Numerical Interpretation of Single Well Chemical Tracer Tests for ASP Injection

摘要

A series of single well ASP pilots using Single Well Chemical Tracer Tests (SWCTT) have been conducted to estimate the efficiency of Alkaline Surfactant Polymer (ASP) flooding. A SWCTT was done after water injection to establish a baseline remaining oil saturation. A second SWCTT was conducted after ASP injection to measure the remaining oil saturation after ASP. Usually analytical methods are used to interpret SWCTT’s and to determine the remaining oil saturation. These techniques work best if the response is close to an, ideal, single peak response. The chemical tracer responses seen in our ASP tests are strongly non-ideal, showing multiple peaks. This character is indicative of complicating factors like cross-flow between layers. To understand this complex response we have used numerical simulation techniques to interpret the SWCTTs. The numerical simulation sequence involves the full injection history pre- and post- ASP SWCTT. The reservoir simulator includes the physics of ASP, i.e. interfacial tension reduction and related reduction in remaining oil saturation. To accurately model tracer dispersion effects we used an explicit passive tracer model. This model allows full control of physical dispersion and does not require the use of numerical diffusion to mimic the effect of physical dispersion. The key challenge of matching the tests was to model the non-ideal response, which was different for each well location. A workflow method was developed and applied successfully to achieve a match of all tests. Assisted history matching and normal sensitivity analysis were used to find a range of matches to demonstrate the uncertainty. This paper presents the results of four single well ASP pilots using SWCTT’s, the workflow followed for interpretation, explanation of the parameters varied to obtain the match and numerical simulation tools used to match the SWCTT’s results.