Experimental Study on the influence of Positive Gel Drilling Fluid on Shale Wellbore Stability

Due to the diversity and heterogeneity of shale composition, the surface of shale is negatively charged and contains clay minerals. When exposed to water, shale is prone to hydrolysis, which is not conducive to the stability of shale formation. Therefore, in this paper; we have optimized the formulation of the positive-gel drilling fluid that can effectively reduce the surface tension and increase the contact angle between the drilling fluid and the shale. To study the parameters of the optimized formula, the basic performance test, swellability test, and rolling recovery test of the water-based drilling fluid were carried out. The results show that both the organic positive gel MMH-1 and inorganic positive gel MMH-2 can effectively reduce the electrical properties of the shale surface. The drilling fluid containing a composite positive gel 0.6% MMH-1 + 1.5% MMH-2 can reduce the surface tension of the shale by 15.2% and increase the contact angle of the shale by 22.1%. The temperature resistance of the composite drilling fluid B is satisfactory, and the rolling recovery rate is as high as 98.4%, which can effectively enhance the stability of the shale formation.