Reservoir Engineering Aspects of Unconventional · PDF fileReservoir Engineering Aspects of Unconventional Reservoirs T.A. Blasingame ... What Models Tell Us: Reservoir Modeling Concepts

"Ask the Expert Session 3" --- Wednesday, 9 December 2015, 0800–0930Qatar National Convention Centre | Doha, Qatar | 06–09 December 2015

Reservoir Engineering Aspects of Unconventional ReservoirsT.A. Blasingame | Texas A&M University

"Ask the Expert Session 3" — Wednesday, 9 December 2015 (0800–0930) Qatar National Convention Centre | Doha, Qatar | 06–09 December 2015

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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Rationale: Analysis of Well Performance — Unconventional Reservoirs

●Objectives: Well Performance Analysis (Unconventional Reservoirs)■To understand the characteristics which control performance.■To evaluate completion/stimulation effectiveness.■To forecast production and estimate reserves (EUR).■To identify processes/factors to optimize production.

●Issues:■Uncertainty/non-uniqueness (data quality?)■Understanding of flow regimes (flow mechanisms?)■Understanding of phase behavior (near-critical fluids?)■Understanding of stimulated volume (drainage area?)■ Integration of geomechanics (pressure dependencies?)

●Key Points for Analysis and Forecasting:■Duration of data required for accurate estimates of EUR.■Optimal well spacing/orientation.■Reserves estimation method(s) must be "reasonably certain."

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Work Path: Analysis of Well Performance

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Guidance: Typical Flow Regimes in Unconventional Reservoir Systems

Required Model Parameters: ●Permeability (k)●Fracture half-length (xf)●Fracture conductivity (Fc)●Drainage area (A)●Skin factor (s)●Well length (Lw)●Number of fractures (nf)

Linear Flow:(fracture flow does not interfere)

"SRV" Flow: ("depletion")(fracture flow does interfere)

"Post-SRV" Flow:("Compound Linear Flow")

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Time-Rate Behavior: (Formation) Linear Flow — TheorySolution for a Single Fracture: (transient linear flow)

Additive Fractures: (transient linear flow)

+ + + →

kc

BppC

tACq

tAk

cB

ppq

tp

twfixf

xft

wfi

DxfD

1)( 128494.8

1 1

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1

1)(

1]...

[

tottot

,4,3,

2,1,tot

tACq

tAAA

AACq

xf

nxfxfxf

xfxf

Note:These solutions are only valid for transient linear flow [i.e., the case of non-interfering pressure distributions (due to the fractures)].

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Time-Rate Behavior: (Formation) Linear Flow (Synthetic Example)●Formation Linear Flow

■ Log-log diagnostic plot: log[q(t)] versus log[t ] (slope = -1:2)■ "qDb" (time-rate) plot: log[q(t)] log[D(t)] log[b(t)] versus log[t ] ■ "Traditional" plot: q(t) versus 1/SQRT[t ] (straight-line portion)■Extrapolation using a linear flow model will over-predict EUR…

Region ofover-

extrapolation…

NO clean-up/ flowback effects…

NO clean-up/ flowback effects…

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Flow Regimes: (Barnett Shale Example)●Schematic illustrates flow regimes exhibited by time-rate-pressure data.●Duration/existence of flow regimes is DIFFERENT for each play.

EURLF (VERY OPTIMISTIC)

EURDep (CONSERVATIVE ???)

Pseudo-elliptical flow regime (flow from matrix to collection of fractures) might exist after fracture interference.

Time-Rate Behavior: Flow Regimes for a Multi-Fracture Horizontal Well

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Linear Flow: Horizontal Shale (Dry) Gas Wells ONLY (Public Data)

Discussion:●START of "Linear Flow" (~3-6 months).●END of "Linear Flow" (~9-36 months).●"Linear Flow" is represented by b = 2.●EUR requires at least 20+ months (except Haynesville ~1 year; and Barnett ~3 years).●Square root time plot used to show linear portion of trend (Gp(t) vs. SQRT(t) best view).

Heckman, T.L., et al (2013): Best Practices for Reserves Estimation in Unconventional Reservoirs — Present and Future Considerations, Keynote presentation presented at the 2013 SPE Unconventional Resources Conference, The Woodlands, TX (USA), 10-12 April 2013.

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Alternate Time-Rate Model: Power-Law Exponential Rate Relation

PLE Rate Relation:

Decline Function: D(t)

Hyperbolic Function: b(t)

nn

i

i ttDDn

nDn

tDdtdtb

2)1( ] ˆ[

)1(ˆ

)(1 )(

]ˆexp[ˆ)( nii tDtDqtq

)1(ˆ

1)(

nitDnD

dtdq

qtD

Ilk, D., Rushing, J.A., Perego, A.D., and Blasingame, T.A.,: "Exponential vs. Hyperbolic Decline in Tight Gas Sands — Understanding the Origin and Implications for Reserve Estimates Using Arps' Decline Curves," paper SPE 116731 presented at the 2008 Annual SPE Technical Conference and Exhibition, Denver, CO, USA, 21–24 September 2008.

Clean-up/ flowback effects

are not significant for

this case

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What Models Tell Us: Reservoir Modeling Concepts for Unconventionals

b. Pressure gradient after 8 months (top) and 10 years (bottom) of production (Note times for different regimes, this is a relatively high permeability shale analog case).

a. Freeman, C.M., Ilk, D., Moridis, G.J., and Blasingame, T.A.: "A Numerical Study of Performance for Tight Gas and Shale Gas Reservoir Systems" paper SPE 124961 presented at the 2009 SPE Annual Technical Conference and Exhibition, New Orleans, LA, USA, 4–7 October 2009.

c. Typical transient response where PSS is seen in the SRV (Note times for different regimes, this is a relatively high permeability shale analog case).

Modeling: (Grand Challenges)● Fully integrated (not coupled) geo-

mechanical/flow simulation model.●Models may not be properly "parameter-

ized" — no data to validate.● Statistical versus deterministic models?

(is the reservoir system "too complex?")● Use simplified models to establish/

validate drainage volumes.● Use models to constrain assumptions

about geomechanics/fluid flow.

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What Models Tell Us: Random Fractures? (A Simplified Study Case)

b. Pressure Map — Random Walk "Quad-Branched" fracture scenario (Case 2).

a. Fracture Map — Random Walk "Quad-Branched" fracture scenario (Case 2).

c. Decline Curve — Random Walk "Quad-Branched" fracture scenario (Case 2). Not that the early-time numerical effect AND that the slope is 7/10 ---not 1:2 as one would expect for linear flow.

10 sec

Numerical "start-Up" effects…

Slope = 7:10(NOT linear flow)

d. Decline Curve — Random Walk "Quad-Branched" fracture scenario (Case 2). Not that the early-time numerical effect AND that the slope is 7/10 ---not 1:2 as one would expect for linear flow.

From: Mhiri, A. and Blasingame, T.A.: "Stochastic Modeling of a Fracture Network in a Hydraulically Fractured Shale-Gas Reservoir," paper SPE 175021 presented at the 2015 SPE Annual Technical Conference and Exhibition held 28-30 September, 2015,Houston, TX, USA.

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"Ask the Expert Session 3" — Wednesday, 9 December 2015 (0800–0930) Qatar National Convention Centre | Doha, Qatar | 06–09 December 2015

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

End of Presentation

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Brief Biography: Tom Blasingame●Role:■Robert L. Whiting Professor, Texas A&M U.■B.S., M.S., and Ph.D. degrees from Texas A&M U. (PETE)

●Counts: (Dec 2015)■57 M.S. (thesis) and 32 M.Eng. (report, non-thesis) Graduates ■13 Ph.D. Graduates■Over 140 Technical Articles

●Recognition:■SPE Distinguished Member (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)■SPE Distinguished Achievement Award for PETE Faculty (2014)■SPE Honorary Member (2015)■SPE Technical Director for Reservoir Description and Dynamics (2015-2018 )

●Current Research Activities: (Dec 2015)■Production Performance Analysis for Shale/Tight Reservoir Systems■Flow Phenomena in Ultra-Low Permeability Reservoir Systems■Correlation of Permeability with Mercury Injection Capillary Pressure■Performance Behavior of Naturally Fractured Reservoir Systems■Development of Time-Rate-Pressure Relations for Unconventional Reservoirs■Numerical Modeling of Ultra-Low Permeability Reservoir Systems■Correlation of Production Metrics with Completion Parameters

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Suggested Questions:●Basic Flow:—Can we model unconventional well performance with Darcy flow concepts?—We understand phenomena at a given scale, but what about multi-scales?—Do we need to worry about PVT confinement issues?

● Production Performance:—Can we correlate production metrics with less than 18-24 months of history?—Are time-rate models a "reliable technology?"—Have we correlated/can we correlate the completion with well performance?

●Rate Forecasting/EUR Predictions:—Who believes we will still be using Arps' relations in: 2020? 2030? 2040? …—Do we need a universal q(t) model?—Where does reservoir pressure fit in rate projections?

●Models:—Proxy reservoir models? (e.g., simple concepts, big data, ?)—How valid is the concept of a "random walk" fracture?—Role of natural fractures?—Role of horizontal fractures?—Role of geomechanics?

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Reservoir Engineering Aspects of Unconventional · PDF fileReservoir Engineering Aspects of Unconventional Reservoirs T.A. Blasingame ... What Models Tell Us: Reservoir Modeling Concepts