The rotary sidewall coring technology first appeared in the 1940s, when the drill pipe was lowered into the well. This coring method can obtain a small amount of cores from the borehole wall, but it still needs to trip the drilling tools, which is complicated, time-consuming and expensive, and the effect is limited. In order to improve the efficiency of sidewall coring, it was later developed into a rotary sidewall coring device using cable to trip. In recent decades, this kind of coring device has been continuously improved and used more and more.
Fig. 4. 10 Xi schematic diagram of continuous cutting borehole wall sampling in an petroleum exploration instrument factory.
The sampling system adopts multi-core cable lifting coring device, which supplies power to underground devices through cables. There is a special control panel on the surface for operation control. The downhole sampling device is mainly composed of motor, propulsion positioning device, drilling coring mechanism, core clamping mechanism, sampling pipe conveying mechanism, sealing device and core storage device. The structure is complex, and the outer diameter is usually large, so it can only be used if the aperture is larger than170 mm. This sampling method has its unique advantages, such as short sampling time for a single core and multi-point coring in one trip. Moreover, this sampling device uses motor or hydraulic motor to drive the diamond bit to rotate at high speed, which can be used in hard rocks. Although the diameter and length of the drilled rock samples are small, most of them are cylindrical, regular and of high quality, which can meet the needs of various geological analysis. In recent years, several major oil service companies in the world have done a lot of research and improvement on this sampler, and obtained many new patents. The former Soviet Union also has its own series of such coring devices. In the main hole coring plan of KTB in Germany, this coring device is also used as the sidewall coring device for the ultra-deep hole section of 6000 ~10000 m. Table 4.4 is a comprehensive questionnaire of rotary sidewall coring technology. Here are some representative examples to introduce this coring device.
Schlumberger's 4.5. 1 MSCT (mechanical sidewall coring tool).
Schlumberger Company is the first company to develop horizontal drilling sampler in the world. It launched its own rotary sidewall coring device in 1947. However, due to the complexity of instruments and equipment at that time and the superb technology required for operation, they were not widely used, and stopped using around 1955 (Wang, 1998). In 1985, Schlumberger Company developed a newly developed sampling device and method for hard rock sidewall-"Hard rock sidewall or downhole instrument". This sampler combines the characteristics of various rotary samplers, adopts advanced hydraulic technology and has a high degree of automation. Figure 4. 1 1 is the latest MSCT picture released by Schlumberger on its website.
Table 4.4 Technical Questionnaire for Rotating Wellbore Coring
Fig. 4. Schematic diagram of11MSCT
According to Schlumberger, the parameters of MSCT are as follows:
Number of coring trips: standard 50 times, optional 20 ~ 75 times;
Core size: diameter 23.4mm, length 38.1mm ~ 44.4 mm; Coring efficiency: 3 ~ 5min/ pill;
Temperature resistance: 177℃, the maximum is 218℃;
Pressure resistance: 138MPa, and the highest can reach172 MPa; ;
Outside diameter of the instrument:136.5mm; ;
Instrument length: 9.54m;
Instrument quality: 340kg；;
Applicable well diameter: 158.7 ~ 482.6 mm, which can be used for the smallest well of 127mm by changing accessories.
4.5.2 RSTT TM (rotary sidewall coring tool) of Halliburton Company.
Halliburton Company of the United States is also one of the suppliers of products and services in the oil and gas industry. The company has RSCTTM technology, which was first developed by Gearhart. Halliburton Company acquired Gearhart Company on 1988. This technology also belongs to Halliburton Company. This technology was once listed as one of the research and development projects of hole wall coring system when designing KTB main hole coring with a length of 6000 ~ 10000 m in Germany. Fig. 4. 12 is the schematic diagram of the system. Figure 4. 13 is the picture of RSTT TM sidewall coring bit published on Halliburton website.
Fig. 4. Partial photo of12 RSCT sidewall coring bit
Fig. 4. Partial photo of13 RSCT sidewall coring bit
RSCT uses a diamond bit to drill holes perpendicular to the borehole sidewall, and it is monitored at any time during the drilling process. After gamma-ray depth positioning, the push arm extends to firmly fix the drilling tool on the stratum to be coring. A diamond drill rotating at 2000 rpm cut a rock sample with a diameter of 23.8 mm and a length of 45 mm from the stratum. By controlling the WOB applied to the drill bit, drilling is optimized by surface control.
When the rock sample is cut, the rock sample falls off the borehole wall by slight vertical movement of the drill bit. Then, the drill bit with the rock sample is retracted into the drilling tool, and the rock sample is poked out and falls into the core barrel with the core. The indicator shows whether coring is successful and the depth of coring. Then, the drilling tool is ready to sample the next core point.
RSCT drilling tool is used for coring in dense formation, tubular bit with diamond cutting edge is used for core cutting, and the supplemented core is cylindrical. Fig. 4. 14 is the borehole core photo obtained by RSCT.
The system works independently of other systems on logging engineering vehicles or slide rails. It only needs AC power. At the same time, a recording instrument is needed to record the relevant data of gamma rays. This downhole equipment is controlled by the control panel on the ground. Figure 4. 15 is a photo of the RSCT ground control panel.
Fig. 4. Photo of14 RSCT borehole core
Figure 4. Photo of15 RSCT ground control panel
RSCT drill has the following characteristics:
1) 30 or more cores can be drilled at a time;
2) Being able to work on high-angle logging system or coiled tubing logging system to obtain cores of deviated wells, multilateral wells and horizontal wells;
3) A core length indicator is designed to avoid determining the core length by guessing when coring;
4) This independent drilling tool can work on a third-party logging tool.
Some technical parameters of RSCT published on Halliburton's website are shown in Table 4.5.
Table 4.5 Table of Technical Parameters
4.5.3 RSCT (rotary sidewall coring tool) of Weatherford Company.
Weatherford is also a well-known multinational company providing oil and gas drilling and related technical services. A rotary sidewall coring tool (RSCT) is also provided, and its structural schematic diagram is shown in Figure 4. 16. The obtained core picture is shown in Figure 4. 17.
Some technical parameters are as follows:
Bit type: diamond bit;
Bit rate: 2000 rpm;
Single coring: 25 times;
Applicable drilling diameter:152 ~ 324 mm;
Instrument diameter:124 mm; ;
Instrument length: 5.1m; ;
Maximum applicable temperature:149℃;
Maximum applicable pressure:138mpa; ;
Instrument quality:159 kg; ;
Core size: 24 mm in diameter and 44 mm in length.
Fig. 4. 16 schematic diagram of weatherford rotary sidewall coring device (RSCT)
Fig. 4. 17 coring photo of weatherford rotary sidewall coring device.
4.5.4 The sampling technology of rotating shaft wall in the former Soviet Union
The former Soviet Union was the first country to develop rotary sidewall sampler, especially after decades of efforts, it has been continuously improved and perfected, and has now entered a practical stage in sedimentary rock drilling. The following are a series of borehole wall sampling instruments introduced by вниити (research institute) from all over the Soviet Union.
(1) ско-8-9 sampler
This sampler is the first sidewall sampler widely used in oil and gas exploration wells in the former Soviet Union. It can be used together with common logging equipment and instruments, and put into the borehole through ктб-6 three-core armored cable.
ско-8-9 sampler can be used for sidewall coring of sleeveless borehole with a depth of 3500m. As shown in fig. 4. 18, the whole set of equipment includes console 1, console 2, booster transformer 3, winch 4, logging cable 5 and sidetracking sampler.
Figure 4. 18 ско-8-9 Multi-sampler Equipment Connection Diagram
The working sequence of the sampler is as follows: run the sampling hole section in the hole, and the ground console provides three-phase alternating current through the logging cable to start the functional components of the sampler, so as to press the sampler against the hole wall, and then start drilling rock samples; When the drilling tool is completely retracted (observed from the console), the sampler and its connected functional components are reversed, so the drilling tool with core and the pressure bar (push arm) are retracted; Then stop the power supply and move the sampler to a new sampling hole part.
As shown in fig. 4. 19, the sidetracking sampler ско-8-9 is powered by the logging cable and cable head 13, and the rock sample is drilled by the drill bit 8 embedded in the end of the drilling tool 6. Motor 18 realizes the rotation of drilling tool through bevel gear and spur gear device. In the process of drilling rock samples, the sampler is pressed against the hole wall by the piston 1 1 push rod 19. The hydraulic pressure generated by the piston pump 3 makes the piston move in the cylinder, and the piston pump is also driven by the motor 18. It is this pressure that acts on the piston and drilling tool, thus providing the rotary drilling rig with the axial force needed for drilling. The axial force can be adjusted by changing the pressure with the help of the feed regulator, and the pressure reducing valve of the feed regulator can be rotated by the micro motor.
In the process of drilling, with the help of the flushing pump 9 started by the hydraulic system of the sampler, the drilling cuttings are washed away by the liquid filled in the drilling. The whole sampler and hydraulic system are filled with transformer oil. The pressure in the sampler is compensated by piston or pore pressure compensator 14. In order to prevent the liquid in the hole from entering the sampler (if any sealing element fails to seal), the spring of the compensator generates overpressure in the sampler relative to the drilling hole. The drilling speed of the sampler can be controlled by changing the resistance of the rheostat 20 on the console, and the slider of the rheostat is connected with the piston of the drilling tool.
When the drill bit completely drills into the hole wall, the motor reverses, changing the rotating direction of the hydraulic pump and the moving direction of the liquid in the hydraulic system, making the drilling tool retreat and the core blocked by the core breaker. The core breaker is used to twist the rock sample by the impact torque generated in the acceleration-impact mechanism and tighten the drilling tool at the same time to break the core.
In this sampler, a backup device is also included, so that when the sampler fails in the drilling process, a section of drilling tools drilled into the hole wall can be cut, and the pressure bar is tightened by spring 10 (the pulling force is 8 ~ 9KN).
Fig. 4. 19 ско-8-9 sampler
The dotted line in figure 4. 19 indicates the hydraulic circuit of the sampler. When the drilling tool is drilling forward, the pump 3 presses the liquid in through the valve 1, and the liquid is delivered to the cylinder of the compacting device and the flushing pump 9 through the trunk line 16, and is delivered to the piston of the drilling tool 6 through the piston of the feed regulator along the trunk line 17. When the motor rotates reversely, it changes the flow direction of the liquid, and the liquid is delivered to the drilling piston and the compression cylinder through the trunk line 4, and the pressure of the hydraulic system is regulated by the valve 2.
(2) скм-8-9 multiple sampler
The application of the ско-8-9 sampler shows that cores with a diameter of 22mm and a length greater than 20mm can be collected under the condition of keeping the best drilling parameters and using the аск-35/22 diamond bit. However, with the increase of drilling depth (>: 4000m), the use efficiency of ско-8-9 drops sharply, because the number of rock samples collected each time is very small (up to 3 cores), and the power supplied to the motor decreases due to the increase of conductor resistance of logging cable. Therefore, a new type of скм-8-9 sampler is developed, which can ensure that more samples can be taken at one time.
Figure 4.20 скм-8-9 sampler
Fig. 4.20 is the general diagram of the скм-8-9 sampler. The rock sample is drilled by the drill bit at the end of the drilling tool 6, and the power motor 4 drives the drilling tool to rotate through the reducer 5 and 16. Before drilling the rock sample, the sampler is pressed against the hole wall by the pressure rod 17 and the piston 9, which is moved by the pressure generated by the hydraulic pump 3, which is rotated by the motor 4. After the core is stuck, the feed and return of the drilling tool is realized by the piston 15 and the pull rod 1 1 acting on the rod 7. The drilled cores are pressed out of each other and fall into the box 8. The axial load required for core drilling is adjusted by the remote controller of the choke, and its size depends on the performance of the rock stratum. The reciprocating motion of the piston 12 of the flushing pump washes the drilling cuttings, and the upper cavity of the flushing pump is communicated with the inner cavity of the drilling tool. The piston port moves periodically under the pressure of the hydraulic system, and the hydraulic system acts on the power piston first. During drilling, the drilling speed of the drilling tool 6 is controlled according to the resistance change of the drilling sensor 14. The pressure of the working liquid in the sampler is compensated by the piston pressure compensator 1 In order to handle the accident in the sampler, the spring 10 is used to tighten the pressure rod 17.
The application shows that compared with ско-8-9, the скм-8-9 sampler has the following advantages:
1) can be sampled many times at a time;
2) The hydraulic protection of the motor is good;
3) The drilling tool flushing system and drilling technology are improved, and the quality of rock samples is good;
4) The operation of the sampler is simplified.
(3) скт- 1 heat-resistant sampler
With the increase of drilling depth, the temperature in the hole will also increase. When the temperature is higher than 100℃, the ск10849 sampler is not suitable. Therefore, a heat-resistant sampler was developed, which can be used under the conditions of hole depth of 5000 meters and temperature of 65438 050℃. In this sampler, each functional part is mechanically driven and an independent cleaning device is adopted.
Fig. 4.2 1 is скт- 1 heat-resistant sampler. The cable head is connected to a light-emitting bridge with a sealed input end; Compensator 2 is used to balance the pressure of the working liquid in the sampler, Wainai pressure; The motor 3 connected with the driving part realizes the rotation and movement of the functional part (pressing the sampler on the hole wall, rotating, feeding and cleaning the drilling tool); The driving part is connected with the shell, and all actuators are arranged in the shell.
The universal shaft 6 transmits the rotation to the drilling part 15, and the drilling part can guide the rod 14 to move axially. There is a core breaker inside the drilling tool, and the drill bit is screwed into the end of the core breaker. The drilling tool rotates in the rubber packing box, which can seal the cavity in the shell. There is a pin 16 on the casing of the drilling tool 15, which is used to fix the copying ruler 12 inclined to the axis of the sampler. The nut 7 is connected with the template ruler, and can interact with the lead screw 13 of the driving part 4. The copying ruler 12 is also connected with the flushing piston 2 1. The lower part of the shell is provided with a mud collector 22, and the inner cavity of the collector is connected with the inner cavity of the drilling tool through a bypass 20. In order to store the drilled rock samples, a core receiving box is used and fixed on the detachable cover 24.
The pressing rod device 23 is hinged and fixed on the shell, and is connected with the claw of the nut 9 through the operating handle 1 1 and the safety pin 10, and the nut interacts with the lead screw 8 of the driving part. The drilling tool 15 is provided with a center stop mechanism 17, 18, 19 and a brake mechanism 5. When the forward drilling reaches the end point, the center stop mechanism is started.
The working principle of the скт- 1 sampler is that after the sampler is fixed at a given sampling position, the motor 3 is started to drive the driver 4, the universal shaft 6, the lead screw 13 and the lead screw 8 to rotate simultaneously. The screw 8 drives the nut 9 to move, so that the pressure bar 23 presses the sampler against the hole wall with a certain pressure, and the screw 8 stops rotating. At the same time, the nut 7 moves along the axial direction together with the nut 9, so that the copying ruler moves. The movement of the copying ruler realizes the rotation of the drilling tool and the feed of the drill bit, and drives the piston 2 1 of the drilling tool flushing system to move.
At the end of drilling tool stroke, start the core blocking mechanism 17, 18, 19 and the brake mechanism 5 of the sampler. The braking mechanism is a pair of conical friction clutches, which act on the central shaft and electric drag (when the end of the copying ruler interacts with the brake sleeve).
Figure 4.2 1 скт- 1 heat-resistant sampler
When the sampler stops (as can be observed from the console, because the current increases sharply at this time), the electric drag reverses, and the pressure rod and drilling tool are tightened. When the actuating mechanism is restored to the original position, the ratchet mechanism installed in the driving part stops the rotation of the central universal shaft, thereby tightening the drilling tool when the drill bit does not rotate, which precludes the screw-out of the drill bit, and the cone of the braking system does not hinder the starting (when the motor runs reversely). The driver can quickly tighten the drilling tool, and the given shape of the copying ruler can ensure the sequence of tightening the piston first and then tightening the drilling tool, so that the drilled rock sample can be sucked into the core receiving box by the flushing fluid.
The test shows that compared with the скм-8-9 sampler, especially when it is used in high-temperature drilling in deep wells, the скт- 1 sampler has the following advantages:
1) Because there is no gear pump (almost half the power of the motor is consumed), the driving efficiency of the sampler is greatly improved; 2) Because there is no regulating valve, reducing valve, slide valve distributor and a large number of hydraulic trunk lines and seals, the reliability of the deep hole sampler is improved;
3) Adopt independent flushing system to improve core drilling technology;
4) The core is sent to the receiving pool by the forced core retaining mechanism and hydraulic way, which improves the recovery rate of rock samples;
5) The number of times that the sampler can't sample due to the loosening of the drill bit is reduced;
6) The operation, pre-inspection and maintenance of the sampler are reduced.
Table 4.6 lists some technical parameters of the former Soviet Union series sidewall sampler.
Table 4.6 Table of Technical Parameters of Borehole Sampler in the Former Soviet Union
4.5.5 Domestic rotary sidewall coring technology
The development of rotary sidewall coring technology in China started late. At first, similar instruments were mainly imported from foreign oil service companies, but the actual application effect was not ideal. 1986, Henan Oilfield Logging Company and Beijing Aerospace Automatic Control Research Institute (No.1 Aerospace Institute 12) developed HH- 1 rotary sidewall coring device (Tian, 2000) after 8 years of scientific and technological research, as shown in Figure 4.22.
Fig. 4.22 HH- 1 rotary sidewall coring device
This device is basically an imitation of RSCT coring device of halliburton Company. The main improvement is that two push arms are added on the basis of one push arm of Halliburton products, and these two push arms are auxiliary push arms. However, in actual use, it is found that the role of the two auxiliary push arms is not too great, so the actual use effect of this sidewall coring device is not very ideal.
Because the application effect of HH- 1 rotary sidewall coring device is not ideal, some domestic companies have made some research and development and improvement on it, and kept the internal actuator of HH- 1, but the application effect after improvement is still not ideal. Among many improvements, the work of Beijing Huaneng Tongda Energy Technology Company is relatively outstanding. The sidewall coring device produced by this company is called FCT (formation coring tool) rotary sidewall coring device (Figure 4.23). Some technical parameters of this instrument are as follows:
Length 6.8m；; Body weight180 kg; ; Maximum diameter127mm; ; The number of cores available for one trip is 25; The size and diameter of the rock sample are 25mm and the length is 50mm. ; Temperature resistance150℃; Bear the pressure of 100MPa.
At present, there are two domestic companies that can provide rotary sidewall coring services: China Offshore Oil Field (COSL) and China Petroleum Logging (CNLC). The corers of these two companies mainly introduce similar foreign products or imitate foreign products.
Fig. 4.23 FCT rotary sidewall coring device