Abstract
This study investigates stuck pipe mechanisms that pertain to rock cuttings under various operations.First,a transient two-layer model considering cuttings sliding down is established.The static friction of the cutting bed is derived dynamically to determine the slip point.Next,a simple method is proposed based on the wetted perimeter to obtain the pipe's different shear stresses during tripping in and out.Finally,various operations,such as pipe connections and tripping with or without circulation,are simulated flexibly by combining the pump on or off and pipe moving in or out based on an extended reach well.The results demonstrate that three kinds of tight spots due to rock cuttings are predicted precisely.The first type is cutting slippage when the pump is off.The most heavily stacked interval is at an inclination of 40°-60°,which is close to the angle of repose.The stacking height increases significantly with initial height and time,approximately 1.06-1.75 times the initial height for 10 min and as high as 1.33-4.18 times for 60 min.Second,the cuttings pile up behind the connectors,and as the diameter increases from 0.16 to 0.28 m,the bed height increases from 1.04 to 1.68 times the original height.In addition,tripping out hastens the rate of growth.The stacking height behind a connector is approximately 1.1-1.5 times the original height under a tripping speed of 0.1-0.8 m/s.Third,several dunes are formed during the iteration of drilling and washing,and the peaks are well-matched with tight spots encountered in actual drilling.The number of dunes-i.e.,the high-risk tight spots-increases with increasing well depth and decreases with increasing washing to drilling time and the flow rate.Moreover,at the surface,cuttings may emerge in 2 or more distinct waves and with a large lag between each wave during circulation.The results serve as an essential guide to predict and control tight spots more accurately for hole cleaning of stuck pipes.
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