What Do Hydraulic Fractures May Look Like?

Roberto Suarez-Rivera

W.D Von Gonten Co and W.D Von Gonten Laboratory

Vaca Muerta shaleOutcrop

Montney shaleOutcrop

Understanding the RockRock Fabric and Heterogeneity

WolfcampCore

WolfcampCore

SEM

SEM

Layered Heterogeneity (Eagleford Example)

Layered Heterogeneity (Wolfcamp Example)

Layering and Fracture Toughness

Hard(High Modulus) material

Hard/SoftCouplets

The layered rock is 40% tougher than the homogeneous rock

sh

sh

sv

sv

Rock Layering and Hydraulic Fracturing

Co

mp

ress

ion

Ten

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ion

Ten

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Layered Rock (High Resolution Logging) Layered Rock HF Model

Consequences of Layering and Weak Interfaces

Stress Concentrators(simulated perforations)

Fracture Toughness Testing under Stress

Rock has preferential directions of failure (i.e., weak interfaces)

Fracture orientation is controlled by the rock fabric

Suarez-Rivera et al., ARMA 2013 Hydraulic Fracturing Workshop.

Consequences of Layering and Weak Interfaces

Layered Niobrara shaleSuarez-Rivera et al., ARMA 2013 Hydraulic Fracturing Workshop.

Fracturing in Layered RocksConsequences of Layering and Interfaces

Propped horizontal fracture in Eagleford vertical pilot well with core

Suarez-Rivera et al., 2016 URTEC.

Core Drilling Induced Fractures

Soft layer

Hard layer

Soft layer

Actual Wellbore Fracture

Fracturing in Layered Rocks

Rock Layers, Weak Interfaces and Fracture Step-

Overs

Conceptual Model

Weak

Weak

ConductivityConductivity

• Thick Reservoir• Fracture Containment within Flow Unit• Multiple Conductivity Pinch Points• Poor Producer

• Thin Reservoir• Fracture Containment within Flow Unit• No Conductivity Pinch Points• Better Producer

Field Evidence Using Pre and Post Dipole Sonic MeasurementsLoss of Connectivity to the Wellbore During Drawdown

(The SRV Shrinks)

Suarez-Rivera et al., 2016 URTEC.

Layering and Fracture Height Growth

16 m

Pf

s11

Loss of Connectivity to the Wellbore During Drawdown

Rockfield (2D TGR) Software

Effective FractureHeight

Stress Controls on Hydraulic Fracture Propagation

Homogeneous Layered Layered and Fractured

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Stre

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nce

Normal Overpressure Highly Overpressure

0.8 – 0.9 psi/ft

0.5 – 0.7 psi/ft

Competition betweenstrength anisotropy and stress anisotropy

Operational Controls for Hydraulic Fracture Propagation

10 fracture stage20 ft spacing200 ft stage length~300 ft fracture half length

Strong differences in geometry are observed between fracture regimes, even for homogeneous materials

E.V. Dontsov, T. Picha, Suarez-Rivera (in progress).

Look for the following:

Rock fabric (Strength anisotropy): Layering and interfaces, including natural fractures and their frequency

Stress anisotropy: High pore pressure, typically means low effective stress and low stress anisotropy

Operational controls: How is the fracture energy dissipated? Viscosity dominated or toughness dominated

Near wellbore effects: Unfortunately the initial fracture geometry has long term consequences on the overall fracture. How we initiate fractures matters.

Drawdown: When the fracture geometry is complex the potential for fracture segmentation is high, and the SRV shrinks as a function of time during drawdown.

Summary: What do Hydraulic Fractures May Look Like Downhole

Thank You