Downhole Distributed Temperature Sensing in Fractured Rock

Newmont’s Leeville Mine is located on the western side of the Tuscarora Range in northeastern Nevada. A 587 meter geotechnical pilot borehole in silty carbonate was drilled during 2012 prior to excavating a 10 m diameter vent shaft using ground freezing technology. Fiber optic cable was installed in the borehole and backfilled with cement-bentonite grout. In 2013 a distributed temperature interrogator was installed, which measured temperature along the fiber optic cable at 0.25 m and 0.02 °C resolution. After initial data were taken, a lower-resolution interrogator was installed for longer-term data collection, which measures temperature along the fiber optic cable at 1 m and 0.2 °C resolution. The intent was to utilize temperature for aquifer characterization. Daily measurements were programmed and run from December 21, 2013 through June 20, 2015 for a total of 546 daily temperature traces comprising 321,048 data points. Descriptive data analysis is presented, indicating a saturated zone 122 m below ground surface where a rapid temperature decrease of near 2 °C was seen. Similar downhole temperature changes are observed at 367 and 528 m coinciding with fracture flow zones where lateral water flow is suspected. Distinct slope profiles of the local geothermal gradient are evident between the fracture flow zones, indicating separate hydrostratigraphic units. The close-by ground freezing provided a thermal tracer of water movement. Temperature generally decreased over time because of the freeze process. Greater than 7 °C difference was observed in zones interpreted as lower permeability where conductive heat transfer was likely dominant. Advective flow at the 366 and 526 m depths showed substantially less temperature variability. It is at these depths where water flows through fractures at a greater velocity than the bulk rock and where the water temperature is indicative of the greater aquifer system. The smallest temperature change was less than 2 °C at 579 meters depth, which is interpreted to be the upper zone of the semi-saturated Roberts Mountain Thrust Fault.

Raw project data is available by contacting [e-mail]

纽蒙特公司的利维尔矿位于内华达州东北部图斯卡罗拉山脉的西侧。在2012年，为了采用冻结技术挖掘直径为10米的通风井之前，在该地区钻探了一个587米的岩土工程试验钻孔，该钻孔位于淤泥质碳酸盐岩层中。在钻孔中安装了光纤电缆，并填充了水泥膨润土浆料。2013年，安装了一个分布式温度询问器，该询问器以0.25米和0.02°C的分辨率测量光纤电缆沿线的温度。在采集了初始数据后，为了进行长期数据收集，安装了一个分辨率较低的询问器，该询问器以1米和0.2°C的分辨率测量光纤电缆沿线的温度。目的在于利用温度对含水层进行特征描述。从2013年12月21日至2015年6月20日，共进行了546天的测量，累计数据点达321,048个。描述性数据分析表明，在地下122米处存在一个饱和区，此处观察到近2°C的快速温度下降。在367米和528米深度，观察到类似的井下温度变化，这些变化与裂隙流动区相吻合，怀疑存在横向水流。裂隙流动区之间的局部地热梯度斜率剖面明显不同，表明存在独立的含水层地层单元。附近的冻结技术为水流提供了热示踪剂。由于冻结过程，温度总体上呈下降趋势。在解释为低渗透性的区域，观察到超过7°C的差异，其中可能以导热传热为主。在366米和526米深度的径流显示出显著较低的温度变化。在这些深度，水流通过裂隙的速度大于岩石，且水温可以指示更大的含水系统。在579米深度的最小温度变化小于2°C，这被解释为半饱和罗伯茨山推覆断层上部的区域。原始项目数据可通过联系[e-mail]获取。