Thermo-Dissoluble Polymer for In-Depth Mobility Control

Gel treatments have been implemented as a cost-effective method for plugging high-permeability zones and thus improving sweep efficiency in reservoirs. However, when extensive cross-flows exist between formation layers, near wellbore gel treatments become less efficient. Polymer was used in polymer flooding to increase the viscosity of the injected fluids in order to improve the oil recovery. However, the efficiency of polymer flooding is limited by the dramatic viscosity loss (80–90%) caused by various shearing degradations during the polymer injection process and polymer transport at extremely high flow rates in near wellbore formations. This research focused on developing a novel polymer, which first is injected into fractures or fracture-like features as a millimeter-sized particle gel (50 um to a few millimeters) and acts as a plugging agent, and then dissolves into polymer solution at a designated time (e.g., 6 months) due to the reservoir's temperature; the dissolved polymer seeps into the depths of the formation to behave as a mobility control agent. The polymer dissolution process occurs under reservoir conditions, so the polymer's viscosity will not be influenced significantly by the degradations from pump, wellbore and near wellbore porous media. This paper will report the evaluation results of the new product. Several evaluation methods have been established to characterize the properties of the new polymer system before and after their dissolution. It has been found that the time it takes for the solution to dissolve depends primarily upon the reservoir temperature and liable crosslinker concentration. ESEM pictures revealed that the 3D polymer network of novel particle gel transformed into linear polymer after the polymer gel totally dissolved. Coreflooding experiments showed that the dissolved polymer exhibited excellent water resistance.