Thixotropy research of laponite-hydrogel composites for water shutoff in horizontal wells

The thixotropy of the hydrogel determines the ultimate hydrogel filling shape in the annulus between the slotted liners and wellbore in horizontal wells. But the common hydrogel cannot be successfully applied for water shutoff in horizontal wells due to its poor thixotropy. In this work, the nanoparticle laponite (LAP) was introduced into the chemically cross-linked acrylamide gelling solution to develop an excellent thixotropic hydrogel. The effect of LAP concentration on thixotropy was investigated through the hydrogel rheometer at 50 degrees C. It was found that the increase of LAP concentration in gelling solution is advantageous for enhancing the thixotropic performance. At the same time, the freeze-etching scanning electron microscopy (SEM) examinations indicated that the LAP hydrogel had a uniform grid structure, which can be broken easily by shear and restored quickly. The high concentration of inorganic salt in gelling solution will reduce the ability of LAP to improve the thixotropy of the gelling solution. Particle size distribution experiments demonstrated that the effect of CaCl2 on the particle size distribution of LAP is more remarkable than that of NaCl when their concentrations are the same. The effect of temperature on thixotropy was also investigated by the hydrogel rheometer. It shows that the increase of temperature will reduce the shear thinning effect of LAP hydrogel. This is because increasing the temperature leads to an increase in the dissociation of hydroxyl groups on the side surface of the LAP particles, which not only increases the pH of gelling solution but also increases the positive charge on the side to facilitate the aggregation of particles. The research results can enrich the rheological theory of nanoparticle/polymer. This study also provides technical guidelines for further increasing the thixotropy of polymers that are commonly used in enhancing oil recovery.

Automated summary

The research successfully developed a thixotropic hydrogel modified by nanoparticles laponite, showing that increasing LAP concentration can enhance the thixotropic performance of the hydrogel. In addition, a high concentration of inorganic salt will reduce LAP's ability to improve the thixotropy of the gelling solution.