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ExxonMobil <br />Global Services Company <br />Colony Shale Oil Project <br />P.O. Box 2567 <br />Houston, Texas 77252 -2567 <br />August 1, 2011 <br />RFCEIVPD <br />AUG 0 4 2011 <br />DNIsion of Reclamation, <br />Mining and Safety <br />Colorado Division of Reclamation Mining & Safetyl/ <br />Grand Junction Office <br />101 South 3 Street, Suite 301 <br />Grand Junction, Colorado 81501 <br />Attention: Travis Marshall <br />Re: ExxonMobil, Colony Oil Shale Project, Permit No. M- 1980 -047 <br />Preliminary Adequacy Review, Technical Revision, TR -15. <br />-fiu�1,5 / DMZ <br />EonMobil <br />An ExxonMobil Subsidiary <br />RECEIVED <br />AUG 0 2 2011 / <br />GRAND JUNCTIUN HELD OFFICE <br />DIVISION OF <br />RECLAMATION MINING & SAFETY <br />Dear Mr. Marshall:'` - <br />This letter is in response to DRMS' letter of June 24, requesting answers to several specific questions <br />concerning ExxonMobil's TR -15 application. Below are reproduced DRMS' specific questions (in italics), <br />followed by ExxonMobil's response. <br />1. What methods and criteria will be used to determine the effectiveness of the "grout curtain "? <br />Please provide in -depth detail as to what type of monitoring and testing will be conducted in the <br />"grout integrity test holes ". <br />Response: Initial grout curtain testing will be conducted as the grout curtain is being constructed. <br />Grouting will begin with a coarse network of holes perhaps drilled on 20 -foot spacing. This coarse <br />network will subsequently be filled in with additional holes. As infill grout holes are drilled, water will <br />be injected into them to gauge whether the previous grouting of nearby holes has formed an <br />effective seal. Additionally, selective coring and borehole cameras will be used to further evaluate <br />grouting effectiveness. This testing will continue until the grout curtain is entirely filled in. <br />Once the grout curtain is installed, "grout integrity test holes" will be drilled from the decline to <br />locations in the lower portion of the grout curtain. These holes may also ultimately serve as `oil <br />drainage holes" in a potential high- temperature Electrofrac experiment. As grout integrity test <br />holes, these holes will be packed off to access only rock inside the grout curtain and will be used as <br />follows: <br />• The water flow rate from the holes will be measured. This will be indicative of the amount <br />of water requiring handling in any future high- temperature experiment. <br />• The holes will then be shut in, with pressure gauges placed on the "wellhead" at each <br />hole. The pressure gauges will read a fluid level in each hole. Common fluid levels <br />among the holes will indicate good fluid communication inside the grout curtain. <br />• Rising fluid levels will be related to the water flow rates previously measured. This will <br />provide a qualitative indication of the grout curtain's integrity. <br />It should be stressed that because of uncertainty in the amount of water entering the grout curtain <br />from above, no hydrostatic test can give an absolute indication of grout curtain integrity. These <br />tests can nevertheless provide a good qualitative indication. <br />