Inaccessible Pore Research Articles

Pressure Transient Behavior for Alternating Polymer Flooding in a Three-zone Composite Reservoir

Alternating polymer flooding has achieved great attractions recently in oil industry, however, the research of pressure analysis in alternating polymer flooding reservoir is rare. This work presents a numerical pressure analysis method of three-zone composite model for formation evaluation. A new numerical pressure analysis model (three-zone composite model) is established by considering diffusion, convection, shear, and inaccessible pore volume, which is based on the rheology experiments. Based on this model, the type curves are then developed and sensitivity analysis is further conducted. The type curves have seven regimes in three-zone composite model. The characteristic is the obvious upturn of pressure derivative curve in transient regime between low concentration and high concentration polymer solution. Formation parameters can be interpreted by history matching and formation evaluation can be conducted based on this model. As an important part of formation evaluation, formation damage as a result of adsorption of polymers in porous media is evaluated by comparing the interpreted permeability with the original value before polymer flooding. The field test data proves that this proposed method can accurately evaluate reservoir characteristics in alternating polymer flooding reservoirs, which emphasizes the potential application of this method in petroleum industry.

Determination of closed porosity in rocks by small-angle neutron scattering

Small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) have been used to study a carbonate rock from a deep saline aquifer that is a potential candidate as a storage reservoir for CO2 sequestration. A new methodology is developed for estimating the fraction of accessible and inaccessible pore volume using SANS/USANS measurements. This method does not require the achievement of zero average contrast for the calculation of accessible and inaccessible pore volume fraction. The scattering intensity at high Q increases with increasing CO2 pressure, in contrast with the low-Q behaviour where the intensity decreases with increasing pressure. Data treatment for high-Q scattering at different pressures of CO2 is also introduced to explain this anomalous behaviour. The analysis shows that a significant proportion of the pore system consists of micropores (<20 Å) and that the majority (80%) of these micropores remain inaccessible to CO2 at reservoir pressures.

Displacement Efficiency for Low-Salinity Polymer Flooding Including Wettability Alteration

SummaryPolymer flooding can significantly improve sweep and delay breakthrough of injected water, thereby increasing oil recovery. Polymer viscosity degrades in reservoirs with high-salinity brines, so it is advantageous to inject low-salinity water as a preflush. Low-salinity waterflooding (LSW) can also improve local-displacement efficiency by changing the wettability of the reservoir rock from oil-wet to more water-wet. The mechanism for wettability alteration for LSW in sandstones is not very well-understood; however, experiments and field studies strongly support that cation-exchange (CE) reactions are the key elements in wettability alteration. The complex coupled effects of CE reactions, polymer properties, and multiphase flow and transport have not been explained to date.This paper presents the first analytical solutions for the coupled synergistic behavior of LSW and polymer flooding considering CE reactions, wettability alteration, adsorption, inaccessible pore volume (IPV), and salinity effects on polymer viscosity. A mechanistic approach that includes the CE of Ca2+, Mg2+, and Na+ is used to model the wettability alteration. The aqueous phase viscosity is a function of polymer and salt concentrations. Then, the coupled multiphase-flow and reactive-transport model is decoupled into three simpler subproblems—the first in which CE reactions are solved, the second in which a variable polymer concentration can be added to the reaction path, and the third in which fractional flows can be mapped onto the fixed cation and polymer-concentration paths. The solutions are used to develop a front-tracking algorithm, which can solve the slug-injection problem of low-salinity water as a preflush followed by polymer. The results are verified with experimental data and PennSim (2013), a general-purpose compositional simulator.The analytical solutions show that decoupling allows for estimation of key modeling parameters from experimental data, without considering the chemical reactions. Recovery can be significantly enhanced by a low-salinity preflush before polymer injection. For the cases studied, the improved oil recovery (IOR) for a chemically tuned low-salinity polymer (LSP) flood can be as much as 10% original oil in place (OOIP) greater than with considering polymer alone. The results show the structure of the solutions, and, in particular, the velocity of multiple shocks that develop. These shocks can interact, changing recovery. For example, poor recoveries obtained in corefloods for small-slug sizes of low salinity are explained by the intersection of shocks without considering mixing. The solutions can also be used to benchmark numerical solutions and for experimental design. We demonstrate the potential of LSP flooding as a less-expensive and more-effective way for performing polymer flooding when the reservoir wettability can be altered with chemically tuned low-salinity brine.

Changes in the pore characteristics of shale during comminution

The correct understanding of shale pore characteristics is the foundation of shale gas exploration and development. Comminution is an essential sample pretreatment in many measurements of shale pore characteristics, but little is known about the influence of comminution on shale pore characteristics. This study utilizes low-pressure nitrogen adsorption and helium porosity measurements to investigate the evolution of shale pore characteristics during comminution. The results show that reducing the proportion of inaccessible pores and improving the gas diffusion efficiency are the main effects of comminution on the shale pore characteristics, resulting in an increase in measured porosity. The recommended analytical shale particle size for low-pressure nitrogen adsorption and helium porosity measurements is below 80 and 20 mesh, respectively. The proportion of inaccessible pores in shale investigated in this study ranges from 13.11 to 45.89% and shows a negative correlation with thermal maturity and a positive correlation with clay content. This suggests an improvement of organic pore accessibility during thermal evolution and a high content of inaccessible pores in clay minerals.

Mathematical model for prediction of oil recovery of core-flood tests in process of viscoelastic polymer flooding

In this study a new mathematical model was developed that considers thermal effects, dispersion, effective concentration, elastic behavior of viscoelastic polymers, polymer retention, permeability reduction of aqueous phase, salt effects, inaccessible pore volume, and equivalent shear rate in porous media to predict oil recovery of core-flood experiments in process of viscoelastic polymer flooding as a tertiary stage of enhanced oil recovery. The model was found highly reliable when compared to material balance and experimental data. Displacement performance of core-flood tests could be predicted by presented model, therefore, experimental costs will be decreased significantly.

Study of the Well-Posedness of Models for the Inaccessible Pore Volume in Polymer Flooding

Inaccessible pore volume, also known as dead pore space, is used when simulating enhanced oil recovery by polymer injection. We show that a widely used model for inaccessible pore volume can lead to an ill-posed problem, resulting in unphysical results. By considering shock solutions of the one-dimensional problem, we derive a necessary condition that an inaccessible pore volume model must fulfill in order to obtain well-posed equations. In this derivation, we use the Rankine–Hugoniot jump condition as a selection criterion for acceptable solutions. There are other possible criteria for the one-dimensional problem, in particular $$\delta $$ -shock solutions, which we also briefly describe, but these are challenging and impractical to use. Based on a heuristic understanding of relative permeability, we subsequently derive two modified models for inaccessible pore volume. The first model follows directly from the modeling assumptions, but it has limited applicability. If the inaccessible pore volume is larger than the irreducible water saturation, then the equations are ill-posed for convex relative permeabilities. A second model is derived by relaxing the assumption of inaccessibility, allowing a limited fraction of the polymer to enter the smallest pores. This second model fulfills our necessary condition for well-posedness for all values of the inaccessible pore volume and any choice of relative permeabilities. Through one- and two-dimensional numerical examples, the different models for inaccessible pore volume are compared. For our second suggested model, the polymer concentration is observed to stay below the maximum injected value, which is not the case for the conventional model. This enables a more stable implementation of the highly nonlinear system, and a reduction in the number of nonlinear iterations is also observed in some cases. As this suggested model is straightforward to implement into existing reservoir simulators and can be used for a wide range of polymer models, it serves as a possible alternative to the conventional model.

Impacts of polymer properties on field indicators of reservoir development projects

Polymer flooding is a mature EOR technique implemented in many successful field projects. Understanding its mechanisms is very important to managing field operations. Generally, more oil is recovered when polymer solution is injected for a longer time. For a real project, optimization of field operations usually requires consideration of economic indicators, such as net present value (NPV) as objective function so polymer and other costs are included in the decision 3process. Several commercial and in-house simulators have the capability to model polymer flooding for the optimization purposes. In this paper, we present the numerical modeling of polymer retention and the reversibility, inaccessible pore volume, shape of the curve of viscosity vs. polymer concentration, salinity, permeability reduction, non-Newtonian behavior and degradation, etc. We first tested these models in simple benchmark cases, and then applied them to two synthetic field cases. The goal is to understand the impact of each polymer property on field performance indicators, especially NPV. The synthetic fields represent target Brazil oil fields which have high average permeability with heavy oil (~14° API). Retention of polymer, salinity, polymer rheology and degradation can decrease NPV by up to 25%. Permeability reduction, adsorption reversibility, inaccessible pore volume and selection of a correlation curve for the function of viscosity vs. concentration can influence NPV by less than 3%. Identification of the crucial polymer properties/simulation parameters helps with the decision for key laboratory tests and reducing uncertainties associated with each. This information also helps on the selection of simulation models and key sensitivity parameters where unimportant parameters can be neglected in simulation studies.

Rate-dependent polymer adsorption in porous media

Laboratory core flood experiments were conducted at different flow rates with partially hydrolysed polyacrylamide (HPAM) oilfield Enhanced Oil Recovery (EOR) polymer and silica sand to investigate the polymer retention in porous media due to flow rate variation. Specifically, the double-polymer bank method was used in a new way to quantify and understand total incremental retention (both reversible and irreversible) induced by flow rate variation for HPAM polymers. Experimental results indicate that adsorption was the dominant retention mechanism. Further, the results obtained show that polymer adsorption was rate-dependent (i.e., as flow rate increased, adsorption increased), and that the adsorption was largely reversible with minimal incremental irreversible adsorption. It was also observed that flow rate impacted polymer inaccessible pore volume (IAPV) decreasing from 32% to 15% as flow rate increased from 0.8 ml/min to 6.0 ml/min. Finally, results from the study also give better insight into understanding HPAM flow-induced adsorption and their effect on permeability reduction processes.

The Use of Tracer Data To Determine Polymer-Flooding Effects in a Heterogeneous Reservoir, 8 Torton Horizon Reservoir, Matzen Field, Austria

Summary Polymer-injection pilot projects aim at reducing the uncertainty and risk of full-field polymer-flood implementation. The interpretation of polymer-pilot projects is challenging because of the complexity of the process and fluids moving out of the polymer-pilot area. The interpretation is increasingly more complicated with the heterogeneity of the reservoir. In the polymer pilot performed in the 8 Torton Horizon (TH) reservoir of the Matzen field in Austria, a polymer-injection well surrounded by a number of production wells was selected. A tracer was injected 1 week before polymer injection. The tracer showed that the flow field in the reservoir was dramatically modified with increasing amounts of polymer injected. Despite short breakthrough times of 4 to 10 weeks observed for the tracer, polymer breakthrough occurred only after more than 12 months although injection and production rates were not substantially changed. The tracer signal indicated that the reservoir is heterogeneous, with high flow velocities occurring along a number of flow paths with a limited volume that are strongly connecting the injection and production wells. By injecting polymers, the mobility of the polymer-augmented water was reduced compared with water injection, and led to flow diversion into adjacent layers. The tracer response showed that the speed of the tracer moving from injection to production wells was reduced with increasing amount of polymer injected. This response was used to assess the changes of the amount of water flowing from the injection well to production wells. After a match for the tracer curve was obtained, adsorption, residual resistance factor (RRF), and dispersivity were calculated. The results showed that, even for heterogeneous reservoirs without good conformance of the pilot, the critical parameters for polymer-injection projects can be assessed by analyzing tracer and polymer response. These parameters are required to determine whether implementation of polymer injection at field scale is economically attractive. Along the flow path that is connecting injection and production well, as shown by the tracer response, an incremental recovery of approximately 8% was achieved. The polymer retention and inaccessible pore volume (IPV) in the reservoir were in the same range as in corefloods. Incremental oil recovery caused by acceleration along the flow path was estimated at approximately 20% of the overall incremental oil production caused by polymer injection and 80% was attributed to improved sweep efficiency.

Bioaccessible Porosity in Soil Aggregates and Implications for Biodegradation of High Molecular Weight Petroleum Compounds.

We evaluated the role of soil aggregate pore size on biodegradation of essentially insoluble petroleum hydrocarbons that are biodegraded primarily at the oil-water interface. The size and spatial distribution of pores in aggregates sampled from biodegradation experiments of a clayey, aggregated, hydrocarbon-contaminated soil with relatively high bioremediation end point were characterized by image analyses of X-ray micro-CT scans and N2 adsorption. To determine the bioaccessible pore sizes, we performed separate experiments to assess the ability of hydrocarbon degrading bacteria isolated from the soil to pass through membranes with specific sized pores and to access hexadecane (model insoluble hydrocarbon). Hexadecane biodegradation occurred only when pores were 5 μm or larger, and did not occur when pores were 3 μm and smaller. In clayey aggregates, ∼ 25% of the aggregate volume was attributed to pores larger than 4 μm, which was comparable to that in aggregates from a sandy, hydrocarbon-contaminated soil (~23%) scanned for comparison. The ratio of volumes of inaccessible pores (<4 μm) to bioaccessible pores (>4 μm) in the clayey aggregates was 0.32, whereas in the sandy aggregates it was approximately 10 times lower. The role of soil microstructure on attainable bioremediation end points could be qualitatively assessed in various soils by the aggregate characterization approach outlined herein.

Polymer flow through water- and oil-wet porous media

The effect of wettability on polymer behavior in porous media is investigated through a series of synthetic polymer floods conducted in water- and oil-wet Bentheim and Berea sandstone cores. A new experimental setup is used in which the core effluent polymer concentrations are not measured during polymer flooding, but instead are passed through a capillary tube that is connected to the core outlet. Using the notion of intrinsic viscosity, an approximate expression is presented that can be used to determine the breakthrough time of the injected polymer solution. In addition, polymer adsorption, inaccessible pore volume, and apparent viscosities are evaluated for all cores and wetting conditions. In general, in the presence of residual oil, the oil-wet cores display the lowest degree of polymer retention (Berea) and the lowest inaccessible pore volume-IPV (Bentheim). The largest wettability impact on the polymer behavior in porous media appears to be for the Berea formation; polymer retention in oil-wet cores decreases 90% and IPV 52% compared to the corresponding amounts for the water-wet ones. On the other hand, the estimated polymer retention and IPV values appear to be similar for the oil- and water-wet Bentheim cores, this is attributed to questionable wettability alteration.

Optimized preparation of activated carbon nanoparticles from acrylic fibrous wastes

In present study, activated carbon is prepared by controlled pyrolysis of acrylic fibrous waste under the layer of charcoal using physical activation in high temperature furnace. The main objective is to study the effect of four factors (i.e. final pyrolysis temperature, holding time at final temperature, heating rate per hour, and number of steps) on carbonization behavior of acrylic fibrous waste. The Box-Behnken design and response surface modeling was performed to get higher specific surface area and higher electrical conductivity. The development of porous morphology having higher surface area is found to increase with increase in pyrolysis temperature, increase in number of steps, decrease in holding time and decrease in heating rate till some optimum value. This behavior is attributed to gradual reaction of atmospheric oxygen with carbonized acrylic fibrous waste, which resulted into the opening of previously inaccessible pores through the removal of tars and disorganised carbon. Moreover, these four factors also found to have significant effect on the development of electrical conductivity of activated carbon. Later on, the carbonized acrylic fibrous waste was pulverized in dry conditions by high energy planetary ball milling to get activated carbon nanoparticles. In addition to refinement of size, the specific surface area and electrical conductivity of pulverized carbon particles was found to increase with increase in milling time. The activated carbon particles obtained after three hours of dry milling revealed the particle size of 521 nm, the electrical conductivity of 21.78 s/m for 0.5 wt % concentration of aqueous dispersion and the specific surface area of 432 m2/g.

Calibration-free quantification of interior properties of porous media with x-ray computed tomography

A method is presented for interpreting the values of x-ray attenuation coefficients reconstructed in computed tomography of porous media, while overcoming the ambiguity caused by the multichromatic nature of x-rays, dilution by void, and material heterogeneity. The method enables determination of porosity without relying on calibration or image segmentation or thresholding to discriminate pores from solid material. It distinguishes between solution-accessible and inaccessible pores, and provides the spatial and frequency distributions of solid-matrix material in a heterogeneous medium. This is accomplished by matching an image of a sample saturated with a contrast solution with that saturated with a transparent solution. Voxels occupied with solid-material and inaccessible pores are identified by the fact that they maintain the same location and image attributes in both images, with voxels containing inaccessible pores appearing empty in both images. Fully porous and accessible voxels exhibit the maximum contrast, while the rest are porous voxels containing mixtures of pore solutions and solid. This matching process is performed with an image registration computer code, and image processing software that requires only simple subtraction and multiplication (scaling) processes. The process is demonstrated in dolomite (non-uniform void distribution, homogeneous solid matrix) and sandstone (nearly uniform void distribution, heterogeneous solid matrix) samples, and its overall performance is shown to compare favorably with a method based on calibration and thresholding.

Field vs. Laboratory Polymer-Retention Values for a Polymer Flood in the Tambaredjo Field

SummaryDuring a polymer flood, polymer retention can have a major impact on the rate of polymer propagation through a reservoir, and consequently on oil recovery. A review of the polymer-retention literature revealed that iron and high-surface-area minerals (e.g., clays) dominate polymer-retention measurements in permeable rock and sand (&amp;gt;100 md). A review of the literature on inaccessible pore volume (IAPV) revealed inconsistent and unexplained behavior. A conservative approach to design of a polymer flood in high-permeability (&amp;gt;1 darcy) sands would assume that IAPV is zero. Laboratory measurements using fluids and sands associated with the Sarah Maria polymer flood in Suriname suggested polymer retention and IAPV values near zero [0±20 μg/g for retention and 0±10% pore volume (PV) for IAPV]. A procedure was developed using salinity-tracer and polymer concentrations from production wells to estimate polymer retention during the Sarah Maria polymer flood in the Tambaredjo reservoir. Field calculations indicated much higher polymer-retention values than those from laboratory tests, typically ranging from approximately 50 to 250 μg/g. Field cores necessarily represent an extremely small fraction of the reservoir. Because of the importance of polymer retention, there is considerable value in deriving polymer retention from field results, so that information can be used in the design of project expansions.

Numerical well testing interpretation model and applications in crossflow double-layer reservoirs by polymer flooding.

This work presents numerical well testing interpretation model and analysis techniques to evaluate formation by using pressure transient data acquired with logging tools in crossflow double-layer reservoirs by polymer flooding. A well testing model is established based on rheology experiments and by considering shear, diffusion, convection, inaccessible pore volume (IPV), permeability reduction, wellbore storage effect, and skin factors. The type curves were then developed based on this model, and parameter sensitivity is analyzed. Our research shows that the type curves have five segments with different flow status: (I) wellbore storage section, (II) intermediate flow section (transient section), (III) mid-radial flow section, (IV) crossflow section (from low permeability layer to high permeability layer), and (V) systematic radial flow section. The polymer flooding field tests prove that our model can accurately determine formation parameters in crossflow double-layer reservoirs by polymer flooding. Moreover, formation damage caused by polymer flooding can also be evaluated by comparison of the interpreted permeability with initial layered permeability before polymer flooding. Comparison of the analysis of numerical solution based on flow mechanism with observed polymer flooding field test data highlights the potential for the application of this interpretation method in formation evaluation and enhanced oil recovery (EOR).

Dual-Beam FIB/SEM Characterization, Statistical Reconstruction, and Pore Scale Modeling of a PEMFC Catalyst Layer

The three-dimensional structure of a PEMFC catalyst layer (CL) was obtained using a dual beam Focused Ion Beam/Scanning Electron Microscope (FIB/SEM). Lower order statistical functions such as porosity and two point correlation functions calculated from the FIB/SEM data were used in the numerical reconstruction of a multi-phase CL domain. A ‘carbon-sphere-based’ initial seed structure, when optimized by simulated annealing, produced a structure for which the two point correlation function matched with the FIB/SEM data with very high fidelity. The reconstructed CL domain with its phase-resolved nano-structure was used to perform numerical simulation and predict effective transport properties. The coupled partial differential equations governing the reactive transport of charged and neutral species in the CL were discretized based on the finite volume method and solved implicitly using parallel computing. The simulated values of the effective oxygen and water vapor diffusivity, proton and electron conductivity, and thermal conductivity were in reasonable agreement with measured data reported in the literature. A parametric study was performed to investigate the impact of inaccessible pores–a feature that is not resolved experimentally. The simulations indicate that the properties most sensitive to the presence of inaccessible pores are the effective O2 and H2O diffusivities and the effective proton conductivity.

Characterization of accessible and inaccessible pores in microporous carbons by a combination of adsorption and small angle neutron scattering

We determine the pore size distribution for five activated carbons (comprising carbide derived as well as commercial activated carbon samples) by the interpretation of experimental small angle neutron scattering (SANS) intensity profiles, based on the primary assumption of an infinitely dilute solution of hollow spherical particles. The interpretation yields the pore size distribution of the carbon samples that have predominantly micropore populations (size <20Å), but not for carbons which have significant mesopore populations of sizes up to 48Å and high mass fractal degrees. The pore size distribution (PSD) results based on SANS data reveal significant populations of micropores of size <6.1Å, and mesopores of size >20Å, which are not present in the PSD results based on adsorption isotherms of either Ar at 87K or CO2 273K. This inaccessible porosity becomes accessible to CO2 and Ar on heat treatment, leading to increase in the adsorption based pore volume. However, the surface area does not commensurately increase, indicating the inaccessible microporosity to predominantly comprise surface defects and roughness that are removed on heat treatment or activation. This finding sheds the light onto the evolution of porosity of activated carbons during gasification or post synthesis-treatment.

Combined on-line differential mobility and particle mass analysis for determination of size resolved particle density and microstructure evolution

A new application of on-line tandem differential mobility-particle mass analysis (DMA-APM) is used to obtain the density distribution, detect the reaction evolution, and investigate the mechanism of porous particle formation. The expected uncertainty of the density measurement is within 5%. The method has several advantages over absorption methods such as BET in which pore model is required. The methodology also enables a size resolved measurement to understand how particle porosity varies over a given particle population. The DMA-APM method is materials independent, and can measure the density even in a particle with inaccessible pores. In this paper we demonstrate the method during the synthesis of mesoporous iron oxide and copper oxide. For example in the formation of iron oxide we found that small particles (∼50nm) in the size distribution had a higher density (∼2.6g/cm3) relative to larger 130nm particles with a measured density of 2.2g/cm3. Syntheses at higher temperatures lead to high density particles which were also less size sensitive.

Pressure Transient Analysis of Polymer Injection Wells

Polymer solution is known as non-Newtonian Fluid. Hence, when a well is injected by polymer solution, the well test data analysis using Newtonian fluid flow model will be erroneous. However, the analysis results usually were inaccurate when generalized non-Newtonian fluid model which considering polymer solution as power law fluid and taking no account of physical and chemical behaviors. These results clearly suggest the need for a study to come up with a new model considering both physical and chemical behaviors when polymer solution flowing in the reservoirs. At first, this study modified two parameter models: viscosity model and permeability decreasing coefficient model, all of them considering diffusion, conduction and IPV (inaccessible pore volume). Then, those models were applied to set up the new well testing model of a well located in an infinite reservoir. The log-log plots of the pressure and pressure derivatives have been prepared through numerical solutions. A further study has been done about the characteristics of the new type curves considering different parameters.

Small-angle neutron scattering characterization of the structure of nanoporous carbons for energy-related applications

We used small-angle neutron scattering (SANS) and neutron contrast variation to study the structure of four nanoporous carbons prepared by thermo-chemical etching of titanium carbide TiC in chlorine at 300, 400, 600, and 800 °C with pore diameters ranging between ∼4 and ∼11 Å. SANS patterns were obtained from dry samples and samples saturated with deuterium oxide (D 2O) in order to delineate origin of the power law scattering in the low Q domain as well as to evaluate pore accessibility for D 2O molecules. SANS cross section of all samples was fitted to Debye–Anderson–Brumberger (DAB), DAB–Kirste–Porod models as well as to the Guinier and modified Guinier formulae for cylindrical objects, which allowed for evaluating the radii of gyration as well as the radii and lengths of the pores under cylindrical shape approximation. SANS data from D 2O-saturated samples indicate that strong upturn in the low Q limit usually observed in the scattering patterns from microporous carbon powders is due to the scattering from outer surface of the powder particles. Micropores are only partially filled with D 2O molecules due to geometrical constraints and or partial hydrophobicity of the carbon matrix. Structural parameters of the dry carbons obtained using SANS are compared with the results of the gas sorption measurements and the values agree for carbide-derived carbons (CDCs) obtained at high chlorination temperatures (>600 °C). For lower chlorination temperatures, pore radii obtained from gas sorption overestimate the actual pore size as calculated from SANS for two reasons: inaccessible small pores are present and the model-dependent fitting based on density functional theory models assumes non-spherical pores, whereas SANS clearly indicates that the pore shape in microporous CDC obtained at low chlorination temperatures is nearly spherical.