Trapped Oil in Low-Permeability Zone Unswept by Water Flooding Under Permeability Heterogeneity Can be Mobilized by Ultra-Low Interfacial Tension: EOR Mechanism of Dilute Surfactant Flooding Proved by Low field NMR Core Flooding and Two-Parallel Core Flooding Experiments

摘要

It is a well-known EOR mechanism that residual oil in swept zone after water flooding (including oil drops, films and clusters) can be mobilized by low interfacial tension (IFT) during surfactant flooding. The aim of this work is to investigate if trapped oil in low-permeability zone (unswept by water flooding) can be mobilized or not by ultra-low IFT in dilute surfactant flooding without any additional conformance control treatment using polymer, gel, or foam, etc. Anionic-nonionic surfactant was used to attain ultralow oil-water IFT of 10-4 mN/m at a low surfactant concentration of 0.2wt% under high salinity without adding any additional solubilizer, alkali, alcohols, etc. Using this surfactant solution, low field NMR core flooding experiment was conducted using heterogenous core. This core was drilled from artificial rectangular-sandstone core with two layers (gas permeability in low- and high-permeability layer is 90mD and 1200mD, respectively). Then, two-parallel core flooding experiment was conducted, where two core holders were parallelly installed (one for low-permeability core, one for high-permeability core) to simulate the heterogenous permeability condition.