As oil and gas reservoirs mature, water production increases. Several techniques are used for water shut-off and one of these techniques is the polymer flooding which is known to be cost effective. Saudi reservoirs are known for their high salinity and high temperature. In addition, these reservoirs are mostly heterogeneous in nature with layering characteristics. Water-soluble biopolymers (e.g. guar and xanthan and mixtures of both) were characterized rheologically in order to be tested for water control in local reservoirs. Pure polymers and polymer mixtures solutions of concentrations ranging from 500 to 3000 ppm were prepared in deionized water and 10% and 20% (w/w) synthetic brine solutions and tested at different temperatures ranging from 25 to 65C. The findings indicate that guar solutions exhibited Newtonian behavior at relatively low concentrations. On the other hand, xanthan gum solutions exhibited shear thinning behavior at all concentrations investigated with higher viscosities than that of guar solutions at the same concentrations. Viscosity of both polymers increases by two orders of magnitude as concentration increases from 500 to 3000 ppm. At high temperature, xanthan/guar gums mixture solutions of 0% salinity show no synergism, however shear viscosity of the mixture increases as xanthan content increases in the solution but does not exceed that of pure xanthan solution. pure guar solution viscosity increases significantly upon incorporating salt. To the contrary, shear viscosity of pure xanthan and xanthan-guar mixture solutions at all mixing ratios decrease and this is clearly seen at higher polymer concentrations. At low shear rate and when xanthan ratio in the mixture is high, inverse-synergism is observed, that is viscosity of mixture is lower than those of pure polymers. Displacement runs were conducted at 65C using 10% salinity solutions of pure guar and xanthan at 1500 and 3000 ppm concentrations. Higher RF and RRF were obtained using xanthan solutions than those obtained using guar solutions at the same concentration. Approximately equal adsorbed layer thicknesses were obtained regardless of polymer concentration with slightly lower values for guar solutions. This indicates that the effective water mobility reduction with xanthan solution is mainly due to the higher xanthan solutions viscosity. The elevated value of the residual resistance factor obtained when flooding with low polymers solutions indicates that brine did not manage to draw great part of the polymer retained

This content is only available via PDF.
You can access this article if you purchase or spend a download.