Rheology and Injectivity Studies on Scleroglucan Biopolymer for Carbonates under Harsh Conditions

Polymer flooding is a mature chemical enhanced oil recovery (EOR) technology with more than 40 years of laboratory- and field-scale applications. Nevertheless, polymers exhibit poor performance in carbonates owing to their complex nature of mixed-to-oil wettability, high temperature, high salinity, and heterogeneity with low permeability. The main objective of this study is to experimentally evaluate the performance of a potential biopolymer (scleroglucan) in carbonates under harsh conditions of high temperature and high salinity. This experimental investigation includes polymer rheological studies as well as polymer injectivity tests. Rheological studies were performed on the biopolymer samples to measure the polymer viscosity as a function of concentration, shear rate, salinity, and temperature. Injectivity characteristics of this biopolymer were also examined through single-phase corefloods using high permeability carbonate outcrops. The injectivity tests consisted of two stages of water preflush and polymer injection. These tests were conducted using high salinity formation water [167,000 ppm total dissolved solids (TDS)] and seawater (43,000 ppm TDS) at both room (25°C) and high temperature (90°C) conditions. The rheological tests showed that the biopolymer has a high viscosifying power, and it exhibits a shear-thinning behavior that is more prevalent at higher polymer concentrations. Also, a pronounced effect was observed for water salinity on both polymer filterability and injectivity. Moreover, the biopolymer exhibited better filterability at the high temperature as opposed to the room temperature. From the injectivity tests, the shear-thinning behavior of this biopolymer in the porous media was confirmed as the resistance factor (RF) decreased with increasing the flow rate applied. The potential biopolymer showed good injectivity at both the room and the high temperatures. A limited number of studies have evaluated the rheological and injectivity performance of this newly developed EOR grade scleroglucan biopolymer in carbonates under harsh conditions of high salinity and high temperature. Most of the previous studies were performed in sandstones under relatively mild salinity and temperature conditions. Hence, this study provides further insight into the performance of this biopolymer and encourages application in carbonates under harsh salinity and temperature conditions.