Abstract: This paper focuses on the problems such as “leakage before flowback” and “leakage in the same layer” when drilling in the horizontal member of Sankai Baijiantan Formation in Mahu 401 Well area, which makes it difficult to greatly improve the pressure bearing capacity. It is found that the Baijiantan Formation has the characteristics of strong permeability and micro-fracture development, and it is easy to produce micro-cracks with the increasing well depth, stress and external force. After the intrusion of drilling fluid filtrate into the well wall, micro-cracks continue to expand, resulting in frequent complications such as well loss. Considering that the crack width of the sampled core of Baijiantan Formation in Mahu 401 Well Area ranges from 1 to 30 μm, multi-micron grade plugging materials are used for optimization, and combined with the optimization of other treatment agents, a set of pressure plugging water-based drilling fluid system and supporting construction technology suitable for this well area are established. The application shows that the maximum leakage velocity, leakage volume and plugging times of the test well are significantly reduced, which indicates that the plugging material has formed an effective sealing and plugging slug, thus improving the pressure bearing capacity of the formation, and its leakage prevention and plugging effect is remarkable.

Key words: Mahu 401 Well Area, micro-nano plugging, bearing capacity, leak resistance and sealing, water-based drilling fluid