Delta Time (Dt)

Delta time represents the time from the beginning of a flow or shut-in period. In a buildup test, delta time is also called the shut-in time. It is the simplest time function to deal with and is used when calculating other time functions such as Horner or superposition time.

For analysis, it should only be used for constant rate drawdown tests, or for buildup tests which have been preceded by a long duration flow (greater than time to stabilization).