Technical Hole Deviation (THD)

Definition - What does Technical Hole Deviation (THD) mean?

Technical hole deviation refers to the geometrical differences between actual and planned well paths. Prior to the start of directional drilling, a mathematically-defined path is planned. The tendency of a drill bit to depart from a preselected borehole trajectory can be costly. An accurate quantitative description of drill hole deviation gives workers the opportunity to make adjustments to correct the drill bit path.

Trenchlesspedia explains Technical Hole Deviation (THD)

Measurement-while-drilling (MWD) is a type of well logging that provides real-time information with regard to horizontal directional drilling. Conventional tools become ineffective for well angles exceeding 60 degrees. An MWD device is one of the tools used to monitor the technical hole deviation.

Interpretation of hole deviation data is important. Traditionally, directional drillers interpreted deviation as a mental exercise. The purposes of hole deviation data provide the directional driller with a log so that he can improve deviation control, provide input for automated directional drilling systems and provide information about directional drilling control performance.

Technical hole deviation is applicable to all forms of directional drilling and any type of directional drilling system. Associating the actual well path with the stated properties of the target path is critical to evaluating the changing state of any directional drilling system.


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