A survey application is a specific operation that the instrument and survey train or assembly is required to perform. Lets look at a few examples:

Directional Surveying provides data that defines the position of the borehole in 3 dimensional space. This provides answers to questions such as "Exactly where did this rock (core or chip) sample come from?" or "Is the hole going to hit the destination target?".

Say, for example, that the hole was being drilled steeply downward to depths of 1000m (3300 feet) using NQ* equipment in a temperate climate. The NQ designation immediately conveys the size of the drilling equipment and the fact that we can lower and retrieve the instrument by the same system that is used to transport the core-barrel assembly inside the drill rods.

If the instrument used is a magnetic azimuth type, then the survey train has to pass through the drill bit to place the instrument beyond the influence of the magnetic drill rods. In this application the drill rods would have to be raised from the bottom of the hole to allow the survey assembly to pass through.

If the instrument chosen used nonmagnetic sensors (see “Azimuth or Heading Direction Surveys”) the survey could be done inside the drill rods. In this case the directional reference would be set at the surface and transferred by the instrument to the survey site.

In this particular application we have a wide choice of instruments because the size of the hole in the bit is fairly large (47.5mm or 1.87 inches), the hole is steep downwards (greater than 40° from horizontal) and the temperature will not be extremely hot nor cold.

The protective casing or container for the instruments may vary in size (both in diameter and length), most instruments have limits on the inclination angles and temperatures they can operate within, and all have depth limits that depend on the strength of the protective casing or the length of cable for systems that can be viewed on the surface for example. 

The survey train has to be at least partly specific to NQ because the train has to attach to NQ lowering gear and pass through the NQ rods or the NQ drill bit (depending on the instrument type) without causing significant survey errors. Errors can arise from the instrument not being perfectly aligned with the drill hole, or, for example, some of the components of the train may be sufficiently magnetic to influence a magnetic azimuth sensor.

The above figure illustrates a commonly used TROPARI application

for the borehole in question.

The borehole had to be directionally surveyed prior to this operation to provide the information that led to the decision to change the heading of the hole and we now need an instrument and application hardware that has tool-facing capabilities.

The e-SYNC on this web site is an example of a tool-facing instrument that will provide the rotational orientation of the wedge referenced to the plumb direction in holes inclined more than a degree from vertical.

Others instruments are available that use relative heading sensors. Some of the wedging applications require accurately aligned in-the-hole devices to be attached to the wedging hardware into/onto which the tool-facing survey train is lowered to obtain the rotational orientation. Again, the availability of wedging application hardware from some instrument manufacturers may be limited.

Pajari Instruments Ltd. has full in-house capabilities for all its surveying products and can therefore expedite the design and manufacture of new application hardware. And it is possible that we have already made something like that for someone's application.

Tool-facing is also used in core orientation, impressions of bore-walls, made by packers and the orientation of in hole "measuring" devices.

Tool-facing surveys provide a rotational position of a tool within the drill string or on the end of the drill string, this coupled with the direction of the bore hole will allow the tool to be positioned correctly for the intended purpose of the tool.

Tool-facing does not give the direction of the hole, only the direction of the tool face.