Borehole surveying is a distinct operation and must be viewed and executed with the same professional dedication as that used in drilling the hole. If those planning steps are not taken, you can rest assured that the necessary mental and equipment preparation will not be there to get the directional, core orientation or other survey data accurately and cost efficiently. Consider which of the questions below apply to planning your survey project:
What kind of accuracy do you need for the project? Here the instrument or the survey train (application hardware) may be the accuracy limiting item.
If the borehole has a target, will the hole hit the target and who will decide when the hole deviates sufficiently so that corrective procedures or abandonment have to be invoked? Surveys at regular intervals as the hole progresses will allow the hole to be plotted and excessive deviation recognized at the earliest and least costly stage.
Is the instrument and the survey train suitable for the application and drilling conditions? There is a wide variation in the ease of use or time required for a survey and this may depend on either or both the instrument and the survey train used for the specific data required. Consider how disruptive the surveys are to the drilling procedures. Compare data and supplementary advice from manufacturers or service providers for your specific requirements.
Are there special conditions at or in the borehole that need to be addressed? These, for example would be temperatures above 85° F or below -20° F in the bore; water, steam, oil or gas discharges that could set up vibrations in the survey train preventing the instrument from stabilizing even at low velocities; and boreholes where the
wall rock is not coherent.
Are site procedures understood by the staff? This could include how the survey train is assembled and armed, how the lowering cable or rods are marked so that hard impacts with in hole-tools or the bottom of the hole are avoided, how the cable is marked so that the survey train is not wrapped around the drill rig when it exits the hole at high velocities, and how the readings are obtained and processed.