Optimization Technology and Application of Well Structure in Leakage Risk Area of Cangdong Shale Oil Well

The target layer of shale oil well in Cangdong sag of Dagang oilfield is Kong2nd member of Kongdian Formation. The upper well section is prone to loss due to its special lithology, crossing fault and high density drilling to balance disordered water injection system. In the past, the design of three-opening well structure was to seal leak-prone and water-flooding layers, and the technical casing had to run down to the formation of Shahejie or Kong. As a result, the casing footage ratio (the ratio of the total depth of each casing run to the total footage of a single well) was high, the drilling cost was high, and the economic benefit was low. To solve this problem, on the basis of drilling completion and geological data analysis, this paper comprehensively evaluates the feasibility of turning a shallow well with three-open optimization into a two-open well structure in the 4000 m Cangdong shale oil well area, and carries out an optimization design in well GY10-2-2, which is equipped with well trajectory optimization and drilling fluid leakage prevention and plugging safety technology. The successful application of smooth drilling and cost reduction has been achieved. The application shows that: (1) The optimized two-borehole structure is reasonable, which can meet the safety drilling needs of Cangdong shale oil well, and the supporting support technology ensures the downhole safety; (2) After the optimization, the casing footage ratio is reduced from 1.72 to 1.31, and the drilling cost is about 3.408 million yuan. The optimization effect is remarkable, and it can be popularized and applied in the leakage risk well area of Cangdong shale oil well.