8.1.3 Cumulative History
|For Standard||WITSML v2.0|
The cumulative history use case refers to the transfer of data corresponding to the whole history of the completion. The ledger described in the previous section is also used to determine all events and equipment changes (additions, replacements, and removals) as shown in Figure 8.1.3-1 .
Figure 8.1.3-1 shows the data for the first few days of a well being drilled and completed. The events are shown as sequentially numbered and this ledger continues to grow through the life of the well. The “Wellbore Equipment” shows the physical installation of the completion. This installation includes the wellbore itself (i.e., the hole drilled in the earth) and the hardware (casing, tubing, etc.) installed in it. Note that each item of equipment contains the ID (the “Exx” in the figure) of the event that installed it, allowing the details (including date and time) of each piece’s installation and removal to be discovered. When an element of equipment is removed, a second ID is added, which has the event that resulted in its removal.
For example, the last element of equipment is a bridge plug used to pressure test the casing; it was installed by event E14 and then later removed by event E16. The pressure test, E15, is between the installation and drilling out. The equipment entry shows both install and remove events at the time of the day 4 cumulative history.
Note also that the borehole equipment entries for each day get “removed” and replaced by a new deeper borehole when appropriate during the drilling phase, with the day’s drilling report being the event that triggers this new equipment entry. This can be seen by looking at, e.g., the second borehole size running on from 450 depth units, which is drilled to 798 by event E10 (“drilling day 2”). Then this borehole data object is removed by event E11 (“drilling day 3”) and replaced by a deeper borehole to 927, and finally is established by E12 as drilled to 1250.
The snapshot use case can be thought of as a query on a cumulative history at a given instant in time. The change log use case can be thought of as a query on a cumulative history between two points in time, giving the “delta” events between those times.