Drill Column Research Articles

Assessment of thermobaric state and change of the mass balance in the subgkacial Lake Vostok after drilling-in

Estimation of temperature and pressure conditions in the subglacial reservoirs is one of the most important tasks of modern subglacial research, since it provides an adequate tool for predicting the process of their accessing. This paper presents the estimation of pressure in the subglacial reservoirs for different baric system statuses. Opening of isolated subglacial reservoirs is attended by disturbance of their thermobaric equilibrium, thus the conditions of phase transition are changed on the entire surface of the ice-water contact. At the same time reducing the pressure in the subglacial reservoirs leads to «lowering» of the phase transition of ice-water boundary and to the growth of additional layer of congelation ice on the entire bottom surface of the ice sheet contact with water. Realized accessing of Lake Vostok and technology re-entry involves water rise into the borehole from the lake as one of the steps to prevent pollution of relict water system. With the use of this technology the reliability of estimate the pressure in Lake Vostok is extremely important and, consequently, the value of the differential pressure when the borehole accesses with lake. The paper presents analysis of the possible consequences of incorrect estimation of the pressure in isolated water system of Lake Vostok, when the borehole accesses in conditions of incomplete compensation of subglacial water pressure by hydrostatic pressure of the drilling fluid column.

WHTSubmersible: a simulator for estimating transient circulation temperature in offshore wells with the semi-submersible platform

Offshore wellbore temperature field is significant to drilling fluids program, equipment selection, evaluations on potential risks caused by casing thermal stress, etc. This paper mainly describes the theoretical basis, module structure and field verification of the simulator WHTSubmersible. This computer program is a useful tool for estimating transient temperature distribution of circulating drilling fluid on semi-submersible platform. WHTSubmersible is based on a mathematical model which is developed to consider radial and axial two-dimensional heat exchange of the inner drill pipe, the annulus, the drill pipe wall, the sea water and the formation in the process of drilling fluid circulation. The solution of the discrete equations is based on finite volume method with an implicit scheme. This scheme serves to demonstrate the numerical solution procedure. Besides, the simulator also considers the heating generated by drilling fluid circulation friction, drill bit penetrating rocks, friction between the drill column and the borehole wall, and the temperature effect on thermal physical properties and rheology of the drilling fluid. These measures ensure more accurate results. The simulator has been programmed as a dynamic link library using Visual C++, the routine interface is simple, which can be connected with other computer programs conveniently. The simulator is validated with an actual well temperature filed developed on a semi-submersible platform in South China, and the error is less than 5 %.

Sensitivity of resistance forces to localized geometrical imperfections in movement of drill strings in inclined bore-holes

The inverse problem about the theoretical analysis of a drill string bending in a channel of an inclined bore-hole with localized geometrical imperfections is studied. The system of ordinary differential equations is first derived based on the theory of curvilinear flexible elastic rods. One can then use these equations to investigate the quasi-static effects of the drill string bending that may occur in the process of raising, lowering and rotation of the string inside the bore-hole. The method for numerical solution of the constructed equations is described. With the proposed method, the phenomenon of the drill column movement, its contact interaction with the bore-hole surface, and the frictional seizure can be simulated for different combinations of velocities, directions of rotation and axial motion of the string. Geometrical imperfections in the shape of localized smoothed breaks of the bore-hole axis line are considered. Some numerical examples are presented to illustrate the applicability of the method proposed.

The computer simulation of drill column dragging in inclined bore-holes with geometrical imperfections

The problem about identification of resistance forces acting on a drill column moving in an inclined bore-hole is stated. It is supposed that the well trajectories can have geometrical imperfections in the shape of cylindrical spiral or plane cosinusoidal curves. The system of ordinary differential equations is derived on the basis of the theory of curvilinear flexible elastic rods. It permits one to describe static effects of the drill column bending accompanying the processes of its raising, lowering and rotating inside the bore-hole. Through the use of this system the direct and inverse problems of the drill column deforming are formulated for calculation of internal and external resistance forces acting on the drill column tube. The methods for numerical solution of the constructed equations are elaborated. With their use the phenomena of the drill columns motion and their frictional seizure inside the bore-holes are simulated for different geometrical imperfections and relations between the velocities and directions of their rotation and axial motion.

Helical traveling waves in elastic rods

We pose the problem on free harmonic bending vibrations of an infinite rotating tubular elastic rod with an internal fluid flow, prestressed by a torque and a longitudinal force. We show that these vibrations can only be realized as traveling circular helical waves. It is shown that, for any wavelength, there exist four waves, two having the form of a left-handed helix and the other two having the form of a right-handed helix. Each of these waves propagates in the positive and negative directions of the longitudinal rod axis at different velocities. These phenomena can manifest themselves in deep-hole drill columns.

Stability of the column of a rotor-type drilling rig

The equation of bending of a heavy rod is used to study the problem of stability of a rotor-type drilling column. We deduce the equation for the critical length in the case of tension–compression and perform a numerical analysis of the critical length as a function of the level of tension in the pulley block of a WIRTH drilling rig.

Toward determination of the eigenvalues of problems on description of the rotation of deep-water drill columns

This paper presents a method for computing the complex eigenvalues for a boundary-value problem describing the rotation of deep-water drill columns for drilling at depths of thousands of meters. A solution is sought for a singularly perturbed boundary-value problem in the form of an asymptotic expansion in a small parameter ε for two parts of the of the drill column: a lower compressed length, and the upper length. The method can be used to investigate the stability of drill columns used for deep-water drilling.

Developing methods of combatting stickages of a drill tool using the dynamic properties of its elements

The theoretical fundamentals of the operations for freeing a drill column and a bit from stickages were formulated on the basis of an analysis of pulsed loading of the stuck elements of a drill tool. Three variations of explosive loading of a drill tool by successive detonation of charges located within the drill column in the zone of stickage and containing the amount of energy necessary for breaking of the bonds of the column with the soil causing stickage are given.

Setting up a facility for heavy drilling and guide tubes

The facility for heavy drill tubes and guide tubes (the DT and GT facility) included in the M. V. Fnmze Scientific Production Unit (NPO) has a closed cycle which includes a flexible automated plant with steel-casting, forging-heat treatment, and mechanical processing sections. The technological processes introduced in the facility make it possible to produce tubes for which scrap iron is used as the starting material. The specialized plant is provided with high-technology equipment and highly reliable controllable production lines. Process control and monitoring is carried out by a central computer (computer automatic control system [ACS]), which based on the number and type of tubes determines the volume of the output with optimum utilization of the production facilities of the plant. The use of a central computer makes it possible to rapidly reorganize and modify the technological process according to the requirements imposed by the final product, and at the same tLrne to monitor how the specified program is carried out. The central computer is directly connected to the individual equipment units. The heavy drilling tube and guide drilling tube (HDT and GDT) produced by the plant satisfy the requirements of the American Petroleum Institute (API) standards, and this is confirmed by quality certificates. The HDT and GDT are used for drilling operations in geological expIoration and in the recovery of petroleum and gas. The HDT is intended for setting up axial forces on the cutting tool, transfer of the torque, and stressing the entire drilling column in order to reduce its flexure and vibration. Depending on the constructional features, the outer tube surfaces are used for aligning deformed wells and for drilling sheafs of fan-shaped inclined wells. The GTDs are intended for the transfer of the torque from the outer drive of the drill column. The DT and GT facility produces 13 types (262 standard sizes) of forged tubes, heat treated over the entire length, from AISI 4145H steel (to the American standard), which is melted in an electric furnace, refined in a flarnace !adle, and subjected to vacuum treatment and electromagnetic mixing. The constructional features of the tubes are shown in Fig. 1 (the types of couplings and nipples are shown according to the API standards), and the tube dimensions and mechanicalpreperties of the steel are given in Table 1. It should be noted that the DT and GT facility produces high-qualityproducts, corresponding to the best in ~e world. The quality is achieved as a result of satisfying the organizational and technical practices during working wi• suppliers, careful

Dynamic behaviour of deepwater drilling column under collisions with drillship moonpool

The paper presents a theoretical and numerical approach to the dynamic behaviour of drilling column (DC) in deep water under various exciting forces, due to seawater motion and drillship displacement allowing for possible collisions between DC-to-moonpool walls. The solutions of motion equations for each section of DC (the first section being located in the moonpool, whereas the second section is submersed in the sea), are presented individually and compared afterwards. For the step-by-step integration of DC equations the implicit Newmark's method is applied. The first section solution is determined by means of quadratures. The second section solution is determined by means of the asymptotic Tupchiev's method and the method of pass. The determination of DC-to-moonpool wall contact points is done iterationally. A computer program of DC dynamic behaviour simulation has been developed. Examples of the simulation have been presented. The program can be used for the analysis of deepwater DC stresses at design stage.

Model of borehole deviation in anisotropic rock

1. The equation of bit rotation in anisotropic rock allows the difference in directions of the bit axis and the borehole axis (the tangent ot the trajectory) to be determined. 2. The asymptotic approach here proposed allows the curvature and the normal to the trajectory with a specified direction of the borehole axis at the face to be determined for weakly deviated borehole trajectories. The equations of the borehole trajectory are thus determined. 3. Combined numerical calculation of the column equilibrium and the borehole deviation is unnecessary in the new method of describing the characteristics of the drilling-column base; instead, the solution is obtained by taking account of just a few simple parameters of the column base, determined separately by solving the problem of elastic deformation of the base of a heavy drilling column in a distorted inclined shaft. 4. The formulas for the curvatures and components of the normal to the borehole trajectory obtained for the case of gyrotropic rock describe the locally independent distortion of the projection of the borehole trajectory in two planes orthogonal to the bed, one of which includes the bit axis.

Effect of Drillstring Vibrations on MWD Pressure Pulse Signals

Axial vibrations of drillstrings produce pressure variations within the drilling fluid column. These pressure variations are imposed on controlled pressure pulse signals from Measurement-While-Drilling (MWD) tools producing background noise in pressure pulse data measured at the rig. The paper shows the effect on signal-to-noise ratio for various operating conditions, such as vibration frequency, valve opening/closing time, pulsing interval, and flow rate.

Use of heating in molten salts for surface hardening of the threaded coupling ends of the elements of a drill column

Use of heating in molten salts for surface hardening of the threaded coupling ends of the elements of a drill column

Pressure pulse detection apparatus incorporating noise reduction feature

An improved apparatus is disclosed for use in a measuring while drilling apparatus which forms a pressure pulse promulgated from a downhole location upwardly through the drill string and column of mud therein. This apparatus includes a mud line section adapted to flow drilling mud in the mud flow line through an axial passage therein. The apparatus includes an encircling bladder which receives hydraulic oil under pressure to inflate to choke the passage. A Pitot tube is focused downstream and thus does not intercept the mud flow from the pump and the noise which is created by pump operation. Mud pressure variations directed upstream from the measuring while drilling apparatus, however, are directed into the Pitot tube. These pressure variations are coupled to a pressure signal transducer which forms an output signal of some type which is recorded. Pump noise is nulled to a minimum.