Application of microgel latex in water-based drilling fluid to stabilize the fractured formation

Fractured formations are complex formations often encountered during oil and gas drilling. Conventional methods such as plugging formation fractures and pores, improving cutting-carrying efficiency, and inhibiting hydration of cements cannot effectively solve the problem of wellbore instability in fractured formations. In this paper, an adhesive microgel latex (MGL) was prepared to improve the cementing strength of fractured forma-tions. The morphology and thermal property were analyzed by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), etc. The plugging effect of MGL was then studied by visualized plugging experiments and high temperature and high pressure (HTHP) plugging experiments. The evaluation methods for strength-ening fractured formation were established, including immersion test, single lap test and compressive strength test, and applied to evaluate MGL. The experimental results show that MGL were spherical particles with a median particle size of 38.9 & mu;m and a glass transition temperature of 61.98 degrees C. MGL could effectively decrease drilling fluid intrusion and plug fractured formations. Wellbore strengthening experiment showed that MGL could enhance the cementing strength of fractured formations. MGL greatly improved the tensile shear strength between core pieces and cementation strength of the fractured formation. After treatment of MGL, the tensile shear strength between core pieces increased by 81.2% compared to asphalt, and the compressive strength substantially increased for both wet and dry sand cores. The mechanism analysis suggests that the adsorption between MGL and rock matrix and the self-adhesion among MGL particles are responsible for wellbore strengthening. This paper innovatively proposes the use of adhesive particles to enhance wellbore stability in fractured formations.