Drilling Fluid Technology for Wellbore Stability of the Diabase Formation in Shunbei Oil & Gas Field

In view of the complex wellbore collapse and instability during the drilling of the diabase formation in Shunbei Oil& Gas Field, X-ray diffraction, scanning electron microscopy (SEM), high-pressure mercury injection, linear expansion, rolling recovery, triaxial rock mechanics tester, and other methods were used to investigate the fabric characteristics and physical and chemical properties of the diabase formation. Meanwhile, the influence of rock mechanical properties and the drilling tool vibration on the wellbore of the diabase formation were analyzed.The results indicated that the weak surface effect of micro-fractures could easily induce wellbore collapse and instability of the diabase rock mass. In addition, the torsional and lateral vibration of the drilling tool had a greater impact on the wellbore instability of the diabase formation. Then, the density , plugging performance, and rock-carrying performance of the drilling fluid were optimized, and the drilling fluid technology for wellbore stability of the diabase formation was proposed with its supporting drilling technologies developed. The technology was applied in the three-section casing of Well Shunbei X, and the diabase formation with a thickness of 22 m was drilled successfully. During the drilling process, the performance of the drilling fluid was satisfactory, and there were no obvious complications, and tripping operated normally. Furthermore, the average borehole diameter expansion rate of the well section was only 6.0%. The drilling fluid technology for wellbore stability of the diabase formation could ensure the safe and smooth drilling of diabase sections and regular boreholes. Thus, it has an excellent effect on solving the complex wellbore instability of the diabase formation.