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Using the slide sheet in figure 47 as an example:
Figure 47: Typical slide sheet.
Looking at the data for BHA 6, we can see a few points where surveys were taken and several changes from rotating to oriented (sliding) mode. The lengths and toolfaces are listed for each slide. Whilst these values will only be approximate it is possible to then estimate the wellbore attitude at the points where the slides began and ended. Firstly if we take the total curvature generated over the BHA run by measuring the angle changes between surveys (see minimum curvature described above in chapter 7) we can work out the dogleg severity capability of this assembly. If we then apply that curvature on the toolfaces quoted, it is possible to determine a fill in survey at the beginning and end of each slide by using the approximation that the inclination change will be:
DLS x length x cos(Toolface) and the azimuth change will be the DLS x length x sin(Toolface) / sin(Inclination)
- where DLS means dogleg severity in degrees per unit length. This allows us to complete surveys at the start and end of each slide and minimum curvature will then be more valid when joining the points.
This assumes that: 1.
The DLS is unchanged during the run The curvature all happens when sliding The toolface was constant during the slide
2. 3.
These assumptions are very simplistic but the analysis will generally give a better idea of TVD than the assumption that the sparse surveys can be safely joined with 3D constant arcs.
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