Reducing drilling costs, protecting and timely discovery of oil and gas formations, and improving exploration efficiency are common issues faced by wellbore technologies. In the past, due to various reasons, drilling process control was often carried out based on experience, lacking scientific basis, resulting in the continuous occurrence of drilling engineering accidents. Especially in the drilling process of highly deviated, extended reach wells and horizontal wells, drilling engineering accidents occur from time to time. Among them, drill bit accidents are the most common. To a certain extent, it affects the data collection, interpretation and the protection of oil and gas layers. Torque transducers can make up for the inherent deficiencies of drilling work. Through the torque parameters, we can gain insight into all kinds of sudden drill bit accidents, and provide a decision-making basis for accurate prediction of engineering accidents. The interpretation and application of torque parameters can correctly guide engineering construction, improve the level of logging technology and data interpretation, and facilitate the rapid discovery of oil and gas shows. It can improve drilling efficiency and ensure safe drilling.
1. Three Common Torque Transducers
There are mainly three types of torque transducers: discus type, bridge wheel type and electric torque transducer.
1.1 Electric torque transducer
The electric torque transducer obtains the torque parameters of the turntable by testing the power supply current of the drive motor. The sensor adopts a clamp-type structure for easy installation and use. The output is a standard current signal of 4-20ma. Installation and use: disassemble the protective cover of the signal cable, loosen the wire clamp, and pass the signal cable into the protective cover through the wire clamp to press the sealing plane tightly. Finally, tighten the cable clamp nut to fix the signal cable on the protective cover. Open the sensor clamp, wrap the wire under test with foam plastic and adjust the thickness of the winding, so that the wire under test can be fixed in the hole after the clamp is closed without shaking.
1.2 Flange torque transducer
The top wire type turntable torque transducer uses a cylindrical resistance strain measurement sensor with a special structure. By measuring the torsion force of the drill disc, it is acted by the self-weight and frictional force of the turntable. In order to make the turntable produce a slight angular displacement by the twisting reaction force, a rubber pad should be installed between the three top wires and the turntable, and graphite oil should be applied to the bottom of the turntable to reduce friction. The flange torque transducer is subjected to force to reduce the influence of external force to improve the sensitivity of the measurement system.
Installation and use
Mechanical installation: first hoist the turntable, apply graphite oil between the turntable and the large frame, then remove the top wire and replace it with the sensor, and put a rubber pad between the three top wires and the turntable, and tighten the top wires and sensor, so that the sensor has a certain prestress. Suspend the sensor wire cable and connector on a large right or derrick with lead wire.
1.3 Bridge wheel torque transducer
During the well drilling process, the torque transducer of the tension wheel rotary table is used to measure the change of the torque of the rotary table driving drilling tool, which can correctly reflect the working condition of the down hole drilling tool and the changes of the bottom hole formation. For example, the wear of the drill bit, the biting or falling off of the cone, the sticking or breaking of the drill string, and the change of the formation hardness will all cause the change of the drive torque of the turntable. Therefore, the correct measurement and display of the torque of the turntable with the tensioner type turntable torque sensor is helpful to grasp the underground working conditions in time. Once the accident seedlings are found in the mountains, corresponding measures can be taken as soon as possible to avoid the occurrence of accidents, so it is an important safety parameter. During the drilling process, the diesel engine drives the draw works and the turntable through a series of transmission devices through the transmission chain, and the turntable drives the drilling tools to realize drilling. The tension of the transmission chain can correspond to the torque of the turntable. When the down hole drilling tool is abnormal or the formation litho logy changes, the torque of the turntable changes, which affects the change of the chain tension. According to this principle, a tension wheel type turntable torque transducer is placed under the transmission chain, which converts the tension force of the chain into oil pressure, and then through a pressure sensor, the output oil pressure signal is converted into an electrical signal. The strength of the electrical signal reflects the change of the drive torque of the turntable, and the electrical signal is transmitted to the secondary torque meter or computer interface through the cable to display and collect the information of the drive torque of the turntable.
Installation and use:
- Installation of the closed chain box Due to the needs of lubrication and dust prevention, the closed chain box has a large amount of lubricating oil in the box. , The torque transducer of the tension wheel type turntable will gradually lift up with the filling of hydraulic oil. When the tension wheel slightly touches the chain, it is necessary to correct the position of the sensor up, down, left and right. After confirming that it is correct, weld the long and short pads on the On the base of the chain box, screw up the limit bolt to contact the suspension, and then tighten the lock nut. In order to connect the pressure sensor and the oil filling pump with it, a 27 hole must be punched in the chain cover, the high-pressure hose joint is passed through it, and the outside is locked with a round nut, the chain cover is closed, and the chain lubricating oil is added. Unplug the oil injection pump and connect the pressure sensor assembly (with a three-way quick connector), and the installation process is completed.
- Installation of the semi-enclosed chain box. The installation method of the semi-enclosed chain box is similar to that of the fully enclosed type, except that there is no need to drill holes on the chain cover. After installation, the pressure sensor assembly can be connected to use.
2. Influencing Factors of Torque Parameter Curve
Torque is an important parameter in drilling engineering. It is affected by formation, drill bit, drilling tool structure, WOB, rotational speed, pump stroke, drilling fluid performance and surface mechanical factors. It is difficult to determine its absolute value when the rotary table is driven. And it is not accurate enough, but in the case of relatively stable factors such as WOB, rotational speed, and litho logy, the relative torque value is very meaningful. The torque parameter is an indirect measurement parameter of the drilling tool vibration, which realizes the measurement of the rotation force of the down hole drilling tool on the ground. The following describes torsional stick-slip, bit run out, and forward deflection of the drill tool assembly.
2.1 Bit run out
The drill bit beats, the drill bit cone and the teeth have a certain distance. With the rotation of the drill bit, the teeth and the formation are in contact with each other. The load acting on the teeth and the cone changes periodically, and the fluctuation of the load can cause the cone. Fluctuations in rotational speed and bit rotational speed, which are reflected in torque as a narrow and uniform oscillating torque curve. If the teeth of the drill bit are worn, the teeth are broken, the roller cones move, the roller cones fall off, the roller cones are stuck, and the drill bit mud bag, etc., the vibration characteristics are uneven due to uneven twisting, which will cause the axial vibration amplitude of the drill bit to be obvious. If it increases, the axial load and torque detection value on the drill bit fluctuate greatly. If a certain cone is stuck, when the bit rotates once, some periodic signals may appear, and the torque curve shows asymmetrical amplitude fluctuations.
2.2 Torsional stick-slip
Torsional stick-slip are caused by the dynamic and apparent friction between the head drill assembly and the borehole wall, which hinders the balanced rotation of the entire drill string. The process is a process of energy accumulation and release. Static friction may be produced by BHA deflection or bending, a deep cut of the bit teeth, the contact of the BHA with the open wall, and the sudden start of the bottom hole bit, etc., will hinder the rotation of the BHA and the bit. When the drill string has a torque sufficient to overcome the static friction, the released drill string rotates rapidly at first, then decelerates, and when its rotation speed falls below a critical value at which static friction acts, the rotation stops again. The duration is about 1 to 40s. The ground sensor samples at a higher speed, and the curve detected by the torque sensor is a sine wave or saw tooth wave that oscillates evenly.
2.3 Forward deflection
The positive deflection of the drilling tool assembly is defined as the rotation of any part of the drill string from the offset center. In the forward deflection of the bottom hole assembly, the movement direction of the center point of the drill collar is the same as the rotation direction of the drill pipe. If the deflection speed of the drill collar is the same as that of the drill pipe, the deflection is fully synchronous forward deflection. If this deflection amplitude remains constant, there is no periodic bending stress in the collar during fully synchronized deflection. If the deflection amplitude varies greatly, the result is bending fatigue. Forward yaw appears as a sudden increase in the torque curve.
The above three factors influence and restrict each other, and they are accompanied in the drilling process. The torque amplitude variation curve measured at the surface can be regarded as a superimposed composite curve of the axial and torsional vibrations of the drill string.
3. Characteristic Analysis of Torque Parameter Curve and Formation Process of Torque Parameter Curve
3.1 Electrical signal processing process in real-time logging, the torque oil pressure is transmitted to the pressure sensor through the pressure pipeline, and then processed into a standard 0-10V voltage signal or 4-20mA current signal through a pressure transmitter. This voltage signal is passed through a/ The d board is converted into a digital quantity and enters the computer, and the current signal enters the computer as a digital quantity through the serial port through the sampling resistor and the signal processing board. The digital signal entering the computer is converted into an analog voltage signal through program processing and displayed on the screen. The logging personnel convert the voltage signal into a torque value by means of calibration. The program collects the torque voltage signal in real time and converts this signal into an actual torque value. displayed on the screen, thus forming what we call the torque parameter curve. The logging software also has the function of parameter playback, that is to say, the real-time recorded data is saved in the computer at the same time, and we can choose the time period to play back the recorded parameter curve, which prevents the real-time data from being lost due to printer failure.
3.2 Calibration of torque parameters, the computer collects the voltage signal, and the user needs the actual torque value, so we need to establish the corresponding conversion relationship between the signal voltage and the torque value, we call this process calibration. In the actual logging, we use the torque type to calibrate the torque parameters. In normal drilling and logging, when the WOB, rotational speed, litho logy and other conditions are relatively stable, the absolute value of the torque parameter changes little, and the resulting curve is uniform and stable, with small fluctuations.
3.3 The torque curve when the drill bit accident occurs, the author is mainly based on the research work carried out in the oil field, and mainly collects the relevant engineering parameters of 15 drill bit accident wells in recent years. The original graphics are comprehensively analyzed by the methods of playback and cutting , Evaluation. Further understand the changes of engineering parameters and the performance characteristics of the torque curve when the drill bit accident occurs. Provide decision-making basis for rapid drilling and scientific well drilling. Due to the sudden increase of the weight on bit or the hard formation, the uneven rotation caused by the uneven force causes the broken teeth of the cone, and then the broken teeth are squeezed into the well wall, the bit jump is reduced, and the torsional fluctuation is weakened. When the drill teeth are completely broken, the torque curve becomes stable. In this process, the intermittent torque fluctuation curve and the normal drilling torque curve are combined into a beaded torque curve characteristic.
3.4 The torque parameter curve is the general rule for judging the state of the drill bit, and the torque parameter is the most direct and effective parameter for judging the down hole drill bit. Generally speaking, different states of the down hole bit have different performance characteristics on the torque parameter curve. Based on this, we divide the state of the down hole bit into four stages for the qualitative discrimination of torque parameters, as shown in Table 1.
|Stage name||Bit status||Curve feature||Take measures|
|Stage 1||Bormal||The curve is uniform, smooth, without spikes, glitches||Fast drilling|
|Stage 2||Drill string stick-slip|
|The curve is uniform, the fluctuation range becomes wider, and there are occasional glitches||Reduce bit pressure, Increase speed|
|Stage 3||Bit broken teeth||The curve fluctuates greatly, and it is beaded||Reduce bit pressure, increase rotation speed or trip out to replace drill bit|
|Stage 4||Cone moving||Increased curve swing, increased burr, rectangular or trapezoidal features||Trip out immediately and replace the drill bit|
- Qualitative discrimination rule of torque parameters.
- Discrimination law of torque parameter quantification. After the torque transducer is installed, the rubber wheel just pushes up the chain. At this time, the torque has a value, which we call the zero value. When the turntable does not rotate and the drilling tool is lifted, the torque The parameter value will return to the zero value. In normal drilling, when the WOB and rotational speed are uniform and the lithology of the formation changes little, we call the torque value at this time as the base value of torque, and the torque parameter value will form a parameter curve with less fluctuation. . With the increase of the use time of the drill bit, the wear of the drill bit increases, and the torque parameter value will fluctuate with the wear of the drill bit.
4. Application of Torque Parameter Curve in Geosteering
The application of torque parameter curve in geosteering, comprehensive logging practice proves that the drilling parameters and logging data under the same conditions are basically stable, but the logging parameters also change with the change of formation litho logy. The most obvious performance is when drilling. Generally speaking, in the contact between sandstone and mudstone, the increase is more than 30% during drilling. In the contact between mudstone and gypsum rock, the drilling time is reduced by about 30%. In the contact between sandstone, mud shale and coal, the drilling time is significantly reduced, and the reduction range is large. Torque parameters are also closely related to formation litho logy.
5. Conclusions and Recommendations
Torque is the main parameter for judging the bit accident, the absolute value of the torque at a certain point cannot reflect the actual situation of the down hole bit, but the relative change in a certain period of time has practical significance. In the on-site logging interpretation system, some drill bit accidents cannot be judged by the torque parameters alone. It should be comprehensively analyzed and judged in combination with parameters such as WOB, drilling time, rotational speed and the changes in formation litho logy, which will be more helpful to improve the drill bit. Accident forecast accuracy. In the field drilling, there are many factors that affect the down hole drill bit, so it is not easy to judge the drill bit accident. This paper collects relatively few typical cases, describes the curve characteristics of different drill bit accidents, and forms a general discrimination rule. When applying this conclusion to judge the on-site drill bit accident, it is necessary to combine the actual engineering situation and the real-time curve of logging parameters to make a comprehensive judgment.