Published October 2026, Pg. 17-21

Section: Well drilling

UOT: 622.276.658.58

DOI: 10.37474/0365-8554/2026-10-17-21

Machine time of drill string descent for one well drilling cycle

Yu.A. Orudjov PhD in Tech. Sc. - Azerbaijan State University of Oil and Industry

F.K. Mammadov - Azerbaijan State University of Oil and Industry

E.N. Salimova - Azerbaijan State University of Oil and Industry

The article examines the problem of determining the machine time required for lowering a drill string during a single well-drilling cycle.
The productivity of drilling rigs during tripping operations is largely determined by the technical condition of the braking systems, the parameters of the hoisting-and-lowering complex, and the depth and conditions of drilling.
The authors analyzed existing methods for calculating the descent time of drilling tools and identified their shortcomings, including the assumption of a constant penetration value per bit run and the failure to account for variable influencing factors.
An improved mathematical model is proposed, based on the sinking curve relationship and accounting for the combined operation of the mechanical and auxiliary brakes of the drilling winch. Correction coefficients are introduced to characterize the dynamics of drill-string descent, the incompleteness coefficient of the tachogram, and the thermal-state parameters of the braking system. The obtained expressions allow us to more accurately determine the machine descent time of the drilling tool at various depths and drilling conditions, which is especially important in the construction of deep wells.
Improving the efficiency of deep well drilling is directly related to reducing the time spent on auxiliary operations, among which tripping operations account for up to 40 % of the total time balance. Existing calculation models often idealize the process, failing to account for the nonlinear increase in time consumption with increasing well depth, as well as the technical limitations of braking equipment under extreme loads. The development of methods that allow the machine time required for lowering the drill string to be objectively evaluated while maintaining structural reliability is therefore a priority task for the oil and gas industry.
The object of the study is the operating cycle of the hoisting system of a drilling rig. The subject of the study is the patterns of variation in machine time consumption depending on well depth, drill string parameters, and braking modes.
The study proposes an integrated approach to calculating lowering time, which, unlike traditional formulas, takes into account the following factors:
Variable footage per drilling cycle: The penetration curve equation is incorporated into the model, eliminating the assumption of a constant number of drill pipe stands per cycle.
Two-stage braking mode: The mathematical model describes the transition from the use of only the main band-and-block brake to the combined operation of the main brake and an auxiliary hydraulic or electrodynamic brake after reaching a critical depth of 1000–1200 m.
Criticism of existing models: It is demonstrated that simplified calculations can result in significant errors in the design of deep wells because they do not account for the thermal loading of the brakes and hydrodynamic resistance in the wellbore.
Analytical relationship: The final Equation (8) has been derived to determine the total machine time required for lowering the drill string throughout the entire well construction cycle. This equation is based on the differential calculation of the lowering time for each individual drill pipe stand.
Thermal factor: The influence of the thermal state of the mechanical brake on the selection of the maximum permissible lowering speed is substantiated. This is a critical safety factor when operating with heavy drill strings.
Practical significance. The obtained results enable engineering and technical personnel to plan well construction schedules more accurately and optimize the operating modes of drilling crews. Application of the proposed methodology contributes to reducing wear of brake bands and sheaves and helps prevent lost circulation and oil and gas influxes caused by excessive hydrodynamic loads during lowering of the drilling tool.
 

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