Friction Reduction for Microhole CT Drilling

Microhole coiled tubing drilling is a new technology that provides many added advantages but at the same time poses numerous operational challenges. This manifests itself in a number of ways, all of which adversely affect the efficiency of the drilling process. These problems include increased wellbore friction, poor hole-cleaning, tubular failures, and associated problems during tripping operations. Presently conventional torque and drag models are used to calculate drag forces and surface loads during microhole coiled tubing drilling. However, these estimates might be under conservative. Therefore, an improved model and more comprehensive analysis are required. Conditions expected during microhole coiled tubing drilling are completely different from those encountered during conventional drilling. Further complexity is added when the wellbore is undulated. This paper describes a new analytical model for estimating drag forces by assuming that pipe in the horizontal portion follows a sine function wave due to residual bends and snubbing force. In addition, the model takes into account when the wellbore is also tortuous. Fluid viscosity (an important force in the microhole) is also included so we can calculate appropriate surface loads in addition to drag. This study concludes that besides wellbore inclination, curvature, and wellbore torsion, parameters such as wave length and contact area also influence the results. This paper documents the comparison between the predicted mathematical simulation results with actual data from wells describing the accuracy and applicability of the model. The analysis results and comparison are presented along with three examples.

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Axial Load Peristaltic Transfer Mechanism of the Drillstring to Improve Penetration Rate

Wang,

Cao,

Zhang

et al. 2024

SPE Journal

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Summary During the drilling of long horizontal wells, the significant frictional resistance generated by the wellbore walls poses a challenge for the drillstring to efficiently transmit load to the drill bit, which eventually reduces drilling efficiency and restricts the extension distance achievable. Inspired by the structure and movement principle of an earthworm, we propose an earthworm-like load transfer method for the drillstring to address this issue. Specifically, the proposed method involves the installation of a pulse generator and multiple vibration subs within the same drillstring, decomposes the drillstring into multiple sections and modulates it to creep like an earthworm, thus facilitating load transfer. Experimental studies and numerical simulations were conducted in this paper to explore the fundamental mechanisms of earthworm-like crawling, aiming to enhance the efficiency of load transfer within the drillstring. The experimental results suggest that adopting earthworm-like excitation can increase the load transfer efficiency of the drillstring by 36–52% compared to conventional drilling methods. However, if the drillstring experiences helical buckling, there is a significant decrease in the efficiency of load transfer. Meanwhile, a dynamic model of the drillstring, considering the 3D wellbore trajectory, multipoint excitation, Stribeck friction, and penetration rate, has been developed. The simulated results from the proposed model align well with the experimental results obtained before the drillstring buckling, with an error of less than 5%. The simulation results for a 1000-m drillstring indicate that the earthworm-like excitation significantly enhances the efficiency of load transfer compared to conventional drilling methods. This improvement is attributed to the increase in the proportion of reverse-motion drillstring segments by 35.8–40.25%, which will greatly reduce the instantaneous total vector frictional force of the entire drillstring.

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Friction Reduction for Microhole CT Drilling

Cited by 3 publications

References 0 publications

Dynamic modeling and load transfer prediction of drill-string axial vibration in horizontal well drilling

Dynamic modeling and load transfer prediction of drill-string axial vibration in horizontal well drilling

Analytical Model to Estimate the Drag Forces for Microhole Coiled Tubing Drilling

Axial Load Peristaltic Transfer Mechanism of the Drillstring to Improve Penetration Rate

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