Application of the new vanishing interfacial tension technique to evaluate miscibility conditions for the Terra Nova Offshore Project

Abstract

Terra Nova oil pool is the second largest oil pool discovered in the Grand Banks of the Canadian East Coast and is under development. As a part of the oil recovery process selection criteria, miscibility conditions were determined for Terra Nova oil with various enrichment levels of gas available from the offshore production facilities using the recently developed vanishing interfacial tension (VIT) technique. The VIT technique is based on the concept that the interfacial tension between the gas and crude oil phases at reservoir temperature must reduce to zero as these two phases approach the point of miscibility. The concept of zero-interfacial tension at miscibility is, in turn, based on the well-accepted fact that the interface between the phases must vanish, as they become miscible with one another. Thus, the minimum miscibility pressure (MMP) and minimum miscibility composition (MMC) can be determined precisely by measuring gas–oil interfacial tension as a function of pressure and gas composition, down to as low an interfacial tension as the measurement technique allows, and then extrapolating the data to zero-interfacial tension. This paper presents the details of this new VIT technique and its evaluation against slim-tube tests, and discusses its application to the Terra Nova gas injection scheme. The interfacial tension data obtained at reservoir conditions using the computerized axisymmetric drop shape analysis (ADSA) technique are presented as a function of pressure, gas composition, and the mode of gas–oil contact (first-contact or equilibrium). In addition to providing visual evidence of miscibility as the point of zero-interfacial tension is approached, the VIT technique is rapid in that it enables the experimental determination of MMP and MMC within about 2–3 days as against 4–6 weeks required by the slim-tube technique.