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Introduction

Drilling operations are an important process in geological exploration and in the production of oil and gas. As a result of complex interactions between the drill bit and rock formations, as well as between the drilling fluid and the drill string, the dynamic system undergoes changes that negatively affect the drilling process. To study the stability of dynamic systems during drilling, it is necessary to construct an effective dynamic model of the drilling system [1].

Under industrial conditions, drilling heterogeneous rocks composed of alternating soft and hard formations often leads to harmful vibrations and oscillations. Severe vibrations of drilling tools may cause drill bit failure at the bottom of the well. The axial and torsional oscillations of the drilling tool are to a certain extent random in nature, and their main causes include the variability of formation lithology and friction between the drill bit and the rock [2].

In many cases, scientific studies must explain unknown dynamic systems not through the development of mathematical models or theories, but through investigation of real conditions. Such studies are common in deep well drilling processes, particularly in the study of phenomena occurring during the operation of rock-destructive drilling tools. For a long time, the radial displacement (oscillation) of drill bits observed at the bottom of the well and the resulting formation of polygonal cross-sections of wells could not be explained from the standpoint of the classical isoparametric principle.

It should be noted that this phenomenon is clearly observed during metal drilling. However, in such cases it was explained not by the circular cross-section of the drilled hole but by the small area of the formed polygonal shape. Nevertheless, it was later established that isoparametric relationships do not play any role in the study of phenomena occurring in dynamic systems.

In fact, static parameters can never be the cause of dynamic phenomena.

Only the developed methods for studying processes occurring in dynamic systems, the principle of least action, and the laws governing energy dissipation in dynamic systems made it possible to scientifically explain these phenomena.

Currently, dynamic systems cannot reach dynamic equilibrium in any of the three operating modes unless certain constraints are imposed. In our case, stabilizers act as such constraints. It is known that energy losses in dynamic systems, under otherwise equal conditions, are limited from below by a rotational pair. In this case, it becomes necessary to limit energy losses to a given level by a certain value of eccentricity (0 < ε < ∞).

In the absence of constraints, the principle of least action forces any dynamic system to search for an operating mode with minimal energy loss. However, such modes cannot exist while the dynamic system is operating. Only in the vicinity of the point (ε ≈ 0, i = –1) can a rotational pair exist with infinitely small energy losses. However, at (ε = 0, i = –1) energy losses increase sharply because the dynamic system instantly switches to the first operating mode.

The first mode (rotation about its own axis) is common for all mechanical systems and fully characterizes them. In other words, this operating mode of mechanisms requires the greatest energy losses. These energy losses are especially evident in models of rapidly rotating shafts where disk friction occurs in gas or liquid media, and in drilling bits where energy losses arise due to friction between the bit teeth and the rock.

Constraints in the form of shafts or drill pipes under certain conditions are not capable of limiting radial oscillations. Thus, while searching for minimal energy losses, the dynamic system may be destroyed. In such cases, it is necessary either to rapidly switch to limiting rotational speeds or to install stabilizers, which is taken into account when designing the bottom-hole assembly of the drill string.

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Proposed Technical Solution

During deep well drilling there are practically no alternative methods for stabilizing rock-destroying drilling tools, since such geometrically large cantilever structures do not require extremely high forces for destruction. Therefore, stabilization of drill bits is possible only through the use of near-bit stabilizers.

The purpose of this study is to confirm or refute theoretical conclusions regarding the causes of radial oscillations in dynamic systems using a device based on the idea of a near-bit stabilizer, namely a roller-cone reamer-stabilizer developed as a patented invention.

The invention relates to the field of well drilling, particularly to the design of a roller-cone reamer-stabilizer, and can be used in drilling oil, gas and other wells.

In engineering practice, reamer-stabilizers with blade-type working elements are known; these blades are usually located at the periphery of a cylindrical body [3] (analogue).

However, such a design has significant disadvantages.

During operation, the blades undergo intensive abrasive wear. Moreover, constant contact between the blades and the wellbore wall during drilling leads to dynamic instability.

The closest technical solution to the proposed design is a roller-cone reamer-stabilizer in which the cones are positioned along the body height and arranged at an angle of 120° in plan view [4] (prototype).

This design increases wear resistance, improves versatility, and enhances the operational capability of the reamer-stabilizer. However, its disadvantage is that long-term stabilization of the drilling tool is ensured only at specific ratios and heights of the cones [5].

The objective of the invention is to develop a roller-cone reamer-stabilizer capable of ensuring reliable stabilization of the drilling tool at the bottom of the well due to its stable position relative to the well axis, where the cones are arranged along the body height at an angle of 120° [6].

The stated objective is achieved by a roller-cone reamer-stabilizer consisting of a cylindrical body with three vertically oriented cones positioned at the edges at an angle of 120° relative to the well axis (Fig. 1).

At the same time, the generatrices of the cones along the body height do not intersect with the height of the tooth tips at their minimum values and satisfy the following condition:

$$b_{min} > (\sqrt{7} \cdot R_{PAC})/2$$

where
b_min – minimum distance between the cones measured at the tooth tips, mm;
R_PAC – nominal radius of the roller-cone reamer-stabilizer, mm.

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Conclusion

The conducted tests demonstrated the following results:

1. Theoretical conclusions about the dynamic stability of the drill bit at the bottom of the well when using the proposed near-bit stabilizer were confirmed. This is supported by Patent of the Republic of Kazakhstan No. 22228 (E21B 10/30).

2. Industrial tests showed that the use of the near-bit stabilizer increased the mechanical drilling rate by 5% and increased bit run length by 7.3%.

3. A reduction in bit balling was observed, indicating that the vertically arranged blades of the stabilizer positively influence the hydrodynamics of the drilling fluid.

4. The drilling company supported the implementation of the proposed scientific innovation described in this work for deep oil and gas well drilling operations.

About the authors

Zhomart K Zhanturin

Atyrau University of Oil and Gas named after Safi Utebayev

Author for correspondence.
Email: aing-zhomart@mail.ru
ORCID iD: 0009-0007-4944-1850
Scopus Author ID: 59245544700

Candidate of Technical Sciences, Associate Professor of Safi Utebayev Atyrau University of Oil and Gas

Kazakhstan, 45A M. Baimukhanov Street, Atyrau 060005

Murat N Abishev

Atyrau University of Oil and Gas named after Safi Utebayev

Email: m_abishev_nik@mail.ru
ORCID iD: 0009-0001-5793-3800
Scopus Author ID: 57216591815

Candidate of Technical Sciences, Associate Professor of Safi Utebayev Atyrau University of Oil and Gas

Kazakhstan, 060005 M. Baimukhanov Street 45A, Atyrau

Nurken M Ahmetov

Atyrau University of Oil and Gas named after Safi Utebayev

Email: n.akhmetov@aogu.edu.kz
ORCID iD: 0009-0008-5892-2530
Scopus Author ID: 57219471805

Doctor of Technical Sciences, Professor at Safi Utebayev Atyrau University of Oil and Gas

Kazakhstan, 060005 M. Baimukhanov Street 45A, Atyrau

References

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