Laserfiche WebLink
410 <br />i <br />Dan Jackson: <br />On the subsidence monitoring you were voicing some concern, are we looking at a surface <br />type of monitoring or will would you be doing a subsurface monitoring? <br />Roger Day: <br />At White River we tried several techniques. One that wasn't good was shooting radioactive <br />bullets in the formation before casing so we'd be able to use a gamma tool to find those <br />bullets to see if they had or had not moved. What really worked was the natural gamma log. <br />We did experience and measure subsidence less then the Bureau of Mines estimate of a <br />stable arch forming at about 125 ft. When we started having problems with the wells and <br />things didn't seem to be right, we found about 90 some feet of disturbed gamma log. It was <br />very evident but not as evident as the torn up casing and casing cement. We had to redrilled <br />down through the rubble and reestablished the casing before we could see how much the <br />gamma had changed. You could tell where the subsidence came to an end (90 ft above the <br />cavity). It was very easy to identify the well damage and see the impact to the gamma log. <br />So, that's real functional underground subsidence monitoring, especially in our case where <br />all the cavity is below the well. At White River we had the wells widely spaced on the <br />surface and we were horizontally drilling and mining. We could not know what was <br />happening out away from the wells. In our case, the mining is right there below the wells <br />and so the subsidence focuses right on the wells and I think we'll have really good, thorough <br />knowledge of that subsidence underground. We'll add the surface monuments to it, just to <br />confirm that there's no movement on the surface. But, the initial and primary subsidence <br />monitoring is broken, bent or missing casing. We basically found rubble and little casing <br />below the stable formation above 90 feet. This had to be redrilled. <br />Dan Jackson: <br />The location of the gamma ray indicator strata, where are they located relative to the A/B <br />Grooves. <br />Roger Day: <br />There is an identifiable feature to the gamma all the way up and down the hole, all the way to <br />the surface. There are multiple locations. <br />Dan Jackson: <br />I guess what I was concerned with, right there at the well location it sounds like there should <br />be rubblization through a line that extends to or perhaps breaches the Mahogany Zone and <br />you'll be able to recognize that. <br />Roger Day: <br />Right. I think we can unmistakably, positively identify if it's there. If there's enough <br />movement to disrupt an aquitard, there's got to be enough movement to have broken the <br />casing and the cement bonds. <br />13 <br />