Injection Tests as a Reliable Alternative to Conventional Well Testing:A Real Field Experience

摘要

Environmental constraints and high costs, especially offshore,are making conventional well testing less and less feasible andaccepted by the public Administration.New options were thoroughly evaluated to find a viablealternative to standard production tests for characterizing thewell productivity without surface production. An accurateinvestigation demonstrated that injection tests could provideall the information needed to calculate the well productivity atreasonably low costs and with a good degree of reliability.Based on the results of laboratory and field pilot tests itwas proved that injectivity tests could be successfully appliedin a real sour oil field. Laboratory tests proved that brine couldbe a suitable injection fluid because there were nocompatibility problems with the oil and the reservoir rock. Itwas verified that the interpretation of the pressure transientsshould be referred to the fall-off period rather than to theinjection phase. The formation permeability thickness product(kh) could be correctly identified from the pressure derivativeanalysis only if multiphase-flow was assumed. The total skinvalue could also be obtained from the test interpretation.The total skin comprises two components, a mechanicalcomponent due to permeability damage, and a bi-phasecomponent due to fluid interaction in the reservoir. The biphaseskin could only be evaluated with numerical welltesting, provided that the fluid relative permeability curveswere available. It was also demonstrated that the bi-phasecomponent mainly depends on the injection rate, but isindependent from the formation permeability.Then, the well-known transient equation was applied todetermine the well productivity index (PI) based on the kh andthe mechanical skin. PI values calculated from injection testscompared satisfactorily with PI values measured from 6 DSTtests performed on appraisal wells.