Diagram - not to scale

The principle in surveying with Tropari SDP instrument in wireline drilling is to raise the drill rod train 10 meters (30 feet) so that the complete survey train can pass through and extend beyond the bit. This will place the Tropari beyond the magnetic influence of the drill bit and rods.

In steep holes, surveying time can be reduced with use of the landing coupling method. The survey train is complete with a spearhead at the top which means the overshot can be connected directly to survey train and therefore the core barrel assembly is not used which reduces handling and assembly time. The survey train can be lowered to stop at the bit using a landing coupling which will go through the rods but not through the bit. The landing coupling method, can only be used when the hole angle is steeper than 45 degrees.

Since the train components below the landing coupling have to pass through the bit, these non-magnetic survey train components must have a smaller diameter than the core. If the core size is significantly larger in diameter than the non-magnetic rods used in the survey train, then a non-magnetic centralizer can be used to improve parallelism between the axes of the instrument and the borehole.

Information to provide when requesting a quotation:

If available, please includes details about your surveying application so we can provide a detailed quotation and/or additional information. Common details to include are:

• What is the core size(s)?

• What is the direction (upward, downward, horizontal, etc) of the hole?

• What is the length of the hole?

• Is the hole water filled?

Magnetic Cake Effects:

Drill rods rotating in the hole frequently deposit a grease-rock-steel powder cake on the walls of the borehole. This cake is frequently magnetic and affects the azimuth readings of all magnetic direction based instruments. We recommend that surveys be carried out at the bottom of the hole as drilling progresses for the most accurate results.