Abstract: The continuous development of ultra-deep oil and gas reservoirs is closely related to the completion design of oil and gas wells. However, due to limitations in drilling equipment, the presence of high-pressure saline layers, geological characteristics such as prone-to-collapse and prone-to-leakage formations, as well as economic evaluation considerations, the completion methods for ultra-deep oil and gas wells exhibit significant diversity (open-hole completions, completions using small-sized reservoir casings not exceeding $\phi$127 mm, and so on). Designs featuring production strings traversing the perforation top boundary and even the perforation bottom boundary are also common, and permanent packers are often preferred. These factors can potentially increase operational difficulties, prolong operation times, elevate costs, and impact well productivity and ultimate recovery rates. By analyzing two already developed ultra-deep oil and gas reservoir blocks as case studies, it was discovered that the accumulation of sand or silt is a crucial factor contributing to low well productivity, subsequently adversely affecting recovery rates. In response, the study proposes that the research and design of ultra-deep well completions should anticipate scenarios of sand or silt accumulation. The objective is to prolong the duration of sand or silt accumulation, thereby creating favorable conditions for subsequent operations and ultimately enhancing recovery rates. To achieve this, the study conducted thorough scientific research and optimization on five key aspects: completion methods, reservoir casing sizes, completion string configurations, packer type selection, and sand pocket designs. Building upon these optimizations, comprehensive calculations were further performed for drilling and completion investments, drilling and completion cycles, and economic evaluation indicators. In cases where economic evaluation indicators fail to meet expectations, increasing single-well production is suggested as a means to resolve potential conflicts between enhancing well construction quality and meeting economic evaluations.

Key words: ultra-deep wells, completion, recovery rate, completion string, economic evaluation