Drill Collar Research Articles

A theoretical analysis of the logging-while-drilling dipole acoustic reflection measurement

Post-drilling wireline acoustic single-well imaging technology can now detect geological structures tens of meters away from boreholes. Further development of this single-well imaging technology in the logging-while-drilling (LWD) environment will have significant values in real-time applications such as geosteering and reservoir navigation. Based on the wireline imaging application, we propose a new method for the LWD application. In wireline imaging, the four-component (4C) dipole acoustic data are azimuthally rotated to scan the reflectors around the borehole. In LWD, azimuthal scanning is achieved by drilling rotation such that the 4C dipole system in the wireline is replaced by a one-dipole-source and two-receiver LWD system, where the two receivers are mounted on opposite sides of the drill collar. For the LWD application, we first developed the theory for LWD dipole shear-wave reflection imaging and validated the theory using 3D finite-difference waveform modeling. Using the analytical solution, we analyzed the far-field radiation directivity of an acoustic LWD dipole source and the effect of drilling rotation on the shear-wave reflection imaging using the LWD acoustic system. The LWD analysis results show that, for fast formations, the SH-wave is the dominant component for imaging, whereas for slow formations, the P-wave becomes important and can be used for imaging. Our results also indicate that the reflection data acquired by the system are affected by the speed of drilling rotation. The take-off azimuth at the wave radiation may be different from the incident azimuth at the wave reception. Knowing the rotation speed, this azimuth difference can be corrected. A further advantage of using the oppositely mounted receivers is that the reflected wave arrives earlier (later) at the front (back)-side receiver; thus, the arrival time difference between the receivers can be used to eliminate the 180°-azimuth ambiguity of dipole acoustic imaging. For reflection imaging, using the proposed LWD system configuration, we tested its azimuth sensitivity and validated its 180°-ambiguity solution using synthetic LWD and field wireline dipole data. The results of this work, therefore, provide a theoretical foundation for the development of the LWD acoustic reflection imaging system.

Research on Drillpipe Stick-slip Vibration and Its Suppression Mechanism in Deep Well Drilling

Abstract During drilling deep wells, stick-slip vibration(SSV) is a reciprocating vibration form of drill bit adhesion, sliding, re-adhesion, and re-sliding. If not suppressed, it can cause serious drilling accidents, such as accelerated wear of drilling equipment, which lead to decreased drilling safety, reduced drilling efficiency, and prolonged drilling cycle. This article establishes a SSV model of the drill string system, considering the three degrees of freedom of the rotary table/top drive, hammer, and drill bit, and analyzes the SSV characteristics of the drill bit during deep well drilling. The SSV analysis of the drill string system was carried out for well XX-X-4, and the sensitivity of rotational speed, viscous damping, drilling pressure, drill bit length, and friction torque coefficient was analyzed. The results showed that the friction torque coefficient and rotational speed are the main factors affecting stick reduction efficiency, while the length of the drill collar is a secondary factor. The WOB and viscous damping have the least impact on stick reduction efficiency. The parameters were optimized to reduce SSV as the target. This article has certain guiding significance for deep well drilling operations.

Factors Influencing Radiation Sound Fields in Logging While Drilling Using an Acoustic Dipole Source

With the increasing number of complex well types in the development stage of oil and gas fields, it is becoming increasingly urgent to use remote detection logging while drilling (LWD) to explore the geological structures in a formation. In this paper, the feasibility and reliability of the dipole remote detection of logging while drilling are demonstrated theoretically. For this purpose, we use an asymptotic solution of elastic wave far-field displacement to derive the calculation formula for the radiation pattern and energy flux of an LWD dipole source. The effects of influencing factors, including the source frequency, formation property, drill collar size, and mud parameter, on the radiation pattern and energy flux are analyzed. The results show that the horizontally polarized shear wave (SH-wave) has a greater advantage in imaging the reflector compared with the cases of the compressive wave (P-wave) and vertically polarized shear wave (SV-wave), which indicates the dominance of the SH-wave in dipole remote detection while drilling. The optimal source excitation frequency of 2.5 kHz and inner and outer radii of the drill collar of 0.02 and 0.1 m, respectively, should be considered in the design of an LWD dipole shear wave reflection tool. However, the heavy drilling mud is not conducive to remote detection during logging while drilling. In addition, the reflection of the SH-wave for the LWD condition is simulated. Under the conditions of optimal source frequency, drill collar size, and mud parameters, the reflection of the SH-wave signal is still detected under the fast formation.

Microstructures and wear properties of CoCrFexNi (x = 0, 1) medium-entropy alloy coatings prepared by laser cladding

PurposeHigh-nitrogen steel is a common material for the manufacture of drilling equipment such as drill collars. However, its poor surface properties often limit its applications. The purpose of this paper is to find a way to enhance the surface performance of high-nitrogen steel, which is expected to improve the wear resistance of high-nitrogen steel.Design/methodology/approachThe CoCrNi and CoCrFeNi medium-entropy alloy (MEA) coatings were prepared on high-nitrogen steel substrate by laser cladding technology. The microstructure, phase composition and element distribution of the fabricated coatings were investigated using scanning electronic microscopy, electron backscatter diffraction and X-ray diffraction. The phase structure, phase stability and structural stability of the CoCrNi and CoCrFeNi MEAs were investigated in combination with phase diagram calculation and molecular dynamics. Then the wear tests were carried out for coatings.FindingsThe results show that both prepared MEA coatings have good quality and contain a single face-centered cubic phase. The wear performance of MEA coatings is improved by the refinement of grain size and the increase of dislocation density. Due to the addition of Fe atoms, the lattice distortion of the CoCrFeNi system increased, resulting in a higher dislocation density of the coating. Cr atoms in the CoCrFeNi system are the largest, and the local lattice distortions induced by them are greater. Through this study, MEA coatings with high hardness can be expanded to drilling field applications.Originality/valueCoCrFeNi and CoCrNi MEA coatings were successfully prepared on the surface of high-nitrogen steel for the first time without obvious defects. The micromorphology and grain orientation of the different kinds of coatings were discussed in detail. The hardness-strengthening mechanism and structure stability of the coatings were illustrated by experiments and molecular dynamics simulations.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2024-0116/

Borehole radiation wavefield for multipole logging while drilling with an eccentric collar

Abstract This study investigates the radiation characteristics of the borehole-source in acoustic logging while drilling (ALWD) with an eccentric collar. Understanding these characteristics is crucial for the development of acoustic remote detection technology, which has shown great potential in ALWD. Considering the frequent occurrence of tool eccentricity during drilling, it is essential to take into account its impact on the acoustic wavefield outside the borehole. In this paper, we establish an ALWD model with an eccentric collar in a dual-cylindrical coordinate system. By applying the translational Bessel addition theorem and the steepest descent method, we obtain the far-field asymptotic solution of the problem and model the radiation wavefield. Our findings indicate that the asymmetrical radiation pattern resulting from drill collar eccentricity can effectively resolve ambiguities in determining the reflector azimuth.

Analysis of secondary makeup characteristics of drill collar joint and prediction of downhole equivalent impact torque of Well SDTK1

Based on the three-dimensional elastic-plastic finite element analysis of the 8” (203.2 mm) drill collar joint, this paper studies the mechanical characteristics of the pin and box of NC56 drill collar joints under complex load conditions, as well as the downhole secondary makeup features, and calculates the downhole equivalent impact torque with the relative offset at the shoulder of internal and external threads. On the basis of verifying the correctness of the calculation results by using measured results in Well GT1, the prediction model of the downhole equivalent impact torque is formed and applied in the first extra-deep well with a depth over 10 000 m in China (Well SDTK1). The results indicate that under complex loads, the stress distribution in drill collar joints is uneven, with relatively higher von Mises stress at the shoulder and the threads close to the shoulder. For 203.2 mm drill collar joints pre-tightened according to the make-up torque recommended by American Petroleum Institute standards, when the downhole equivalent impact torque exceeds 65 kN·m, the preload balance of the joint is disrupted, leading to secondary make-up of the joint. As the downhole equivalent impact torque increases, the relative offset at the shoulder of internal and external threads increases. The calculation results reveal that there exists significant downhole impact torque in Well SDTK1 with complex loading environment. It is necessary to use double shoulder collar joints to improve the impact torque resistance of the joint or optimize the operating parameters to reduce the downhole impact torque, and effectively prevent drilling tool failure.

Study on lateral vibration characteristics of BHA with double-span drill collar

The severe vibration of BHA directly affect the drilling efficiency, borehole trajectory, and wellbore quality. Therefore, it is crucial for developing dynamic mechanics of drill string system by studying the mechanical behavior of BHA. In this paper, considering the continuity condition of double-span drill collar, the expression of lateral vibration of drill collars is firstly obtained by using the assumption mode method. Then, the lateral vibration equation of double-span drill collar is derived by Lagrange equation. Finally, a self-programming model is established based on dynamic mechanics of drill string system, the lateral vibration characteristics of double-span drill collar in four different types of BHA is further determined by the fourth-order Runge-Kutta algorithm. It is obviously found that the lateral vibration is enhanced with increasing the length of drill collar; the rotation speed of BHA, weight on bit (WOB), and the size of stabilizer have a significant influence on the lateral vibration of drill collar. In the practical application, the lengths of the first-span and the second-span drill collar are given as 10 and 19 m, respectively; and the stabilizer diameter approached to bit diameter is recommend in practical gas drilling engineering; under WOB of 10–40 kN, the rotation speed of the drilling string should be controlled nearby 60 r/min. The theoretical investigation is a guidance for structure design of BHA and optimization of drilling parameter.

Self-Stabilizing Control Strategy of Stabilized Platform for Rotary Steerable Drilling System Based on Adaptive Backstepping Control

To enhance the robustness of the toolface angle control in a fully rotary steerable drilling tool, a backstepping control law and a drilling fluid flow adaptive law are devised based on the dynamic model of the stable platform. The Lyapunov function is constructed, and it is proven that the adaptive backstepping control system of the stabilized platform is stable. Furthermore, in order to address problems such as the friction dead zone and excessive rotational kinetic energy in the stabilized platform system, which could cause toolface angle oscillations and the rapid rotation of the stabilized platform, we additionally propose an online estimation method for the balancing torque and velocity-angle control switching strategy. By combining the backstepping control law, drilling fluid flow adaptive law, and velocity-angle control switching strategy, a self-stabilizing control strategy for the stabilized platform is established. In comparison with the PID control method, the simulation results show the superiority of the proposed scheme under complex disturbances from a downhole environment. And the drilling simulation experiment results indicate that the proposed control method has a good anti-interference capability under various conditions, including drilling fluid flow rate, inclination angle, and drill collar rotational speed. Therefore, the proposed control method can improve the robustness of the stabilized platform control system.

A New Bottom-Hole Assembly Design Method to Maintain Verticality and Reduce Lateral Vibration

Well deviation is a prevalent problem in deep oil and gas exploration, leading to a significant increase in drilling costs. The conventional bottom-hole assembly (BHA) anti-deviation design method does not consider the impact of the BHA structure on lateral vibration. This paper proposes an integrated BHA design method that takes into account both anti-deviation and vibration reduction. This method evaluates the BHA’s anti-deviation ability using the drilling trend angle. A negative value of the drilling trend angle indicates that the BHA can correct well deviation. A finite element linearized dynamics method is used to evaluate the lateral vibration intensity of the BHA. This method involves calculating the bending displacement caused by mass imbalance and then determining the magnitude of the bending strain energy based on this displacement. The structural factors affecting the anti-deviation ability and potential lateral vibration intensity of pendulum BHAs and bent-housing mud motor (BHMM) BHAs were studied, and field tests were conducted for verification. The research shows that for pendulum BHAs, the factor that has the greatest impact on anti-deviation ability and vibration intensity is the distance from the stabilizer to the drill bit. For BHMM BHAs, the length of the short drill collar has a significant impact on the vibration intensity. Compared with current design methods, the mechanical specific energy (MSE) of the single stabilizer pendulum BHA decreased by 12%, while the MSE of the BHMM BHA decreased by 26.4%. Both decreases indicate a reduction in vibration intensity. This study will help to further increase drilling speed while preventing well deviation.

Universal apparatus module of radioactivity logging for the investigation of oil-and-gas reservoirs while drilling

Logging-while-drilling (LWD) is the most advanced technology in geophysical well logging. It is widely used for determining the petrophysical and other parameters of oil-and-gas reservoirs in vertical, deviated, and horizontal boreholes.
 The LWD is particularly important for horizontal boreholes, obtained by directional drilling from vertical boreholes into predetermined hydrocarbon reservoirs. Horizontal boreholes allow multiplying the yield of hydrocarbons, increasing overall production, and using effectively both new vertical boreholes and exploited ones, as well as old boreholes. The opportunity of horizontal drilling to local (isolated) deposits, which are at a certain distance from vertical boreholes, is of also essential importance. All these factors are favourable for increased hydrocarbon production, which is of great significance for Ukraine.
 This paper concentrates on the apparatus developments aimed at creating a new module of radioactivity logging for LWD; the module is universal in the sense that it can be used in drill collars, which are employed while drilling all types of boreholes. The tool implements neutron-neutron logging, neutron-gamma logging, gamma-gamma logging, and gamma-ray logging. It allows a direct and combined determination of a broad set of petrophysical reservoir parameters.
 The advantages and disadvantages of the known nuclear logging modules for the LWD have been analyzed, and the features and merits of the proposed one are shown. During the laboratory and borehole operations with a pilot sample of the module, trends for its improvement were outlined.
 As an example of using the new module for LWD, the results of determining the petrophysical parameters of oil reservoirs of varying lithology in three horizontal boreholes are given. The process of LWD measurements demonstrated high technologicness and efficiency of the module. Comparison of the obtained parameters of the reservoirs with the data of independent measurements carried out in the open hole of the same boreholes using the PEX tool (Schlumberger) showed a qualitative consistency and a quantitative convergence of the results.

STUDY OF THE DYNAMICS OF ASSOCIATED DRILL STRINGS INTERACTING WITH THE WELL WALL

The depth of exploration and production wells during the development of oil and gas fields can exceed 5-10 km, and the insufficient strength and reliability of the drill string often limits the possibility of further increasing labour productivity. In addition, accidents at wells lead to significant material costs. Therefore, the design and operation of drill strings, as well as the implementation of work to eliminate complications during drilling, should be carried out on the basis of a science-based approach, taking into account the latest advances in the field of drill string dynamics and technologies related to work to eliminate stuck problems. Unsteady vibrations of inhomogeneous distributed systems is a very complex problem in the mechanics of a deformable solid and the theory of vibrations. In connection with the rapid development of the extractive industries, solving this problem is of particular importance. This is due to ensuring the strength of drill string structures with increasing power and speed of drilling units and mechanisms. The study of the problem revealed a number of little-studied problems, which include issues of nonlinear interaction of the column with the surrounding soil, accompanied by various types of complications (sticking, pipe ruptures, etc.), wave and oscillatory processes in the elements of the drilling dynamic system (DDS), finding the boundaries of the interaction areas of the column with the walls of the well using low-cost techniques. The purpose of the work is theoretical research of wave and oscillatory processes in the pipes of the drilling assembly and the dynamics of associated drill strings interacting with the well wall. In this work, a homogeneous rod was used as a drill string model. The drill string consists of a drill pipe string (DPC) and a bottom drill string assembly (BDSA), which includes a bit, a downhole motor, wellbore forming elements: calibrators, centralizers, sections of drill collars (DC), the main purpose of which is to creating an axial load on the bit. The DPC consists of sections of drill pipes that are identical in their characteristics (type, outer diameter, wall thickness, joints used, etc.). Therefore, in general, the drill string is a heterogeneous structure.

Improvement Plan Using Fatigue Analysis Minimizes Jar Twistoff

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 210723, “Service Quality Improvement Plan Using FEA Fatigue Analysis Minimizes Jar Twistoff in Challenging Applications,” by Chaouki Boufama, SPE, Baozhong Yang, and Sultan Alfaraedhi, Schlumberger, et al. The paper has not been peer reviewed. _ Jar twistoff is a well-known service quality issue for some applications, especially in relatively large borehole sizes such as 22 and 16 in. The jar is one of the weakest points in the drillstring because of moving parts, which include complex shapes, resulting in stress concentration. The complete paper presents results of a study focusing on placing the jar in the bottomhole assembly (BHA) to reduce bending moments and bending stresses on the jar connections. As a result, the risk of twistoffs during drilling is minimized, while the effectiveness of the jar is maintained if a stuck event occurs. Introduction Jars traditionally are placed between drill collars in the applications described in this study. These applications include 22- and 16-in. vertical holes with simple BHA designs, either rotary or with positive displacement motors. In cases of lateral vibration that creates high bending stress, this design is likely to cause the jar to experience extreme stress levels. The design concept of placing the jar between other components with lower weight and stiffness appears to be the most logical approach. This design would have to be validated with finite element analysis (FEA) dynamic modeling simulations to confirm lower stress at the jar and that a new weak point has not been introduced in the string. Impact and impulse also must be evaluated to confirm the effectiveness of the jar in the case of a stuck-pipe condition. The study is based on the work flow shown in Fig. 1 of the complete paper. Statement of Theory and Definitions A more in-depth analysis was performed on a 22-in. vertical drilling application with nonhomogeneous formations. A downhole real-time recording tool was added to the drillstring above the BHA to evaluate and verify the magnitude of vibration and bending moments acting on the BHA during drilling operations. The 22-in. vertical section was selected because it was determined to be the most challenging section. The following key observations were made during the drilling run when the circulation was lost to the formation: - Significant lateral vibration levels - Chaotic whirling motions - High bending moment Mechanical specific energy (MSE) and drilling parameters were controlled during the run to alleviate vibration. Vibration severity could have been influenced by the absence of the mud column as well as the borehole quality because of formation washout and an oversized hole. However, this was never verified using a caliper log. The string entered a state of chaotic whirl as the loss of circulation fluid began. The parameters, and thus the MSE, were reduced, but the severe vibrations persisted. Even though the run did not cause any jar-component failure or crack, multiple previous incidents showed similar failure modes in the same downhole conditions. These failures, which included the fractured face of each of the parted components, were analyzed and evaluated (Fig. 1). The slanted fracture indicated a high combined stress-related fracture. In addition, beach marks present near the fracture area also indicated fatigue-induced damage.

Changing the Game: Well Integrity Measurements Acquired on Drillpipe

The industry is continuously challenged to improve the efficiency and safety of operations. This is evident over the last 30 years in the development and improvement of measurements acquired while drilling. However, this has, in general, until now not been applied to well integrity measurements such as casing integrity and cement evaluation, which have traditionally been acquired utilizing wireline deployment. This paper will show the results of a new drillpipe-deployed tool that can be run in parallel with existing well operations. The results from two differing North Sea wells will be compared to traditionally acquired wireline-deployed tools and will demonstrate that these measurements and the resultant interpretation can successfully be acquired on drillpipe. This allows for much improved efficiency of operations and, in fact, the ability to acquire this important data in well conditions and environments where it is difficult or, in some cases, impossible to log with conventional wireline techniques. Two wells were selected with different degrees of difficulty in terms of measurement acquisition and showing different well trajectories and mud types. Both wells were logged with both the new drillpipe-deployed technology and traditional wireline technology, allowing a direct comparison of the techniques and tools and paving the way for acceptance of the new drillpipe-conveyed technology. The new drillpipe-conveyed tool can be run anytime drillpipe is utilized in the well. A radial distribution of ultrasonic transducers arranged on the circumference of a drill collar allows for full azimuthal interpretation of the casing and cement while rotating the drillpipe. Analysis of the acquired data allows for the interpretation of caliper thickness and an evaluation of the material in the annular space behind the casing. In addition, the tool can provide casing collar location in real time and has the ability to orient downhole devices such as whipstocks, perforating guns, and oriented cutters. The two well examples conclusively demonstrate that the tool can be run in parallel with existing operations to minimize rig time and eliminate the need for a dedicated, standalone wireline operation. Also, the cement evaluation interpretation was comparable to the equivalent wireline technology. We will investigate which measurements and applications the new tool can be used for and where there may be further room for improvement.

Fracture failure analysis of 5 “drill collar double shoulder external thread in a well

This article analyzes a well using 5 “Based on the analysis of the chemical composition of the drill collar, mechanical property testing, metallographic structure analysis, fracture morphology and energy spectrum analysis, as well as the analysis of the stress, bending strength ratio, and double shoulder structure of the drill collar, combined with the deviation of the well section where the drill collar fracture occurred and the drilling pressure during drilling, it is clear that the main reason for the failure of the drill collar is that there is a large well deviation in the area and the drilling pressure is not properly reduced, resulting in The drill collar undergoes severe bending alternating stress and initiates fatigue cracks and propagates at the root of 1-2 threads at the large end of the external thread.

Effects of collar eccentricity on azimuthal response characteristics for acoustic reflection measurement while drilling

Acoustic reflection imaging has been successfully applied in postdrilling wireline logging, and the technique is potentially more valuable in acoustic logging while drilling (ALWD), particularly in geosteering while drilling. Because of the common occurrence of tool eccentering in drilling, the impact of drill collar eccentricity on the acoustic wavefield inside and outside the borehole must be considered. Therefore, we analyze the effect of an eccentric drill collar on acoustic reflection imaging while drilling using analytical solutions in a dual-cylindrical coordinate system. The virtual source analogy and the translational addition theorem for cylindrical Bessel functions are used to calculate the response of the fluid-filled borehole with an eccentric collar to the incident wavefield from a formation reflector. The analysis results are validated with those from 3D finite-difference simulations. We also have studied the azimuthal variation of the received wavefield and compared the results with their centralized counterparts, for which the effects of collar eccentricity, frequency of the source, and formation elastic property are analyzed. The results indicate that the asymmetric feature of the wavefield due to the eccentric collar allows for determining the azimuth of the reflector, providing a solution to the azimuth ambiguity problem of borehole acoustic reflection imaging. Our results, besides developing an effective method for eccentric collar ALWD modeling, can be used to provide a theoretical foundation for ALWD tool development and data interpretation.

Study on Directional Drilling Coupling Dynamics Based on Drill String Rotary Controller

Abstract In the process of long horizontal well in directional drilling, serious contact between drill string and wellbore leads to weight on bit loss. Therefore, this paper proposes a drill string rotary controller (DSC) for directional well, and its function test is completed through the experimental platform. Connected DSC working mechanism, a drill string coupling dynamic model is established under conditions of horizontal well in directional drilling. In the case study, the coupling dynamic characteristics of different units, including drill pipes and bottom-of-hole modules in axial and torsional directions, are studied. The results show that the effective value of drilling rate increases while the axial vibration velocity and amplitude of drill bit decreases. Moreover, in torsional direction, when drill string system is stable state, the rotating angular velocity of different drill pipes, rotary table, and collar is 31.16 rad/s, and the angular velocity of drill bit is 43.19 rad/s, respectively. It indicates the DSC working performance, which enhances the drilling system balance capacity. Overall, different from the sliding friction between wellbore and drill string, the addition of DSC realizes the separation and meshing of drill string and bottom hole modules, which can significantly increase the transition efficiency of weight on bit and torque value. Theoretical and experimental researches prove that the tool can effectively solve the problem of serious weight on bit loss in directional drilling process, and provides a new reference and idea for developing directional drilling technology when facing new challenges.

Design of double-shoulder threaded joints of drilling string elements

Purpose. Development of a method for simulating the screwing torque/moment and researching the design of double-shoulder threaded joints while preserving their geometric parameters. Determination of the optimal length of the additional shoulder pin part for the developed drill collar (DC) of NC50, NC55 type of various standard sizes. Establishing the dependence between the pin part length of the additional shoulder and other geometric parameters of the double-shoulder joint of the DC for further use when developing other standard sizes of similar design threads. Methodology. The development of design and the method for simulating the screwing torque of double-shoulder threaded joints was carried out using the finite element method and parametric modeling. Finding. A method for simulating the screwing torque of threaded joints was proposed and developed, which made it possible to improve the model of their automated design. The optimal lengths of the pin part of the additional shoulder of the developed design of double-shoulder threads of the NC50, NC55 types were determined. For planning threaded joints of similar design with the above-mentioned types of threads, a dimensionless coefficient was derived and its value was calculated. A nomogram was built to determine the length of the joint additional shoulder pin part due to the value of this coefficient. Originality. The model of automated design for double-shoulder threaded joints of drill string parts has been improved. This model preserves their geometric parameters and enables modeling a wide range of standard sizes of similar joints. Practical value. The optimal geometric parameters of the developed structures of double-shoulder threaded joints of the drill string elements were determined. A nomogram was built to determine the length of the additional shoulder pin part of the joint by the value of the dimensionless coefficient.

Seismoelectric Coupling Equations of Oil-Wetted Porous Medium Containing Oil and Water

For porous medium containing multiphase fluid, such as oil-wetted porous medium with oil–water dual phase fluid, its fluid interface will also produce electric double layer (EDL), which will play a role in the seismoelectric effects. At this time, the principle of seismoelectric effects is more complex. The existing theory for the seismoelectric effects is the Pride theory used in the water-saturated porous formation, which cannot meet the actual needs of the theoretical research of seismoelectric exploration in the porous formation with multiphase fluid. Carbonate porous formations are often oil-wetted; therefore, it is necessary to study the electrokinetic effects of oil-wetted porous medium containing multiphase fluid. In this paper, we treated the oil–water mixture as an effective fluid, and solved the effective elastic parameters and extended the Biot equations to the case of oil-wetted porous medium with oil–water dual phase fluid. We calculated the effective electromagnetic parameters and derived the macroscopic coupling equations of seismoelectric effects and electroseismic effects, and proposed the new electrokinetic coupling coefficients of the oil-wetted porous medium with dual phase fluid. We also deduced the coupling functions of electric and magnetic fields relative to the solid displacement in the homogeneous porous medium, and studied the polarization characteristics of the electric field. We use the derived coupling equations to simulate the seismoelectric logging while drilling in the model of oil-wetted porous formation with dual phase fluid under the excitation of multipole sources. The influence of drill collar wave on the acoustic field and electric field under the excitation of different sources was investigated, which has a certain guiding role in the selection of electrokinetic logging tools.

Structural Design of Small-size At-bit Azimuthal Gamma Geosteering Tool Based on Axiomatic Design

To revitalize old wells and reduce costs, sidetracking has become an effective technical means to excavate the remaining oil reservoirs of old wells. The small-size at-bit azimuthal gamma geosteering tool designed in this paper is used for sidetracking. First, according to axiomatic design, we determine each functional module. Second, according to the function module, we design the structure of the geosteering tool. Finally, we conduct finite element strength analysis on the geosteering tool. The results are as follows: the geosteering tool realizes the structural design under limited space; its maximum stress is lower than the yield strength of the non-magnetic drill collar under the actual working conditions. The structure meets the strength requirements. The research method based on the axiomatic design proposed in this paper makes a beneficial exploration of the structural design of geosteering tools in the petroleum industry.

Mechanical characterization of bottom hole assembly in air drilling engineering

To study the mechanism and control of well deviation in air drilling, a mechanical model of bottom hole assembly (BHA) with double stabilizer is established by using the beam-column method. The mathematical model related to side force of BHA and deviating force of strata are derived by analyzing the characteristics of gravel strata in the practical engineering. The effects of weight on bit (WOB), expansion ratio of borehole diameter (ERBD), angle of well inclination, diameter of drill collar and strata bending moment on side force of BHA are explored. Then, the superposition of bit side force and deviating force of strata is obtained. The results display that side force of BHA is obviously influenced by ERBD, angle of well inclination, diameter of drill collar and strata bending moment; and the deviation force and azimuth force of gravel strata are significantly affected by comprehensive cutting anisotropy index, angle of well inclination and dip angle of strata. Finally, the variation tendency of inclination angle and azimuth angle in field measurement is consistent with the theoretical and numerical researches. The present work can provide theoretical guidance to control the well deviation in the practical air drilling.