The data of well-test pressure could be used to describe reservoir heterogeneity. Whenderivative curves bend downward in middle stage

the storage coefficient of the reservoir increases; on the contrary

the storage coefficient decreases. When the derivative curves stepup or step down from horizon

the flow coeficient of the reservoir also decreases or increases

and the obliqueness of the straight part of radial flow on Horner on.rve would become biggeror smaller accordingly. Several examples in Tarim basin have proved this.