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Showing papers on "Effective porosity published in 1993"


Journal ArticleDOI
TL;DR: In this article, a new pressure loss correlation predicts flow through screens for the wire Reynolds number range of 10 -4 to 10 4 using the conventional orthogonal porosity and a function of wire Reynolds numbers.
Abstract: A new pressure loss correlation predicts flow through screens for the wire Reynolds number range of 10 -4 to 10 4 using the conventional orthogonal porosity and a function of wire Reynolds number. The correlation is extended by the conventional cosine law to include flow that is not perpendicular to the screen. The importance of careful specification of wire diameter for accurate predictions of porosity is examined. The effective porosity is influenced by the shape of the woven wires, by any local damage, and by screen tension

74 citations


Journal ArticleDOI
01 Jan 1993
TL;DR: In this paper, four mechanisms are recognized by which enhanced porosity may be generated or maintained during burial: the development of overpressures due to restricted pore fluid escape, inhibition of mechanical compaction by selective cementation; inhibition of cementation as a result of hydrocarbon accumulation; or generation of secondary porosity due to either grain or cement dissolution together with simultaneous removal of reaction products.
Abstract: With increasing burial depth, intergranular porosity declines in a predictable manner according to theoretical and empirically established mathematical relationships. In basins with simple structural and thermal histories, average porosity can often be represented as an exponential function of depth. There are, however, common significant deviations from such a simple model of porosity evolution. Four mechanisms are recognized by which enhanced porosity may be generated or maintained during burial: development of overpressures due to restricted pore fluid escape; inhibition of mechanical compaction by selective cementation; inhibition of cementation as a result of hydrocarbon accumulation; or generation of secondary porosity due to either grain or cement dissolution together with simultaneous removal of reaction products. Secondary porosity may be generated either near the surface by the ingress of dilute meteoric-derived waters or at depth by the generation of ‘aggressive’ pore fluids. Deep burial diagnesis may encompass both closed and open system porosity generating reactions. In closed systems, increase in temperature concomitant with burial overcomes kinetic barriers enabling dissolution of metastable detrital minerals. By contrast, in more open systems, movement of fluids from either mudstones or evaporites to either overlying or adjacent sandstones introduces chemical disequilibrium that may cause mineral dissolution. Rapid, intermittent movement of fluids along active faults may additionally introduce temperature disequilibrium to further facilitate mineral dissolution in the proximity of faults. Over geological periods of time, however, faults are barriers to fluid flow and provide a mechanism for generating overpressure. In the Central and Northern North Sea basins, an upper diagenetic regime is separated from a lower diagenetic regime by a regional cover of Cretaceous mudstones and chalks. The Cretaceous sediments provide a regional seal which often coincides with the development of overpressure above deep graben centres reflecting restricted pore water escape. Fluid and solute movement between these two regimes is only possible where faults or gas chimneys penetrate the Cretaceous seal. In the upper regime, porosity loss in Tertiary sediments broadly conforms to the predicted decline of porosity with depth. In the lower regime, Jurassic sandstones on structural highs are characterized by extensive secondary porosity resulting from feldspar grain and carbonate cement dissolution, best preserved where oil accumulation rapidly follows porosity generation. Enhanced porosity can be expected either where sandstones interdigitate with mudstones or in graben centre plays adjacent to faults. This contrasts with graben margin plays where faults are the locus of pronounced cementation and complex diagenetic sequences are developed. In the absence of either oil accumulation or overpressure, secondary porosity either compacts or is occluded by a characteristic deep burial authigenic mineral assemblage. The present heat flow in the North Sea can be interpreted in terms of a residual thermobaric fluid flow from basin centres to basin margins which was probably initiated during the early Tertiary, coincident with the onset of rapid thermal relaxation subsidence.

43 citations


Journal ArticleDOI
TL;DR: In this paper, tracer tests are facilitated by a simple method for injecting and evenly distributing the tracer solution into a wellbore, and by new ion-selective electrode instrumentation, specifically designed for submersible service, for monitoring the concentration of tracers such as bromide.
Abstract: When the purpose of aquifer testing is to yield data for modeling aqueous mass transport, pumping tests and gradient measurement can only partially satisfy characterization requirements. Effective porosity, ground water flow velocity, and the vertical distribution of hydraulic conductivity within the aquifer are left as unknowns. Single well tracer methods, when added to the testing program, can be used to estimate these parameters. A drift, and pumpback test yields porosity and velocity, and point-dilution testing yields depth-discrete hydraulic information, A single emplacement of tracer into a test well is sufficient to conduct both tests. The tracer tests are facilitated by a simple method for injecting and evenly distributing the tracer solution into a wellbore, and by new ion-selective electrode instrumentation, specifically designed for submersible service, for monitoring the concentration of tracers such as bromide.

40 citations


Journal ArticleDOI
Awad M. Helalia1
TL;DR: In this paper, a field study was conducted to examine the relationship between in situ steady state infiltration rate (IR) and some textural and structural soil properties, including the effective porosity (EP), which is defined as total porosity minus soil water content at 0.33 bar.

36 citations


Journal ArticleDOI
Salman Bloch1, Stephen G. Franks
TL;DR: In this article, the abundance and distribution patterns of secondary porosity formed by dissolution of plagioclase were examined in 216 samples of middle Eocene-Oligocene shallow marine to nonmarine arkosic sandstones from the southern San Joaquin basin, California.
Abstract: The abundance and distribution patterns of secondary porosity formed by dissolution of plagioclase were examined in 216 samples of middle Eocene-Oligocene shallow marine to nonmarine arkosic sandstones from the southern San Joaquin basin, California. The proportion of plagioclase intragranular porosity and plagioclase moldic porosity is depth dependent. For purposes of this study, pores containing less than approximately 40% of remnant plagioclase were counted as "moldic" plagioclase porosity. Pores within skeletal plagioclase grains or mostly enclosed by skeletal grains were counted as intragranular plagioclase porosity. Moldic porosity is most significant at shallow (< 5000 ft or 1500 m) depths, whereas the relative importance of intragranular porosity increases belo approximately 5000 ft (1500 m). These trends are most likely caused by gradual, preferential collapse, with increasing burial, of moldic porosity generated predominantly at shallow depths. Intragranular porosity in more deeply buried sandstones is partly inherited from shallow depths. Feldspar dissolution porosity formed in shallow, "open-system" settings typically is not accompanied by aluminosilicate (e.g., kaolinite) by-products. This porosity, either moldic or intragranular, can be preserved during burial, particularly in sandstones with high percentages of nonductile detrital grains. Removal of much of the aluminum released by feldspar dissolution in shallow "open-system" settings coupled with incorrect petrographic interpretations, placing extensive feldspar dissolution at deep (late) burial conditions, may account for the controversial aluminum source-sink imbalance. The presence of plagioclase dissolution porosity (moldic and intragranular) is important, but it does not have a significant impact on the accuracy of empirical porosity predictions. Such predictions are based on an approach that uses a calibration data set and multiple regression analysis to determine the relationship between known, geologically significant variables and reservoir quality. High accuracy of porosity predictions (within 2% porosity of the mean measured porosity) in sandstones containing dissolved plagioclase is possible because the presence of secondary porosity is implicitly accounted for by independent variables (e.g., composition, grain size, sorting, burial history) in the calibration data set that provides the basis for empirical predictions.

20 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the extent to which seismic amplitude maps can contribute to the analysis of hydrocarbon reservoirs for clastic and carbonate reservoirs worldwide by using a petrophysical-based, forward modeling process called incremental pay thickness (IPT) modeling.
Abstract: The extent to which seismic amplitude maps can contribute to the analysis of hydrocarbon reservoirs was investigated for clastic and carbonate reservoirs worldwide. By using a petrophysical-based, forward modeling process called incremental pay thickness (IPT) modeling, five lithology types were quantitatively analyzed for the interplay of seismic amplitude versus lithology, porosity, hydrocarbon pore fluid saturation, bedding geometries, and reservoir thickness. The studies identified three common tuning curve shapes (concave, convex, and bilinear) that were primarily dependent upon the lithology model type and the average net porosity therein. While the reliability of pay and porosity predictions from amplitude maps varied for each model type, all analyses showed a limited thickness range for which amplitude data could successfully predict net porosity thickness or hydrocarbon pore volume. The investigation showed that systematic forward modeling is required before amplitude maps can be properly interpreted.

19 citations


Patent
23 Feb 1993
TL;DR: In this article, a technique was developed to reconstruct deep induction conductivity and to compute effective porosity and water saturation consistent with the high vertical resolution tools such as the Dipmeter.
Abstract: Evaluation of thinly laminated shaly sand reservoirs has long been one of the most difficult problems of log analysis. A primary reason is that only shallow shale indicators such as a Dipmeter, other microresistivity devices, or an ultra high frequency dielectric tool, etc. accomplish resolutions compatible with the most thinly bedded shale or sand laminae. To overcome this problem a technique has been developed to reconstruct deep Induction conductivity and to compute effective porosity and water saturation consistent with the high vertical resolution tools such as the Dipmeter. To achieve greater accuracy in the evaluation of shale content and porosity, the volumes of shale are initially estimated from both a density-neutron crossplot and a high resolution shale indicator which has been integrated to the vertical resolution of the density and neutron logs. Then shale parameters for these logs are automatically adjusted within limits suggested by log data in such a way that computed shale volumes from the shale indicator and density-neutron crossplot match each other. The adjusted parameters are used to compute porosity and shale volume and the mode of distribution from the density and neutron logs and to recompute these results to the high vertical resolution level. This information is in turn used to reconstruct the deep Induction conductivity to the same vertical resolution. The technique allows water saturation determination from a Waxman-Smits type model when both dispersed and laminated clay types are present.

17 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured porosity, permeability and pore size distribution of amphibolite samples under gas and water fluid pressure of 300 MPa and at temperatures up to 850°C.

8 citations


Proceedings ArticleDOI
TL;DR: In this article, NMR measurements on three different shales from the North Sea were performed to investigate whether one may employ NMR, which is a fast, non-destructive analytical tool, to measure the effective porosity of lowpermeable shales.
Abstract: We present NMR measurements on three different shales from the North Sea. The motivation was to investigate whether one may employ NMR, which is a fast, non-destructive analytical tool, to measure the effective porosity of lowpermeable shales. The latter porosity is relevant for possible correlations to permeability. Presently, log-derived porosities (neutron, density) tend to yield closer to the total porosity which may differ significantly from in shales. Core porosities may be determined by means of timeconsuming, destructive drying-up techniques, restricting the access to the cores. Our measured NMR-porosities seem to agree with those attained by the loss of water. However, there may occasionally arise an extra NMRcontribution from the “dry” sample. This part may tentatively stem from bound or confined water within the shale. Even though more work remains to be done, NMR has proven its potential as a tool for petrophysical measurements on shale.

4 citations



Journal Article
TL;DR: In this paper, analytical and numerical solutions are employed to examine the concentration history of a dissolved substance in water pumped from a leaky aquifer, where the solute of interest is dissolved radon gas.
Abstract: Analytical and numerical solutions are employed to examine the concentration history of a dissolved substance in water pumped from a leaky aquifer Many aquifer systems are characterized by stratification, for example, a sandy layer overlain by a clay layer To obtain information about separate hydrogeologic units, aquifer pumping tests are often conducted with a well penetrating only one of the layers When the initial concentration distribution is also stratified (the concentration varies with elevation only), the concentration breakthrough in the pumped well may be interpreted to provide information on aquifer hydraulic and transport properties To facilitate this interpretation, we present some simple analytical and numerical solutions for limiting cases and illustrate their application to a fractured bedrock/glacial drift aquifer system where the solute of interest is dissolved radon gas In addition to qualitative information on water source, this method may yield estimates of effective porosity and saturated thickness (or fracture transport aperture) from a single-hole test Little information about dispersivity is obtained because the measured concentration is not significantly affected by dispersion in the aquifer


01 Jan 1993
TL;DR: In this article, a calibration of the so-called Archie's law, based on hydrogeological and geophysical data, is presented, where the vanishing of surface conductance effect in the electrical flow inside the porous medium, permits to express total porosity only in terms of formation factor without regards to textural composition of finer matrix.
Abstract: SUMMARY A calibration of the so called Archie's law, based on hydrogeological and geophysical data, is presented. This petrophysical law, originally employed by petroleum geologists as an aid to interpret geophysical well logs, if suitably calibrated with direct measurements of the involved parameters, may represent an useful tool for the hydrogeological prospecting in areas with a quifers encroached by salt water. Particularly, the vanishing of surface conductance effect in the electrical flow inside the porous medium, permits to express total porosity only in terms of formation factor without regards to textural composition of finer matrix. As an example of this approach, the hydro-geophysical investigation of lower Cornia plain (Western Tuscany) is presented; data coming from 50 Vertical Electric Soundings, the majority of which calibrated with stratigraphical records, from direct testing of groundwater salinity in wells and from granulometric analysis of acquifer, were used. According the colected data, Archie's law is validated in the tested area; average value obtained of apparent formation factor for the acquifer of Cornia plain is 5,4; the intrinsic formation factor, depending only on total porosity, is 12. The value of total porosity obtained is 25%; on the basis of this datum and the granulometric composition of acquifer, it is estimated a value of 15% for the effective porosity.

01 Mar 1993
TL;DR: In this paper, the porosity and permeability of Cambro-Ordovician dolomite specimens were determined using helium porosimetry and gas permeability measurements using a gas permeameter.
Abstract: Dolomite is the host rock for Mississippi Valley-type (MVT) ore deposits concentrated in Southeast Missouri as well as other locations worldwide. Deposition of MVT ores occur when hot basinal brines are circulated through porosity in dolomite aquifers. Additionally, dolomites are important reservoirs for hydrocarbon accumulations and are important ground water aquifers. Two basic textural types of dolomite exist: (1) planar dolomite which is characterized by rhombohedral faceted crystals with straight intercrystalline boundaries, these are formed in shallow and burial diagenetic environments; (2) nonplanar dolomite which is characterized by crystals with irregular intercrystalline boundaries. Cambro-Ordovician dolomite specimens were collected from core and from surface locations throughout Southeast Missouri. Effective porosity was determined using helium porosimetry and permeability measurements were made using a gas permeameter. Total porosity as well as dolomitic texture was determined from thin section analysis. Texture was classified according to the system of Sibley and Gregg (1987) and total porosity was classified according to Choquette and Pray (1970). Porecasts of selected samples were prepared and examined using scanning electron microscopy and the binocular microscope to evaluate pore throat geometry. Preliminary analysis of textural, porosity, and permeability data suggests that effective porosity and permeability can be related to crystal sizemore » and crystal boundary relationships. Fine crystalline dolomites tend to have lower porosity and permeability than coarser crystalline dolomites. Nonplanar dolomites have lower porosity and permeability than planar dolomites.« less

Journal ArticleDOI
TL;DR: In this paper, the relationship between acoustic impedance (velocity) and rock properties such as porosity and clay content was analyzed in the reservoir interval based on the results of well log data analysis.
Abstract: Predicting the reservoir rock properties such as porosity and clay content is essential for estimating reserves and planning the optimum development of oil and gas fields. Modern seismic data, especially 3-D seismic data, has played an important role in reservoir characterization. A study has been performed to predict the reservoir disrtibution and the rock properties using 3-D seismic data in the Amarume oil field. The reservoirs are mainly in Kitamata Formation of Miocene which is considered to be deep-sea sediment gravity flow deposits. Several sandstone layers, which are discontinuous in horizontal direction, bear hydrocarbons. Productive sandstone reservoirs lie approximately 900m below the surface and vary from 5m to 20m in thickness. 3-D seismic survey area is about 2km in East-West direction and 1km in North-South direction. Acoustic impedance was derived from the 3-D data volume by seismic inversion method. Such impedance data can be related to rock properties and physical conditions in the reservoirs. The relationship between acoustic impedance (velocity) and rock properties such as porosity and clay content was analyzed in the reservoir interval based on the results of well log data analysis. An empirical equation was obtained by linear regression analysis to effective porosity versus acoustic impedance with a correlation coefficient of 0.87. The correlation was improved by addition of a clay, shale or tuff content term in the linear regression analysis. These relationships indicate that an increase in clay or shale content rises P-wave velocity. This observation differs from that quoted by several other investigators. Seismically derived acoustic impedance (I) was converted to effective porosity (φ) using the equation [I=5.72-8.15φ]. Depth structures, effective porosity and effective porosity-thickness of the reservoirs were mapped based on the converted effective porosity. The results were consistent with well data. 3-D seismic data can be a powerful tool for predicting the areal distribution of reservoir rock properties.