Abstract
Drilling is being used to access ever-deeper oil and gas reservoirs, thereby presenting various challenges to the design and operation of down-hole tools. Slip inserts are suspension devices that are used to lower the drill pipe into the borehole and lift it to the wellhead, and their performance determines the extended depth of the borehole. In this paper, based on the field and laboratory test of the slip system, parameter sensitivity analysis is applied to the performance of a slip insert to guide the design of the latter. First, a mechanical model is developed of the drill pipe with the slip insert acting on it, and the stress acting on the drill pipe is analyzed theoretically by regarding the drill pipe as a thick-walled cylinder. Next, a numerical model is established to investigate how the slip-insert structure influences the drill-pipe stress, wherein the drill-pipe diameter is 5″ and the axial load is 180 tons. Finally, the results of a series of numerical simulations are presented. For the present slip insert and drill pipe, the optimum slip-insert parameter values are a front-rake angle of 70°, a back-rake angle of 30°, a tooth height of 2 mm, and zero chamfer.
Highlights
Drill bit clamping the DP in this way causes irreversible damage to the outer surface of the DP as well as the slip inserts [13, 14], and the stress concentrations between the slip inserts and the DP can initiate fracture or fatigue, thereby causing the DP to fail in subsequent use and resulting in a serious drilling accident [15, 16]
Based on the finite element method (FEM), Tang et al [35] developed a finite element (FE) model to study how the slip-insert geometry affects the mechanical behavior of the DP, but little other research related to optimizing the slip insert can be found. e die marks are likely to give rise to problems related to fracture and fatigue
We develop several variants of the FE model to solve this problem, wherein the frontrake angle (FRA) is 70°, the back-rake angle (BRA) is 30°, and the tooth height is 2 mm. e stress contours of the DP and slip insert are shown in Figures 19 and 20, respectively
Summary
Based on the FEM, Tang et al [35] developed a finite element (FE) model to study how the slip-insert geometry affects the mechanical behavior of the DP, but little other research related to optimizing the slip insert can be found. For a certain part in the contact area of the DP, it is interesting that the stress of the inner surface is higher than that of the outer surface, which means the crush
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