Impact of Formation Water Mineralization onOil Displacement by Polymer Solutions

摘要

Mobile metal ions existed in the reservoir impact on polymer sorption as well as onsolution viscosity. Decisive factors of this process are the polymer physical chemicalproperties, characterized by the Henry's coefficient, applicable for its sorption (Г 1) and thereservoir ability to ion exchange, characterized by the Henry's coefficient, applicable for iondesorption (Г 2 ) from the rock. When Г 1 > Г 2 , polymer solution and brine fronts do notinteract at all, and reservoir water mineralization has no any impact on oil recovery factor.When Г 1 < Г 2, interaction zone sizes, adsorbed polymer quantity and phasepermeability reduction, caused by it vary dependent on polymer properties (Г 1). This leads toprevailing either positive factors (phase permeability reduction) or negative factors (polymersolution viscosity lowering and polymer front going behind the water front due to polymersorption) on oil displacement mechanism. The higher reservoir sorption capacity (Г 2), thewider interaction zone between polymer and salts and more intensive ion exchange impact onpolymer flooding process. This is the reason why the polymer selection should be effectedwith due to respect to the reservoir rock ability to ion exchange.Laboratory tests showed that not only water-free ultimate oil recovery, but thedynamic of oil withdrawal in general depends essentially on ion exchange activity (figure).?F and ?COR are the difference between their values at application of the given type ofpolymer and at waterflooding. For the low exchange capacity reservoirs (Г 2) application ofthe polymer solution prepared on fresh water base, is more effective - produced oil has lesswater content F and coefficient of oil recovery (COR) increases. For the high ion exchangecapacity reservoirs (Г 2) impact of the polymer solution based on mineralized formation wateris preferable.