Core Barrel – Extended Memory Drill String Accelerometer (CB-DSA-XM)
Description
The Core Barrel- Extended Memory Drill String Accelerometer (CB-DSA-XM) was developed during ODP at USIO Science Services/LDEO as a modification of the CB-DSA, which was used on several ODP legs. The CB-DSA-XM operates as a memory tool that measures and records drill string acceleration and ambient pressures during coring. The tool contains a single-axis (vertical) High Sensitivity Accelerometer (HSA) for heave measurements, a three-axial Low Sensitivity Accelerometer (LSA) for drill bit variations, and a high resolution pressure sensor. The tool can operate in acceleration (LSA and HSA signals recorded at high sampling rate) or pressure ((LSA signal and ambient pressure recorded at high sampling rate) mode; in both cases ambient pressure is recorded at low sampling rate (1 sample/sec).
For ease of deployment, the CB-DSA-XM has been designed as a removable extension of the APC/XCB/RCB core barrels. Using standard threaded connections, the CB-DSA-XM is attached to the top of a selected core barrel prior to core barrel deployment. The tool does not need connection to the logging cable and the data are downloaded to a computer after the tool is retrieved from the hole. During initialization and data downloading procedures, communication with the tool is handled by the CB-DSA-XM LabView program.
The modified tool has a longer data recording time, higher reliability and improved operations capabilities. It allows data recording on consecutive coring trips, and the used of hot-swappable non-volatile memory modules virtually eliminates any delay related to data retrieval procedures. The tool continuously monitors battery voltage and temperature inside the electronics module and preserves recorded data in case of battery failure or at temperatures in excess of the maximum specified for tool operation.
Applications
• Drill string vibration analysis
• Heave evaluation
• Reference signal for Seismic-While-Drilling measurements
• Fluid pressure measurement
• Drilling equipment performance evaluation
• Geotechnical applications (i.e. sediment compaction analysis)
Tool Specifications
| Temperature rating: | 185° F (85° C) |
| Pressure rating: | 10 kpsi (69 MPa) |
| Diameter: | 3.375 in (8.57 cm) |
| Length: | 7 in (1.2 m) |
| Weight: | 75 lbs (34.1 kg) |
| Acceleration sampling rate: | 100 Hz |
| Pressure sampling rate: | 1 Hz |
| Frequency bandwidth (HSA Channel): | 0-2 Hz |
| Frequency bandwidth (LSA Channel): | 0-50 Hz (at 100 samples/sec) 0-25 Hz (at 50 samples/sec) |
| Total data recording time: | 2.9 hrs (at 100 samples/sec) |
| Power source: | 6 “AA” alkaline batteries |
| Battery life: | about 18 hrs |
Measurement Specifications
| Acceleration | |
| Range (LSA channel): | 2 to +2 g |
| Range (LSA channel): | |
| Option 1: | |
| Option 2: | ±25 g |
| Temperature | |
| Range: | 32-185° F (0-85° C) |
| Resolution: | 0.9° F (0.5° C) |
| Pressure: | |
| Range: | 0-10 kpsi (6.9 MPa) |
| Resolution: | 4 psi (27.6 kPa) |
| Precision: | 0.1 % FS |