Directional Drilling Limits Analysis Based on Downhole Drill String Mechanics for Shale Gas Cluster Well Engineering

Under the uniform parallel well pattern widely used in shale gas cluster well, the directional drilling limits (DDL) can better reflect the productivity of shale gas cluster well than extended-reach limits (ERL). In this paper, the concept of directional drilling limits is proposed to predict the productivity of shale gas cluster well. Around this concept, the forecast model of mechanical directional drilling limits is established by introducing the objective function, geometric constraints, mechanical constraints and operation conditions. A shale gas cluster well developed by Sinopec in Fuling field is analyzed. The mechanical directional drilling limits for different constraints are calculated, and the laws of the directional drilling limits under different operation conditions are analyzed. The results indicate that the cluster well optimized by the established model can drill more horizontal wells than that without optimization. The mechanical directional drilling limits firstly increases and tends to stable with the increases in the holding angles. Besides, running-in is the limit operation in sliding and rotating mode, and high friction coefficient is the fundamental mechanical constraint for directional drilling limits. The constrained optimization model established in this paper can provide a theoretical guidance for shale gas cluster well engineering to improve outputs and avoid drilling hazards.

Automated summary

The concept of directional drilling limits was proposed and a forecasting model was established in this study. The optimized cluster well can drill more horizontal wells, and the mechanical directional drilling limits tend to stabilize with increasing holding angles. High friction coefficient serves as the fundamental mechanical constraint for directional drilling limits.