Geology topics
Publications and source records attributed to L.M. MacCary.
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No abstract available.
The need for large quantities of energy has created interest in the Fort Union coal region of the Northern Great Plains. Extensive development of this coal, which may include onsite steam-power generation, gasification, liquefaction, and slurry-pipeline transport of the coal from this region, would place a heavy demand on the region's limited streamflow. Paleozoic rocks that underlie the Fort Union coal region and aquifers in these rocks, including the Red River Formation and the Madison Limestone, might supply, at least on a temporary basis, a significant part of the water required for coal development. The area of study covers approximately 200,000 square miles, and includes eastern Montana, western North Dakota and South Dakota, northeastern Wyoming, and northwestern Nebraska. This report, one of a series in the Madison Limestone study, uses hydrologic and geologic data to outline potentially favorable areas for well construction - that is, areas in which there is a good probability that large-yield wells (more than 500 gallons per minute) can be completed in the Red River Formation and in the Madison Limestone. Potentially favorable areas in terms of aquifer characteristics, for both the Red River Formation and the Madison Limestone, are given a numerical evaluation from 1 to 3 based on the number of the following criteria that are met: (1) the presence of more than 100 feet of relatively porous rock, (2) the presence of more than 100 feet of dolomite, and (3) the presence of known geologic structures which could affect yield. Areas rated 3 are those in which all three criteria are satisfied; areas rated 2 are those in which two criteria are satisfied; and areas rated 1 are those in which only one criterion is satisfied. The criteria selected for this analysis were chosen because they can be recognized and mapped over the entire study area. Local features such as minor structures, solution zones, and rock facies of small extent were not included in this regional evaluation. In addition, water quality was considered in a general way in defining the favorable areas, by excluding areas in which the electrical resistivity of formation water, as calculated from geophysical well logs, was less than 1 ohm-meter. The numerical scales of the Red River Formation and Madison Limestone are summed to show potentially favorable areas for the combined aquifers. Certain additional factors which may be important to a prospective water user were not included in the numerical ranking - these include depths to the two aquifers, calcite saturation, water temperature, total dissolved solids, and piezometric head in relation to land surface. For a complete evaluation, potential users should consider these factors plus local structures, facies, and solution zones in conjunction with the numerical rankings reflecting aquifer characteristics. To facilitate consideration of piezometric head, maps are included in this report showing areas in which the piezometric head falls in certain ranges with respect to land surface.
This report describes the log analysis of the Randolph and Sabial core holes in the Edwards aquifer in Texas, with particular attention to the principles that can be applied generally to any carbonate system. The geologic and hydrologic data were obtained during the drilling of the two holes, from extensive laboratory analysis of the cores, and from numerous geophysical logs run in the two holes. Some logging methods are inherently superiors to others for the analysis of limestone and dolomite aquifers. Three such systems are the dentistry, neutron, and acoustic-velocity (sonic) logs. Most of the log analysis described here is based on the interpretation of suites of logs from these three systems. In certain instances, deeply focused resistivity logs can be used to good advantage in carbonate rock studies; this technique is used to computer the water resistivity in the Randolph core hole. The rocks penetrated by the Randolph core hole are typical of those carbonates that have undergone very little solution by recent ground-water circulation. There are few large solutional openings; the water is saline; and the rocks are dark, dolomitic, have pore space that is interparticle or intercrystalline, and contain unoxidized organic material. The total porosity of rocks in the saline zone is higher than that of rocks in the fresh-water aquifer; however, the intrinsic permeability is much less in the saline zone because there are fewer large solutional openings. The Sabinal core hole penetrates a carbonate environment that has experienced much solution by ground water during recent geologic time. The rocks have high secondary porosities controlled by sedimentary structures within the rock; the water is fresh; and the dominant rock composition is limestone. The relative percentages of limestone and dolomite, the average matrix (grain) densities of the rock mixtures , and the porosity of the rock mass can be calculated from density, neutron, and acoustic logs. With supporting data from resistivity logs, the formation water quality can be estimated, as well as the relative cementation or tortuosity of the rock. Many of these properties calculated from logs can be verified by analysis of the core available from test holes drilled in the saline and fresh water zones.
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This manual is intended to be a guide for hydrologists using borehole geophysics in ground-water studies. The emphasis is on the application and interpretation of geophysical well logs, and not on the operation of a logger. It describes in detail those logging techniques that have been utilized within the Water Resources Division of the U.S. Geological Survey, and those used in petroleum investigations that have potential application to hydrologic problems. Most of the logs described can be made by commercial logging service companies, and many can be made with small water-well loggers. The general principles of each technique and the rules of log interpretation are the same, regardless of differences in instrumentation. Geophysical well logs can be interpreted to determine the lithology, geometry, resistivity, formation factor, bulk density, porosity, permeability, moisture content, and specific yield of water-bearing rocks, and to define the source, movement, and chemical and physical characteristics of ground water. Numerous examples of logs are used to illustrate applications and interpretation in various ground-water environments. The interrelations between various types of logs are emphasized, and the following aspects are described for each of the important logging techniques: Principles and applications, instrumentation, calibration and standardization, radius of investigation, and extraneous effects.
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No abstract available.
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