Effects of Fracture and Matrix on Propagation Behavior and Water Shut-off Performance of a Polymer Gel

The influence of reservoir parameters on water shut-off treatment in hydraulic or natural fractured reservoirs remains unclear. In the present study, effects of fracture width and matrix permeability on propagation behavior and water shutoff performance of a polymer gel have been investigated. Results show that the fracture width can greatly affect the injection pressure of the gelant, but the effect of the matrix permeability is relatively slight. During the gelant propagation in fracture, because of the concentration and pressure differences, the gelant loses itself from fracture into matrix to form a gelant filter cake on the fracture face. The smaller the fracture width is, the greater the gelant loses; moreover, a higher gelant loss degree occurs in relatively high permeable matrix. After the cross-linking reaction between polymer and chromium, the gelant filter cake becomes into a gel filter cake. The cementing strength of the gel filter cake and the strength of the gel inside fractures greatly affect the shut-off performance of the gel for fractures. Therefore, an appropriate loss degree of the gelant which improves the thickness and the rigidness of the gel filter cake can enhance the water shut-off performance. Moreover, due to that both the narrow fracture and the high permeable matrix contribute to the gelant loss, the polymer gel presents favorable water shut-off performance in cores with a small fracture width or high permeable matrix.