Interpretation of Water Injection/Falloff Test—Comparison Between Numerical and Levitan's Analytical Model

摘要

Water injection /fall off tests are normally associated withrnwater flood project. Recently, interested in this type of wellrntests has developed in the area of reservoir appraisal. In thernvast majority of situations associated with explorationrnactivities, there is no infrastructure and equipment in place torncollect and export the hydrocarbon produced during well test.rnThe common practice used in the industry is to burn thernproduced fluid.rnThe demands to reduce emission during well tests putrnenormous pressure to avoid these tests together. This bringsrnlarge uncertainties to the reservior appraisal and increases therninvestment risk if a decision is made to sanction a project andrnto develop the field.Replacing a production/build up testrnsequence by an injection/fall off test sequence solves thernproblem of emission.rnLevitan [1] stated that three main problems due to using waterrninjection / fall off test might happen which are listed below:rnThe first problem is that the character of the system changesrnand Instead of single-phase flow we face now with two-phasernwater-oil flow by their own relative permeabilities. Thernsecond problem is injection of cold water includes temperaturernchanges in the formation and brings additional complication tornpressure behaviour through temperature effects on the oil andrnwater viscosities and the third one is injection of water mayrnresult in the formation fracturing and in coupling of rockrnmechanics and fluid flow problems. It is therefore, importantrnfor successful test interpretation to avoid fracturing and torninject water at below the formation fracturing pressure.rnThis paper is divided into two parts. In the first part we arerngoing to compare Numerical and Levitan's Analytical modelrnfor different injection and fall off periods using numerical partrnof Saphir well test software.In the second part as far as we have validated SaphirrnNumerical model compared with W-O Levitan Analyticalrnmodel, now this model is used to generate pressure responsesrnin order to investigate the influence of reservoir parameters.rnMethods of interpretation will be used and some specificrnadvantages of the numerical model will be shown.