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

Gas wells always have higher skin factors than oil wells

Answer

Gas flow is always turbulent, requiring special corrections unrelated to fluid properties

Answer

Pseudo-pressure corrects for wellbore storage effects in gas wells

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 wellbore radius beyond which formation damage exists

Answer

The radius at which turbulent non-Darcy flow transitions to laminar Darcy flow

Answer

The radial distance at which the pressure equals initial reservoir pressure

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

Radial flow regime has been established

Answer

A hydraulic fracture with finite conductivity is present

Answer

The reservoir boundary has been reached

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 show quarter-slope; finite conductivity fractures show half-slope

Answer

Both fracture types produce identical pressure derivative responses

Answer

Finite conductivity fractures always result in bilinear flow with a unit slope

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

When the well has been produced to pseudosteady state before shut-in

Answer

When skin factor equals zero

Answer

When the wellbore storage coefficient is negligible

Question 6

During a multi-rate transient test using superposition theory, why must the principle of superposition be applied instead of simple single-rate analysis?

Accepted Answer

Superposition allows each rate change to be treated as an independent transient whose effects sum linearly

Answer

Superposition accounts for the changing fluid composition during rate changes

Answer

Superposition corrects for non-Darcy flow effects at high rates

Answer

Superposition eliminates the need for pseudo-pressure in gas well analysis

Question 7

In an interference test between two wells, what is the primary information obtained that a single-well buildup or drawdown test cannot provide directly?

Accepted Answer

Interwell permeability and porosity-compressibility product between the two wells

Answer

Wellbore skin factor of the active well

Answer

Wellbore storage coefficient of the observation well

Answer

Near-wellbore damage radius of the observation well