Key Drilling Technologies for Complex Fracture-Cavity Formation in Jingyan-Qianwei Area

The Jingyan-Qianwei Area, characterized by complex geological conditions and developed fractures and karst caves, has technical difficulties such as wellbore instability, lost circulation, and drill pipe sticking. In order to solve the problems, the formation three-pressure profiles and the development of karst caves in the area were comprehensively considered to optimize the casing program. According to the geological characteristics of continental formations, an anti-collapse drilling fluid with potassium-based polymers was used to prevent the mudstone from hydration swelling and keep wellbore stability. Based on the types of lost circulation that occurred during drilling, three plugging methods were developed, namely plugging fracture-induced lost circulation with the conventional bridge plugging slurry, resolving severe lost circulation with multi-functional and pressure-bearing consolidation plugging slurry, and handling complicated situations such as multiple loss formations and upper blowout and lower loss with a packer while drilling. Through the research above, key drilling technologies for complex fracture-cavity formation in Jingyan-Qianwei Area were developed. The technologies have been tested in well PR1 in Jingyan-Qianwei Area, the results showed that the technologies can be used to solve problems such as formation collapse and severe lost circulation and keep safe drilling.