Application of Internal Olefin Sulfonates and Other Surfactants to EOR. Part 2: The Design and Execution of an ASP Field Test

Abstract

Abstract This paper discusses the design and application of an alkaline-surfactant-polymer (ASP) system for the West Salym field in West Siberia. The discussion in the paper focuses on surfactant selection, and less on polymer selection. The optimum surfactant system for the West Salym crude is a combination of IOS 24-28 (internal olefin sulfonate with a tail length of 24-28 C-atoms) and IOS 15-18 and also includes an alcohol as co-solvent. The IOS surfactants are manufactured commercially by Shell Chemicals as the ENORDET™ O series. In an accompanying paper1 the properties of the IOS family of surfactants are discussed in more detail. For optimum performance, the surfactant needs to be tailored to the crude oil. Although the oil is not too heavy (API density is 30), and has a near-zero TAN, it contains a significant fraction of heavier components such as asphaltenes and resins, which are surface active and can interfere with the surfactant in the oil-brine interfacial layer. It is discussed in the paper how the crude oil composition affects the surfactant selection process. From test results and theoretical considerations, it was concluded that these types of crude require a surfactant with a long alkyl tail, such as an IOS 24-28. Further optimisation of the surfactant formulation was based on phase behaviour, surfactant solubility and core flow tests. To adjust optimal salinity, and to improve solubilisation, a co-surfactant (IOS 15-18) and an alcohol (2-butanol) were also added. Polymer tests were performed as part of the ASP design program. The purpose was to optimise the ASP/oil mobility ratio. Based on filtration and rheology tests, a hydrolysed poly-acrylamide polymer with a molecular weight in the range 5-8 million was selected. The optimised ASP system was tested in the field in a single well chemical tracer (SWCT) test. The test design, execution and result will be discussed in the paper. The goal of the SWCT test was to measure -under field conditions- the ability of the ASP system to reduce the residual oil saturation. A tracer test was performed, to measure remaining oil saturation (ROS), before and after ASP injection. The test was executed successfully. Analysis of tracer response indicated that 90% of the ROS after waterflood was mobilized by the ASP flood.