Tropari - Applications

e Tropari/PDSI is a single shot directional surveying instrument that provides magnetic azimuth for direction and an inclination reading from a plumb device. Its primary design purpose is to function as a surveying instrument used to monitor the directional progress of a borehole as it is drilled and to provide directional data after corrective measures such as wedging has been carried out.

Open-hole Surveys without casing
		This group of surveys include those drilled by percussion, rotary, or conventional coupling-rod techniques and where there is no unobstructed passage within the drill rod or pipe. The TROPARI can be lowered into steep down holes (> 40° from horizontal) by cable if a winch is available. The survey train shown in Fig. 1 is an example of a cable lowered application. If drill rods are used to insert the instrument into the hole, then the inclination of the hole, whether up or down, is immaterial. The survey train in Fig. 1 is converted to rod insertion simply by replacing the cable swivel with a connector that joins the aluminum rods to the drill rods or drill pipe. The aluminum rods separate the instrument in the "container" from the magnetic effects of the lowering devices. The surveys of steep short holes can be done by rope lowering or, for holes at any inclination, by light aluminum rods hand inserted. Aluminum rods for hand insertion are available in 1.5 m connectable lengths in sizes that weigh as little 7 kg (15 lb.) per 30 m (100 feet). Hole sizes from 36mm (1.4 inches) to 600mm (24 inches) can be carried out in holes drilled by any technique. The hole size, and if drill rod insertion will be used, the type or description of the drill rod thread is required information to select the components of the survey train.

Wireline surveys, also called through-the-bit surveys, require that the survey rods be lifted the length of the survey train from the bottom of the borehole. The instrument can pass through the bit and is then separated from the magnetic drill rods by the aluminum buffer rods. Reliable and accurate magnetic azimuth measurements can be obtained by this method and it is widely used in core drilling operations.

Two methods are common in wireline coring procedures: the connector on the upper end of the survey train can connect to the inner tube and the core-barrel assembly is used to lower or pump-in the Tropari to its destination (Fig. 3); or in steep holes, the rod assembly can be lowered to stop at the bit using a landing coupling which will go through the rods but not through the bit (Fig 2).

Alternately, non-magnetic drill rods (non-magnetic drill collars) can be used in the drill rod/pipe string above the drill bit and within which a magnetic azimuth survey can be made. The nonmagnetic collars are expensive, but if the rods are too costly an operation to remove from the hole for each survey and the drill bit blocks access beyond the bit, it may be a cost effective technique and is widely used in the oil and gas drilling industry.