The Dual Downhole System (DDS) consists of two 3C borehole receiver which are placed at 2m distance to each other in one borehole.

Each borehole receiver contains x,y,z directed geophones. The lowest receiver does have an in-built magnetic compass for orientation. Receivers are inflated by air and coupled to the borehole wall.

Typical seismic signals generated at surface signals and travelling to the DDS do have same trigger time and same source signal. In this case, the first break or even the maximum amplitude are qualitative good measures for an interval velocity.

Further, the DDS system can be lowered at any desired depth interval making it possible to obtain interval velocities every meter or less.

Standard

Dual Downhole System

Coupling conditions of a single borehole receiver may vary from point to point as well as hammer blows may not show same signal for every depth.

Same source conditions, same coupling pressure

Accurate trigger time not always available

Same trigger time

Errorneous traveltime picks may lead to unrealistic velocities

Maximum/Minimum amplitude picking available