MRI Studies of Permeability Control Using Biopolymers

Abstract

ABSTRACTSevere changes in rock permeability among adjacent oil bearing horizons presents an enhanced oil recovery problem. Fluids used to displace indigenous oil tend to follow the high permeability avenues, bypassing large reserves of oil.The use of a modified biopolymer, starch, as a method to enhance oil recovery was evaluated by analyzing: 1) changes in rock permeability caused by the macromolecular gel matrix of the polymer solution, 2) mobility reduction due to the higher viscosity of the polymer solution compared to that of water, 3) the chemical and mechanical stability of the biopolymer at reservoir conditions, 4) the effect of various polymer injection strategies, and 5) sweep efficiencies by Nuclear Magnetic Resonance Imaging (NMR/MRI).Artificially as well naturally consolidated porous media with initial permeabilities ranging from 1,500 to 2,500 md were used. The average permeability reduction was from 1,500 to 500 md when a 1% by weight biopolymer was used. NMR/MRI proved to be a very useful tool to evaluate the effectiveness of a starch biopolymer for rock permeability control. Vertical sweep efficiencies measured by NMR means improved from 25% to 95% with the introduction of the biopolymer. Oil recovery was dramatically enhanced from 2% of the Original Oil in Place (OOIP) using brine as driving fluid to 98% when the in-house biopolymer was used during the displacement tests. Differential pressure (Δp) across 3-inch long samples constantly increased from 10 to 130 psi. A xanthan-gum based commercial biopolymer yielded a recovery of only 58% of the OOIP when used under similar conditions. Displacement experiments were conducted at 1,000 psi and 160°F. The polymer solution exhibited moderate shear thinning viscoelastic behavior and pronounced shear thickening viscosity with increasing brine and polymer concentration.