Analysis of Slug and Drillstem Tests Under Water-Oil Two Phase Flow Conditions

摘要

Special procedures for the analysis of Slug and DrillStemrnTests when the produced fluid does not reach the surface havernappeared in the literature over the last ten years. However,rnsuch analysis techniques are based on single phase theory. Thisrnpaper considers the effects of water-oil two phase flow on thernpressure analysis of such tests. In particular, this work verifiesrnwhen the single phase analysis procedure modified by Perrine-rnMartin theory can be extended to Slug and DST withrnsimultaneous water and oil production.rnTwo cases are considered: (1) uniform initial water saturationrnprofile within the area investigated during test time,rnrepresenting tests run in a transition zone; (2) a region ofrnhigher water saturation exists near the wellbore, whichrnsimulates the case where a significant wellbore fluid invasionrninto the formation have occurred during drilling or wellrncompletion.rnIt is shown that when saturation gradients are small, thernwellbore and reservoir equations are weakly non-linear. Inrnsuch cases the pressure solution for two phase flow can berncorrelated with the single phase analytical solution for bothrndrawdown and buildup periods. For cases with a high waterrnsaturation region close to the well, the total mobility contrastrnbetween the invaded zone and the virgin zone can be representrnby an apparent skin factor. During the flow period thisrnapparent skin rapidly changes due to the cleaning effect in therninvaded zone, thus the two phase pressure solution cannot berncorrelated with the constant skin-slug test analytical solution.rnThe main conclusions of this work are: (1) single phasernanalysis procedures can be applied to both flow and builduprndata, provided the saturation profile is nearly uniform; (2)rnwhen an invasion zone exists near the wellbore, single phasernanalysis procedures applied to buildup data give an excellentrntotal mobility estimate of the virgin zone. Skin factorsrncalculated from such buildup data represent a total skin, that is,rnthe mechanical skin plus the apparent skin at the moment ofrnshut-in. Calculated values from the flow period may notrnrepresent the virgin zone total mobility and the total skinrnfactor.