Well logging data acquisition and control systems are fundamental oilfield measurement and control equipment used to acquire, process, and control signals generated by various downhole instruments placed in the formation. Due to their highly specialized nature, previous systems typically relied on custom-designed data acquisition and control units, resulting in long development cycles, high costs, and poor stability. Now, using data acquisition cards from National Instruments and VC++ combined with the Measurement Studio software package, we have achieved the design and development of well logging data acquisition and control units based on standard industrial data acquisition products. This significantly reduces system development and maintenance costs, shortens the development cycle, and improves system stability and reliability. Currently, over 20 sets of this system have been manufactured and successfully applied in major oilfields across the country, achieving considerable economic benefits.
System Principles
The well logging data acquisition and control system mainly consists of an industrial computer, an NI general-purpose data acquisition card, a signal conditioning module, a plotter, a comprehensive control box, a DC power supply, an AC power supply, a UPS power supply, and an oscilloscope. The system principle block diagram is shown in Figure 1.
Figure 1 System Schematic DiagramMain unit 1 is primarily used for system data acquisition, processing, and control. The plotter is used for real-time plotting of logging curves. The depth signal conditioning module conditions the photoelectric encoder signal and other wellhead signals, and controls the depth display; the digital signal conditioning module is used to connect to downhole instruments using various encoding methods (e.g., Manchester encoding), such as dual-source C/O energy spectrum logging tools and pulsed neutron oxidation logging tools; the pulse signal conditioning module mainly connects to downhole instruments using pulse and periodic signal transmission, as well as instruments with various pulse encoding types, such as wellbore ultrasonic imaging logging tools; the DC signal conditioning module mainly connects to downhole instruments using DC and low-frequency analog signal transmission. The DC power supply provides DC power to the downhole instruments, and the AC power supply provides AC power to the downhole instruments, pumps, valves, relays, and release devices. The integrated control box is responsible for cable core switching and power supply control. The UPS power supply ensures power supply for a period of time during power outages or when external power is unavailable, preventing the loss of logging data due to delayed storage. All the above units are installed in two 19-inch standard cabinets. The signal flow is shown in Figure 1. We categorize the signals entering the data acquisition and control system into two types: wellhead signals and downhole signals. Wellhead signals originate from the wellhead and cable winch, including cable tension signals, cable magnetic signatures, and photoelectric encoded signals from the depth system. Downhole signals refer to signals from downhole instruments. Inductive or pulse signals from downhole instruments, two photoelectric encoded signals from the depth system, wellhead tension signals, and cable magnetic signatures enter the depth conditioning module, pulse signal conditioning module, or DC signal conditioning module within the acquisition box via cables. After conditioning, they are output to the NI data acquisition card. Downhole instrument encoded signals, after separation and preprocessing by the integrated control circuit, enter the digital signal conditioning module via cables for signal conditioning and decoding. The decoded signals are also output to the NI data acquisition card. The NI data acquisition card controls the data acquisition method and sampling interval, and simultaneously realizes real-time acquisition of pulse signals, DC signals and digital signals. The acquired data is transferred to the data buffer in the host in the DMA mode, and the system software controls the display, processing, printing and saving of the data according to different sampling methods.
Data acquisition scheme design
The core of well logging data acquisition and control system design lies in its data acquisition scheme design. This design primarily comprises: a system depth data acquisition and depth interruption management scheme; a multi-channel composite signal real-time synchronous acquisition scheme; a high-speed transmission and acquisition mode design for complex encoded digital signals; a high-precision DC signal acquisition scheme; and a system status and downhole instrument control scheme. Due to its highly specialized nature, previous systems typically relied on self-designed data acquisition and control units. This resulted in long development cycles, high costs, and poor stability, frequently leading to system crashes and inaccurate depth measurements, significantly increasing maintenance costs. Furthermore, due to technological limitations, self-developed systems could only connect to downhole instruments with simple signal types and low transmission rates, lacking the capability for real-time synchronous acquisition of multiple signals and high-speed digital signal acquisition and processing. To overcome the shortcomings of the existing system, based on thorough research and trial use of data acquisition products from various companies, we selected a series of data acquisition cards and the Measurement Studio software development kit produced by NI. After careful study and in-depth development of each NI acquisition card, we completed the core system design in just 3 months, which would have taken more than 2 years in the past. We also achieved the industry's first well logging data acquisition and control system design based entirely on standard industrial data acquisition products. At the same time, the system achieved a comprehensive and significant improvement in key technical indicators such as sampling accuracy, depth control, and acquisition speed.
(1) Design of system deep data acquisition and deep interruption management scheme:
The system depth module is the most industry-specific module in this system. It needs to measure the orthogonal photoelectric encoder signal to obtain the current depth data of the system. Simultaneously, it must generate equidistant depth trigger signals to synchronize the acquisition of various signals based on the current depth data. For example, when the photoelectric encoder rotates clockwise, a trigger signal is generated every fixed displacement interval (e.g., 5 cm). This trigger signal notifies the system to acquire all measurement signals. If the photoelectric encoder suddenly rotates in the opposite direction, no trigger signal is generated, and the system does not acquire any data, thus ensuring that the system only acquires data according to a unidirectional equidistant displacement state. Furthermore, this module must also have anti-jitter and anti-slip processing functions for the orthogonal photoelectric encoder signal. During system development, we found that the user manuals for the NI PCI-660X series products did not implement the basic functions of this working mode. To achieve this function, we conducted in-depth research and development, utilizing a special state signal generated by the counter channel of the PCI-6602 that processes photoelectric encoder signals, and combining it with the pulse generation function of other counter channels, ultimately generating the continuous equidistant depth trigger signals we needed. In the final product design, we implemented this function through program initialization control using the five counter channels of the PCI-6602. This is the first time we have achieved precise reading of depth data and fixed-distance output of trigger signals using a standard industrial data acquisition card, laying a solid foundation for the successful development of the entire system.
(2) Design of a real-time synchronous acquisition scheme for multi-channel composite signals:
Well logging data acquisition systems typically require real-time synchronous measurement of multiple DC signals, pulse signals, and digital signals based on interval or timed trigger signals. This necessitates ensuring the consistency and real-time nature of data acquisition between multiple acquisition cards and between multiple measurement channels within the same acquisition card; otherwise, the obtained data will not reflect the true condition of the downhole instruments in the formation. We use NI 6070E or NI6024E with RTSI (Real-Time Synchronization Interface) bus for DC signal measurement, PCI-6602 or PCI-6601 for pulse and depth signal measurement, and PCI-6534 or PCI-6533 for digital signal measurement. Any card in the system can act as a master card to generate synchronization trigger signals or as a slave card to receive synchronization trigger signals, depending on its operating mode. We load the synchronization trigger signals generated by the master card onto the RTSI bus, which synchronizes the data acquisition of various measurement channels on other slave cards. Data acquired by each acquisition card is transferred to its respective data buffer in the host computer via DMA. Because the entire triggering and acquisition process is independently controlled by the system hardware, the acquisition latency of each measurement channel can be controlled at the nanosecond level. All acquisition cards use DMA mode to transfer data, which greatly improves system efficiency compared to the interrupt mode used in previous systems.
By using the RTSI bus, we transformed the original method of sequentially reading data from each channel through system software polling into a method where the working state of each acquisition card is initialized, and then the RTSI of each acquisition card (i.e., system hardware) controls the synchronization of acquisition. This change in working method not only reduces the system load but also significantly improves the synchronization and real-time performance of system measurements. This is also an important reason why we chose NI data acquisition cards to implement system data acquisition.
(3) Design of high-speed transmission and acquisition mode for complex encoded digital signals:
Due to the wide variety of logging instruments, a well-designed logging system must be compatible with downhole instruments using different encoding formats. Since the PCI-6534 typically has a sampling rate of 40 MS/s, our system design fully utilizes the PCI-6534's Pattern I/O functionality to achieve complex, high-speed digital acquisition and decoding. Furthermore, considering the characteristics of downhole instruments, signals triggered by the conditioning module to the PCI-6534 can be loaded onto the RTSI bus to synchronize the acquisition of system depth and other data. Distance-based or time-based trigger signals can also be loaded onto the PCI-6534 via the RTSI bus to control the digital signal acquisition mode. The PCI-6534, used in conjunction with the system's front-end digital signal conditioning module, enables the system to connect to various high-speed logging downhole instruments with complex encoding protocols.
(4) Design of a high-precision DC signal acquisition scheme:
Some logging instruments transmit signals that include DC, pulse, and digital signals, and the sampling frequency of the DC signal is generally required to reach 1ms/s. In addition to high-speed acquisition of the DC signal from the downhole instrument, the acquisition system also needs to acquire other DC and pulse signals in timed or distanced modes with lower sampling rates. In our design, we integrated the programming and control of four cards—NI 6070E, PCI-6024E, PCI-6602, and PCI-6534—employing multi-channel, multi-stage composite synchronous triggering technology. Simultaneously, we fully developed the digital signal mode triggering control technology of the PCI-6534, achieving a working mode that acquires the DC signal from the downhole instrument at a high sampling rate under timed or distanced triggering conditions, while simultaneously acquiring the pulse signal from the downhole instrument, the DC signal from the wellhead, and digital signals at a low sampling rate. This was the most challenging aspect of the entire logging data acquisition system design.
(5) System status and downhole instrument control scheme design:
In the design of the system conditioning module and downhole instrument status control, we selected the PCI-6601. Utilizing its Digital I/O capabilities, we established a powerful 32-bit command output system. The PCI-6601 was chosen primarily to reduce the overall system cost; however, dedicated digital I/O cards or other multi-functional cards can be selected as needed.
System software design
The well logging data acquisition and control system software mainly consists of field measurement and control and data acquisition software, and post-logging data analysis and processing software. For software development, we chose a development approach combining VC++ and NI's Measurement Studio software package. VC++ was used to develop programs related to the operating system's underlying layers and curve printing output programs, while the class libraries provided by Measurement Studio and CVI were used to develop programs related to real-time data acquisition and curve display. This development approach not only allows for flexible control of the operating system but also fully utilizes the development tools provided by NI, thereby significantly shortening the system software development time. We completed the design, development, and testing of the system software in just three months. Figure 2 shows the interface of the pulsed neutron oxygen activation logging and interpretation software within the system software. Figure 3 shows the overall block diagram of the system software.
Figure 2: Interface of pulsed neutron oxygen activation logging and interpretation software. Figure 3: Overall block diagram of system software.in conclusion
We used data acquisition cards and software development tools from NI (National Instruments) to design and develop a well logging data acquisition and control system based on standard industrial data acquisition products. This significantly reduced system development and maintenance costs, shortened the system development cycle, and improved system stability and reliability. Furthermore, we can customize the system's data acquisition cards in various ways or upgrade the system to a PXI bus system to achieve well logging data acquisition and control systems with different functional focuses, according to user needs. Currently, more than 20 sets of this system have been produced and successfully applied in Daqing Oilfield and other oilfields across the country, achieving considerable economic benefits and demonstrating a broad application prospect.
