Simulation and Evaluation on Polymer Damage near Wellbore Region in Low-Permeability Reservoirs

Polymers are widely used in drilling as a common agent of drilling fluids and their damage to reservoirs is increasingly drawing attention. Based on investigations on the simulation evaluation techniques of polymer damage, a damage model of polymers near wellbore region of low permeability reservoirs was established for a fast and accurate evaluation method. The method of solving differential equations was also given. This method can be used for computer programming. Main factors influencing polymer damage in drilling were qualitatively analyzed by using the proposed model. The results showed that the polymer damage occurred in the vicinity of a wellbore and damage radius and the degree would decrease with the reduction of formation permeability. In addition, the degree of polymer damage would increase as the increase of pressure differential. An increase of polymer concentration could reduce the filter loss of drilling fluid and polymer damage radius. It also showed that capillary force had less effect on polymer damage and the starting pressure gradient might reduce polymer damage. But the influence on polymer damage would be much less when starting pressure gradient was quite low.