Drilling Design and Construction of a Discovery Well in Bozhong 26-6 Oilfield

The Bozhong 26-6 Structure in Bohai Oilfield has a superior background of oil and gas accumulation in the Archaean group, and the buried hill is subject to long-term erosion, which thus has good reservoir conditions for facilitating reservoir formation. In order to clarify the reserves of the Archean buried hill at the east high point of the structure and explore the buried hill accumulation model, it was decided to drill Well 26-6-2 in this structure, and the main target layer was the Archean buried hill. However, the geological condition of Well Bozhong 26-6-2 is complicated, and drilling is thus difficult. Therefore, the main drilling lithology and drilling technological difficulties of the well were analyzed, and it was considered that the well was faced with some problems such as a high risk of leakage, easy wellbore instability, easy well deviation, and high risk for well control. To this end, a series of optimization designs for the well were carried out from the aspects of the casing program, drill bit, acceleration tool, bottom hole assembly, and drilling fluid. During the on-site construction, in order to separate the weathered crust and the inner cover in tests, the design had been innovatively updated, and a one-section was added. The liner smoothly entered the inner cover of the buried hill and successfully sealed the pipe shoes. Finally, the test of Well Bozhong 26-6-2 obtained industrial oil flow, and a Bozhong 26-6 Oilfield of a hundred million tons was discovered. The relevant drilling technologies can guide the subsequent drilling design and on-site construction of Bohai Oilfield.