Application of W/O Drilling Fluid in Horizontal Well with Long Horizontal Sections in Oil Shale Formations

To address the challenges of oil shale formation well wall instability,micro and nano pore blocking, long horizontal section well friction and borehole purification.We have analysed the nature of formation lithology,matrix pore size and specific surface by using linear expansion method,rolling recovery method and nuclear magnetic resonance method,and developed a white W/O drilling fluid system with an oil-to-water ratio of 70:30 by developing emulsifiers,tackifying and shear strength-improving agents,plugging agents and preferably filter loss agents,and wetting agents.The system was evaluated by using the breakthrough pressure test triaxial compression test and relaxation measurement method in the laboratory. The evaluation results showed that the system could not only maintain the strength of the rock sample but also improve the plasticity of the rock sample after the drilling fluid soaked with the breakthrough pressure of 6.5MPa,and it had good suspension capacity after the relaxation value reached 60s.The field test results show that the system has stable rheological properties and solves the problems of well wall instability and borehole purification,with the well diameter expansion rate of only 3.8% and the mechanical drilling speed of up to 10.85m/h.The SY-1 well has set a record for the longest horizontal section of 1800m in the Liaohe River oil area.