVT data to create an EOS

model for generating black-oil properties which should be applicable for many wells.

■Excellent match of oil and gas rate data with models until shut-in.

Modeling Case History: Ilk — SPE 160076

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Forecast: ■Oil and gas rates are extrapolated using the model (80 acres).■EUROIL = 0.23 MMSTB, EURGAS = 1.05 BSCF.


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Forecast: ■Constant pressure simulation results are imposed on productivity index and

cumulative production plots.■No dominant straight line behavior is observed.■Forecast is different with respect to drainage area.

Oil productivity index andcumulative oil production plot.

Gas productivity index and cumulative gas production plot.


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Discussion: ■EUR is a function of well spacing for less than 100 acres drainage area,

assumption (not affected over 100 acres).■EUR values are estimated at 30 years of production.■ In our simulation runs, 100 acres drainage area corresponds to 738 ft

distance between two wells.


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Summary



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Summary:●Shale Gas/Shale Liquids Resources■ In-place resources are well understood.■ Flow mechanisms are NOT well understood.■ These systems MUST BE STIMULATED to yield economic rates.

●Practical Issues on Reserves■ Use sufficient data to make appropriate estimates (18-24 months).■ The equation does not really matter — use the DIAGNOSTICS!■ Reserves estimation must become more diagnostic (less analogs).

●Take-Aways on Reserves■ Reserves are defined by stimulation, geology, and fluid type.■ There are no clear alternatives to the multi-fracture horizontal well.■ You must use diagnostics (not statistics) to define reserves.

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End of Presentation



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