Core Porosity Research Articles

Stoneley Wave Predicted Permeability and Electrofacies Correlation in the Bangestan Reservoir, Mansouri Oilfield, SW Iran

Reservoir characterization is one of the most important goals for the development of any oilfield. Determination of permeability and rock types are of prime importance to judge reservoir quality. In this research, Stoneley waves from dipole sonic tools were used in order to discover changes in permeability in the Bangestan reservoir, Mansouri oilfield. Index (tortuosity) could be estimated by Stoneley waves. After comparing the permeability resulting from Stoneley waves, cores and the Timur method, it was concluded that all the three permeabilities were very similar. The core porosity and effective porosity from the analysis of well logs were found to match as well. Electrofacies (EF) method, as a clustering method, was utilized to find rock types in order to define reservoir and non-reservoir zones. Simultaneous with EF clustering, gamma ray, neutron porosity, density, sonic, water saturation and porosity (PHIE) data from 78 wells were also considered and interpreted. Nine clusters were defined as a result of the analysis, being reduced to only four clusters after applying PC (capillary pressure) data. Among the four clusters, clusters 1 and 2 contained more vuggy pores than the others. Fracture abundance and solution seams were observed more frequently in EF-3 as compared to other EFs. Based on the matrix type, Archie porosity classification types I and III were recognized. The pore sizes in EFs-1 and 2 were mostly of the B type while in EF-3, it was A type. The EFs generated and determined by Stoneley waves and the well log data were also compared, showing a good correlation.

Long-term efficient deammonification operation with PVA/alginate carrier modified by foaming agent

This study investigated long-term deammonification operation, of 400 days, utilizing PVA/alginate carriers prepared with the addition of foaming agent (FA) adjusted from 0 to 1.2% (F-0 to F-1.2). FTIR spectra showed variations in the extent of crosslinking in the surface and the core areas of carriers. FA addition improved the already low crosslinking in the core areas and porosity in the surface areas, yielding higher endurance to internally produced gas. In the start-up period of continuous test, FA addition favored deammonification bacteria over denitrifiers. Increasing the FA decreased the extent and duration of heterotrophic denitrification that was superseded by deammonification after 30 d of operation. After 100 d, F-0.6 had the highest deammonification to denitrification ratio and gave a nitrogen removal rate (NRR) of 3.2 kg N.m−3.d−1 at 317 d of operation. Also, the 16S rRNA gene concentration of the deammonification bacteria was highest in F-0.6, which corresponded with the specific anammox activity (SAA) results. Overall, the improved PVA/alginate carriers gave higher SAA and deammonification bacteria concentration resulting in a stable long-term deammonification operation with high NRR.

Microstructures and performance of CaO-based ceramic cores with different particle size distributions for investment casting

A series of calcium-based ceramic cores for casting titanium alloy were prepared by mixing different amounts of coarse and fine powders through injection molding. The effects of particle size on the microstructures and properties of the ceramic cores were investigated using quantitative and statistical analysis methods. It is found that the shrinkage and room-temperature strength of the ceramic cores were enhanced as increasing the contents of fine particles. Moreover, the creep resistance of the ceramic cores increased initially and then decreased. The increase in the fine particle content of the cores reduced the number and mean diameter of pores after sintering. The grain boundary density decreased firstly and then increased. The flexural strength of the ceramic cores at room temperature decreased with increasing porosity of ceramic cores, whereas the creep resistance increased with decreasing grain boundary density. A core exhibiting the optimal property was obtained when mixing 65 wt% of coarse powders (75–150 μm) and 35 wt% of fine powders (25–48 μm).

Alam El Bueib reservoir characterization, Tut oil field, North Western Desert, Egypt

An integrated petrophysical well log and core data analysis of the Alam El Bueib-3D (AEB-3D) and Alam El Bueib-3E (AEB-3E) reservoirs, Tut oil field, North Western Desert, Egypt, allows the evaluation of those parameters critical to their reservoir characterization. The determined reservoir properties investigated are lithology, depositional paleoenvironments, shale volume, porosity, fluid saturation and net pay thickness. As the analysis of reservoir pressure is essential to specify the driving mechanisms that control the behavior of fluids within reservoirs, pressure analysis identified the Alam El Bueib-3D reservoir to be partial water drive and Alam El Bueib-3E to be an active water drive. In addition, the pressure analysis identified two additional hydrocarbon-bearing reservoirs in the Alam El Bueib-3D. Stacking patterns of the Alam El Bueib-3D reservoirs are generally fining upward sequences reflecting fluvial to braided fluvial paleoenvironments. The Alam El Bueib-3E channel shows blocky patterns with sharp bases and tops diagnostic of distributary channels. Statistical analysis of core permeability and porosity values of the Alam El Bueib reservoirs indicate very good reservoir quality. Scatter diagrams of porosity values derived from core analysis for the AEB-3D and AEB-3E reservoirs reveal correlation coefficient (r) values of 0.93 and 0.64, respectively, indicating strong linear relationships. Plots of porosity values against permeability values also show strong linear relationships in all the reservoirs indicating that the AEB-3D and the AEB-3E are permeable and with strong pore communication. The permeability measurements indicate restricted reservoir heterogeneity as plots of vertical permeability values against horizontal permeability values exhibit linear trends. Altogether, the reservoir characterization of the Alam El Bueib reservoirs demonstrates their excellent potential for hydrocarbon production.

Co-extrusion of zirconia core-shell rods with controlled porosity in the core

A method for manufacturing bi-layered zirconia rods of core-shell geometry with a porous core and a dense shell has been developed. Core-shell rods were successfully prepared by thermoplastic co-extrusion of assembled feed rods composed of core and shell zirconia feedstocks. Rheological analysis and adjustment of the feedstock viscosities enabled co-extrusion of regular core-shell rods of uniform shell thickness. Tapioca starch was used as a pore-forming agent in the core feedstock. Binder removal and high temperature treatment had to be modified in order to safely remove the starch particles. Sintering analysis revealed constrained sintering of porous cores in the core-shell rods due to the rigid dense shell, which resulted in an increased porosity in the core. Defect-free core-shell rods with a core porosity of up to 40% and different thicknesses of the dense shell were prepared.

Data mining in the Dutch Oil and Gas Portal: a case study on the reservoir properties of the Volpriehausen Sandstone interval

Abstract This paper presents the results of a data mining exercise on core measurements and reports of the Triassic Lower Volpriehausen Sandstone Member (RBMVL) in The Netherlands. The availability of a large accurate online dataset via the Dutch Oil and Gas Portal (NLOG) enables the definition of general reservoir property trends on a regional–subregional scale. Accurately defined trends are capable of restricting the uncertainty range of key parameters in exploration studies (e.g. porosity and permeability), and thus of reducing risk. Plotting core porosity v. core permeability resulted in a curved data cloud on a log-normal plot. Although porosity–permeability relationships are often defined by straight lines, the dataset in this study shows that a curved relationship results in a better fit with permeability measurements over the entire porosity range. Two methods were applied to define a porosity–depth relationship for sandstones of the RBMVL. The results of both methods confirm, and enable quantification of, the well-known trend of decreasing porosity with depth. By assigning grain density attributes to the core measurements, the dependency of the porosity–depth relationship on sedimentary facies and diagenesis type/grade could be determined. This case study demonstrates the power of this free online dataset in understanding reservoir quality.

Hybrid porous‐core microstructure terahertz fibre with ultra‐low bending loss and low effective material loss

A hybrid porous-core microstructure optical fibre (MOF) is proposed and its guiding properties are characterised for efficient terahertz wave guiding. A numerical investigation using the finite element method showed that a hybrid-core MOF consisted of a diamond-shaped cell and the circular arrangement of air holes exhibited an extremely low-bending loss of 5.24 × 10−13 cm−1 for a bending radius of 1 cm and an operating frequency of 1.0 THz. The proposed fibre also showed a low effective material loss of 0.08 cm−1 at an optimised core porosity of 52%. Moreover, single mode propagation, dispersion and fabrication feasibility of the proposed MOF are discussed. Due to the excellent guiding properties, this MOF can be potentially used in THz imaging, sensing and flexible communication applications.

Uncertainty assessment of porosity and permeability by clustering algorithm and fuzzy arithmetic

A hybrid clustering-fuzzy arithmetic algorithm is here proposed, which uses cluster analysis to quantify porosity uncertainty, then the uncertainty is projected to the irreducible water saturation and permeability by the means of fuzzy arithmetic. The proposed method is applied to five wells of the carbonate Sarvak Formation, in an Iranian onshore oil-field. First, cluster analysis is applied to the porosity logs including neutron porosity, bulk density and sonic transit time. The uncertainty range of porosity is defined by the range of neutron porosity in each cluster. In order to estimate the core porosity, neutron porosity is calibrated to the core porosity in each cluster. Due to the average of error, the calibrated clustering-based porosity is at least 33% more accurate than the conventional methods. Based on the generalization ability of porosity estimators, a homogeneous porosity zone is determined northward. Irreducible water saturation, analyzed by the proposed method, has less overestimation, compared to the conventional evaluation of irreducible water saturation. Permeability fuzzy number is compatible with core tests, except in well S1, which is drilled in a location, compressed by two stress regimes (N-S and NW-SE). Two criteria are defined for validating the fuzzy numbers by core data: (i) Crit1 finds an average α-cut of core values; (ii) Crit2 finds the best α-cut to optimize uncertainty interval of the fuzzy number. The α > 0.90 is the most appropriate for porosity and permeability studies.

Facile synthesis of hollow Ni0.2Mn0.8O1.5 twin microspheres for electrochemical energy storage

Novel hollow Ni0.2Mn0.8O1.5 twin microspheres were synthesized through a facile solvothermal reaction followed by calcination. The prepared hollow twin microspheres were composed of a large number of aggregated nanoparticles, with many pores homogeneously distributed across the whole of the twin microspheres. Benefiting from such structural advantages, such as the void core and high porosity, the prepared hollow Ni0.2Mn0.8O1.5 twin microspheres, as an electrode for supercapacitors, exhibited remarkable electrochemical performance with a large specific capacitance (491 F g−1 at 0.5 A g−1), desirable rate capability (81% of capacity retention at 5 A g−1), and excellent cycling stability (94.6% of the initial capacity after 2000 cycles). Moreover, a fabricated asymmetric supercapacitor cell based on Ni0.2Mn0.8O1.5 and active carbon demonstrated an energy density of 19.5 Wh kg−1 at a power density of 799 W kg−1, suggesting a promising practical application for these microspheres in supercapacitors. Novel hollow Ni0.2Mn0.8O1.5 twin microspheres have been synthesized based on the oriented attachment and Ostwald ripening effects, demonstrating high energy density and power density for the promising application in energy storage devices.

Porosity Identification of Carbonate Core Reservoir Using Digital Rock Physics Method

Indonesia is an archipelago country so rich with coral reefs that are a major component of the carbonate rock constituents. Where as much as 40% of carbonate rocks in Indonesia is a hydrocarbon reservoir is still rarely done exploration. This is because conventional hydrocarbon exploration technology has not been able to provide detailed information about the physical quantities. Hydrocarbon exploration technologies currently leads on digital technology to know the physical quantities of a reservoir of more detail such as porosity. Porosity which is physical quantities related to the presence of hydrocarbons in the pores of rocks. Digital Rock Physics (DRP) is a digital image-based method as an alternative method to find the physical quantities of rock samples to make it more effective and efficient. This study aims to identify the physical quantity using the method of porosity of the DRP until obtaining porosity of rock core carbonate reservoir by analyzing the binary image of the two rock cores from the same reservoir but has different dimensions to find out the exact core rocks to analyze the value of porosity. Binary image obtained from a scanned image of a projection of rock that has been reconstructed to become the greyscale image and have gone through the process of thresholding. The results of this study showed that the method can identify the physical quantities of DRP porosity and non-damaging rock pore structure (non-destructive). Analysis of the porosity of the rock core with histogram variations performed (by adjustingting the histogram), using the otsu method of thresholding and pixel size of the image has high (5.343750 μm) used to analyze the value of porosity. The porosity values acquired for 18.040 and has precision 96.20%.

Diagenetic evolution and its implication for reservoir quality: a case study from the Eocene Es4 interval, Dongying Depression, Bohai Bay Basin, China

Petrographic analysis combined with thin section observation, fluid inclusions, burial history analysis, and core porosity and permeability, were used to determine diagenetic evolution and its effect on reservoir-quality of beach-bar sandstone reservoirs of Eocene Es4s interval in the Boxing sag, Bohai Bay Basin. Diagenesis is mainly characterized by strong compaction, undercompaction, cementation of carbonate, quartz, pyrite and clay minerals, dissolution of detrital grains and carbonate cements, lime-mud matrix recrystallization and hydrocarbon filling. Paragenetic sequence is determined as “early compaction / precipitation of calcite, dolomite and framboidal pyrite → dissolution of feldspar grains and early-formed carbonate cements/precipitation of quartz → hydrocarbon filling → precipitation of ferroan calcite and ankerite/lime-mud matrix recrystallization → dissolution of ferroan carbonate cements”. In the same diagenetic environment, diagenetic processes for different lithofacies significantly varied and subsequently resulted in great heterogeneity for reservoir quality during progressive burial. Lithofacies for both bar body and beach edge subfacies which are far from sandstone-mudstone contacts, are well sorted and have a strong ability to resist compaction. Abundant primary and secondary porosities are well developed because of modifications by acidic dissolution and hydrocarbon filling. The present physical properties are relatively well and numerous oil beds are developed through shallow to deep burial depth. Lithofacies for both bar body and beach edge subfacies which are adjacent to sandstone-mudstone contacts, are typically characterized by extensive cementation of calcite and dolomite. The present physical properties are bad and dry beds are extensively developed for sandstone reservoirs in both bar body and beach edge subfacies which are adjacent to sandstone-mudstone contacts. Lithofacies for both bar edge and beach mat subfacies were deposited in weak hydrodynamic conditions with high contents of limemud matrix. The reservoir porosity decreases continually due to strong compaction and weak dissolution. The present physical properties are extremely poor and dry beds are commonly developed through shallow to deep burial except for minor oil beds developed in the shallow burial.

Predicting the Porosity of Natural Fractures in Tight Reservoirs

Predicting the fracture porosity of tight fracture reservoirs represents a difficult problem for log interpretation, although studying conventional log responses of tight fracture reservoirs provides helpful insights. Comparisons and analyses of the log response characteristics of the natural fracture zone of a tight reservoir are performed, and the results indicate that the acoustic (AC) and density (DEN) data are highly sensitive to fractures. First, the log response of the AC and DEN data are sensitive to tight fracture reservoirs, and differences in the AC and DEN log responses are obvious. Second, based on these differences, a model for calculating the fracture porosity is constructed, and an improved Willie difference method for the AC and DEN responses is proposed to calculate the fracture porosity. Finally, we apply the methodology to a case study of a tight reservoir in the Sichuan Basin, China, and then calculate the AC–DEN correlation coefficient and fracture porosity. The calculated fracture porosity is consistent with the fracture porosity from the full borehole micro-resistivity imaging results and core porosity. The results indicate that the method is applicable for predicting the porosity of fractures.

Gas permeability measurements from pressure pulse decay laboratory data using pseudo-pressure and pseudo-time transformations

This paper presents a pseudo-pressure and pseudo-time straight-line approach to interpret laboratory pulse decay data in order to estimate rock core permeability using gas as the pore fluid. The implementation of the straight-line approach provides a practical method to estimate gas permeability from experimental data, as long as changes in gas viscosity and compressibility are negligible. On the other hand, pseudo-pressure and pseudo-time allow the transformation of the compressible flow equation from its highly nonlinear form to a quasi-linear partial differential equation, where changes in gas viscosity, gas compressibility and compressibility factor are accounted for. The purpose of this work is to combine both, pseudo-functions and the straight-line approach to estimate gas permeability from pressure pulse laboratory data with a more rigorous treatment of gas properties. Five pulse decay experiments were performed in Marcellus shale cores at pore pressures ranging from 130 to 700 psi in a triaxial cell to estimate permeability and porosity of ultra-low permeability cores. The experiments were made in an increasing order of equilibration pressure starting from 130 until 700 psi, and vertical and radial stresses kept constant at 1500 psi. Permeability estimates were compared against the P2-approach to show the validity of the proposed method at low gas pressures.

Thermo-Fluidic Comparison between Sandwich Panels with Tetrahedral Lattice Cores Fabricated by Casting and Metal Sheet Folding

This numerical study compares single-phase forced convective heat transfer between two sandwich panels with tetrahedral metallic lattice cores separately fabricated by investment casting and the more cost-effective metal sheet folding method. The numerical model is validated against available experimental data. For a given Reynolds number and core porosity, the results reveal that the brazed sandwich outperforms the casted sandwich, exhibiting a 13% to 16% higher Nusselt number. Bigger vertexes and more evident blockage of mainstream by the ligaments are found to intensify the horseshoe vortex and the counter-rotating vortex pair upstream and downstream of each vertex. Relative to the casted sandwich panel, therefore, endwall heat transfer is enhanced by 22% to 27%, while similar heat transfer is achieved on the ligaments. It is also found that, for a given Reynolds number, the brazed sandwich induces a 1.6 to 1.7 times higher pressure drop relative to the casted sandwich due to more severe flow separation caused by the sharp edges of the rectangular ligaments. Finally, for a given pumping power, both sandwiches provide a similar heat transfer performance. Given that the brazed sandwich is more cost-effective and easier to fabricate than the casted one, the former may be superior from an engineering application point of view.

Petrographic and Petrophysical Characteristics of the Upper Devonian Three Forks Formation, Southern Nesson Anticline, North Dakota

Petrographic and Petrophysical Characteristics of the Upper Devonian Three Forks Formation, Southern Nesson Anticline, North Dakota

The influence of climate on early and burial diagenesis of Triassic and Jurassic sandstones from the Norwegian–Danish Basin

AbstractClimate changes preserved in sandstones are documented by comparing the sediment composition and early diagenetic changes in sandstones deposited during arid to semi‐arid conditions, the Skagerrak Formation, with sandstones of the Gassum Formation deposited in a humid well‐vegetated environment. The study area covers the easternmost part of the Norwegian–Danish Basin, for which the Fennoscandian Shield functioned as sediment source area. The depositional environments of the formations, their distribution and burial depths are well‐constrained, facilitating a comprehensive petrographical and geochemical study complemented by porosity and permeability measurements of cores widely distributed in the basin (1700 to 5900 m burial depth). The Skagerrak Formation had an immature composition with more abundant feldspar, rock fragments and a larger variability in the heavy mineral assemblage when compared to the Gassum Formation, which was characterized by quartz and more stable heavy minerals. The arid to semi‐arid climate led to early oxidizing conditions under which abundant iron‐oxide/hydroxide coatings formed, while the evaporative processes occasionally resulted in caliche and gypsum precipitation. Under the humid climate, kaolinite precipitated due to leaching of feldspar and mica, and the abundant organic matter caused reducing conditions, which led to other Fe‐rich phases, i.e. pyrite, Fe‐chlorite and siderite. The inherited early diagenetic pore fluids and mineral assemblage also affect the mineral changes occurring during deeper burial, so dolomite preferentially formed in the sandstones deposited in an arid environment, while ankerite characterizes sandstones deposited under humid conditions. In addition to climate‐induced burial diagenetic changes, there are also temperature‐dependent phases, such as illite and quartz cement. Despite the same sediment source area remaining active during the entire period, the sediments that reached the Norwegian–Danish Basin were immature during the arid interval, although mature during the humid period. This has implications for provenance investigations as well as diagenetic investigations of sandstone reservoir quality.

Diagenesis and its controls on reservoir properties and hydrocarbon potential in tight sandstone: a case study from the Upper Triassic Chang 7 oil group of Yanchang Formation, Ordos Basin, China

The sandstones in the Chang 7 oil group are typically recognized as unconventional tight clastic rock reservoirs. These sandstones are fine-grained and have low permeability and porosity and low textural and compositional maturity. In the present study, optical microscopy, SEM, cathodoluminescence, and wireline log, core analysis permeability and porosity, and production test data are applied to analyze the diagenesis and its controls on hydrocarbon potential in these tight sandstones. The results indicate that the sedimentary environment and diagenesis controlled the physical properties of the reservoir. Three different diagenesis processes were likely occurred in these sandstones. Early strong carbonate cementation is a key factor for other subsequent alterations and the final reservoir properties. The sandstones dominated by dissolution and compaction have more capacity for hydrocarbon preservation.

Probabilistic analysis and comparison of stress-dependent rock physics models

A rock physics model attempts to account for the nonlinear stress dependence of seismic velocity by relating changes in stress and strain to changes in seismic velocity and anisotropy. Understanding and being able to model this relationship is crucial for any time-lapse geophysical or geohazard modelling scenario. In this study, we take a number of commonly used rock physics models and assess their behaviour and stability when applied to stress versus velocity measurements of a large (dry) core data set of different lithologies. We invert and calibrate each model and present a database of models for over 400 core samples. The results of which provide a useful tool for setting a priori parameter constraints for future model inversions. We observe that some models assume an increase in VP/VS ratio (hence Poisson’s ratio) with stress. A trait not seen for every sample in our data set. We demonstrate that most model parameters are well constrained. However, third-order elasticity models become ill-posed when their equations are simplified for an isotropic rock. We also find that third-order elasticity models are limited by their approximation of an exponential relationship via functions that lack an exponential term. We also argue that all models are difficult to parametrize without the availability of core data. Therefore, we derive simple relationships between model parameters, core porosity and clay content. We observe that these relationship are suitable for estimating seismic velocities of rock but poor when comes to predicting changes related to effective stress. The findings of this study emphasize the need for improvement to models if quantitatively accurate predictions of time-lapse velocity and anisotropy are to be made. Certain models appear to better fit velocity depth log data than velocity–stress core data. Thus, there is evidence to suggest a limitation in core data as a representation of the stress dependence of the subsurface. The differences in the stress dependence of the subsurface compared to that measured under laboratory conditions could potentially be significant. Although potentially difficult to investigate, its importance is of great significance if we wish to accurately interpret the stress dependence of subsurface seismic velocities.

Tight rock wettability and its relationship to other petrophysical properties: A Montney case study

Understanding and modelling the wettability of tight rocks is essential for designing fracturing and treatment fluids. In this paper, we measure and analyze spontaneous imbibition of water and oil into five twin core plugs drilled from the cores of a well drilled in the Montney Formation, an unconventional oil and gas play in the Western Canadian Sedimentary Basin. We characterize the samples by measuring the mineralogy using XRD (x-ray diffraction), total organic carbon content, porosity, and permeability. Interestingly, the equilibrated water uptake of the five samples is similar, while, their oil uptake increases by increasing the core porosity and permeability. We define two wetta-bility indices for the oil phase based on the slope and equilibrium values of water and oil imbibition curves. Both indices increase by increasing porosity and permeability, with the slope affinity index showing a stronger correlation. This observation suggests that part of the pore network has a stronger affinity to oil than to water. We also observe that the two indices decrease by increasing neutron porosity and gamma ray parameters measured by wireline logging tools. The samples with higher gamma ray and neutron porosity are expected to have greater clay content, and thus less effective porosity and permeability.

Low-loss polarization-maintaining THz photonic crystal fiber with a triple-hole core.

In this paper, we report a novel low-loss and polarization-maintaining terahertz (THz) photonic crystal fiber with a triple-hole unit inside the core. The properties of birefringence, effective material loss, confinement loss, bending loss, power fraction, dispersion, and single-mode condition are analyzed in detail by using the finite element methods. Simulation results show that high birefringence at a level of 10-2 can be achieved by simply reducing the diameter of one air hole of the triple-hole core. And low effective material loss down to 30% of its bulk material loss can be achieved in our interested band around 3 THz, due to the high core porosity of the designed triple-hole core. Moreover, this design dramatically facilitates the fabrication process, because of the typical hexagonal structure with all circular air holes and avoiding the troublesome multiple sub-wavelength air holes in the core area. The results reveal that this proposal has potential for efficient THz transmission and other functional applications.