Depth - one of the most important formation evaluation measurements but one of the most difficult to define accurately. With longer and deeper wells in deep water provinces around the world, this problem becomes more acute.

A new approach has been developed for a more systematic treatment of, and hence better reconciliation of, depths from current logging data acquisition systems. This paper concentrates on LWD and wireline depths where common place discrepancies in depth are often ignored for a favoured reference to which all depths are correlated. This chosen reference is often picked arbitrarily (with no quantification and results in a incorrect assignment of final depth in the reservoir model. More than likely, this discrepancy is unknown to the analyst and un-quantified.

We demonstrate case histories of a systematic approach to the treatment of LWD and wireline depths that includes consideration of their relative measurement uncertainties, and the primary acceptance that all depths are valid and a consideration/use of their combined uncertainty. The resulting single reference depth for tying geological and petrophysical analyses is more accurate and a quantification is given as to its uncertainty.

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