Question

In a pressure buildup test, what specific feature on a Horner plot indicates that the well has reached a closed reservoir boundary?

Accepted Answer

On a Horner plot, which is a graph used to analyze pressure buildup data by plotting bottom-hole pressure against the logarithm of a time ratio, a closed reservoir boundary is indicated by an upward deviation from the straight-line trend known as the middle-time region. The middle-time region represents the period where the pressure transient, or the expanding wave of pressure change, is moving through the reservoir away from the wellbore. When this transient encounters a closed boundary—an edge of the reservoir where no fluid can flow across—it can no longer expand into new rock, causing the pressure to build up faster than it did during the infinite-acting phase. Imagine this like a ripple in a circular pool hitting the wall; the reflection causes the water level to rise more rapidly at the center than it would if the ripple were still spreading across an open surface. This sharp upward curve on the plot signifies that the pressure support from the rest of the reservoir has been cut off, confirming that the well is interacting with a finite, bounded drainage area.

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In a pressure buildup test, what specific feature on a Horner plot indicates that the well has reached a closed reservoir boundary?

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