SCA2006-54 1/6 MEASUREMENT AND MODELING OF GAS-OIL MISCIBILITY FOR IMPROVED OIL RECOVERY Subhash C. Ayirala and Dandina N. Rao 1 The Craft & Hawkins Department of Petroleum Engineering Louisiana State University, Baton Rouge, LA 70803-6417, USA This paper was prepared for presentation at the International Symposium of the Society of Core Analysts held in Trondheim, Norway 12-16 September, 2006 ABSTRACT Laboratory measurement as well as modeling of gas-oil miscibility conditions are essential for success of any gas injection improved oil recovery process in the field. The conventional slim-tube technique currently used by industry for gas-oil miscibility evaluation is time consuming (4-5 weeks) and is not cost-effective. However, recently a new experimental technique of vanishing interfacial tension (VIT) has been reported, relating miscibility with interfacial tension. This technique is based on the concept that, at miscibility, the value of interfacial tension between the two phases is zero. This new technique, being rapid, enables cost-effective determination of gas-oil miscibility. In this paper, we discuss the experimental measurements of gas-oil miscibility conditions determined using the VIT technique for a simple standard gas-oil system as well as for a complex real crude oil-solvent system. The gas-oil interfacial tension measurements reported in this study were made using the pendent drop shape analysis and capillary rise techniques. The paper also provides experimental validation for VIT technique by comparing the results of gas-oil miscibility with the other conventional techniques. The gas-oil miscibilties measured were effectively modeled in both the systems studied, using the mechanistic modification of Parachor model for mass transfer effects. This study thus demonstrates the usefulness of a new technique, with supporting experimental data and modeling results, for optimization of miscibility conditions in gas injection improved oil recovery field projects. 1. INTRODUCTION Miscible CO 2 gas injection has become one of the most effective improved oil recovery (IOR) processes for light and medium oil reservoirs in United States today. Out of 1581 large reservoirs covering almost all the ten basins in US, 1035 reservoirs have been screened to be favorable for implementing CO 2 gas injection IOR (Advanced Resources International, 2006). Among these 1035 reservoirs, about 900 reservoirs are concluded to be amenable for miscible CO 2 gas injection IOR. This clearly shows the growing importance of miscible CO 2 gas injection in the US IOR scenario. There is about 374 billion barrels of trapped crude oil in depleted oil fields in the US alone and it is possible to recover about 160 billion barrels of this trapped oil using the CO 2 IOR technology 1 To whom correspondence should be addressed Fax: 225-578-6039; Phone: 225-578-6037; e-mail: danrao@lsu.edu