The Research Of DC Carrier Communication Applied In The Down-hole Tools

In zonal oil production and the process of separated layer water injection,downhole instrument sub not only needs power,but also has to communicate bi-directionally with ground controller.This paper designed and developed a communication sub based on DC power line carrier communication technology.There is only one single core armed cable connected between the ground and the downhole instrument sub.On one hand,all the controlling instructions and data detected in the downhole can be transmitted by the cable;on the other hand,the cable can be used as the power supply from the ground to the downhole.By taking this data transmission way,the transmission channel can be simplified,the cost is cut down and the reliability of the whole system is improved.This paper mainly completed the following work.Firstly,through series of simulation experiments and analysis of transmission characteristics of a single core armored cable in the oilfield,the channel bandwidth of length from 1km to 5km cable and the signal amplitude attenuation are obtained.The result provided important reference for the design of hardware circuit and the selection of sub communication baud rate and signal processing.Secondly,the communication sub in the downhole and the ground controller were designed and developed based on DC carrier communication technology.Those two worked together to complete the two-way communication between the ground and the downhole instrument short.The coupling circuit of the communication sub was designed according to "composite coupling technology” which was mainly made of a capacitor and a transformer,realizing the modulation and demodulation of the signal,coupling the coded signal to the 70-110 V DC power cable,meanwhile effectively protecting the “low-voltage module” from the “high-voltage module”.The signal conditioning and Manchester coding and decoding were realized by software in the interior of the DSP controller,which reduced the hardware space effectively! In order to adapt to the impedance changes caused by different length of communication cable,programmable amplifier was used to adjust adaptively the signal amplitude.The PC monitoring program was designed by virtual instrument technology.Laboratory tests and field debugging with the actual single core armored cable show that under the circumstances of the baud rate 12.5kbps,the ground power supply 70-110 V,the cable length 1~5Km,the communication sub could realize two-way communication between the ground and the downhole instrument sub accurately and reliably,and meets the communication requirements of oil fields.