Abstract: Mesozoic volcanic rock formations in Bohai Oilfield have geological characteristics, such as abnormal pressure traps, well-developed fractures, and frequent lost circulation, etc. Based on the special requirements for protecting the reservoir using solid-free drilling fluids, an in-depth analysis of the high risk of lost circulation faced during the drilling process of exploratory wells in deep Mesozoic volcanic rocks in Bohai Oilfield was conducted, as well as the technical difficulties such as poor temperature resistance of high temperature-resistant solid-free drilling fluid, low rate of penetration due to high formation hardness, and well deviation caused by strong heterogeneity. By studying the lost circulation prevention and control technologies, solid-free drilling fluid with high temperature-resistant and high-density, drilling speeding-up technologies, and dynamic deviation prevention bottom hole assembly (BHA), the key drilling technologies for exploratory wells in deep Mesozoic volcanic rocks in Bohai Oilfield were formed. The technologies were applied in two exploratory wells in deep Mesozoic volcanic rocks in Bohai Oilfield, significantly improving the drilling efficiency, reducing the drilling cost, and yielded high production rate during testing. Research and field applications show that the developed key drilling technologies can solve the technical difficulties of drilling exploratory wells in deep Mesozoic volcanic rocks in Bohai Oilfield. They can also provide technical support for the subsequent exploration and development of Mesozoic volcanic rock formations in Bohai Oilfield and has important reference value for oil and gas exploration under similar complex geological conditions.