# Application of Seismic Sensors in Measurement While Drilling

## TL;DR

This paper explores how seismic sensors can improve the identification of rock properties and fractures during drilling compared to traditional mechanical sensors.

## Contribution

The study introduces the use of seismic sensors to complement mechanical sensors in measuring rock properties during drilling.

## Key findings

- Seismic sensors can clearly identify voids and weak interfaces in rocks that mechanical sensors miss.
- Geophones provide clearer data than accelerometers for identifying material interfaces and fractures.
- Sensors mounted directly on the rock sample are more sensitive than those on the drill head.

## Abstract

Rock geotechnical properties can be reflected in drill signals while drill rod penetrates through rocks. The rate of penetration, rotary speed, torque, load, sound, vibration, etc., are different for various rock types, since they are influenced by rock properties. Therefore, a close analysis and derivations of these drill signals can provide valuable insights into rock geotechnical properties. The drill returned signals from the mechanical sensors; for example, torque and load are commonly interpreted to characterize the rock properties. There are still limitations to such sensors and interpretation methodologies that can confidently characterize rock properties. In this research, mechanical sensors were compared and complemented with seismic sensors, for example, accelerometers and geophones, to characterize rocks and interfaces. This paper presents experimental results conducted with synthetic rock samples using mechanical and seismic sensors with a field scale drilling machine. The results show that seismic sensors can identify voids or weak (fractured) interfaces clearly compared to mechanical sensors. Smaller gaps have smaller span of low frequency and vice versa. The sensors attached to the drill head were less sensitive than the sensors attached to the sample. Drill signals showed the capacity to effectively identify material interfaces and weak fractures up to 4 mm thick, with geophones providing clearer data than accelerometers. Neither sensor distinguished fractured zones from voids. Sensors mounted directly on the sample were more sensitive than those attached to the drill head, likely due to vibration-induced signal attenuation at the drill head.