# Inclination Only IPMs Sensitivity to Zero Inclination

## Background

ISCWSA’s position is that inclination only surveys do not constitute a true survey of wellbore and they recommend that they not be used. However, there are many legacy inclination only surveys in the industry and these should be handled in a suitable and consistent manner. As a result, Well Seeker Pro can utilize inclination only IPMs in its anti-collision calculations. This set of IPMs has an inherent behaviour that Innova wish to highlight to its users, so that they are equipped with the best information to use these IPMs correctly.

## Description

It should be noted that when using an inclination only IPM, the difference in the calculated error ellipse for a portion of a well with a zero degree inclination, when compared to a portion of a well with a positive inclination (0.01 degrees or greater) can be very large. This is caused in a large part by the misalignment term XYM1 in the inclination only models that has a very large magnitude and is based upon the sine of the inclination.

![](/files/-MjUcgiUBElYlD9TvBCK)

When inputting surveys for a well that is using an inclination only IPM, ensure that the surveys are input as per the inclination only survey results. Inputting an inclination of zero, where in reality it is not, will have a huge impact on the calculated error ellipse.


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