Showing papers on "Effective porosity published in 2010"

Rock thermal conductivity of Mesozoic geothermal aquifers in the Northeast German Basin

Abstract: This study reports laboratory-measured thermal-conductivity values of Mesozoic sandstones from eight wells (predominantly geothermal boreholes) of the Northeast German Basin (NEGB). The measurements were made on drill core using the optical scanning method. Bulk thermal conductivities of sandstones corrected for in situ thermal conditions range between 2.1 and 3.9 W/m/K. In general, the Mesozoic sandstones show a large effective porosity typically ranging between 16% and 30%. Matrix thermal conductivity ranges from 3.4 to 7.4 W/m/K. The higher values reflect the large quartz content in sandstone. Based on the in situ thermal conductivity and corresponding interval temperature gradient, obtained from high-precision temperature logs measured under thermal borehole equilibrium, interval heat-flow values were computed in the Middle Buntsandstein section (between 1400 and 1500 m) of two boreholes located in the Stralsund area. The heat flow averages to 74 mW/m² (Gt Ss 1/85 borehole) and 78 mW/m² (Gt Ss 2/85 borehole) and, by adding a heat-flow component of 1.8 mW/m² for the heat production in the overburden, are in good correspondence with previously reported surface heat flow of 77 mW/m². Based on these values and the temperature log information, thermal conductivity was indirectly calculated for the entire borehole profiles. The discrepancy between laboratory-measured and computed thermal conductivities in the two boreholes is in the order of 0.24 and 0.56 W/m/K. Formation in situ thermal conductivity of the Mesozoic section ranges between 1.5 and 3.1 W/m/K.

A New Method To Simultaneously Measure In-Situ Permeability and Porosity Under Reservoir Conditions: Implications for Characterization of Unconventional Gas Reservoirs

Abstract: Accurate estimation of gas-in-place is crucial for successful evaluation and exploitation of unconventional gas reservoirs, such as shale gas, coalbed methane, and tight gas. However, gas effective porosity, one of the most important parameter in estimating gas in-place, is commonly measured on crushed samples of cores or cuttings at ambient pressure although many studies have shown that the porosity and permeability of reservoirs rocks decrease with increasing effective stress, and thus the pore volume/porosity measured on crushed samples at ambient (zero stress) conditions will be larger than porosity measured under in-situ reservoir stress conditions. Normally the stress-dependence of porosity is simply accounted for by a correction factor based on the linear poro-elastic deformation, which is likely an over-simplification. In present study, we developed a new protocol for simultaneously measuring stress-dependent In-Situ Permeability and Porosity (ISPP) that provides a method for routine characterization of effective porosity and permeability under simulated reservoir conditions. our new method can significantly reduce the uncertainties of porosity introduced by testing crushed samples under ambient conditions, testing time, and the need for good quality core samples that are usually unavailable. Preliminary test results indicate that the stress dependence of porosity (or pore compressibility) of fine grained reservoir rocks follows a unique trend of each tested sample, which cannot be simply adjusted from ambient porosity by a universal factor. Physical and numerical sample tests suggest that our ISPP method can obtain permeability similar to the normal pressure Pulse-decay Permeability (PdP) technique if samples are homogeneous or transversely layered along their axes. otherwise, our ISPP method likely tests the geometrical average permeability of longitudinally layered samples instead of the weighted arithmetical average permeability tested by the PdP method. overall, our approach of simultaneously measuring effective porosity and permeability under reservoir conditions offers intrinsically consistent porosity-permeability data to characterize unconventional reservoirs. our study also reveals that utilization of different methods to test samples in different orientations and different sizes is necessary to rigorously characterize the hierarchical permeability and porosity of heterogeneous and microporous unconventional reservoir rocks. To order the full paper, visit http://www.onepetro.org/mslib/servlet/onepetropreview?id=SPE-138148-MS

Scale dependence of intragranular porosity, tortuosity, and diffusivity

Abstract: [1] Diffusive exchange of solutes between intragranular pores and flowing water is a recognized but poorly understood contributor to dispersion. Intragranular porosity may also contribute to the “slow sorption” phenomenon. Intragranular pores may be sparsely interconnected, raising the possibility that accessible porosity and diffusive exchange are limited by pore connectivity. We used a pore-scale network model to examine pore connectivity effects on accessible porosity, tortuosity, and diffusivity in spherical particles. The diffusive process simulated was release of a nonsorbing solute initially at equilibrium with the surrounding solution. High-connectivity results were essentially identical to Crank's analytical solution. Low-connectivity results were consistent with observations reported in the literature, with solute released at early times more quickly than indicated by the analytical solution, and more slowly at late times. Values of accessible porosity, tortuosity, and diffusivity scaled with connection probability, distance to the sphere's exterior, and/or the sphere's radius, as predicted by percolation theory. When integrated into a conventional finite difference model, the scaling relationships provide a consistent and physically sound way to incorporate such nonuniformities into models of intragranular diffusion.

Parameter estimation based on vertical heat transport in the surficial zone

Abstract: Measured groundwater temperatures in the surficial zone are dependent on the properties of porous media and vertical flow velocity. Sensitivity analyses, collinear diagnostics and an inverse numerical solution to the one-dimensional heat-transport equation are used to determine which parameters can be estimated from temperature measurements in the surficial zone. This is done for heat transport in the saturated zone considering a constant vertical flow velocity. The use of temperature profiles, temperature time-series and temperature envelopes are considered. There is an important difference between a conduction and a convection dominated system. Sensitivity analysis shows that temperature measurements are sensitive to effective thermal conductivity and heat capacity and are insensitive to effective porosity and thermal dispersivity. In a conduction dominated system, temperature is also insensitive for vertical velocity. Collinear diagnostics show that in a conduction dominated system, only the combination of heat capacity and effective thermal conductivity, the thermal diffusivity, can be derived. In a convection dominated system, both the vertical velocity and the effective thermal conductivity can, theoretically, be derived.

Effects of uncertainty of lithofacies, conductivity and porosity distributions on stochastic interpretations of a field scale tracer test

Abstract: We investigate the importance of selecting two different methodologies for the determination of hydraulic conductivity from available grain-size distributions on the stochastic modeling of the depth-averaged breakthrough curve observed during a forced-gradient tracer test experiment. The latter was performed in the Lauswiesen alluvial aquifer, located near the city of Tubingen, Germany, by injecting NaBr into a well at a distance of about 50 m from a pumping well. We also examine the joint effect of the choice of the transport model adopted to describe solute transport at the site and the way the spatial distribution of porosity is assessed. In the absence of direct measurements of porosity, we consider: (a) the model used by Riva et al. (J Contam Hydrol 88:92–118, 2006; J Contam Hydrol 101:1–13, 2008), which relates the natural logarithms of effective porosity and conductivity through an empirical, experimentally-based, linear relationship derived for a nearby experimental site; and (b) a model based on a commonly used relationship linking the total porosity to the coefficient of uniformity of grain size distributions. Transport is described in terms of a purely advective process and/or by including mass exchange processes between mobile and immobile regions. Modeling of flow and transport is performed within a Monte Carlo framework, upon conceptualizing the aquifer as a random composite medium. Our results indicate that the model adopted to describe the correlation between conductivity and porosity and the way grain-sieve information are incorporated to depict the heterogeneous distribution of hydraulic conductivity can have relevant effects in the interpretation of the data at the site. All the conceptual models employed to describe the structural heterogeneity of the system and transport features can reasonably reproduce the global characteristics of the experimental depth-averaged breakthrough curve. Specific details, such as the peak concentration and the time of first arrival, can be better reproduced by a double porosity transport model when a correlation between conductivity and porosity based on grain size information at the site is considered. The best prediction of the late-time behavior of the measured breakthrough curves, in terms of the observed heavy tailing, is offered by directly linking porosity distribution to the spatial variability of particle size information.

Occurrences of Shale Gas and Their Petroleum Geological Significance

Abstract: As unconventional gas resources,shale gas is mainly consistent of the free,adsorbed and dissolved gas accumulated in dark shale beds.Among these occurrences,adsorbed and free gases are the dominated phases.The occurrence of shale gas and various influence factors,such as gas component,material composition(sedimental organic carbon,mineral components,and water saturation),rock texture(porosity,pore structure,and permeability),temperature and pressure,are summarized and evaluated based on previous geological and experimental studies.Because effective porosity and gas saturation are the key factors determining the reserves of free gas,and gas adsorption capacity of shale is the maxium limit of the content of adsorbed gas,it is important to disclose the occurences of shale gas and evaluate potential influencing factors,which will improve the reliability of resource assessment based on volumetric method.Development of new characterization techniques of nano-pores structure of shale,and study on the adsorption behaviors of metane on clay surface and in nano-pores under various geological conditions should be carried out urgently to promote the understandings of the occurrences of shale gas,and to acquire reliable parameters used in resource assessment.

Improved estimation of mineral and fluid volumetric concentrations in thinly-bedded and invaded formations

Abstract: Calculation of mineral and fluid volumetric concentrations from well logs is one of the most important outcomes of formation evaluation. Conventional estimation methods assume a linear relationship between volumetric concentrations of solid/fluid constituents and well logs. Experience shows, however, that the relationship between neutron logs and mineral concentrations is generally non-linear. More importantly, linear estimation methods do not explicitly account for shoulder-bed and/or invasion effects on well logs nor do the account for differences in the volume of investigation of the measurements involved in the estimation. The latter deficiencies of the linear estimation method can cause appreciable errors in the calculation of porosity and hydrocarbon pore volume. We introduce a new non-linear inversion method that uses fast modeling of nuclear and resistivity logs to estimate porosity, hydrocarbon saturation, volumetric concentration of shale, and volumetric concentrations of mineral constituents in the presence of complex mineral compositions, invasion, and shoulder beds. The method assumes a multi-layer reservoir model constructed with the detection of bed boundaries from density and gamma-ray (GR) logs. Subsequently, nonlinear inversion is initialized with petrophysical properties and volumetric mineral concentrations obtained with a conventional linear estimation method combined with resistivity-saturation equations. We progressively reduce the differences between simulated and measured logs via linear iterative steps to render final estimates of porosity, fluid saturations, and volumetric concentrations of mineral constituents that honor the well logs, their volume of investigation, the process of invasion, and the assumed rock-physics model. Synthetic and field examples of application indicate that non-linear inversion is an efficient and reliable method to quantify complex mineral and fluid composition in the presence of thin beds and invasion. Comparison of results against those obtained with commercial linear estimation methods confirm the advantage of non-linear inversion in quantifying thinly-bedded carbonate formations.

Petrophysical evaluation of subsurface reservoir sandstones of Bengal Basin, Bangladesh

Abstract: The present study has been carried out for core and log based petrophysical evaluation of subsurface reservoir sandstones considering at least one well from each of the Kailas Tila, Titas, Bakhrabad and Shahbazpur gas fields of Bangladesh. Core analysis results show that average core porosity, permeability and pore throat values are 20%, 209 mD and 44020 A, respectively. These measured values support that the sandstone reservoirs are categorized as good quality reservoirs. Core porosity values usually exceed thin section porosity. Different cross-plots indicate that permeability is largely dependent on porosity. Permeability and porosity are also dependent on textural parameters that include size, shape, sorting and matrix of the reservoir sandstones. It reveals from both thin section study and different cross plots that diagenetic cements are the main controlling factors of the reservoirs. Quantitative determination of the volume of cements shows that cements have inverse correlation with porosity and permeability. Log based petrophysical parameters include shale volume, porosity, water and hydrocarbon saturation, permeability, moveability index and bulk volume of water. The average values of the mentioned parameters are 20%, 22%, 26%, 74%, 110 mD, 0.28 and 0.05, respectively. The most important parameters are porosity and permeability, which indicate that log porosity exceeds core porosity and log permeability significantly lags behind core permeability. The study also reveals that 23 gas zones covering total thickness of 385 m sandstones mostly posses good quality reservoirs except few moderate quality reservoirs.

Compound copper powder for manufacturing capillary structure of inner wall of heat pipe

Abstract: The invention provides compound copper powder for manufacturing a capillary structure inside a heat pipe, which is a mixture consisting of copper powder and pore-forming agent powder. The compound copper powder ensures that a more favorable capillary structure layer can be produced under the condition of not changing the conventional heat pipe manufacturing process. The compound copper powder obtained by the invention is ram-jolted and sintered and then is prepared into the capillary structure layer with high porosity; and the effective porosity and the through hole ratio thereof are greatly improved compared with that of ordinary copper powder, and the permeability is also greatly improved compared with that of materials fired by the ordinary copper powder, which greatly improves the heat transfer efficiency of the heat pipe.

Porosity Partitioning and Permeability Quantification in Vuggy Carbonates, Permian Basin, West Texas, U.S.A.

Abstract: Using high-resolution electrical borehole images and other open-hole log data in 13 wells, a case study was conducted to analyze the porosity and permeability heterogeneity in the Means field in the Permian Basin, west Texas. Because of negligible clay and other conductive minerals in the predominantly dolomitic rocks, the electrical images are converted into microporosity maps of the boreholes using a modified Archie equation. The vug porosity is then partitioned from the total porosity by analyzing the porosity spectra around the boreholes in the sliding windows of 1-in. (2.5-cm)-thick interval. A practical workflow was also developed to compute a sonic vug-porosity index using the sonic, neutron, and density logs. The two vug porosities based on the independent measurements support each other in the Means field except that the sonic vug-porosity index has much lower resolution than the image-derived porosity. Through iterative experiments, a synthetic permeability model is established using the total porosity and vug-porosity logs. The core permeability in the vuggy dolomites varies exponentially with the product of the vug-porosity and vug-connectivity factor. Thin superpermeable vuggy zones below the resolution of the conventional logs are revealed by the electrical images and the permeability quantification. These superpermeable zones sandwiching thick oil-bearing reservoir rocks are the primary cause for the early high water cut and the bypassed oil. Integration of the continuous high-resolution permeability logs, the petrophysical facies from supervised neural network (SNN) processing, and the production data from both producers and injectors provide valuable insights to reservoir modeling.

Porosity and Permeability

Abstract: Porosity is the fraction of a porous medium that is void space. Most porous media contain a fraction of pores that are not in communication with the flow path. This pore volume is ineffective. Effective pore volume is the interconnected pore volume that communicates with a well. Effective porosity is defined as the ratio of effective pore volume to bulk volume. Permeability averaging poses a problem in the estimation of a representative average permeability for use in Darcy's equation. Permeability can be obtained from core plugs and well tests. Core plug permeability and well test permeability are measurements of permeability at different scales. Several techniques exist for estimating an average value of permeability. It is often useful to represent permeability heterogeneity with a single number. This number is referred to as a measure of permeability heterogeneity. Several such measures exist. These measures may be used to verify that the permeability distribution used in a model has comparable heterogeneity to the permeability distribution observed in an analysis of field data.

Application of Kozeny–Kovàcs Model to Predict the Hydraulic Conductivity of Permeable Pavements:

Abstract: Permeable pavements provide a frictional surface for vehicles during rainfall runoff and function as a porous infrastructure interface, allowing the infiltration and evaporation of rainfall runoff, as well as treatment of pollutants when designed for solute and particulate separation. The hydraulic conductivity (ksat) of permeable pavement is an important hydraulic property. A series of empirical and pore structure models using constant head and pore-based measurements, including total porosity (θt), effective porosity (θe), and pore size distribution indices generated through X-ray tomography (XRT) were used to study permeable pavement. XRT results indicate that the pore matrix is heterodisperse, with θt θ e. Results indicate that the traditional models based on a simple pore structure do not reproduce measured ksat values. More complex pore structure models, even with modification from the original form, gave better results. A modified Kozeny-Kovacs model was used to reproduce the measured ksat values. ...

Variable‐Density Flow and Transport Simulation of Wellbore Brine Displacement

Abstract: Borehole dilution tests have been used for characterization of aquifer hydrogeologic properties for several decades. Based on the principles of borehole dilution tests, we conducted what more appropriately may be considered a wellbore fluid displacement test in a limestone aquifer in South Carolina. Our study area is a quarry in the coastal plain of South Carolina. Using a solution of reagent grade NaCl and deionized H(2)O as a tracer, a brine slug was introduced into a 5 cm (2 in.) diameter Schedule 40 PVC well with a 6-m slotted screen at the bottom. Immediately following addition of the brine, a recording electrical conductivity (EC) sensor was placed in the well opposite the screen and set to record EC in 2-min intervals for 5 days. An alternative to previous methods for analyzing data from wellbore brine displacement tests was developed. Results were analyzed using SEAWAT-2000 to account for the density dependency of brine flow and transport. The high spatial resolution, three-dimensional numerical simulation enabled direct incorporation of well construction peculiarities, including the sand pack and length of screen, in the data analysis. Hydraulic conductivity, effective porosity, and longitudinal dispersivity were adjusted in the simulation model until the best match of simulated wellbore fluid concentrations to observed concentrations was achieved. Using this procedure, we were able to obtain a very close agreement between observed and simulated concentrations and, hence, reliable estimates of the hydrogeologic properties of the aquifer in the vicinity of the test well.

Logging Evaluation of the Ordovician Carbonate Reservoir Beds in the Lungudong Region, Tarim Basin

Abstract: In recent years, great progress has been made constantly in oil and gas exploration in the Lungudong region of the Tarim Basin. However, progress has been slow in the evaluation of its main oil-producing horizons — the Ordovician carbonate reservoir beds. Based on previous researches and on the various data such as drilling, geology and oil test, in combination with the interpretation of each single-well imaging and conventional logging data, and through analysis and comparison, the identification methods in imaging and conventional logging for four types of carbonate reservoir beds in this region are summarized in this paper. Calculation formulas for four reservoir bed parameters, i. e. shale content, porosity, permeability and oil saturation in this region are proposed; and reservoir beds in this region are divided into three levels (I, II and III) by combining oil test data and logging data, The lower limits of the effective porosity of reservoir beds and the fracture porosity of effective reservoir beds are determined as 1.8% and 0.04%, respectively. The physical property parameters are calculated by conventional logging curves, and the most advantageous areas for reservoir development are predicted comprehensively. On the plane, the high-value zones of reservoir bed parameters are mainly concentrated in the N-S-trending strike-slip fault, the Sangtamu fault horst zone and near the LG38 well area; vertically, the reservoir bed parameters of the Yijianfang Formation are better than those of the Yingshan and Lianglitage formations.

Study on fluid-solid coupling of physical variation of gas hydrate reservoirs during natural gas development

Abstract: Considering the effects of gas hydrate dissociation and the interaction between porous fluid flow and rock deformation,a gas-water two-phase non-isothermal fluid-solid coupling mathematical model was established for gas hydrate reservoirs,and a corresponding finite element program was developedTaking a gas hydrate reservoir of Mexico Gulf as an example,the distribution and variation of the stress state and the physical parameters were analyzedThe results show that the effect of gas hydrate dissociation,fluid-solid coupling and borehole effect are the three major influential factors with different mechanisms,influence degrees and influence areasThe effect of dissociation is the main controlling factor and obviously causes the increases of effective porosity and permeability and the decreases of the elastic modulus and cohesion forceThe fluid-solid coupling effect has obvious inhibiting effect on the varying trends of the physical and mechanical parameters caused by the effect of hydrate dissociationMore attention should be paid to the fluid-solid coupling effect

Effective Porosity Measurement of a Marine Clay

Abstract: Effective porosity commonly represents only the voids in soils or rock that contribute to the advective transport of groundwater. In the extreme case, all the pores or fractures are interconnected and contribute to the transport of groundwater. However, in most cases, some pores or fractures are dead-ended or isolated and, therefore, do not contribute to the advective movement of water through the soil or rock mass. The effective porosity is often estimated to be some fraction of the total porosity. The purpose of this study was to compare a glacial marine clay deposit's effective and total porosities. The inner connection of the soil pores and the importance of the clay minerals on the pore spaces are at the root of the effective porosity testing described herein. Based on the results of three tracer tests on a low-plasticity, glacial marine clay, the effective porosity was found to be approximately equal to the total porosity within an error of less than 10%. Based on visual appearance of this uniform clay, the longitudinal dispersivity was assumed to be small compared to the tracer specimen length. However, it was found that larger test specimens would have made the tracer breakthrough curves less complicated.

Porosity Estimation From Seismic Data At Dickman Field, Kansas For Carbon Sequestration

Abstract: We present results from seismic inversion study of a 3D pre-stack seismic data volume collected over a carbonate brine reservoir in the Dickman Field, Kansas. This reservoir is a candidate for CO2 storage and therefore, the purpose of this study is to use seismic data to quantitatively estimate some reservoir parameters (porosity, permeability) of this formation. Our analyses include extensive pre-stack velocity analysis, pre-stack inversion and mapping of inversion results to porosity. Seismic inversion results together with several other attributes derived from seismic data were used in a multi-attribute linear regression to estimate an effective porosity volume. The porosity is one of the most crucial parameters in assessing different possible scenarios for injecting CO2 within this reservoir. Our results will be incorporated in a reservoir simulator to investigate different ‘what if’ time-lapse scenarios.

Empirical model to estimate the thermal conductivity of granite with various water contents

Abstract: To obtain the input data for the design and long-term performance assessment of a high-level waste repository, the thermal conductivities of several granite rocks which were taken from the rock cores from the declined borehole were measured. The thermal conductivities of granite were measured under the different conditions of water content to investigate the effects of the water content on the thermal conductivity. A simple empirical correlation was proposed to predict the thermal conductivity of granite as a function of effective porosity and water content which can be measured with relative ease while neglecting the possible effects of mineralogy, structure and anisotropy. The correlation could predict the thermal conductivity of granite with the effective porosity below 2.7% from the KURT site with an estimated error below 10%.

3D acoustic impedance and porosity mapping from seismic inversion and neural networks

Abstract: In this work we have applied a two-fold methodology to obtain porosity 3D maps from post-stack 3D seismic amplitude data and well log data. Firstly, acoustic impedance values are derived from seismic amplitudes by applying a L1-norm sparse-spike inversion algorithm in the time domain, followed by a recursive inversion performed in the frequency domain, where low-frequency impedance trends estimated at well-logs are used as constraints. Secondly, a feed-forward Neural Network (NN) is trained, validated and tested using effective porosity data observed at the well locations as input. The trained NN is applied for the whole reservoir volume to obtain a 3D effective porosity map. The results suggest that this simple workflow can be applied successfully specially in reservoirs for which the observed relationship between porosity and acoustic impedance is non-linear.