Effectiveness of Surfactant-Polymer Flooding at High-Temperature and High Salinity Reservoirs: Moderate-Low or Ultra-Low Ift?

Abstract

Abstract To implement an effective chemical flooding process in enhanced oil recovery in a sustainable way, it requires a careful selection of surfactant-polymer (SP) formulation, regarding on the interfacial tension (IFT) with oil. Usually, a unltra-low IFT is preferred to achieve a low residual oil saturation and a high oil production rate. The question is how low of the IFT is enough for an effective oil production. Targeting at high temperature and high salinity carbonate reservoirs, this work deeply discussed the interfacial tension (IFT) factor on the effectiveness by injecting two SP formulations with similar viscosity but moderate-low and ultra-low IFT respectively. The SP formulations BC-O1/PST-10 (zwitterionic surfactant / sulfonate polyacrylamide) and APA-H1/SPAM-A5 (zwitterionic surfactant / sulfonate polyacrylamide) were selected since their good compatibility with a high salinity brine with total dissolved solids of 57,670 ppm. The IFT measurements of both SP formulations were conducted using a spinning drop tensiometer (SVT20N, Dataphysics) at a temperature of 90 °C. The rheological properties were measured using a rheometer (Discovery HR-2, TA Instruments). And the injection of BC-O1/PST-10 and APA-H1/SPAM-A5 for oil displacements was performed in a homogeneous medium oil-wet microchannel slice at 90°C, following a water injection process. The incremental oil production rate was calculated from the microchannel images. It was observed that the IFT values between oil and the SP solution composed of BC-O1/PST-10 and APA-H1/SPAM-A5 are in the moderate-low range (10-2 mN/m) and ultra-low range (10-3 mN/m), respectively. It also presented the viscosities of the polymer solutions are similar when polymer concentrations were at 2,000 ppm, which ensured a similar sweeping efficiency in the displacing process. The oil displacement experiments showed the incremental oil production rate of BC-O1/PST-10 injection (40%) was a little higher than APA-H1/SPAM-A5 injection (37%) though the IFT was a magnitude higher. This study presented that in oil-wet or mixed wet carbonate reservoirs, despite IFT factors, other influences such as surfactant-polymer interactions also play an important role. The moderate-low IFT could be sufficient for SP flooding in high salinity high temperature reservoirs. This work intends to provide an effective SP flooding technique regarding the interfacial tension. In high salinity high temperature carbonate reservoirs, zwitterionic surfactants with a medium-low IFT for oil production could be a good choice. This gives more options to select green surfactants instead of pursuing lower IFT.