part 10 buildup followed cr drawdown note on page

8/13/2019 Part 10 Buildup Followed CR Drawdown Note on Page

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Well Test Analysis 1

MOnur September 2013




Consider the rate histor for an idealized buildu test. A well is


produced at rate q for a time t p , then is shut in for a buildup test.The rate history can be represented as the algebraic sum of twodifferent constant rate flow periods – one at rate q , beginning at t

= 0, and another at rate -q, beginning at∆t = 0.




The ressure res onse for the rate histor shown on the revious


slide can also be obtained by adding the pressure responses fromeach of the two rate flow histories.




Note that t includes both wellbore stora e and skin effects if


these effects are important, and is the rate-normalized constant-unit-rate pressure change.

This equation forms the basis of Horner Analysis to be discussed.




This e uation is obtained b subtractin buildu ressure chan e


from the constant-rate drawdown pressure change at tp. Thisforms the basis of MDH analysis to be discussed.




As with the drawdown e uation, this e uation ma also be written


in the same form as the equation of a straight line.

y~pws

x~t

ttlog

p10

∆

∆+

m~kh

qB6.162 µ

−

b~pi




The uantit is called the Horner time ratio .ttp ∆+


A graph of p ws vs. should fall on a straight line

Slope m of the resulting straight line allows us to estimatepermeability

Intercept b at = 0 or = 1 gives us the initialpressure pi.

∆

∆+

t

ttlog

p

10

∆

∆+

t

ttlog

p

10

∆

∆+

t

ttp




* obtained from Horner lot re resents i if and onl if the


reservoir is infinite acting radial flow.





y~pws

x~t

ttlog

p10

∆

∆+

m~kh

qB6.162 µ

−

b~pi




• Two arallel no-flow boundaries encountered durin test


• Well must be much closer to sides of channel than to ends




Drawdown


• Wellbore storage

• Radial flow

• Hemiradial flow (if well is much closer to one edge than to theother)

• Linear flow

Similar responses

• Well between two sealing faults

• Hydraulically fractured well with high conductivity fracture

• Horizontal well during early linear flow




Buildu


• Derivative has slope of -1/2 when shutin time is much largerthan producing time




Buildu


• Radial equivalent time not the most appropriate form

• Linear equivalent time works well as long as channel ends donot affect pressure response




Buildu


• Derivative with respect to equivalent time vs time similar to, butnot identical to, drawdown response

part 10 buildup followed cr drawdown note on page

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