Abstract
Polymers and gels have been used in the past to reduce water production (water shutoff). However, only a limited number of treatments have been reported as being successful. The control of the placement of the chemicals is key factor ensure the success of water shutoff treatments. Due to the risk inherent in the use of plugging agents (polymers and gels) it became current practice to use zone isolation or dual fluid injection to ensure the placement of the chemicals in the high permeability water bearing water streaks. However mechanical zone isolation is costly and, more significantly, cannot be practiced in most wells.
Polymer and gel treatments without zone isolation (i.e., bullheaded treatments) may be expected to have a wider range of applicability provided the penetration of the chemicals in the low permeability oil bearing streaks is very small. The bridging adsorption of flexible polymers has been identified as a mechanism that can help achieving such low penetration and divert the chemicals from low (oil bearing) to high (water bearing) permeability streaks.
The aim of this work is twofold. First we improve the theory for the bridging adsorption previously presented to take into account the effect of the adsorption energy. Secondly we develop a model for the placement of polymers in linear and radial layered reservoir systems, taking into account the layer and bridging adsorption mechanisms and the Non-Newtonian character of the polymeric fluids. Steady state flow conditions are assumed for mathematical simplicity.
We found that the rheology of the polymer and the layer adsorption as such have a limited influence on the penetration depths of the polymers in the different layers as has been discussed in the literature. When bridging adsorption is taken into account, however, the penetration in the low permeability layers decreases sharply confirming our previous observations. Hence a good bullheaded placement may be achieved if the bridging adsorption is well controlled.
