DSP chip in ultrasonic drilling fluid leak detector of
Oil and gas exploration drilling an important part, in order to ensure efficient and safe drilling, blowout prevention of lost circulation and the need to use in the drilling process has certain bonding properties of the mud as the drilling fluid. It is a combination of raw materials according to geological conditions underground preparation made according to proper proportion, and its costs are around one-third of the entire drilling costs. As the complexity of the structure of underground strata, often encountered in cracks and pore formation, resulting in mud leakage This not only seriously affected the conduct of drilling operations, 10 million unnecessary economic losses, but mud is a kind of harmful substances, leakage will add resources and the formation of groundwater pollution, threatening the living environment for future generations.
Mud leakage phenomenon occurs, the most important thing is to identify as accurately as possible leakage locations in order to adjust leakage pulp composition and particle size, plug the cracks and other drain-source formation. Historically, the method has been introduced there are mainly two: One is the with the temperature sensor to monitor the temperature at different depths underground changes. Due to the temperature spread of non-real-time and small amount of leakage did not change significantly when the temperature and other factors, this method can not accurately determine the location of the mud leakage. the other is using direct measurement of air velocity meter, thus determine the location of the mud of the leakage. but because of the constraints of measurement of the environment itself, using the flow meter contains a rotor and other moving parts, while the moving parts susceptible to drilling in the sand measurement of the impact caused by unreliable or failure.
Described in this paper the main ultrasonic drilling fluid leak detector are: (1) uses ultrasonic sensors, there is no mechanical moving parts; (2) has a very good real-time; (3) using the same two properties ultrasonic sensors on the hair, on the income, not as a direct measurement of pressure sensors as sensitive surface; (4) using a TMS320VC33 floating-point digital signal processor to improve measurement accuracy.
1 Measurement principle
1.1 The leak detector of the structure and installation method
Ultrasonic fluid leak detector of the structure and installation method shown in Figure 1. Measuring circuit installed in the upper and lower cavity formed sleeve, two ultrasonic sensors were installed in the upper and lower ends of the sleeve surface, central hole through the drill pipe into the mud hole and then drill the outer wall and the wall constituted by the annular space back to the ground.
1.2 development of ultrasonic sensor
Can be seen from Figure 1, the sensor axis and the distance between the outer wall of the drill pipe is very limited, in order to ensure the ultrasonic sensor signals can be received through the mud directly into the sensor, ultrasonic sensors need to control the center of angle. Located a distance of two sensors L, sensor axis distance from the shaft axis D, drill pipe diameter d, angle θ should be to enable the Center to meet:
θ = tg -1 [(2D-d) / 2L]
Θ is the actual structure allowed 2.95 °, which in general ultrasonic sensor is a much more stringent targets, addition, since the downhole temperature of up to 150 ℃, pressure 100Mpa, hence developing a special ultrasonic sensor, its working frequency 600kHz.
1.3 Measurement principle
Two sensors alternately transmit and receive ultrasound signal, recorded as close to the ground, a B, one near the mine recorded as A, then A sent, B received the time spent as follows:
tAB = L / (C + V) (1)
Similarly, B sends, A receives the time spent as follows:
tBA = L / (CV) (2)
Available from the above two type:
Δt = tBA-tAB = (2LV) / (C 2-V 2) (3)
Where, c for the ultrasonic propagation velocity in the mud, V for the mud flow rate.
As the C>> V, so C2-V2 ≈ C2, therefore:
V = ΔtC2/2L (4)
Can be seen that as long as the measured time difference Δt, you can find the mud flow, and thus infer the situation underground leakage. Leakage layer of location is through time and depth of the conversion relationships established, the ground computer and downhole measurement circuit at the same time start running, because the ground can be easy to grasp the depth of downhole equipment and downhole tools can also record any point in time the mud flow rate, when the device is only raised to the ground, it will playback of recorded data to a computer, you can know where the depth of the flow rate.
2.1 leak detector circuit structure
Leak detector circuit shown in Figure 2. Map IC1 is a DSP chip, where the company's TMS320VC33 using TI floating-point digital signal processor, which is the core of the whole measuring circuit, its instruction cycle of 17ns, word length of 32 , extended precision 40-bit, internal memory capacity of 34K × 32bit, addressable space-16M, with a 32-bit serial port, a DMA channels, two timers, two external interrupt sources; chip supply voltage to 3.3V, core power supply voltage of 1.8V, provided by IC5. As the chip is running at high velocity, the external oscillator circuit in order to prevent high frequency interference caused by radio frequency, the external oscillator uses an internal frequency-doubling technology.
2.2 interface Technology
Figure 2 for the DS1251 storage in IC2, which is a non-volatile memory, the output voltage is high as 5V. But TMS320VC33 the I / O level of 3.3V, can not afford high as 5V for TTL signal. In order to TMS320VC33 able to exchange data with the DS1251 circuit used in IC3 (74LVC164244) to achieve 3.3V and 5V level conversion. The chip also has two kinds of 3.3V and 5V power supply, and DSP connected to I / O pins level of 3.3V, and memory connected to I / O pin level of 5V.
Boot (Boot Loader) is stored in external program memory in the program code is loaded into a one-time all the high-speed DSP chip memory to achieve the program instructions of the high-speed operation. TMS320VC33 There are four lead the way in which the first three way to boot from external memory, a fourth way to boot from the serial port. they are by four external interrupt pins INT0 ~ INT3 someone in a low setting achieved. In this paper, Table 1 as shown in the second guide means, that is DSP boot process from the beginning 400000H.
The user program loaded into the DSP on-chip high-speed RAM is a DSP-chip ROM-based machine program (factory set) complete. After power, DSP reset pin from "0" to "1" at the same time ensure that the circuit connected to pins MCBL / MP = "1", solidified in the on-chip boot program queries INT0 ~ INT3 in which a lower, according to Table 1 shows the corresponding interrupt pin and addresses the relationship between the guide.
Table 1 guided mode
|Way||INT0 INT1 INT2 INT3||Description||First Address|
|1||0 1 1 1||External memory||1000H|
|2||1 0 1 1||External memory||400000H|
|3||1 1 0 1||External memory||FFF000H|
|4||1 1 1 0||Serial|
Be guided through the compilation of user program must first connect to generate DSP code for the machine can recognize. In the generated code must also include a pre-boot header. To guide the concrete structure is shown in the first reference document, and its role is:
(1) The realization of word length of 32-bit DSP with 8-bit, 16-bit or 32-bit external program memory interface.
(2) enable high-speed DSP and low-speed ROM interface.
(3) The realization of the user program with DSP and internal storage space matching.
2.4 Data Processing
Using TMS320VC33 timer every 100ms to send a string of a fixed number of pulse-like excitation signal, the excitation signal through the amplification and drive back via the DSP control alternately applied to the two ultrasonic sensors. When a sensor in the sending state and the other only on the receiving state, that is, each sensor every 200ms to complete a close and hair. received ultrasonic signal is sent through the post-amplification and shaping DSP-INT0 pins, while taking advantage of TMS320VC33 timer 2 test from sent to the receiving time spent and thus the basis of (3), calculated and collected the starting time difference, then by (4)-type floating-point calculated by the mud flow, and the results stored in the DS1251. During the same time storing data, using DS1251-chip clock, the time corresponding to the data stored in the data region together. This provides the ground corresponds to the velocity and depth that provides a foundation, because in the underground through the DS1251 time at the same time, the ground is also a set and The synchronized timer to time with the depth of the corresponding records.
DSP timing interval is set to double the number of instruction cycles, namely:
T = 2 × Tp = 34ns (5)
Right tAB and tBA timing error as follows:
ΔT = ± Tp / 2 = ± 17ns (6)
The resulting slurry flow rate of error as follows:
ΔV = ΔTC2 / L (7)
Take C++ = 1560m / s, L = 10m, then ΔV = 4.14mm / s, we can see that the measurement error of measurement lower than the current a few times.
3 data playback and Test
General-purpose DSP with I / O interface to the preparation of RS232 communication program, testing is completed, will be measured with ground data playback to a computer. TMS320VC33 computer RS232 port interface circuit shown in Figure 3. Which IC7 using 74LS06, the output will be TMS320VC33 3.3V to 5V level conversion level, this is because both equal to the minimum input high, all 2.4V; IC13 using MAX2202, is used to convert the TTL level RS232 level.
Ultrasonic fluid leak detector developed after repeated laboratory tests and field applications, the measured location of the leakage layer of error of less than 10m, not only for drilling in the process of plugging providing effective technical support , and drilling cost savings, reduced leakage in case of a leak detection cycle, preventing the leakage of underground resources, pollution.
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