Drilling difficulties of deep explorations wells in the southwest zone of Bozhong sag and their technical countermeasures

The deep oil/gas bearing structures in the southwest zone of Bozhong sag, Bohai Oilfield have abundant reserves and their development potential is great, but this block is characterized by complex geological conditions, high-temperature and high-pressure target layers, complex pressure systems and poor drillability of deep strata, which bring several challenges to the drilling operation. To deal with the technical difficulties in the deep drilling operation in the southwest zone of Bozhong sag, the casing program of “non-standard borehole + reaming while drilling + non-standard casing” is adopted innovatively to ensure the isolation of setting positions in each horizon and meet the requirements of formation evaluation. A set of full-hole ROP (rate of penetration) improvement technologies are formed by optimizing the BHA (bottom hole assemblage) based on the conditions of different hole sections, so that the rock breaking efficiency is improved greatly. A high-temperature, solid-free drilling fluid system with the capacity of reservoir protection is developed, whose limit temperature tolerance is increased from 170 ℃ to 200 ℃, so as to meet the performance requirements of reservoir protection in buried hills. The precise pressure technology is developed for buried hill reservoirs to improve the ROP, which effectively alleviates the risks of lost circulation and pressure difference induced pipe sticking in buried hill reservoirs. The research results play a guiding role in ensuring the safe drilling, ROP improvement and cost reduction of deep exploration wells in the Bozhong area.