1. n. [Well Testing]
The testing of wells in which fluid is being injected into the reservoir. The most common type of test is a falloff test, in which injection is halted and the pressure decline is measured as a function of time. The most common situation is a waterflood. In many reservoirs, the formation pressure is high enough to maintain a full column of fluid in the wellbore and the pressure can be monitored at the surface. The bottomhole pressure is then calculated by adding the weight of the fluid column to the surface pressure. Gas-injection wells, although less common, lend themselves to similar testing. The rise in fluid pressure as a function of time while injection is taking place could theoretically be used also, but this type of approach is rarely used. The equations and theory for these tests are an exact mirror image of those for buildup and drawdown testing. Calculated results for these wells are usually good because the formations are commonly liquid-filled. Frequently water-injection wells are inadvertently fractured at some time in their life and consequently have a negative skin effect.