Abstract
In this study,a thixotropic and high-strength gel system(THSG)is developed,which is experimentally proven to be feasible for conformance control in fractured reservoirs.The THSG is based on in-situ polymerization of the acrylamide monomer,incorporating a weak gel system.It is found that the superior rheological properties of THSG are beneficial for injection and placement of gelant into the fractures.The viscosity of THSG at varying shear rates can be well fit by the Carreau-Yasuda model,and its shear thinning behavior contributes to low injection pressure during the gelant injection.Moreover,this THSG system exhibits much better thixotropy than the traditional Cr(III)-acetate-HPAM gel system(HPAM/Cr(III)gel),which would enable the THSG an easier access to the small apertures.It is also found that the injection pressure is greatly increased with decreasing of the diameter of aperture during injection of the HPAM/Cr(III)gel,while little effect of the aperture size on injection pressure was observed during THSG injection.Additionally,the yield stress of the thixotropic gelant is noticeably high,which would greatly mitigate the adverse effect of gravity segregation in fractures during well shut-off.This would be also beneficial for plugging the whole fractures.To better understand the properties of THSG,the gelation performance,the microstructure of the gel and the blocking ability of gel in the tubes were investigated.The results show that the clay particles strengthened gel exhibits a large storage modulus and excellent thermal stability.Scanning electron microscopy(SEM)results show that the clay particles were readily distributed on the polymer chains,and the clay particles could facilitate the gel to form a firm and uniform network.Consequentiy,the clay particles strengthened THSG gels have relatively high rupture pressure,which would be exceedingly favorable for efficient gel treatments in fractured reservoirs.
NSTL