Pilot Test of Surfactant/Polymer Flood with Mixtures of Anionic/Cationic Surfactants for High-Temperature Low-Permeability Sandstone Reservoir

Abstract

Summary The first pilot test of a surfactant/polymer (SP) flood in the world with mixtures of anionic/cationic surfactants (Sa/c) was performed in a high-temperature and low-permeability sandstone reservoir with a high content of clay to demonstrate the potential of this novel technique to improve oil recovery. Low critical micelle concentration of 2.78×10−6 mol/L, ultralow interfacial tension (IFT) of 10−3 to 10−4 mN/m when surfactant concentrations were greater than 0.025 wt%, and lower phase microemulsion with solubilization ratio of 22, as well as oil-washing rate of 61%, were obtained by using Sa/c. Carboxymethylcellulose sodium was adopted as an adsorption inhibitor (AI) to reduce the adsorption because of the high clay contained in the natural core. With the addition of AI, dynamic adsorption of Sa/c was approximately 0.30 mg/g sand, and the IFT remained nearly unchanged before and after adsorption. The viscosities of polyacrylamide with molecular weight (MW) of 6.16×106 daltons and SP were 3.0 and 4.1 mPa·s, respectively. Coreflooding results showed that more than 16% of original-oil-in-place (OOIP) crude oil was recovered by SP over waterflood. The pilot test of SP containing Sa/c was performed in a Sinopec reservoir with temperature of 83°C, salinity of 1.69%, permeability of 41.5 md, and clay content of 10 to 16%. A total of 0.40-pore volume (PV) chemicals, including 0.1-PV polymer preslug, 0.25-PV SP main slug, and 0.05-PV post-polymer drive, were injected from August 2012 to December 2017 with an injection rate of 0.08 PV/yr. Then, waterdrive was conducted. Maximal water cut decreased from 82.2 to 62.1%, and the peak daily oil production increased from 12.2 to 32.3 t. The oil recovery was increased by 8.0% of OOIP within 4 years.