CONTINUOUS FULL-WAVE SONIC LOGGING IN A DRY HOLE
Rotary Drilling Rigs, DTH Hammers, DTH Drilling Rigs
Drilling Today >Technical Papers
 
Drilling Today Contact
CONTINUOUS FULL-WAVE SONIC LOGGING IN A DRY HOLE

Toshiyuki Kurahashi and Tomio Inazaki, Public Works Research Institute, Tsukuba, Ibaraki, Japan

Abstract
This paper describes a new concept of continuous full-wave sonic logging (FWS) in a dry hole. The continuous FWS in a tube provides physical properties at narrow intervals under the dry condition. The method uses a synthetic rubber tube that enables continuous FWS to be conducted in a dry hole, by sealing the dry hole wall and preventing water leakage. The addition of water made the tube expand and contact firmly to the hole wall. FWS collects sonic signals as waveforms through the tube, and successively provides a larger quantity of higher resolution data than conventional downhole measurement under the dry condition by receiving sonic signals more precisely and effectively. Although the method could identify individual fractures in bedrock in all hazards, it cannot be used at a low velocity part of less than 1.5 km/sec in water due to the structure of the tube.
Introduction
This paper describes a new concept of continuous full-wave sonic logging (FWS) in a dry hole. The continuous FWS in the tube provides physical properties at narrow intervals under the dry condition. However fractured bedrock causes water leakage and reduces groundwater level, FWS in this study can be conducted even in a dry hole.
A synthetic rubber tube prevents water leakage and enables us to continuously receive sonic signals of FWS in a dry hole. The synthetic rubber tube was placed in a dry test hole drilled in fractured bedrock, then the hole wall was sealed to prevent water leakage. Water was added to make the tube expand and contact firmly to the hole wall. FWS continuously collected sonic signals as full waveforms through the tube more precisely and effectively than the conventional downhole technique under the dry condition. As seismic travel-times are known to depend on the effect of fractures, individual fractures in bedrock could be identified.

Figure 1.: Continuous Full-wave Sonic Logging (FWS) in a dry hole. An inflatable synthetic rubber tube is set in a dry hole and to prevent water leakage. Water is added to inflate the tube and make it contact firmly to the hole wall. The FWS transmits and receives sonic signals.