Page 381 - Numerical Analysis and Modelling in Geomechanics

362 RESERVOIR COMPACTION, SUBSIDENCE AND WELL DAMAGE

Figure 11.14 Three-dimensional wellbore model.
wells in the immediate vicinity of the two-dimension, field-scale model were
checked against model calculations. The data set od wells for this model included
23 failed wells, with various failure modes, not just in shear. Wells without
apparent damage or failure were also included in the database. The first
occurrence of well damage was defined as the inability to run or pull tools, such
as packers, scrapers, or plugs, into or out of a well. The real elapsed time in the
life of the well at which this occurred was compared with the simulated time in
the field-scale model calculation. Often, field personnel noted the size of the tool
on the workover ticket, which could be checked against the wellbore model.
Permanently bent tubing pulled during a workover also indicated sheared casing,
and this was checked.
The relative slip on the Al and Dl shale layers and the Tulare-diatomite
unconformity for simulated wells was tracked and plotted. Workover records for
these wells were checked to determine if problems occurred. If problems did
occur, the depth at which problems were encountered in the well was noted. This
field data was compared with the relative slip in the simulated well. For the
example shown in Figure 11.18, well 551G did incur damage in about 1987 and
a survey tool would not pass at the depth of the Tulare-diatomite unconformity in
1995.
The capability of the two-dimensional, field-scale model to predict the onset
of well damage was fairly reliable. In areas of Section 33 where casing damage