GENERAL42099

• Permit No: M1983194
• IBM Index Class Name: General Documents
• Doc Name: COVER SHEET 4 APPENDICES
• Media Type: D
• Archive: No

4.2 APPENDIX B
and potential loss of borehole are to be avoided. WRC
will use LC materials in the mud when drilling through
and beyond the Leached Zone. This type of mud in the
hole, if not removed, is not conducive to efficient
displacement of mud by the cement.
Failure to adequately remove the mud in the hole during
the cementing operations may result in cement channeling
and subsequent fluid migration, elevated pumping pressures,
reduction in cement bonding capability, and total job faflure.
Prior to cementing, a reduction in fluid loss, viscosity, yield
point, and gel strength of the mud will increase the
displacement efficiency.
Much haz been written regarding proper cementing Dow
regimes. Most authors agree that turbulent Dow provides
the highest displacement efficiencies, but with most cements,
turbulent Oow cannot be achieved. Plug flow was once
thought to be nearly az effective az turbulent flow. However,
the curtent trend in industry seems to indicate that the greatest
possible permissible velocity, given surface equipment and
downhole wostraints, should be used. Laminar flow results
in the lowest displacement efficiencies.
Wazbes, flushes, and spacers also promote displacement
efficiency by thinning the mud ahead, preventing a cemen[-
mud interface that facilitates channeling and cement
contamination, removing pockets (washouts) of thick,
viscous gel and the fdm of mud on the casing. Turbulent
flow is obtained more easily with these fluids than with
the cement slurry.
Although not much has been written about contact time
(the time cement Flows past a certain point in the well bore),
many authors feel that adequate zonal isolation cannot occur
without a "minimum" contact time. The greater the contact
time, the greater the chances are in displacing all drilling
mud from a point in the well bore and achieving a good
cement job. A 10-minute contact time is recommended.
Improved displacement efficiency can be realized when
pipe movement is conducted. Pipe movement is accomp-
lished by reciprocating or rotating the pipe. tE the casing
is adequately centralized, hole conditions (i.e., gauge and
deviation) and mud properties are good, reciprocation is
the better choice of the two. Rotation adds more of a lateral
motion component to the system that facilitates mud rernoval
from the narrow side of the annulus but also induces
additional stresses on the pipe.
When scratchers or wipers are installed on the using
across the cementing interval and pipe motion is used,
displacement efficiency improves. The greatest benefit occurs
io regions of hole washout. Scratchers help in breaking the
gelled mud within washouts and increases the amount of
cement Flow into washouts. With a properly treated cement,
removal of the mud cake during cement circulation vastly
improves the cement to formation bond. However, caution
must be exercised to avoid flash setting or dehydration of
the cement. A low fluid loss cement will eliminate this
problem. Removal of the mud cake, in the presence of mud,
adds little benefit since the mud cake will be quickly replaced.
Dislodged mud cake must be removed prior to cement
circulation if contamination is to be avoided.
The shoe of the 836-inch casing will be set approximately
30 feet into the Saline Zane with [he cement top extending
across the dissolution surface and into the Leached Zone.
Rock quality data (RQD) obtained from W RC for [he leased
area indicates that the lower half of the 100-foot cementing
interval is fractured and rubblized but maintain an RQD
of 60 percent (Note: All RQD percentages presented are
approximate with a simple average given for specific
intervals). Portions of the remaining 100 feet are composed
of nahcclite, nahcolitic halite, and nahcolitic oil shale subject
to dissolution by the drilling fluid, casing pack, and cement.
The RQD for this interval is 10 percent. Hole enlargements
will occur across this interval making mud removal difficult.
The leached zone above the 100-foot cement top exhibits
low RQD percentages; however, these percentages increase
to 30 percent over an interval from I(b feet to 200 feet
above the shoe of the 8 3§-inch casing. Additional cement
bonding may occur through this interval.
An anticipated oceurtence az a result of forming solution
mined gvities is the collapse of cavity roofs. Caving of
the overlying strata into the cavity would extend vertically
until the cavity was bulked full. The predicted height of
the caving is 53 feet which would extend through the
dissolution surface into the leached zone. Since the bottom
50 feet of the 100-toot cementing interval presents the
greatest opportunity far cement bonding, isolation of the
cavity would be severely jeopardized if caving was to occur.
Subsequent horizontal drilling will occur that will further
jeopardize what little integrity, if any, the I00 foot annular
column of cement exhibits. Many surface casing shoes in
oil and gas wells have been "wobbled off' for lack of
adequate cementjobs.
Operational parameters dictate the presence of mining
solution within the 835-inch casing. Air compressed to
approximately 800 pounds per square inch gunge (psig) will
be exerted on the 544-inch by 8 i4-inch casing annulus
to prevent mining solution from occupying the interior of
the 8 ye-inch casing. The pressure will be monitored for
possible 8 i4-inch casing leaks. If the pressure falls to 700
prig, casing failure may have oceurted. A pressure drop
of 100 prig equates to a Fluid rise in the 8 i6-inch casing
of approximately 300 feet. If a casing leak were to occur
above the 100-foot column of cement and did not invoke
a pressure drop greater than 100 psig, mining solution would
enter the annulus and may contaminate uphole resources.
4.2-2