Vadim Tikhonov

Method of Dynamic Analysis for Rod-in-Hole Buckling

The problem of a postbuckling dynamic behavior of weighted rod, which is inserted into an arbitrary profile hole with some clearance, under the axial compression load is considered. In practice, this analysis is important for calculation of the friction drag of the drillstring in inclined and horizontal wellbores. The mathematical model and numerical method of the rod-in-hole contact interaction are developed. The contact model is based on a nonlinear dependence of the normal-directed contact force on the depth of interpenetration of rod in hole. The tangential interaction of bodies with the contact surfaces is described using a model of “elastic-plastic” friction. The developed system of substantially nonlinear differential equations with partial derivatives of 3-D rod dynamics is approximated by the finite differences and integrated by the Runge-Kutta method. A simplified model for axial motion of rod is suggested to make the process of numerical integration faster. The results of numerical simulation of stress-deformed state of rod in horizontal, inclined and curved holes are presented. The results of numerical simulation are compared with the results of experiment. The effect of the friction factor on the rod buckling has been studied. The effect of local outside bulges of the drillstring on a postbuckling behavior of the drillstring is considered.© 2006 ASME

Numerical Simulation of the Drillstring-in-Hole Dynamics at Rotary Drilling

A numerical solution is suggested for the problem of drillstring buckling under the action of compressive load, torque and drillstring rotation in a hole of an arbitrary axial line. This problem is of great practical importance when assessing the pass ability and wear of drillstring. The developed 3D dynamic model of drillstring-in-hole and numerical solution of the problem provide a means to analyze stress-deformed state of the drillstring in contact with the wellbore. The model of normal contact force is based on nonlinear dependence of the contact force on the depth of interpenetration of bodies. The tangential contact is described using a model of modified Coulomb friction. The model of transition of sliding friction to rolling friction is suggested to take account of the effect of drillstring planetary motion. The set of partial differential equations is solved numerically based on the method of lines. A number of examples are presented to analyze the drillstring motion under the action of compressive load, torque and angular velocity, and other parameters.Copyright

Numerical Simulation of Well Trajectory While Drilling Isotropic and Anisotropic Formations

In spite of research efforts to develop a numerical model for predicting wellbore trajectory, there isn’t an adequate model for simulating new hole creation and predicting wellbore curvature and build rates that accounts for bottomhole assembly (BHA) dynamics, geometric constraints, rock properties, and steering tool action.This paper presents new, comprehensive 3D model of BHA dynamics for lateral and torsional modes of motion. This model includes the presence of stabilizers and sections with different geometric and mechanical properties along the BHA. It considers changes in trajectory due to action of bent subs or rotary steerable systems (RSS); allows for abrupt changes to friction factors during transitions from sliding to rolling motions in the wellbore; and accounts for the effects of the bit’s side-milling capacity and side load changes due to changes in the formation.The DYNTUB software, an advanced simulation tool for predicting well trajectories while drilling, was developed based on this model. This paper presents a mathematical model for the BHA and the well trajectory, the numerical integration method, and the results calculated for various examples steering tools and formations.Copyright

Modulation equations for slug flow in vertical pipes

A gas−liquid flow in a long vertical pipe is considered. A new mathematical model of the flow generalizing the known drift-flux model is constructed. The gas velocity and the average flow velocity in this model are connected by the Zuber−Findlay relation. The model is obtained by averaging the quasi-periodic slug flow regime. Contrary to the drift-flux model, it is possible to restore the internal structure of the flow and, in particular, to give the criterion of transition to the new regime.

Lagrangian approach to modeling unsteady gas-liquid flow in a well

The purpose of this paper is to develop a numerical method of solving the problem of evolution of the finite gas volume that entered in a liquid flow at a set flow rate. The drift- flux model is used as gas-liquid mixture equations. The velocities of both phases, mixture and gas, are related by the Zuber-Findlay equation which coefficients depend on flow regime and gas void fraction. Lagrangian coordinates are used to simplify the initial equations. The numerical solution scheme is proposed. The numerical solution of the Riemann problem is verified by comparison with the exact self-similar solution. The model and numerical method efficiency is illustrated by examples of gas kick calculations in a vertical well.

Aluminum Catenary Production Riser: Design, Testing Results, Ways to Improvement

One of the widely used systems for offshore oil production in water depths up to 500–2500 meters is a steel catenary riser (SCR). Requirements for long-term corrosion resistance of SCR are very stringent, that obliges to manufacture it from expensive steels. Still, the increased water depth leads to increased riser tension, grown pressure, aggravated buckling and oscillation problems. Among alternative materials to manufacture catenary risers, i.e., steel, titanium and aluminum alloys, the aluminum is the best from the “Strength/Weight/Cost” aspects with its high corrosion strength.Design of an aluminum catenary production riser (ACPR) was developed in Russia; and comprehensive tests were performed on mechanical characteristics and corrosion resistance properties of ACPR tubes and their connections. Two possible connections of riser sections were considered, i.e., welded and threaded. Strength analysis of threaded connection was performed by FEM.Mechanical testing included: testing of small samples of pipe material and welded connection cut out of riser section, testing of full-scale specimens of connection prototypes, and measurement of residual stresses. Structural and corrosion tests of samples consist of investigation of standard metallographic characteristics of pipe material and welded connection, and assessment of effects of different types of corrosion in seawater and oil fluid. The results of performed work have led to the conclusion that welded connection is most prospective for ACPR manufacturing. At the same time, the testing revealed certain improvements need to be done in the course of further work on this project.Copyright

Aluminium Pipes - a Viable Solution to Boost Drilling and Completion Technology

The modern Ultra Extended Reach Drilling projects become more and more challenging. Some of the lately drilled ERD’s probably reached or came close to the edge of available drilling technology. The most breathtaking well was Maersk BD-04A completed by May 2008 offshore Qatar with 12 290 m (40 320 ft) TMD and 11 569 m (37 956 ft) departure [1]. Other wells with less TMD are as much complicated as BD-04A.

Analysis of Postbucking Drillstring Vibrations in Rotary Drilling of Extended-Reach Wells

One of the most serious concerns of extended-reach drilling is the dynamic behavior of the drillstring and cleaning of well. Good cleaning requires an increased angular speed. However, at higher rotary speeds, the drill string sections lying on the borehole horizontal sections tend to buckle, first, in the form of “snake”, sliding up and down the borehole bottom wall, and then in the form of whirling as the angular velocity increases. This paper presents the 3D nonlinear dynamic model of drillstring in a wellbore of 3D profile. The model suggests the possible contact/lift-off of drill pipes with/from the wellbore wall. The interaction of lateral, torsion and axial vibrations is taken into account. The relation between the normal component of contact force and the deformation of the wellbore wall is taken as quadratic-elastic. The friction force is described based on a hysteretic dynamic model. The friction force model also takes into account the transition from a sliding to a whirling. The equations of the drillstring dynamics are solved numerically using the method of lines. The DYNTUB computer program is developed to analyze the drillstring time-varying processes under different loading. The program is used to study the effects of the angular velocity, compression load, torque, friction factor, well profile, and availability of connectors on the drillstring dynamic behavior.Copyright

Stick-Slip Model for PDC Bits Accounting for Coupled Torsional and Axial Oscillations

Drilling with PDC bits can cause severe torsional and axial oscillations. These oscillations are accompanied by periodic sticking of the bit followed by accelerated rotation. The so-called “stick-slip” increases bit wear and fatigue and causes premature failure of BHA and drillstring components. It is well known that these torsional oscillations are nonlinear and self-induced. The present study investigates the coupling between axial and torsional oscillations.The cutting process is based on the Detournay model, which provides for the effect of the bottomhole pressure and the local pore pressure. The axial stiffness of the drillstring is taken into account with the axial motion equations coupled with the torsional equations, in contrast to previous models where axial equations were considered independently. Axial oscillations are allowed to occur even when the bit is in the stick phase. The new model also includes bit “bouncing” when it loses contact with the bottomhole. The equations are solved by time integration. By results of the analysis of transient processes the spectral density is determined.The objective of the paper is to improve understanding of stick-slip oscillation nature and assess the contribution of parameters that influence their intensity.The study includes the effect of the rotor rpm, intrinsic specific energy of rock, number of PDC blades, wear flat length of blades, etc.Results of the study will help drillers to select and change drilling parameters more efficiently to reduce severe stick-slip oscillations.© 2014 ASME

Comparative Strength Analysis of Aluminum Drill Pipes With Steel Connectors Assembled by Different Methods

Aluminum alloys continue to be among the promising materials for manufacture of drill pipes and risers for deepwater and ultra-deepwater environment. Steel tool-joints attached to aluminum alloy pipes increase the number of make-ups and break-outs. Currently, aluminum drill pipes (ADP) are assembled by “cold” or “hot” methods. By the first method, the pin and box are screwed on the pipe with a “sufficiently” high specified make-up torque. By the second method, the pin and box of the tool joint are heated and screwed on the ends of the pipe without effort. After cooling, the shrinkage of the tool joint units creates a reliable permanent threaded “pipe – tool joint” connection. The first method is easier than the second one; however the comparative strength of these ADP connections has not been enough clear. The paper presents the results of comparative strength analysis of both types of connection after assembly at applying tensile load and alternating bending load. The theoretical aspect of the study includes a detailed FEA of “hot” and “cold” assembly connections at applying tensile load and alternating bending load with SCF evaluation. The experimental data are presented as the results of tensile testing of small-scale specimens, removed from different aluminum pipe sections that were heated during “hot” assembly. Finally, full-scale specimens of both types of connections were tested for tensile capacity and fatigue. The comparative strength of both types of connections is concluded.Copyright