Downhole Circuit System Technical

1. System Overview

The downhole circuit system serves as the core control unit for intelligent drilling and logging equipment in oil and gas exploration, designed to operate stably under extreme conditions: high temperature (up to 300℃), high pressure (210MPa), strong vibration (20g RMS), and corrosive media. Adopting a modular architecture, the system integrates four functional modules—sensing, processing, communication, and control—and ensures an MTBF (Mean Time Between Failures) exceeding 10,000 hours through three-level redundancy design.

2. Technical Characteristics of Key Subsystems

2.1 High-Reliability Signal Acquisition System

● 24-bit Σ-Δ ADC (e.g., ADI AD7779) combined with programmable gain amplifier (PGA)

● Supports 16-channel synchronous sampling at 100kSPS

● Integrates adaptive digital filtering (FIR/IIR) and temperature drift compensation algorithms

● Signal integrity design: LVDS differential transmission with impedance matching error <5%

2.2 High-Temperature Processing Unit

● Main control: Radiation-hardened FPGA (Xilinx XQR5VFX130)

● Coprocessor: HT-SOI architecture MCU (e.g., Honeywell HT83C51)

● Storage system: FRAM (Fujitsu MB85RS256A) + ceramic-packaged NAND Flash

● Real-time operating system: VxWorks 653 (DO-178C Level A certification)

2.3 Special Power Management System

● Input range: 18–120VDC (compatible with batteries and turbine generators)

● Multi-stage conversion architecture: SiC-based Buck-Boost (front-end) + LDO (post-stage)

● Efficiency curve: >85% @ 200℃ (12V/5A output)

● Intelligent protection: Three-level safeguards for overvoltage (OVP), reverse polarity (RPP), and surge (TVS)

2.4 High-Speed Data Transmission System

● Wired transmission:

● Fiber channel: 1000BASE-ZX (single-mode, 5km transmission)

● Coaxial transmission: QAM-256 modulation, 200Mbps rate

● Wireless transmission:

● Electromagnetic wave short-range: 2.4GHz DSSS, bit error rate <1E-6

● Mud pulse: Adaptive Coding Modulation (ACM) technology

3. Advanced Manufacturing Processes

3.1 Substrate Technology

● High-temperature ceramic substrates (AlN/DBC)

● Multi-layer wiring (8–12 layers, line width/spacing 50μm)

● Blind/buried via design (via diameter 80μm)

3.2 Packaging Process

● Hermetic sealing (He leak rate <5×10⁻⁹ atm·cc/s)

● Gold-tin eutectic bonding (Au80Sn20, melting point 280℃)

● 3D stacking (TSV interconnection density >10⁴/cm²)

4. Typical Application Cases

4.1 LWD Azimuthal Resistivity Tool

● Six-transmitter eight-receiver coil array drive circuit

● 1MHz high-frequency phase-locked amplifier module

● Anisotropy correction processing unit

4.2 Intelligent Completion System

● Brushless motor drive for electric valves (three-phase full bridge)

● Downhole flow PID control module

● Pressure-temperature fusion sensing unit

5. Technical Challenges and Development Trends

5.1 Existing Technical Bottlenecks

● Reliability of semiconductor devices above 300℃

● Multi-physical field coupling effects (thermal-mechanical-electrical)

● Energy-constrained downhole systems (average power consumption <15W)

5.2 Cutting-Edge Research Directions

● Self-powered technology (vibration/thermoelectric generation)

● Photonic integrated circuits (PIC) replacing traditional PCBs

● Artificial intelligence edge computing (downhole real-time decision-making)

This type of system has obtained international certifications such as API 19G and IEC 61508, and has been widely applied in scenarios like shale gas development (e.g., Changning block in Sichuan) and deepwater oilfields (e.g., "Deep Sea No.1" in the South China Sea). With the development of semiconductor materials (e.g., diamond semiconductors) and heterogeneous integration technologies, downhole circuit systems are evolving toward intelligence, miniaturization, and ultra-high temperature tolerance.