SPE Well Testing and Pressure Transient Analysis 3

Question 1

In gas well testing, why is it necessary to use 'pseudo-pressure' (m(p) or real-gas potential) instead of pressure in the flow equations?

Accepted Answer

Gas viscosity and z-factor are both pressure-dependent, so simple pressure analysis introduces significant error

Answer

Both gas viscosity (μg) and z-factor vary significantly with pressure; pseudo-pressure integrates μg and z through the pressure range, linearizing the gas flow equation for accurate analysis.

Question 2

The concept of 'radius of investigation' (ri) in pressure transient testing describes which physical phenomenon?

Accepted Answer

The maximum distance from the well that a pressure disturbance has reached at a given time

Answer

The radius of investigation estimates how far from the wellbore a detectable pressure disturbance has propagated at time t, given by ri ≈ 0.029√(kt/φμct).

Question 3

In pressure transient analysis, what does a 'unit slope' (slope = 1) on a log-log plot of Δp versus Δt during early time indicate?

Accepted Answer

The test is dominated by wellbore storage (afterflow)

Answer

A unit slope (1:1) on the log-log plot of Δp and its derivative at early time is the diagnostic signature of wellbore storage domination, where all flow comes from wellbore fluid expansion.

Question 4

Which of the following correctly describes the difference between 'infinite conductivity' and 'finite conductivity' vertical fractures in pressure transient analysis?

Accepted Answer

Infinite conductivity fractures show half-slope on the derivative; finite conductivity fractures show quarter-slope

Answer

Infinite conductivity fractures (negligible fracture pressure drop) exhibit a half-unit slope (linear flow), while finite conductivity fractures show a quarter-unit slope (bilinear flow) because fluid flows in both the fracture and the formation simultaneously.

Question 5

A well is tested and the extrapolated Horner straight line gives a false pressure P* instead of true average reservoir pressure (P-bar). Under what condition does P* equal P-bar?

Accepted Answer

When the well has been producing for an infinite time (the reservoir is effectively infinite-acting at shut-in)

Answer

P* equals P-bar only in an infinite-acting reservoir where no boundary effects occurred during production; in bounded reservoirs, corrections (e.g., Matthews-Brons-Hazebroek) are needed to convert P* to true average pressure.

(SPE) Society of Petroleum Engineers Certification Practice Test

(SPE) Society of Petroleum Engineers Certification Practice Test

SPE Well Testing and Pressure Transient Analysis 3