Fractured Carbonate Rocks Research Articles

The relative contributions of summer and cool-season precipitation to groundwater recharge, Spring Mountains, Nevada, USA

A comparison of the stable-isotope signatures of spring waters, snow, snowmelt, summer (July thru September) rain, and cool season (October thru June) rain indicates that the high-intensity, short-duration summer convective storms, which contribute approximately a third of the annual precipitation to the Spring Mountains, provide only a small fraction (perhaps 10%) of the recharge to this major upland in southern Nevada, USA. Late spring snowmelt is the principal means of recharging the fractured Paleozoic-age carbonate rocks comprising the central and highest portion of the Spring Mountains. Daily discharge measurements at Peak Spring Canyon Creek during the period 1978–94 show that snowpacks were greatly enhanced during El Nino events.

Estimation of transmissivity from specific capacity data in fractured carbonate rock aquifer, central Jordan : A. El-Naqa, Environmental Geology, 23(1), 1994, pp 73–80

Estimation of transmissivity from specific capacity data in fractured carbonate rock aquifer, central Jordan : A. El-Naqa, Environmental Geology, 23(1), 1994, pp 73–80

Estimation of transmissivity from specific capacity data in fractured carbonate rock aquifer, central Jordan

Transmissivity of an aquifer is determined from pumping test analysis, but due to the difficulty of performing such tests as well as the relatively high cost of these test, it is often estimated from specific capacity data. In this study an empirical relation is derived using 237 pairs of transmissivity and specific capacity values that are obtained from groundwater wells penetrating a fractured and karstified carbonate aquifer. Linear and logarithmic regression functions have been performed and it is found that the logarithmic relationship predicting transmissivity from specific capacity data has a better correlation (r=0.95) than linear one (r=0.84). This is logically true because both transmissivity and specific capacity are lognormally distributed. The spatial distribution of transmissivity is also affected by the presence of fracturing and karstification phenomena within the aquifer matrix.

Double porosity well testing in the fractured carbonate rocks of the Ozarks : McConnell, C L Ground WaterV31, N1, Jan–Feb 1993, P75–83

Double porosity well testing in the fractured carbonate rocks of the Ozarks : McConnell, C L Ground WaterV31, N1, Jan–Feb 1993, P75–83

DISCUSSION OF “Double Porosity Well Testing in the Fractured Carbonate Rocks of the Ozarks,” by Cary L. McConnell

DISCUSSION OF “Double Porosity Well Testing in the Fractured Carbonate Rocks of the Ozarks,” by Cary L. McConnell

REPLY TO the preceding Discussion by Garry Grimestad of “Double Porosity Well Testing in the Fractured Carbonate Rocks of the Ozarks”

REPLY TO the preceding Discussion by Garry Grimestad of “Double Porosity Well Testing in the Fractured Carbonate Rocks of the Ozarks”

Mechanical properties of a pervasively fractured carbonate rock mass : Faiella, D; Garino, A; Ribacchi, R; Rossi, P P Proc ISRM Symposium: Eurock'92, Chester, 14–17 September 1992P81–87. Publ London: Thomas Telford, 1992

Mechanical properties of a pervasively fractured carbonate rock mass : Faiella, D; Garino, A; Ribacchi, R; Rossi, P P Proc ISRM Symposium: Eurock'92, Chester, 14–17 September 1992P81–87. Publ London: Thomas Telford, 1992

Seismic velocities of fractured carbonate rocks (southern Apennines, Italy)

SUMMARY A study of the effect of fractures on seismic velocities has been carried out through a comparative study in the field and the laboratory. P- and S-wave velocities were obtained from surface and borehole seismic measurements and, in the laboratory, ultrasonic velocities were measured on intact and artificially fractured specimens of carbonate rocks from the Miranda area (southern Apennine chain, Italy). Calcareous and calcareous-chert sequences are present in the area, with a discontinuity spacing from very close to very wide. Essentially dry rocks have been tested. A correspondence was found between visible rock fracturing and compressional wave velocities from surface seismic measurements. The downhole velocities were lower than the corresponding ultrasonic velocities on core specimens and increased with depth. Specimens were then cut to simulate field discontinuities, and loaded to study the influence of vertical pressure on the seismic velocities. Laboratory and field velocities were finally compared as functions of vertical pressure. It turns out that fractures reduce and vertical pressure increases velocities. Since the rock quality designation (RQD) indices were generally very low, the increasing seismic velocities with depths in poor quality rocks can be explained in terms of better contact between fracture surfaces.

Calculation of Low‐Range Flow Velocities in Fractured Carbonate Media from Borehole Hydrochemical Logging Data Comparison with Thermometric Results

AbstractFlow rates and concentrations from fractures intersected by a borehole can be estimated by matching simulated concentration profiles to the observed variations in water chemistry along the borehole. Experiments in karstic rocks prove that hydraulic short circuits between fractures yield a very complex flow pattern, and that flow velocities in the borehole may be higher than the velocity at which the piezometric level varies. Combined temperature and concentration studies characterize flow in both high permeability channels and slightly fissured blocks, as chemical profiles detect low velocity flows that cannot be identified on temperature profiles. Such studies are therefore advisable to characterize natural flow in fractured carbonate rocks, but also in other fractured media.

Double Porosity Well Testing in the Fractured Carbonate Rocks of the Ozarks

AbstractThe objective of this research was to determine a well test model which could be used for determining the hydraulic parameters of T and S in the complex fractured carbonates of the Ozarks of southern Missouri. Municipal water well testing in the Ozarks is performed on deep wells completed in confined fractured carbonate aquifers where all of the flow to the wellbore is through the fractures but most of the storage is in the matrix blocks. Observation wells are not used because of cost. The methodology uses double porosity well test analysis including the inner boundary conditions of skin and wellbore storage. Using this method, S and T are obtained as well as the storativity ratio, ω, and the block to fracture flow parameter λ. Because wellbore storage, skin, and storativity are interrelated, a computer simulation to find the final S was necessary. Derivative curve analysis provided a constraint in determining the correctness of the simulation results. Failure to use this well test method proved to result in storativities which are much too large. An example is presented.

Computerized Process for Interpretation of Well Logs in Naturally Fractured Reservoirs: ABSTRACT

A computerized process is presented which allows the determination of primary and secondary porosities, and water saturation in the primary porosity, secondary porosity, and composite system, in naturally fractured reservoirs. The process utilizes conventional well logs such as resistivity, density, neutron, and sonic. The theoretical background behind the interpretation techniques is presented with examples of its application in the recompletion of an Austin Chalk well, and in the completion of fractured carbonate rocks in the Williston basin of Montana and in Canada. End_of_Article - Last_Page 1495------------

Major carbon 14 anomaly in a regional carbonate aquifer: Possible evidence for megascale channeling, South Central Great Basin

The carbon 14 content of groundwater at the center of a 16‐km‐long fault‐controlled spring line at Ash Meadows in south central Nevada is 5 times greater than that in water from other major springs along the lineament. The difference in carbon 14 stands in marked contrast to the near identity of all springwaters in alkalinity, pH, carbon 13, oxygen 18, deuterium, tritium, and other major and trace ions. Ten possible explanations of this major carbon 14 anomaly are evaluated by using all available chemical and isotopic data from basin‐wide wells and upland springs tapping the regional carbonate aquifer discharging at Ash Meadows. The four most plausible hypotheses require the presence of a major longitudinal heterogeneity in the distal portion of the groundwater basin to explain the anomaly. Flow channeling with an amplitude of at least 11 km is indicated. The simplifying assumption commonly used in simulation of basin‐wide flow through fractured or solution‐riddled aquifers, namely, that the aquifer is ‘homogenous in its heterogeneity,’ is not applicable to the dense fractured Paleozoic carbonate rocks comprising the Nevada aquifer; heterogeneities in this aquifer do not cancel each other areally.

Radar Geology--Petroleum Exploration Technique, Eastern Panama and Northwestern Colombia

Petroleum exploration in eastern Panama and northwestern Colombia has gained impetus by recent side-looking-radar, geologic reconnaissance mapping. Radar-derived geologic information is now available for approximately 40,000 sq km where previous reconnaissance investigations have been extremely limited because of inaccessibility and almost perpetual cloud cover. With radar imagery as the sole source of remote-sensing data, the distribution, continuity, and structural grain of key strata provide evidence that the eastern Panamanian Isthmus can be divided into three main physiographic-structural parts: two composite coastal mountain ranges separated by the taphrogenic Medial basin, which trends southeastward from the mouth of the Bayano River to the Atrato River valley of northwestern Colombia. Within the Medial basin, most of the clearly exposed surface structures are not particularly attractive petroleum prospects because prime reservoir strata have been stripped from their crests. However, several large geomorphic anomalies which have been mapped in the Medial basin may be reflections of subsurface structures having a complete stratigraphic ection. Possibilities for gravity-type hydrocarbon accumulations in fractured organic shales, siltstones, and carbonate rocks are suggested within several synclinal elements along the axis of the Medial basin. The southwestward extension of the Medial basin trend, coincident with the western Gulf of Panama, may have potential as a future petroleum-producing province. A relatively thick marine stratigraphic section should be present here, with associated paralic and deltaic clastic rocks derived from acidic San Blas terrace since mid-Miocene time. The occurrence of active shell bars in the Bay of San Miguel and present reef trends on the northern Caribbean coast suggest possible offshore sites for geophysical surveying.

Geological aspects of thermal water occurrences in Hungary

In Hungary geothermal resources are in the form of low enthalpy waters within Pliocene - Upper Pannonian reservoirs consisting of sand and sandstone series, and within fractured carbonate rocks mainly of Triassic age. These low temperature reservoirs, maximum water temperature is about 100°C, are presumably heated by conduction and little is known about the nature of the heat source. Geothermal phenomena are controlled primarily by sub-crustal magmatic processes and secondarily by other geologic factors such as tectonics, sedimentation, compaction. Due to a particular crustal structure, the resulting geothermal anomaly accompanied by favorable hydrogeologic conditions, allows an abundance of thermal waters in many parts of the country, particularly in the SE part of the Great Hungarian Plain. For the time being there are more than 450 thermal water wells producing waters warmer than 35°C in Hungary.

Hydrology of fractured rocks: October–November 1971

The recent high level of interest in the hydrology of fractured, and particularly fractured carbonate, rocks was again demonstrated at the 1971 annual meeting of the Geological Society of America. A field conference, which dealt with the hydrogeology and land‐use problems in fractured carbonate rocks in south‐central Pennsylvania, was conducted on October 30–31, and a Symposium on the Hydrology of Fractured Rocks was held on November 1 in Washington, D.C.Both events were initiated by the U.S./IHD Work Group on the Hydrology of Carbonate Terranes (V.T. Stringfield, Chairman) as complementary parts of a single, over‐all presentation of current thinking in the hydrology of fractured rocks.

Deuterium as a Tracer of Regional Ground-Water Flow, Southern Great Basin, Nevada and California

Hydrogeologic studies of the southern Great Basin differ widely in their conclusions about the origin of several groups of major springs discharging at valley level from Paleozoic carbonate rocks. Delineation of watersheds feeding these springs is complicated by interbasin movement of ground water through areally extensive and highly fractured Paleozoic carbonate rocks and by the structural complexity of, and sparse subsurface hydrogeologic data for, the carbonate aquifer. The mean, median, and standard deviation of the deuterium content of ground water at, and the number of samples collected from, four of these major discharge areas and one major recharge area (Spring Mountains–Sheep Range) are given below. The deuterium data are expressed in δ D units (permil deviations from SMOW); the number of samples is given in parentheses. Pahranagat Valley: −113, −113, 1, (9); Spring Mountains–Sheep Range: −102, −102, 3, (12); Ash Meadows: −106, −107, 3, (15); Death Valley: −109, −109, 1, (4); Muddy River: −100, −100, 1, (5). A nonparametric test (Kolmogorov–Smirnov statistic) of the data for the first three areas indicates different deuterium populations at the 0.01 level of significance. The deuterium data indicate that Ash Meadows springs are fed by a mixture of recharge derived from the Spring Mountains–Sheep Range uplands, 30 to 60 mi east of the springs, with underflow from Pahranagat Valley and vicinity, 90 mi northeast of the springs. Mass balance considerations suggest that the underflow amounts to about 35 percent of the spring discharge. Underflow to Ash Meadows from Pahrump Valley, a source area proposed in the literature, is not supported by the data. The Death Valley springs may be fed, in part, by water derived from Ash Meadows. The Muddy River springs may originate as precipitation on the Spring Mountains–Sheep Range area. The suggested sources for the Ash Meadows and Death Valley springs are in agreement with sources previously identified by hydrogeologic and hydrochemical studies of the region. The source proposed for the Muddy River springs, however, is not supported by water-budget studies. A major assumption in utilization of deuterium as a natural tracer of regional ground-water flow is that the mean deuterium content of recharge to proposed source areas remained relatively constant during the residence time of water in the aquifer of interest. Available data are insufficient to test this assumption for the southern Great Basin region.