Showing papers on "Effective porosity published in 2014"

Permeability Description by Characteristic Length, Tortuosity, Constriction and Porosity

Abstract: In this article we investigate the permeability of a porous medium as given in Darcy’s law. The permeability is described by an effective hydraulic pore radius in the porous medium, the fluctuation in local hydraulic pore radii, the length of streamlines, and the fractional volume conducting flow. The effective hydraulic pore radius is related to a characteristic hydraulic length, the fluctuation in local hydraulic radii is related to a constriction factor, the length of streamlines is characterized by a tortuosity, and the fractional volume conducting flow from inlet to outlet is described by an effective porosity. The characteristic length, the constriction factor, the tortuosity, and the effective porosity are thus intrinsic descriptors of the pore structure relative to direction. We show that the combined effect of our pore structure description fully describes the permeability of a porous medium. The theory is applied to idealized porous media, where it reproduces Darcy’s law for fluid flow derived from the Hagen–Poiseuille equation. We also apply this theory to full network models of Fontainebleau sandstone, where we show how the pore structure and permeability correlate with porosity for such natural porous media. This work establishes how the permeability can be related to porosity, in the sense of Kozeny–Carman, through fundamental and well-defined pore structure parameters: characteristic length, constriction, and tortuosity.

Dehydration Effect on the Pore Size, Porosity, and Fractal Parameters of Shale Rocks: Ultrasmall-Angle X-ray Scattering Study

Abstract: The characterization of pore networks is extremely important in understanding transport and storage phenomena in unconventional gas and oil reservoir rocks. An ultrasmall-angle X-ray scattering (USAXS) measurement has been performed on Silurian black shales from the Baltic Basin, Poland, from a wide range of depths along a burial diagenetic sequence. This study provides insight into the nature of the pore structure, including the pore size distribution, total porosity, and fractal dimensions of the rocks. Samples were measured in both their air-dried state, equilibrated at ∼50% relative humidity, and prior to dehydration by drying at 200 °C to make a comprehensive comparison of the pore structure changes induced by dehydration. Two trends were observed: porosity values decreased with depth as expected from the models of porosity evolution with burial and increased upon sample dehydration. The USAXS-measured porosity values show very good correspondence with the measurements by immersion porosity methods. ...

Elongation of textile pelvic floor implants under load is related to complete loss of effective porosity, thereby favoring incorporation in scar plates.

Abstract: Use of textile structures for reinforcement of pelvic floor structures has to consider mechanical forces to the implant, which are quite different to the tension free conditions of the abdominal wall. Thus, biomechanical analysis of textile devices has to include the impact of strain on stretchability and effective porosity. Prolift(®) and Prolift + M(®), developed for tension free conditions, were tested by measuring stretchability and effective porosity applying mechanical strain. For comparison, we used Dynamesh-PR4(®), which was designed for pelvic floor repair to withstand mechanical strain. Prolift(®) at rest showed moderate porosity with little stretchability but complete loss of effective porosity at strain of 4.9 N/cm. Prolift + M(®) revealed an increased porosity at rest, but at strain showed high stretchability, with subsequent loss of effective porosity at strain of 2.5 N/cm. Dynamesh PR4(®) preserved its high porosity even under strain, but as consequence of limited stretchability. Though in tension free conditions Prolift(®) and Prolift + M(®) can be considered as large pore class I meshes, application of mechanical strain rapidly lead to collapse of pores. The loss of porosity at mechanical stress can be prevented by constructions with high structural stability. Assessment of porosity under strain was found helpful to define requirements for pelvic floor devices. Clinical studies have to prove whether devices with high porosity as well as high structural stability can improve the patients' outcome.

The effective porosity and grain size relations in permeability functions

Abstract: . Hydrogeological parameters of coherent and incoherent deposits are deeply dependent of their granulometric characteristics. These relations were shaped in formulas and defaultly used for calculation of hydraulic conductivity, and are valid only for uniform incoherent materials, mostly sands. In this paper, the results of analyses of permeability and specific surface area as a function of granulometric composition of various sediments – from siltey clays to very well graded gravels are presented. The effective porosity and the referential grain size are presented as fundamental granulometric parameters which express an effect of forces operating fluid movement through the saturated porous media. Suggested procedures for calculating referential grain size and determining effective (flow) porosity result with parameters that reliably determine specific surface area and permeability. These procedures ensure successful appliance of Kozeny–Carman model up to the limits of validity of Darcy's law. The value of an effective porosity in function of referential mean grain size has been calibrated within range from 1.5 μm to 6.0 mm. Reliability of these parameters application in KC model was confirmed by very high correlation between predicted and tested hydraulic conductivity – R2 = 0.99 for sandy and gravelly materials and R2 = 0.70 for clayey-siltey materials. Group representation of hydraulic conductivity (ranged from 10-12 m s-1 up to 10-2 m s-1) presents coefficient of correlation R2 = 0.97, for total sum of 175 samples of various deposits. These results present the new road to researches of porous material's effective porosity, permeability and specific surface area distribution, since these three parameters are critical conditions for successful groundwater flow modelling and contaminant transport. From the practical point of view, it is very important to be able to identify these parameters swiftly, cheaply and very accurately.

Hydraulic flow units and permeability prediction in a carbonate reservoir, Southern Iraq from well log data using non-parametric correlation

Abstract: The determination of permeability in heterogeneous and anisotropic reservoirs is a complex problem, because core samples and well test data are usually only available for limited number of wells. This paper presents hydraulic flow units and flow zone indicator for predicting permeability of rock mass from core and well log-data. The concept is applied to some uncored wells/intervals to predict their permeability. Flow zone indicator depends on geological characteristics of the material and various pore geometry of rock mass; hence it is a good parameter for determining hydraulic flow units (HFU). Flow zone indicator is a function of reservoir quality index and void ratio. We are determined flow zone indicator from well log and core data and divided the reservoir into various hydraulic flow units using K-means. Then will be develop a correlation (The Alternating Conditional Expectation (ACE) technique will be used and tested in this study) between hydraulic flow units from the core and the well log data which can be used to estimate permeability in un-cored wells, these correlations enable to estimate reservoir permeability at the "flow unit" scale. Finally, having effective porosity and flow zone indicator, permeability was calculated in each hydraulic flow unit. Results of permeability prediction based on HFU were examined for a number of wells and were compared with the measured permeability value of cores. Then will be evaluate a good correlation between the predicted and measured permeability.

A Method for Estimating Crack-initiation Stress of Rock Materials by Porosity

Abstract: Crack-initiation stress of a rock under compression is the stress level that marks the initiation of the rock microfracturing process or in other words, the onset of new damage to the rock. This paper proposed a simple methodology with justifications to explore the feasibility of using total and effective porosities as estimators of crack-initiation stress of brittle crystalline rock materials under uniaxial compression. The validity/applicability of the proposed method was examined by an experimental study of granitic materials from Malanjkhand, Madhya Pradesh. It was found that effective porosity depicts better correlation with crack-initiation stress than with uniaxial compressive strength of the granitic materials. On the other hand, total porosity does not show any perceptible correlation with uniaxial compressive strength and crack-initiation stress. Plausible reasons for the nature of the obtained results were also explained in view of rock failure process under compression. It is concluded that following the proposed method, effective porosity can be used as a physical index to obtain a quick estimate of crack-initiation stress of the investigated rocks empirically.

Compact rock material gas permeability properties

Abstract: Natural compact rocks, such as sandstone, granite, and rock salt, are the main materials and geological environment for storing underground oil, gas, CO 2, shale gas, and radioactive waste because they have extremely low permeabilities and high mechanical strengths. Using the inert gas argon as the fluid medium, the stress-dependent permeability and porosity of monzonitic granite and granite gneiss from an underground oil storage depot were measured using a permeability and porosity measurement system. Based on the test results, models for describing the relationships among the permeability, porosity, and confining pressure of rock specimens were analyzed and are discussed. A power law is suggested to describe the relationship between the stress-dependent porosity and permeability; for the monzonitic granite and granite gneiss (for monzonitic granite (A-2), the initial porosity is approximately 4.05%, and the permeability is approximately 10 −19 m 2 ; for the granite gneiss (B-2), the initial porosity is approximately 7.09%, the permeability is approximately 10 −17 m 2 ; and the porosity-sensitivity exponents that link porosity and permeability are 0.98 and 3.11, respectively). Compared with moderate-porosity and high-porosity rocks, for which φ > 15%, low-porosity rock permeability has a relatively lower sensitivity to stress, but the porosity is more sensitive to stress, and different types of rocks show similar trends. From the test results, it can be inferred that the test rock specimens’ permeability evolution is related to the relative particle movements and microcrack closure.

Reconsideration at field scale of the relationship between hydraulic conductivity and porosity: the case of a sandy aquifer in South Italy.

Abstract: To describe flow or transport phenomena in porous media, relations between aquifer hydraulic conductivity and effective porosity can prove useful, avoiding the need to perform expensive and time consuming measurements. The practical applications generally require the determination of this parameter at field scale, while most of the empirical and semiempirical formulas, based on grain size analysis and allowing determination of the hydraulic conductivity from the porosity, are related to the laboratory scale and thus are not representative of the aquifer volumes to which one refers. Therefore, following the grain size distribution methodology, a new experimental relation between hydraulic conductivity and effective porosity, representative of aquifer volumes at field scale, is given for a confined aquifer. The experimental values used to determine this law were obtained for both parameters using only field measurements methods. The experimental results found, also if in the strict sense valid only for the investigated aquifer, can give useful suggestions for other alluvial aquifers with analogous characteristics of grain-size distribution. Limited to the investigated range, a useful comparison with the best known empirical formulas based on grain size analysis was carried out. The experimental data allowed also investigation of the existence of a scaling behaviour for both parameters considered.

Well log analysis and hydrocarbon potential of the Sa'ar–Nayfa reservoir, Hiswah Oilfield, eastern Yemen

Abstract: Sa'ar–Nayfa reservoir is mainly made up of carbonate sediments with bands of shale that contain a substantial amount of proven oil in the Hiswah Oilfield, Sayun–Masila Basin, eastern Yemen. Several vertical wells have been drilled and penetrated these sequences. This study is concerned on the petrophysical evaluation and well log analysis of the Lower Cretaceous of 11 wells at the Hiswah Oilfield, Hadramawt Governorate, eastern Yemen. Computer-assisted log analyses were used to evaluate the petrophysical parameters such as shale volume, total porosity, effective porosity, water saturation, hydrocarbon saturation, flushed zone saturation and reservoir and pay flags. Cross-plots of the petrophysical parameters versus depth were illustrated. The Lower Cretaceous Sa'ar–Nayfa reservoir reflects that the matrix components are mainly carbonates and shales. Moreover, the lithological-geologic model reflected that these shales are strongly affecting the porosity and, consequently, the fluid saturation in the Sa'ar–Nayfa reservoir. In this study, the thickness of the Sa'ar–Nayfa reservoir increases from central toward north-eastern and north-western parts within the Hiswah Oilfield. The porosities analyses of the investigation of the Sa'ar–Nayfa reservoir for the 11 studied wells concluded that the average total porosity ranges from 5.4 % to 16.8 % while the effective porosity ranges from 5.2 % to 14.8 %. Water saturation of the Sa'ar–Nayfa reservoir ranges from 6.9 % to 75.8 %. On the other hand, hydrocarbon saturation matches with water saturation in a reverse relationship. Sa'ar–Nayfa reservoir is interpreted as good quality reservoir rocks with high average effective porosity reaching to 20 % and high hydrocarbon saturation exceeding 93 %. The Sa'ar–Nayfa reservoir reveals promising reservoir characteristics especially the upper reservoir unit, which should be taken into consideration during future development of the oilfields area. The hydrocarbon saturation map of the Sa'ar–Nayfa reservoir shows a regular pattern of distribution with a general increasing to the northeast, northwest and east directions while decreasing southwest wards, recording the maximum value of 93.1 % at the Hiswah-21 well.

A comparison of experimental methods for measuring water permeability of porous building rocks

Abstract: This paper compares different experimental methods for measuring water permeability in 17 different porous building rocks. Both commercial apparatus and specially made designed permeameters are used for characterising intrinsic permeability and hydraulic conductivity, k, of rocks in the range of 10 −12 to 10 −4 m/s (~ 10 −19 −10 −11 m 2 or ~ 10 −4 −10 4 mD). We use both falling head and constant head permeameter methods including the triaxial and modified triaxial tests and a classical constant head permeameter. Results showed that for very low and low permeability samples (k −6 m/s), triaxial conditions were found the most accurate procedures and they provided similar or slightly lower permeability values than constant and falling head methods. The latter techniques were highly recommended for permeable and high permeable porous building materials. Water permeability values were also linked to effective porosity and interpreted in terms of interparticle and vugs porosity. Finally, some modifications in the apparatus and procedures were carried out in order to assess water permeability in soft materials, which involve the use of non-saturated samples.

Relating electrical conduction of alluvial sediments to textural properties and pore‐fluid conductivity

Abstract: Electrical conductivity of alluvial sediments depends on litho-textural properties, fluid saturation and porewater conductivity. Therefore, for hydrostratigraphic applications of direct current resistivity methods in porous sedimentary aquifers, it can be useful to characterize the prevailing mechanisms of electrical conduction (electrolytic or shale conduction) according to the litho-textural properties and to the porewater characteristics. An experimental device and a measurement protocol were developed and applied to collect data on eight samples of alluvial sediments from the Po plain (Northern Italy), characterized by different grain-size distribution, and fully saturated with porewater of variable conductivity. The bulk electrical conductivities obtained with the laboratory tests were interpreted with a classical two-component model, which requires the identification of the intrinsic conductivity of clay particles and the effective porosity for each sample, and with a three-component model. The latter is based on the two endmember mechanisms, surface and electrolytic conduction, but takes into account also the interaction between dissolved ions in the pores and the fluid-grain interface. The experimental data and their interpretation with the phenomenological models show that the volumetric ratio between coarse and fine grains is a simple but effective parameter to determine the electrical behaviour of clastic hydrofacies at the scale of the representative elementary volume.

Factor analysis of borehole logs for evaluating formation shaliness: a hydrogeophysical application for groundwater studies

Abstract: The calculation of groundwater reserves in shaly sand aquifers requires a reliable estimation of effective porosity and permeability; the amount of shaliness as a related quantity can be determined from well log analysis. The conventionally used linear model, connecting the natural gamma-ray index to shale content, often gives only a rough estimate of shale volume. A non-linear model is suggested, which is derived from the factor analysis of well-logging data. An earlier study of hydrocarbon wells revealed an empirical relationship between the factor scores and shale volume, independent of the well site. Borehole logs from three groundwater wells drilled in the northeastern Great Hungarian Plain are analyzed to derive depth logs of factor variables, which are then correlated with shale volumes given from the method of Larionov. Shale volume logs derived by the statistical procedure are in close agreement with those derived from Larionov’s formula, which confirms the validity of the non-linear approximation. The statistical results are in good accordance with laboratory measurements made on core samples. Whereas conventional methods normally use a single well log as input, factor analysis processes all available logs to provide groundwater exploration with reliable estimations of shale volume.

The Porosity Trend and Pore Sizes of the Rocks in the Continental Crust of the Earth: Evidence from Experimental Data on Permeability

Abstract: The depth trends of permeability are constructed from the measurements of the tight rocks typical of the basement of the continental crust at temperatures up to 600°C and pressures up to 200 MPa. It is established that the permeability decreases with depth. The statistical processing of the experimental data yielded the generalized dependence logk = −12.6-3.23H 0.223. The method is suggested and, based on the experimental data on permeability, the estimates are obtained for the effective diameters of the pore channels and effective porosity at the PT parameters corresponding to the in situ deep zones of the continental crust. It is found that porosity decreases with depth, while distinct depth dependence of the pore sizes is not observed. The dependence of porosity on the depth is approximated by the relationship logφ = −0.65–0.1H + 0.0019H 2. The porosity is estimated at a few percent for a depth of 10 km with a decline to 0.01–0.1% at 35 km. The estimates of porosity retrieved from the experimental data agree with the theoretical calculations based on the present-day ideas of the structure of the discrete media and with the results of magnetotelluric sounding. Thus, according to three independent estimates, the porosity of the rocks of the continental crust decreases with depth. At the same time, in both the intermediate and lower crust there are intervals where the porosity values suggest the presence of fluid-saturated horizons at these depths.

Porosity Reviewed: Quantitative Multi-Disciplinary Understanding, Recent Advances and Applications in Vadose Zone Hydrology

Abstract: Porosity—one of the most basic mechanical properties of a medium—has implications in a vast range of disciplines and used for a similar vast range of applications. These include, for instance, the storage and flow of water; the compressible component of earth materials, which can be subjected to consolidation under loading; the variable parameter in the swelling and shrinkage of clays; and possibly a governing parameter in the formation of wetlands and perched water tables. This review notes the relevance of a fourfold quantification of porosity for vadose zone studies, viz. (1) type (matrix or structure), (2) scale (submicro to macro scale), (3) connectivity, and (4) water saturation. This is followed by a review of recent advances in the quantification and description of porosity in porous media (visual and remote sensing methods, porosimetry, geometrical approaches, empirical estimations, densest packing simulations, etc.), the applications to quantification of hydrological parameters, and a brief glimpse into the significance of porosity in a temporary hillslope wetland underlain by Archaean Lanseria gneiss in South Africa. Final comments are made regarding areas where quantification of porosity is problematic.

Analysis of Flow Duration and Estimation of Increased Groundwater Quantity Due to Groundwater Dam Construction

Abstract: 지하수 , 지하댐, 유효공극률 , 유황곡선 , 대체 수자원This paper aims to calculate the increase in groundwater quantity following groundwater dam construction, and toassess its impact on surface water. In the study area of Osib-cheon, Yeongdeok, we estimated groundwater quantity,groundwater level, and effective porosity, and examined surface water fluctuations with respect to the increasedgroundwater quantity based on the flow duration. The results reveal that the increased groundwater quantity was atmost 91,746 m

Water Saturation and Porosity Prediction Using Back-propagation Artificial Neural Network (BPANN) from Well Log Data

Abstract: Porosity and water saturation are two fundamental parameters in reservoir characterization. In this study, for predicting both mentioned parameters artificial neural network was used as intelligent technique. Five variables include neutron log, effective porosity, caliper log, bulk density, and sonic log were used from 3 wells from one of the Iranian oil fields. After normalizing data Seventy percent of data were used as training dataset and remainder for testing the network. Several feed –forward neural networks were operated to obtain best performance of different algorithms to train the network. Levenberge-Marquardt back-propagation algorithm was chosen as the training algorithm which had the best performance and was faster than other algorithms. Optimum neurons in the hidden layer for porosity and water saturation were obtained respectively. Results shown that Backpropagation artificial neural network (BPANN) has a high ability to predict porosity and water saturation which correlation between real output and predicted output using BPANN were 0.82 and 0.93 respectively.

Diagenetic analysis of the Early Eocene Margala Hill limestone, Pakistan: A synthesis for thin section porosity

Abstract: The diagenetic fabric and its implications for the thin section porosity in carbonate facies of the Margala Hill Limestone in the Haripur area of North Pakistan is documented here. The facies analysis suggests deposition of the unit in a carbonate shelf platform setting having characteristic sediments of the inner shelf lagoon to middle shelf subtidal environments. The diagenetic overprinting of these facies includes micritization, neomorphism (microspar, aragonite calcite transformation, dolomitization) and compaction (disorientation of biocalst, pressure dissolution fabric). The inner shelf facies have an enhanced porosity due to transformation of calcite to dolomite and micritization of skeletal fragments. The occlusion of the effective porosity in the middle shelf and sub-tidal distal shelf facies is related to the stylonodular, stylobrecciated fabric and calcite filled veins. The overall assessment of the unit suggests that the middle part of rock intervals have fair porosity (8-13%), in contrast to the lower and upper part which has negligible porosity (0-5%).

Device and method for measuring effective porosity of low-permeability rock on basis of inert gas experiment

Abstract: The invention discloses a device and method for measuring the effective porosity of a low-permeability rock on the basis of an inert gas experiment. The device comprises a pressure chamber (1), an air pressure loading system (2), a confining pressure loading system (3), the to-be-measured low-permeability rock (4) and a high-precision pressure gauge (5) which are communicated through a communicating pipeline, wherein the to-be-measured low-permeability rock (4) is placed in the pressure chamber (1); the air pressure loading system (2) loads air pressure to the upper and lower surfaces of the to-be-measured low-permeability rock (4); the high-precision pressure gauge (5) is used for measuring the air pressure in the communicating pipeline; the confining pressure loading system (3) loads confining pressure to the periphery of the to-be-measured low-permeability rock (4). According to the method, after air pressure loading, the high-precision pressure gauge is used for measuring pressure changes of inert gas so as to derive the effective porosity of the rock sample under different confining pressure. The device has the advantages that the operation is simple, the range of confining pressure measured in the experiment is wide, the measuring accuracy is high, the experiment period is short, and the final result is easy to convert.

A petrographic coded correlation between interface conductivity and other pore space properties

Abstract: Electrical conductivity is an important property in geoscience and petroleum engineering. It gives not only information about the porosity and water saturation, but also about interfacial conductivity and about specific internal surface of the pore space. Archie’s equation correlates the electrical resistivity of a water-saturated rock sample and the resistivity of the pore water. A more detailed investigation with brine of different salinities results in the observation of interface conductivity, which is correlated to a specific internal surface. Measurements with increasing salinity of the brine were carried out on different samples: sandstone, carbonate and magmatic rocks. Additionally, permeability and effective porosity were determined. The resulting true formation factor and interfacial conductivity were then correlated with porosity and permeability. Analysis of data allows the application of the interface term as a measure of specific internal surface. For the interpretation of results, the simple capillary model a semi-empirical equation is used and delivers permeability as function of porosity, formation factor and interface conductivity. Determined permeability out of the calculations is compared with measured permeability. The developed equation which is dependent on the porosity, interface conductivity, formation factor and covers additionally the lithology influence can be used for a permeability calculation with a reasonable fit.

Method for grading evaluation of tight sandstone gas resource

Abstract: The invention relates to a method for grading evaluation of an oil field gas resource, in particular to a method for grading evaluation of a tight sandstone gas resource. The method comprises the specific steps that a tight reservoir sample is collected, porosity and permeability are actually measured, and a water saturation well logging calculation model is built; an effective porosity well logging calculation model is built through the actually-measured porosity; a permeability calculation model is built according to the relation between the actually-measured porosity and the actually-measured permeability; tight sandstone gas stored energy evaluation parameters are created according to well logging calculation data obtained through the previous steps. According to the method for grading evaluation of the tight sandstone gas resource, microscopic features of a tight reservoir are fully utilized, the method for grading evaluation of the resource is established from the perspective of the unconventional hydrocarbon accumulation enrichment characteristic on the basis of changes in pore structures, the stored energy evaluation parameters with the consideration of the hydrocarbon accumulation capacity and the seepage capacity are created, and the scientific and effective method is provided for grading evaluation of the tight sandstone gas resource.