GENERAL42099

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

4.Z APPENDIX B
Placement of the 100-foot cement column must occur
with proper borehole preparation and displacement
techniques, and precise volumetric tr~easurements, taking
hole enlargements into consideration. A 100-foot column
of cement does not leave much room for error given the
operational difficulties with placing the cement and the
importance in obtaining a good cement job. WRC did not
provide much information concerning the procedures
proposed to prepare the borehole and place the cement.
Very tew of the items listed above were identified in the
mine plan. WRC claims that the 100-fcat column of cement
will effectively seal the mining cavity from the above annular
region and support two strings (5 4r and 8 ye inches) of
casing. BLM has no argument with WRC about the cement
bonding necessary to support the weight of the casings;
however, exception is taken to tht:ir statements about
isolation of the mining cavity.
BLM believes the 100-foot annular column of cement
will not provide an adequate barrier between the mining
cavity and the annular region behind the 8 ye-inch casing.
No information was provided by WRC that would justify
the intended (unction of the cement. Therefore, increasing
the total annular cement column length from 100 feet to
250 feet with confirmation of the cement job obtained by
running a Cement Evaluation Tool log or equivalent log
is dcemed necessary and will be required.
Hole abandonment is dictated primarily by the type of
wmpletion progr9m used. BLM has no objection to the
use of mud between cement plugs within the borehole. We
do, however, object to the use of mrid in place of cement
when attempting to permanently secure the well bore and
provide resource isolation or protection. Cement will
immediately ensure (within 8 hours) that a hole is adequately
plugged. The regulations and lease terms do not allow
approval of plugging procedures that provide temporary or
speculative resource protection or isolation. The full scale
commercial mine plan calls for drill holes on 300- to 600-
foot spacings within cavities and 78 feet between cavities.
The potential for resource contamination is magnified many
times by the scale of this operation.
Plugging gel is subject to dynamic: well bore conditions
that may compromise its intended function for the Gfe of
the Piceance Basin. The technical expert presenting the
characteristics of the plugging gel at the July 30, 1986,
meeting could not provide information concerning the gel's
physical properties (upon mixing and aver time) except to
state that if it is made properly and no Fluids are Bowing
to the surface, adequate aquifer protecton is indicated. BLM
cannot base resource protection decisions on such an
unsubstantiated viewpoint.
WRC provided some background into the history of the
type ofplugging gel they propose to ace in their statement
of reasons supplied with the appeal of the mitigating measures
in the EA. The produM analyzed was a hightluaiity sodium
bentonite-polymer base compound (Shur-gel mud
conditioner-product of NL Baroid/NL Industries Inc.).
WRC proposed to use Shur-gel as their plugging gel. In
almost every case (ten mineral exploration drill holes), the
mud level dropped at or just above the piezometric surface
of the first aquifer 6 to 10 weeks after placement. The article
states that the common characteristics of the fluid after
placement is a drop in fluid level to the piezometric surface.
No information was provided concerning the specific
downhole geology of the exploration drill holes, but it is
doubtful that the geology approximates the conditions found
in the Piceznce Basin. What little technical data that could
be obtained from [he article about viscosity development
seemed encouraging. However, Buid sampling techniques
and consistency were questioned and the viscosity increase
was termed a "tendency". Other background articles/letters
recommend Ote use of cement, if artesian Bow is encountered
or if the use of a plugging gel is not adequate.
The only justification provided conceming the sealing
characteristics of the plugging gel were mining intercepts
of boreholes that were plugged with Shur-gel. No information
about depths or formation characteristics were presented.
Therefore, considering the potential for gas migration from
oil shale regions or water influx from the aquifers into the
well bore, leaching of the plugging gel into vuggy,
unconsolidated zones, possible future use of the aquifers,
and development of the oil shale, BLM believes the plugging
of critical intervals within the well bore should be
accomplished with cement. [f cement is used and all mud
within the well bore is evacuated after abandonment, the
exating cement plugs will provide the required resource
isolation or protection.
The unproven technology and scale of this type of solution
mining operation requires a logical progression from theory
to fact. Accurate data should be obtained by applying new
procedures and operations in a step-wise fashion. Thus,
developing problem areas can be easily identified and
corrections and modifications made quickly. If the entire
scope of new technology is utilized immediately, several
attempts at changing different operational aspens may be
necessary before problem areas are found and corrected.
Experience obtained from the fast few well pairs should
allow responsible modifications with sufficient justification
and confidence. Part of the proposed mitigation in the EIS
provides the operator an opportunity to submit for approval
"any technical considerations and/or proposed changes in
operation".
4.2-3