# Research on Key Technologies of 260 \({}^{\circ}\)C/210 MPa Ultra-Deep Logging Equipment
## 3 Research on Key Technologies of Ultra-High-Temperature and High-Pressure Logging
### 260 \({}^{\circ}\)C/210 MPa Ultra-High Temperature and Pressure Logging Sensors
#### 3.1.3 Induction Coil System  
The coil system is the detector part of the array induction logging tool, as shown in Figure 8. It consists of a central joint sealing assembly, beryllium copper tube assembly, coil  
Figure 6: Installation diagram of the mandrel, insulating material, copper strip, and wires. Figure 7: (a) End-face seal and shaft-hole seal structure; (b) Improved shaft-hole seal structure. array assembly, outer tube of the coil system, lower sealing assembly, and pressure balance subassembly. The coil array consists of one transmitter coil and multiple sets of receiver coils. The receiver coils are distributed with source distances of 06, 10, 16, 24, 39, 60, and 94 inches, covering a detection depth range of 0.25 to 3.0 m longitudinally. The source distances of the coil sub-arrays increase sequentially, and the signal response relationship, as shown in Figure 9, illustrates the one-dimensional radial differential geometric factor response relationship. The resolution and detection depth are controlled by the spacing between the primary receiver and transmitter coils of the sub-arrays. Short spacing results in a high resolution but shallow detection depth, while long spacing results in deep detection depth but a low resolution. Maintaining consistent coil array spacing, the balance between the internal and external oil chambers of the coil system, and stable electrical characteristics of the coil system are the foundation for the accurate measurement of the induction logging tool based on the principles of electromagnetic wave logging. The induction logging tool's coil array components must withstand temperatures of 260 \({}^{\circ}\)C and pressures of 210 MPa and need to be made from non-metallic, non-magnetic materials. For material selection, the coil array framework uses ceramic with minimal deformation at high temperatures to reduce the changes in coil magnetic flux due to thermal deformation across a wide temperature range. The insulating sleeves between coils are made of polyether ether ketone (PEEK), which has a load-bearing thermal deformation capability of up to 318 \({}^{\circ}\)C and can operate for extended periods at 260 \({}^{\circ}\)C. The insulating outer tube of the coil system uses glass-reinforced plastic (GRP) rated for 280 \({}^{\circ}\)C. The central joint and lower joint sealing assemblies use multiple 260 \({}^{\circ}\)C/210 MPa multi-core sealing plugs for wiring. The beryllium copper tube assembly uses 32.2 \(\times\) 11.225 mm  
Figure 8: MIT1531 array induction tool. Figure 9: One-dimensional radial differential geometric factor. C17200 beryllium copper tubes as the support structure and wire conduit for the coil array components, meeting the 260 \({}^{\circ}\)C/210 MPa temperature and pressure requirements. The gap between the coil system outer tube and the coil array components is filled with silicone oil, and the pressure balance subassembly contains an adjustable oil chamber supported by springs, internally connected to the coil system's oil circuit to achieve pressure balance inside and outside the GRP tube in high-temperature and high-pressure environments. The technical challenges and solutions for electromagnetic interference and sealing in high-temperature environments are as follows:  
1. Multi-Core Pressure Sealing Plug Solutions for the Central Joint and Lower Joint: The pressure sealing plug uses a five-core structure, with four sets distributed circumferentially in the central joint to accommodate the seven sets of receiver coil array wires. In the lower joint, two sets are axially distributed to accommodate the transmitter and temperature probe wires. Physical separation of the transmission and reception lines solves the issue of crosstalk between the transmitter signal and the receiver lines.