Wellbore Flow Model and Process Optimization for Gas-Lift Leakage Drilling for Shallow Shale Formations

[Image: see text] The shallow surface karst landform in the Nanchuan-China shale gas area, with developed caves and underground rivers, frequently lost circulation during the drilling operation. To solve the issue, first, according to the actual drilling engineering, this paper analyzes the geological factors and drilling and completion characteristics, optimizes the construction plan, and suggests a new technology for gas-lift leakage drilling based on double-wall drill pipes. Second, a distributed coupling improved Beggs–Brill gas–liquid–solid multiphase flow model is established. This model is used to complete the optimization design of the gas-lift leakage penetration construction scheme of the well sy20-2. Finally, the accuracy, process feasibility, and effect of the model are verified after the field application. The test results show that this method can establish a full drilling fluid circulation without plugging the leakage, control the leakage rate to within 0.5 m(3)/h, more than 90% reduction in the loss of circulation, and significantly shorten the nonproduction time limit with good application prospects.