Determination Of Polymer Molecular Weight For Polymer Flooding In Low Permeability Reservoirs

Experts and scholars at home and abroad have had a lot of work on polymer flooding for low permeability reservoirs, pointed out that we can carry out polymer flooding in low permeability reservoirs, but must give full consideration to the polymer injection performance and the inaccessible pore volume, namely, we must choose the polymer relative molecular mass matching with permeability. The purpose of this paper is to establish evaluation methods of the polymer injection performance, establish the chart of polymer injection pressure and relative molecular weight、concentration on the different permeability condition, provide guidance on how to select the polymer relative molecular mass with good injection and oil displacement effect for the site.The results show that the expression of good injection is:(1)there is showing polymer injection platform or pressure rise is slow on the polymer injection phase, subsequent water flooding pressure drops rapidly, leveling off, and the residual resistance coefficient is generally less than 5;(2) Polymer solution has good migration performance in formation, inlet pressure is stable, the ratio of the measured side hole pressure and computing side pore pressure Pbr is bigger. Establish the chart of polymer injection pressure and relative molecular weight、concentration, provide guidance on select the suitable polymer relative molecular mass. Viscosity constant, polymer solution with different relative molecular mass have different injection performance, but have the same effect of enhancing oil recovery. The inaccessible pore volume have bad influence on enhancing oil recovery under the same viscosity of oil displacement system. For low permeability reservoirs, enhancing oil recovery of pure polymer flooding is limited, because restricted by injection.