Question

Which of the following option(s) is/are CORRECT for well testing analysis of a reservoir?

• A. Permeability, skin and reservoir geometry are calculated using data from pseudo steady state.
• B. Permeability, skin and reservoir geometry are calculated using data from transient state.
• C. Reservoir geometry is calculated using data from pseudo steady state.
• D. Absolute open flow potential is calculated from back pressure test for a gas well.

Answer 1

The Correct Option is C, D

Step 1: What information comes from transient (infinite-acting) data? 
During a well test, the transient or infinite-acting radial flow period is mainly used to calculate formation properties. From this region:

• Permeability ($k$) is obtained from the slope of the semilog plot.
• Skin factor ($s$) is obtained from the intercept or equivalent transient equations.

Therefore, both $k$ and $s$ are evaluated using transient-state data, not pseudo-steady-state data.

 

Step 2: What information comes from pseudo-steady-state (boundary-dominated) flow?
When the pressure response reaches the boundary-dominated or pseudo-steady-state flow regime, the effect of reservoir limits becomes visible. This late-time behavior mainly reflects:

• Drainage area
• Reservoir boundaries
• Overall reservoir geometry

Hence, reservoir geometry is typically interpreted from pseudo-steady-state data, making option (C) correct.

 

Step 3: Understanding Absolute Open Flow Potential (AOFP).
For gas wells, back-pressure (deliverability) tests are conducted to establish the deliverability relationship. By extrapolating the flow equation to $p_{wf} \to 0$, the Absolute Open Flow Potential (AOFP) is obtained. Thus, statement (D) is also correct.

Step 4: Checking each option.
(A) Incorrect: Permeability and skin are not mainly calculated from pseudo-steady-state data.
(B) Incorrect: Reservoir geometry is not normally determined from early transient data unless boundaries appear.
(C) Correct.
(D) Correct.

Step 5: Final conclusion.
The correct answers are:

\[ \boxed{(C)\ \text{and}\ (D)} \]