The longitudinal vibration of the drill pipe contains considerable energy which can be used to improve the rock-breaking efficiency during drilling. It is very important to the development of drilling speed-up tools to have a comprehensive understanding of the energy conversion efficiency of downhole drill string vibration. In this paper, the characteristics of downhole bit load and longitudinal vibration of drill string under different conditions were studied in the experiment, and the analysis method of energy conversion efficiency from drill string vibration to spring potential energy was proposed. The experimental analysis showed that the fluctuation of the downhole bit load was reduced by 10%–90% after the spring was installed in the bottom hole assembly. The rotation rate and the spring elastic stiffness had a significant and positive influence on the fluctuation amplitude of the downhole bit load. Meanwhile, the longitudinal vibration amplitude and acceleration of the drill string peaked at the elastic stiffness of 1 kN/mm. The closer the spring position to the drill bit was, the more severe the longitudinal vibration of the drill string above the spring component was. The bit load and the rotation rate had a positive influence on the severity of longitudinal vibration. The analysis of energy conversion efficiency showed that the available mechanical energy range of the longitudinal vibration of the drill pipe was about 200–420 kW. The work power of the drill string vibration to the spring component increased sharply and then decreased with the increasing of elastic stiffness. The energy conversion efficiency came to the optimal value when the elastic stiffness was between 1 kN/mm and 2 kN/mm. Increasing the rotation rate, keeping the bit load below 134.5 kN and installing the spring component near the drill bit are beneficial for improving the energy conversion efficiency of drill string vibration. This paper reveals the main factors affecting the energy conversion efficiency of drill string vibration and their influencing laws, and determines the range of WOB, rotation speed, spring position and stiffness to obtain the best energy conversion efficiency.

Dynamic Characteristics of Downhole Bit Load and Analysis of Conversion Efficiency of Drill String Vibration Energy

Modeling and analyzing the motion state of bottom hole assembly in highly deviated wells

We have integrated rock mechanics and acoustic experiments, full-wave array acoustic testing, formation microscanner image logging, and hydraulic fracturing data to evaluate the coupling relationship between current in-situ stress and natural fractures. We used the data of the Yanchang Formation in the DL block of the western Ordos Basin, China, as an example. Our results find that the Yanchang Formation mainly develops high-angle fractures and vertical fractures. Furthermore, the in-situ stress state of the target sandstone strata satisfies σv> σH> σh. Nearly vertical and high-angle fractures are formed in the environment when σv is the maximum principal stress. Therefore, the current in-situ stress state of the target layer matches the induced fractures (longitudinal tensile-induced fractures) and natural fractures. As the buried depth increases, the difference between the horizontal maximum and minimum stresses ( σH- σh) has a tendency to first decrease and then increase, and its conversion depth is approximately 2000 m. Natural fractures are not developed in the distributary bay (the lowest horizontal stress area) and the thick sand area in the middle of the main river channel (the largest horizontal stress area). Natural fractures are mainly developed on the two wings of the main channel, and their horizontal stress is approximately 2–4 MPa lower than the central part of the main channel. We determined a correlation between fractures and sedimentary facies, and we have an important reference value for improving the drilling success rate of tight oil reservoirs. Furthermore, our study provides insights into the prediction of fractures and sweet spots for further exploration and hydraulic fracturing activities in the studied area and elsewhere in continental tight sandstone reservoirs.

Coupling relationship between current in-situ stress and natural fractures of continental tight sandstone oil reservoirs

In this paper, the numerical simulation is used to study the rising mechanism of rotary-percussive drilling, which is under the combination of rotary cutting and axial impact. The main objective of the present work is to compare and investigate the breaking process of rock element and the motion state of drilling bit under the conventional drilling and rotary punching drilling. Additionally, the single-factor analysis is used to analyze the effects of impulse load, impulse frequency, rotary speed and formation hardness on rock breaking efficiency and acceleration effect of rotary percussion drilling. Through the investigation, it is found that there are more areas of tension stress breakage in rock elements under rotary-percussive drilling. Rotary percussion drilling can effectively alleviate the stick–slip vibration of drilling bit. At the same time, the relationship between the average penetration rate of the bit and the impulse load, impulse frequency, rotary speed and formation hardness is shown. The results of the study will be beneficial to provide some theoretical reference for the development of tools and the selection of working parameters of rotary-percussive drilling technology, as well as for the drilling methods of deep wells and hard rocks.

The Numerical Research on Rock Breaking and Rising Mechanism of Rotary-Percussive Drilling

Simulation study on cutting transport in a horizontal well with hydraulic pulsed jet technology

A novel tool to improve the rate of penetration by transferring drilling string vibration energy to hydraulic energy

The utility model relates to underground equipment for oil gas drilling, in particular to an underground check valve for oil gas drilling. The technical scheme is as follows: the underground check valve mainly consists of a valve body, a valve core pressing sleeve, a sealing assembly, a valve core, a return spring and a valve seat, wherein the top and bottom of the valve body are both provided with a connection thread; the outer side of the valve core pressing sleeve is of a trapezoidal thread structure, a runner and a center hole are arranged at the middle of the valve core pressing sleeve, and the valve core pressing sleeve is mounted at the top end of the valve body; the sealing assembly is compacted and positioned in the valve body by the valve core pressing sleeve and matched with the valve core; the valve seat is mounted at the bottom of an inner cavity of the valve body; and the return spring is arranged at the bottom of the valve core and mounted between the valve seat and the valve core. The underground check valve provided by the utility model has the beneficial effects that the return spring is away from a channel of high-speed flowing drilling fluid, and the limiting of the valve core is realized through the match between the upper step surface of the valve seat and the lower step surface of the valve core, thus the overpressure damage of the return spring is prevented, and the working life of the easily-damaged return spring is effectively prolonged.

Underground check valve for oil gas drilling

The utility model relates to a bottom ultrahigh-pressure pulse jet assisted rock-breaking speed-increasing system. The utility model adopts the following technical scheme: the system comprises an upper bearing assembly, a torque bearing assembly, an elastic return element assembly, a pressure cylinder body, an ultrahigh-pressure drilling fluid transmission assembly and an ultrahigh-pressure drill bit. The system has the benefits as follows: part of drilling fluid is intermittently pressurized by the reciprocating movement of a drill column or the drill pressure fluctuation, so that ultrahigh-pressure pulse jet flow can be formed at a nozzle of the ultrahigh-pressure drill bit, thereby greatly improving the bottom cleaning efficiency, assisting in rock breaking at the same time and greatly increasing the drilling speed; the system is well-designed, so that the overall structure is greatly simplified and all parts are easier to process, mount, dismount and repair; and meanwhile, the system is good in stability and reliability on the aspects of structural mechanics and mechanical kinematics, so that the service life of the system is prolonged, the rock breaking efficiency is greatly improved, the service life of the drill bit is prolonged, and the mechanical drilling speed is increased.

Bottom ultrahigh-pressure pulse jet assisted rock-breaking speed-increasing system

The utility model relates to a down-hole check valve for oil and gas drilling, in particular to a valve element reset system of a down-hole check valve for oil and gas drilling The valve element reset system consists of a valve element, a return spring, a valve seat, a spring wire plug and a plug locating ring, wherein the bottom of the valve element is connected with the valve seat, the spring wire plug and the plug locating ring are mounted at the bottom end of the valve seat, the return spring is disposed between the spring wire plug and the valve element, the inner side of the valve seat is provided with a step face which is matched with a lower step face of the valve element The valve element reset system of the down-hole check valve for the oil and gas drilling has the advantages that the return spring is no longer exposed in drilling fluid which flows in high speed, limit of the valve element is achieved by means of matching of the step face on the inner side of the valve seat and the lower step face of the valve element, overpressure damage to the return spring is prevented, and service life of the return spring which is prone to damage is prolonged effectively Besides, the valve element reset system of the down-hole check valve for the oil and gas drilling is simple in structure and stable in performance, and cannot bring other risks to drilling operation in the process of use

Hongning Zhang

Papers

Dynamic Characteristics of Downhole Bit Load and Analysis of Conversion Efficiency of Drill String Vibration Energy

A novel tool to improve the rate of penetration by transferring drilling string vibration energy to hydraulic energy

Underground check valve for oil gas drilling

Bottom ultrahigh-pressure pulse jet assisted rock-breaking speed-increasing system

Valve element reset system of down-hole check valve for oil and gas drilling