16.1 Common Human errors

Common Pitfalls
The following common well planning pitfalls are listed to raise awareness. Past experience has shown that these are likely errors that can be overlooked. Best policy is to review this list after producing a new well plan.

Missing Data
The most frequent reason for collision is not poor surveying but rather that the object well came as a “surprise”. It is essential that the well planner ensures that he has all the data needed to plan a safe well path. Always check a list of wells with the client to ensure that nothing was lost in migration.

Using Gyro Error Models for Undrilled Sections
It may well be that a gyro survey is planned in for example, 9 5/8 casing. But prior to this gyro survey “confirming or more accurately describing” the well path of the well, this section will usually be a 12 ¼ inch hole which will be drilled with MWD. It is important during well planning that the anticipated survey program as each well section is drilled, is used. The updated or most accurate survey and error model should be entered and used for anti-collision purposes right before a new section is drilled. But during the initial planning the as drilled error models should be used to the total depth of the well to confirm the entire well can be drilled conforming to required separation factor rules.