Question:
Pressure change and derivative type curves (Bourdet type curves) are used in well test analysis. Which of the following statements is/are CORRECT about these type curves?
Pressure change and derivative type curves (Bourdet type curves) are used in well test analysis. Which of the following statements is/are CORRECT about these type curves?
Show Hint
The horizontal axis is actually the group \(t_D/C_D\), and both \(P_D\) and its derivative share the vertical axis.
Updated On: Jul 28, 2026
- These curves are on Log-Log plot
- Horizontal axis is for dimensionless time \(t_D\)
- All derivative type curves merge in the middle time region
- Vertical axis is for dimensionless pressure \(P_D\) only
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The Correct Option is A, C
Solution and Explanation
Step 1: Recall what Bourdet type curves are:
Bourdet type curves are standard diagnostic plots in pressure transient analysis that overlay the measured dimensionless pressure change and its logarithmic derivative against a dimensionless time group for a family of curves labeled by the wellbore storage and skin combination, \(C_D e^{2s}\). They are used to identify flow regimes such as wellbore storage, transition, and infinite acting radial flow directly from the shape of the field data once matched to the correct curve.
Step 2: Check option A, log log plot:
Bourdet type curves are plotted on a log log scale for both axes. This is essential because flow regimes appear as straight lines or flat trends only on a log log scale, for example unit slope during pure wellbore storage and a flat derivative during radial flow, both of which would not stand out clearly on a linear or semi log plot. So option A is correct.
Step 3: Check option B, horizontal axis is \(t_D\):
The horizontal axis of the Bourdet type curve is not the plain dimensionless time \(t_D\) but the dimensionless time group \(t_D / C_D\), that is dimensionless time divided by the dimensionless wellbore storage coefficient. This particular grouping is what allows a single family of curves, distinguished only by \(C_D e^{2s}\), to represent all combinations of storage and skin on one chart. Since the statement claims the axis is \(t_D\) alone, it is not correct.
Step 4: Check option C, curves merge in the middle time region:
In the middle time region the well has moved past pure wellbore storage into infinite acting radial flow. During radial flow the pressure derivative becomes constant at a value of 0.5 regardless of the particular \(C_D e^{2s}\) value of the well, because storage and skin effects have already died out. This means all the individual derivative type curves converge onto the same flat line in this region, so option C is correct.
Step 5: Check option D, vertical axis is \(P_D\) only:
The vertical axis of the Bourdet plot actually carries two families of curves plotted together, the dimensionless pressure \(P_D\) and its dimensionless derivative \(t_D \, dP_D/dt_D\), both plotted on the same log scale so they can be compared directly during matching. Since the derivative is also plotted on the same axis and is in fact the key diagnostic feature of the Bourdet method, the statement that the axis is for \(P_D\) only is not correct.
Final Answer:
\[ \boxed{\text{Options A and C: log-log plot and merging in the middle time region}} \]
Bourdet type curves are standard diagnostic plots in pressure transient analysis that overlay the measured dimensionless pressure change and its logarithmic derivative against a dimensionless time group for a family of curves labeled by the wellbore storage and skin combination, \(C_D e^{2s}\). They are used to identify flow regimes such as wellbore storage, transition, and infinite acting radial flow directly from the shape of the field data once matched to the correct curve.
Step 2: Check option A, log log plot:
Bourdet type curves are plotted on a log log scale for both axes. This is essential because flow regimes appear as straight lines or flat trends only on a log log scale, for example unit slope during pure wellbore storage and a flat derivative during radial flow, both of which would not stand out clearly on a linear or semi log plot. So option A is correct.
Step 3: Check option B, horizontal axis is \(t_D\):
The horizontal axis of the Bourdet type curve is not the plain dimensionless time \(t_D\) but the dimensionless time group \(t_D / C_D\), that is dimensionless time divided by the dimensionless wellbore storage coefficient. This particular grouping is what allows a single family of curves, distinguished only by \(C_D e^{2s}\), to represent all combinations of storage and skin on one chart. Since the statement claims the axis is \(t_D\) alone, it is not correct.
Step 4: Check option C, curves merge in the middle time region:
In the middle time region the well has moved past pure wellbore storage into infinite acting radial flow. During radial flow the pressure derivative becomes constant at a value of 0.5 regardless of the particular \(C_D e^{2s}\) value of the well, because storage and skin effects have already died out. This means all the individual derivative type curves converge onto the same flat line in this region, so option C is correct.
Step 5: Check option D, vertical axis is \(P_D\) only:
The vertical axis of the Bourdet plot actually carries two families of curves plotted together, the dimensionless pressure \(P_D\) and its dimensionless derivative \(t_D \, dP_D/dt_D\), both plotted on the same log scale so they can be compared directly during matching. Since the derivative is also plotted on the same axis and is in fact the key diagnostic feature of the Bourdet method, the statement that the axis is for \(P_D\) only is not correct.
Final Answer:
\[ \boxed{\text{Options A and C: log-log plot and merging in the middle time region}} \]
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