Day 4 2 fractures summary

10/19/15 5 Material Balance Total Injected volume leak-off coefficient, permeability frac volume height, length, width‏ Stored in fracture Lost to formation The role of fracture mod

Why fracturing? 

Hydrocarbon saturation 30 % or more

Gross reservoir height 10 m or more

Permeability Gas < 5 mD, Oil < 100 mD*

Reservoir pressure Gas: 2x the abandonment pressure

Oil 80 % depletion

Production system Current production not more than

80 % of max capacity of facilities

* Skinfracs can also be applied at higher permeability

Inflow Performance of Fractured Well

2 

8 

6 

4 

0.1 

0.7 

0.5  0.3 

F CD 

L CD 

re/rw = 2500 

FCD ≥ 10 

Prat’s steady‐state solution 

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Material Balance 

Total Injected volume

leak-off coefficient, permeability

frac volume (height, length, width)‏

Stored in fracture

Lost to formation

The role of fracture model is to determine

this split

η = Vfp/Vi

Vpad = (1- η)/(1+ η)100‏ %

For instance:

η = 33%

Pad volume is (0.67/1.33)*100 = 50%

In practice 40% Pad is a good starting point

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Critical Parameters

f (Width, Height, Length)‏

Injected volume = Frac volume + Leak-off volume

f (Time, Height, Length)‏

f (Stress profile, Net pressure)‏

f (Fluid-loss coefficient)‏

f (YoungÕs Modulus, PoissonÕs ratio, Net pressure)‏

Design input data 

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! σ3 from shut-in pressure

! Pressure decline trend with frac open is

different from decline trend with frac closed

! Identify trend change

! Many different methods

P vs log Δt

P vs log t log P vs Δt log P vs log t

P vs log [(t+ Δt)/Δt]

G function pseudo plots

Minifrac 

¥  Determine frac closure pressure, Pc

¥  Ideally, Pc = σ3

¥  In reality

!  frac geometry dependent

!  frac length change

!  frac height recession

!  multiple closures

!

w

σ3 P

c

σ3c

σ3b

σ3a

BHP "

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¥  Widely used by many service companies

¥  Interpretation model dependent

¥  Non-unique solution

!  stress and permeability contrasts

!  tip screen-out, etc

¥  Assumes accurate BHP data

Pumping time (mins)‏

1

1000

100

10

100

10

M = 1/8 to 1/4 contained height

M > 1 near well restriction

M < 0 rapid or unstable height growth

M = 1 restricted height

& length

M = 0 stable height growth

! Injectivity test with brine (or solvent)‏

! Minifrac with frac fluid

!  Shut in

! Main frac

! Shut in Ð Forced closure

MFrac

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