1. n. [Well Testing]

A multirate test designed as a series of drawdown and buildup sequences at different drawdown flow rates, with each drawdown and buildup of the same duration. The purpose of the test is to determine well deliverability, and this type of test is most commonly done in gas wells.

See: isochronal test

2. n. [Production Testing]

A type of deliverability test conducted in gas wells to generate a stabilized gas deliverability curve (IPR). This test overcomes the limitation of the isochronal test, which requires long shut-in times to reach the average reservoir pressure. In the modified isochronal test, the shut-in periods are of equal duration, as are the flowing periods. The final shut-in pressure before the beginning of the new flow is used as an approximation of the average reservoir pressure. The same procedure is typically repeated four times. A stabilized point (pseudosteady state) is usually obtained at the end of the test. Modified isochronal tests are commonly used in gas wells, because they require less time and money to produce results comparable to the isochronal test.