Abstract: Well testing is a simple and direct way to determine the deliverability of gas well. However, whether the test duration is long enough or not will affect the readings from the test, which will in turn influence the computation of gas well deliverability.Based on the deep gas well configuration, we investigated the
method, the principle and other factors to estimate the reason-able testing time. We presented a couple of ways to estimate the reasonable testing time, and case study was also provided. We think that our research work is of practical significance in guid-ing test design of deep gas wells.

Key words: well testing, test duration, determination, deep gas well