A 1D Analytical Solution to Determine Residual Oil Saturations fromSingle-well Chemical Tracer Test

摘要

Single well chemical tracer tests(SWCTT)have been extensively used in the field to estimate residual oilsaturation in a reservoir for more than 50 years.They are often used as characterization methods to gaugeEOR potential/performance.Therefore,an accurate estimation of Sor from SWCTT's is critical.Currentapproaches for SWCTT interpretation use a combination of history matching with numerical modeling toolsor use of an approximate analytical technique developed for partitioning interwell tracers.History matchingis more accurate,requires multiple assumptions and can be potentially time consuming.The basic analyticalsolution for partitioning inter-well tracer neglects tracer hydrolysis and provides approximate estimationsof Sor.We solve for the exact solution of the 1-D convection-reaction solution using the modified methodof moments.No additional simplifying assumptions such as slow reaction rate,fast flowback etc.weremade while solving the flow equation.We tested the resulting exact solution against synthetic numericalsimulations and 50+ published field cases and compared actual versus calculated oil saturations.Thesynthetic tracer data was generated for different heterogeneities,tracer reaction rate,partition coefficientsand tracer soak time.Analysis of the synthetic SWCTT result shows that our analytical approach correctlyestimates oil saturation.The calculated residual oil from our analytical model was consistently within ±0.02saturation units while the original analytical model consistently underpredicts oil saturation.Novelty of this model is in its simplicity in calculating residual oil saturation from SWCTT's.The modelrequires only tracer concentration histories as an input to be able to calculate the near-wellbore residual oilsaturation.The developed method can be solved directly in Microsoft excel without requiring any advancedcomputation/simulation tools.