Core drill

Drilhng. Glass is dtiUed with carbide or bonded-diamond dtiUs under a suitable coolant such as water or kerosene. Other drilling processes include a metal tube rotating about its axis (core drilling), an ultrasonic tool in combination with an abrasive slurry, or an electron beam. Tolerances less than 0.1 mm are readily obtained with diamond-core drilling and, if required, holes smaller than 25 )J.m-dia can be made with the electron-beam method. 

Preparing for mining in the United States involves studying cores drilled initially on 1.6 km centers and later at 1.5-3 cores/km (4-8 cores/mi ), depending on the occurrence of discontinuities. The actual mining takes into account the variation of deposit properties in terms of percent moisture, ash composition, ash content, and grindabiHty as a function of moisture (9). 

Natural Deposits. Natural deposits, eg, minerals and fossil fuels, are located by drilling operations. An auger, eg, a screw or worm, is turned in the earth and pulled out, and material is scraped from the auger for analysis. Alternatively, samples can be taken by hoUow core drills which, when withdrawn, enclose a core of the earth that is representative of the strata through which the drill has passed. Such core samples are used in geological surveys for fossil fuels. As the drill drives deeper into the strata, each core is extracted and placed in a shallow box and coded so that a complete cross section of the geological strata can be reconstmcted. From this, the relative thickness of coal and mineral seams can be directly measured. 

The commercial value of a clay deposit depends on market trends, competitive materials, transportation faciflties, new machinery and processes, and labor and fuel costs. Naturally exposed outcrops, geological area and stmcture maps, aerial photographs, hand and power auger drills, core drills, earth resistivity, and shallow seismic methods are used ia exploration for clays (32). Clays are mined primarily by open-pit operation, including hydraulic extraction however, underground mining is also practiced. 

Diatomite deposits are usually discovered by observation of outcrop, and the value of the deposits is deterrnined by geological prospecting and exploration. Samples are taken from the surface outcrops by digging or trenching underground samples are secured from test holes, core drill holes, or tuimels. 

Several laboratories therefore intend to measure profiles of these isotopes on ice cores drilled in polar ice caps. The new technique also makes possible measurements of the 14C in the C02 occluded in about 30 kg of ice. From the 14C measurements again twofold information is expected ... 

Acker, W. L., 1974, Basic Procedures for Soil Sampling and Core Drilling Acker Drill Company, Scranton, PA, 246 pp. 

Most of the samples for this study were collected by air-core drilling through the regolith. Samples were 1 kg splits taken with a sample spear from larger bulk... 

The oxygen-isotope ratio ( 0/ 0) found in the calcareous tests has been used as an indicator of the amount of water locked up in glaciers, which reflects the state of the global climate. Another source of continuous records of oxygen-isotope variation, as well as dust content and acidity, is found in the long cores drilled in polar ice caps in which annual layers can be counted and seasonal variation can be established [65]. 

Natural oxygen is 99.8% l60, 0.2% lsO, and 0.04%, 70. Small variations in isotope ratios in H20 in the ocean, the atmosphere, and rain and snow depend on local temperature. The warmer the air, the more enriched it is in H2I80. The lsO content of snow preserved in glaciers provides a record of air temperatures for 250 000 years in 2-km-long cores drilled from ice sheets in Greenland and Antarctica. Depth in the ice pack has been correlated with age in years by a variety of measurements. 

In some deep-sea sediment columns, records of IDP fall-out can be traced back to several ten million years with the help of extraterrestrial He as a tracer. Such a remarkable example was reported by Farley (1995). Farley measured 3He/4He ratios in a pelagic sediment core drilled from the central North Pacific. The core is thought to carry a nearly complete sedimentation record to 72Ma. Figure 5.6 shows records of the He concentration and the isotopic ratio in the drilled core. 

Application of core drilling and core analysis to the recovery of oil. Intern. Petroleum Tech., 8 157-167. 

Fig. 1.14 An example of forced core drilling of a rubber stopper.

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