12.2.3.2 MD Datum

Because the RESQML data model does not extend beyond the wellbore see 12.1 Special Requirements for Using WITSML 1.4.1 Data Objects with RESQML (in an EPC File) , the MD datum is a mandatory component of the wellbore. It includes an MD reference enumeration that is identical to that of WITSML, with one exception: it also has an “arbitrary point” to support reservoir modeling workflows for well planning and field development.

The MD datum is a top-level data object so that it may be shared among multiple wellbores (e.g., in multi-lateral wells) or several versions of trajectories. The MD datum exists independently of the wellbore trajectory representation and needs to have a uniquely defined local 3D coordinate reference system (CRS), though the datum and the trajectory must refer to the same local coordinate system.

In practice, the local 3D CRS used by the MD datum is often the composite of a projected CRS and a vertical CRS, without any translation or rotation. The local 3D CRS is also a top-level data object, which means that it can be shared between the MD datum and the geometry of the wellbore trajectory representation, although there is no requirement that they do so. For example, the CRS of the MD datum may be shared among multiple wellbores from the same wellhead, while the CRS of the wellbore trajectory representation may be chosen to be the same as that of a reservoir modeling grid, to facilitate intersection calculations.