Depth Control: Reconciliation of LWD and Wireline Depths, Standard Practice and an Alternative Simple but Effective Method

摘要

Depth is one of the most important formation evaluation measurements, but it is also one of the most difficult to define accurately. LWD measurements, which rely on driller's depth, are becoming more prolific and widely used. Wireline measurements, with their independent determination of depth, are still commonplace, while the use of both wireline and LWD measurements together is still largely unavoidable in a full data acquisition program. Reconciliation of depth, including survey error when converting to TVD's, is still one of the key problems faced when evaluating and fully interpreting these data sets.This paper reviews the current common practices applied to correction and correlation of depth. Generally, these practices are intended to correct all other measured depths to a single definitive depth reference. The extent to which the intended goal is achieved is assessed. The paper also describes an alternative approach which accepts all depths as valid, but assigns uncertainties to each. A real well is used to compare the outcomes for each approach. One conclusion is that correction of drill pipe depths for stretch effects is desirable, and a simple but effective correction method is described.