Net Fracturing Pressure and Slurry Efficiency

Liberty Engineering Concepts

Indirect Measurements to Determine Frac Dimensions

PayPay

pnet

L?H?

W?

Injected VolumeBalloon ElasticityNet Pressure Pnet

Injected Volume, EfficiencyLayer Rock PropertiesNet Pressure pnet

R?pnet

Radius RLength L, Height H, Width w

V, ε, E, ν,

,V, E

Critical Concepts – Net Pressure

Net Pressure = Pressure Inside Fracture – Closure Pressure

Critical Concepts – Net Pressure & Fracture Width

Critical Concepts – Slurry Efficiency

DefinitionLow Slurry Efficiency

Smaller dimensions; higher leakoff

Vpumped (t)Vfrac (t)

efficiency (t) =

Important at the end of pumping, as frac volume, and thus dimensions, are likely at their maximum

High Slurry Efficiency

Larger dimensions; lower leakoff

Pore Pressure

Basic Measurements - Pressure Decline AnalysisWhat is obtained?• Instantaneous Shut-In

Pressure (ISIP)• Fracture closure

stress (minimum stress)

• Net pressure (at the end of job)

• Fluid efficiency (at the end of job)

• Reservoir permeability and pore pressure

Tp+Tc

Botto

mho

le p

ress

ure

Rate

Closure

Efficiency ~

TimeTc

Pnet

Tp

Tc

ISIP

Tc

Tc + Tp

Permeability

closureEOJnet ISIPp σ−=,

injectionclosure

closureEOJ tt

t+

≅ε

ISIP

pnet,EOJQ

σclosure

Bot

tom

hole

Pre

ssur

etpumping tclosure

( ) ( ) ( )( )( )3/2 1/23/2 1/2 1

1 1 11 4 15 21 1 sin 1

EOJcD cD cD cD cD

t t t t tπε

−−

= − + − + − + + +

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