TESTING INJECTION WELLS WITH RATE AND PRESSURE DATA

Injection tests can give such information as the effective mobilities of fluids, wellbore damage, and saturation change during displacement, which often require use of rate and pressure data. Although exact sol utions for injection and falloff pressure response of a well in an inf inite reservoir may be obtained for a constant injection rate, they ar e not readily extended for the general case of varying flow rates and bounded reservoirs. We present a perturbation theory for multiphase te sting that leads to a weakly nonlinear convolution and give a techniqu e to calculate pressure response rapidly for arbitrary flow rates for this form of convolution. The technique is specifically suited for sol ving inverse problems with nonlinear estimation. We present modificati ons to the solutions for positive and negative skin factors and demons trate that the effect of wellbore storage is not easily accounted for in an injection test, unlike single-phase well testing. We give a proc edure to correct the system response to storage and propose a variable -rate injection test to improve system parameter estimation. The main idea of the test is to excite the reservoir sequentially and continuou sly to keep it under strong transient conditions. We present interpret ation results for such a sequential testing.