The Depth Measurement System Of No-cable Logging

With the development of oil exploitation, complex well conditions, such as horizontal well and highly-deviated well increase. No-cable logging technology, which has the characteristics of being fast, reliable and safe, can make up for the inadequacy of conventional in complex well. As an important part of no-cable logging system, depth measuring system acquires the information of depth, which is an important parameter of well logging. It has important practical significance to get accurate information of oil and gas reservoir.The paper analyzes the application of depth measuring system in no-cable logging and concludes the design requirements of depth measuring system. An MCU + CPLD overall scheme design is proposed to complete data acquisition and transmission through Ethernet. The main research contents of this paper are as follows:① In connection with quadrate-encoder pulses circuit which is output by drawworks encoder, this paper designs a waveform shaping and stabilization pretreatment circuit, to avoid miscount. For pressure sensor signal, I/V conversion, low-pass filtering and AD conversion are pretreated, so as to facilitate the high precision acquisition by SCM.②CPLD is used to complete quadrate-encoder pulse circuit’s functions of phase demodulation and counting to simplify the hardware circuit, and besides, it can complete hardware reconfiguration by modifying the software, which improves the flexibility of this system. The count results from CPLD transmit to SCM through the UART module.③SCM is used to complete the processing of depth and pressure data, acquiring the depth of underground instruments and the hook load. Effective data is extracted by judging the hook’s state of overload or light load, and the depth error is reduced by means of piecewise calibration.④ C8051F340 and CP2200 are used to generate Ethernet interface, by transplanting TCP/IP protocol and the designing of Ethernet driver, the depth measurement system of network communication is completed, achieving real-time, reliable and fast data transmission.⑤A test platform is built in the laboratory for quadrate-code counts validation test and tension collection validation test, Results show that quadrate-code counts accurately, tension collection of linearity and accuracy were 0.77% and 0.0021 k N. The actual logging process experiment under the condition of laboratory is simulated. Results show that the depth and pressure data can be correctly collected, uploaded and displayed. The obtained depth-time curve satisfies the requirements in no-cable logging and has a certain accuracy.