BHEMA

Autonomous Downhole EM Exploration

Autonomous Operation

The BHEMA (Borehole ElectroMagnetic Autonomous) probe is our solution for downhole EM surveys. By operating completely autonomously and offering superior noise performance, it overcomes major logistical and data quality hurdles associated with traditional borehole systems.

Logistical Freedom: This autonomy provides immense logistical advantages and cost savings. The probe is deployed on a simple, non-conductive Kevlar cable using a lightweight winch. It can also be deployed via a standard wireline or even at the end of a drill string, enabling surveys from underground platforms or through an NQ bit.

Simplified Acquisition: With no surface receiver to manage, data acquisition is streamlined. The operator simply lowers the probe and lets it dwell at a series of pre-programmed depths. All data is stored internally for post-survey download. The probe can even be used as a high-quality, untethered sensor for surface EM surveys.

Full length view of the BHEMA probe.
Close-up of the BHEMA probe connector.

Data Quality and Precision

BHEMA is engineered for low noise performance, with noise levels up to 50 times better than a 3-axis fluxgate sensor.

  • High-Speed Sampling: It captures the full 3-axis B-field with a high sampling rate of 19,500 samples per second at 24-bit resolution, over a wide 0.2 Hz to 4 kHz passband.
  • Automatic Gain Control: The pre-amplifier gain is adjusted automatically (1/8x, 1x, 2x ... 128x), ensuring the sensor always operates at its optimal level to capture the highest quality data without saturation.
  • Precise Timing and Orientation: The probe establishes an absolute GPS timing reference at the surface before deployment. This allows for precise synchronization with transmitter waveforms and even other BHEMA probes. An integrated high-precision IMU (1 degree-per-hour gyro drift) continuously records 3-axis magnetometer, accelerometer, and gyro data for accurate spatial orientation.

Technical Specifications

Dimensions

45mm diameter, 4m assembled length (in two 2m sections)

Durability

Built to withstand pressures of 3500 psi, equivalent to a water depth of 2500 meters

Battery Life

12-hour battery life ensures completion of long surveys without interruption

Sensor Technology

Feedback induction coil with B-Field passband between 0.2Hz and 25kHz

Noise Performance

X,Y noise: 6pT/√Hz @ 1Hz, 500fT/√Hz @ 10Hz, 50fT/√Hz @ 100Hz, 20fT/√Hz @ 1kHz

Z-Axis Performance

Z noise: 1pT/√Hz @ 1Hz, 200fT/√Hz @ 10Hz, 20fT/√Hz @ 100Hz, 5fT/√Hz @ 1kHz

Field-Tested Performance

The BHEMA system is being used as an integral part exploration programs for its superior signal-to-noise performance compared to fluxgate sensors and for its strong value proposition.

more details