Numerical analysis of the connector effect on cuttings bed transportation while Tripping

This study investigates the cuttings transport while tripping with a connector. First, a transient two-layer model is enhanced to simulate the cutting transport while tripping with a connector. Two mechanisms are thus analyzed regarding the cutting's pile up around the connectors: on the one hand, the difference in the cross-sectional area around the connectors and the corresponding change in the fluid velocity may cause cuttings to accumulate behind the connectors; on the other hand, the connector will push or pull the bed layer and suspension layer, like a “bulldozer”, which make the cuttings bed pile up behind the connector. Second, the backreaming operation can be further analyzed by combing the circulation and pipe rotation. The results demonstrate that the cuttings pile up behind the connectors while tripping, and the stacking height increases with initial bed height, the tripping velocity, the diameter, and the length of the connector, and decreases with the flow rate. Moreover, the stacking height behind the connector decreases with the drill pipe rotation speed significantly while backreaming, especially when the rotation speed is more than 120 rpm. Furthermore, the safety of the tripping procedure is highly related to the remaining cuttings bed. Thus the total circulation time to remove the residual wavy cuttings bed is optimized, which increases with the flow rate, ROP, the well depth, and initial bed height significantly; however, the total number of bottom-up operations changes very little, basically around 2 to 3. This can serve as a guide to reduce the high-risk tight spots, especially for an extended-reach well.