Injection well testing In many reservoirs, especially in mature waterflooded fields, the injection wells may be as numerous as the producing wells. Consequently, testing injection wells is particularly important for efficient planning and operation of both secondary and tertiary recovery projects. Satisfactory injection performance over a long period of time and prompt detection of increasing wellbore damage are important to the economics of any recovery project. This chapter begins with a discussion of injectivity and falloff testing in liquid-filled, unit-mobility ratio reservoirs. Then, we address methods for determining average reservoir pressure and for analyzing composite systems in nonunit mobility-ratio reservoirs. Finally, we discuss well testing and analysis with the step-rate method.