The Behavior of Partially Hydrolyzed Polyacrylamide Solutions in Porous Media

Abstract

Results of laboratory tests show that the extent of polymer adsorption from solution may be quite high if the solution is very saline or is in contact with carbonate rock. They also suggest that solution salinity, flow rate, rock pore size and polymer molecular weight greatly influence the reduction of mobility and permeability by polymer solution. Introduction Polymer flooding is one of the more attractive Polymer flooding is one of the more attractive recovery methods proposed in recent years. Requiring little more technology and equipment than conventional waterflooding, the process is simple to implement. However, its apparent simplicity belies the complicated behavior of polymer solutions in porous media. The argument for polymer flooding is that, in comparison with conventional waterfloods, greater fractions of the reservoir volume may be swept. Increased sweep efficiency, however, depends on lowering the mobility of the injected water for an appreciable distance into the reservoir. The extent of low-mobility penetration into the reservoir is limited in part by penetration into the reservoir is limited in part by adsorption of polymer onto the rock surfaces. The degree of mobility reduction is proportional to the apparent viscosity of the solution and to the reduction in reservoir permeability to water caused by passage of the polymer solution. Several laboratory studies of polymer flooding have been reported recently. These studies have shed light on some particular aspects of polymer solution flow behavior. However, there is still a lack of information defining all the physical variables that control polymer solution behavior. This paper concerns one class of polymers that apparently is being tested widely as an additive for injection water; it is partially hydrolyzed polyacrylamide. The present investigation surveys some ways in which polymer solution properties are affected by polymer molecular weight, rock and fluid properties, polymer molecular weight, rock and fluid properties, flow rate and temperature. Experimental Polymer Solutions Polymer Solutions Samples of three different partially hydrolyzed polyacrylamides were examined; all were furnished by polyacrylamides were examined; all were furnished by the same commercial supplier. The three types were all substantially linear and differed mainly in molecular weight. They may be described as follows:Polymer HHighest average molecular weight, between 3 and 10 million. High degree of hydrolysis.Polymer MMedium molecular weight, about 3 million. Degree of hydrolysis essentially the same as that of Polymer H.Polymer LLowest molecular weight. Very low degree of hydrolysis. The preceding description of the polymers is not precise, but viscosity and filtration results given for precise, but viscosity and filtration results given for the polymers below appear to characterize them sufficiently well in regard to the sizes and shapes of their molecules in solution. All polymer solutions were prepared carefully to avoid mechanical degradation of the polymer molecules. Reagent grade sodium chloride and calcium chloride were added to achieve the desired salt concentrations. The concentration units used are gm/100 ml, but are abbreviated as "percent". The solutions were protected from bacteria with a low concentration of formaldehyde. For all flow experiments the polymer concentration was 0.05 percent. The solution pH was 7.0 0.5. JPT P. 148