Formation Resistivity Factor Research Articles

Effect of the mineralogical composition on the petrophysical behavior of the amygdaloidal and vesicular basalt of Wadi Wizr, Eastern Desert, Egypt

This paper gives an account of the petrophysical characteristics and the petrographical descriptions of Tertiary vesicular and amygdaloidal olivine basalt flows from Wadi Wizr in the central Eastern Desert of Egypt. The petrographical studies indicated that the studied vesicular basalts are rich in calcic-plagioclase, augite and olivine in addition to numerous amounts of fine opaque minerals and vesicles filled with carbonate and quartz amygdales. The degree of oxidation and alteration of magnetite and ilmenite are discussed in detail. Petrophysically, the studied samples can be grouped into two main groups; the first group includes amygdaloidal basalts and the second group consists of vesicular basalts. The vesicular group (the permeable one) is characterized by fair to very good porosity (∅), good permeability (k), very low true formation resistivity factor (F) and contain micro to ultra micropores. On the other hand, the amygdaloidal basalt group (impermeable group) is characterized by very low storage capacity properties, fair porosity, negligible permeability, medium to high true formation resistivity factor and ultra micropores. The mercury injection capillary pressure technique (MICP) indicates that the pore throats of the studied vesicular samples have a binomial distribution (rank IV), while that of the amygdaloidal samples have a trinomial distribution (rank V). It has been found in this study that the petrophysical behavior of basalts is dependent on the degree of oxidation and alteration; and in particular on the rate of cooling and oxidation of the opaque minerals which caused filling in the primarily produced vesicles by low temperature secondary minerals.

Formation factor in Bentheimer and Fontainebleau sandstones: Theory compared with pore-scale numerical simulations

Accurate quantification of formation resistivity factor F (also called formation factor) provides useful insight into connectivity and pore space topology in fully saturated porous media. In particular the formation factor has been extensively used to estimate permeability in reservoir rocks. One of the widely applied models to estimate F is Archie's law (F=ϕ−m in which ϕ is total porosity and m is cementation exponent) that is known to be valid in rocks with negligible clay content, such as clean sandstones. In this study we compare formation factors determined by percolation and effective-medium theories as well as Archie's law with numerical simulations of electrical resistivity on digital rock models. These digital models represent Bentheimer and Fontainebleau sandstones and are derived either by reconstruction or directly from micro-tomographic images. Results show that the universal quadratic power law from percolation theory accurately estimates the calculated formation factor values in network models over the entire range of porosity. However, it crosses over to the linear scaling from the effective-medium approximation at the porosity of 0.75 in grid models. We also show that the effect of critical porosity, disregarded in Archie's law, is nontrivial, and the Archie model inaccurately estimates the formation factor in low-porosity homogeneous sandstones.

A model for calculating the formation resistivity factor in low and middle porosity sandstone formations considering the effect of pore geometry

Pore geometry is one of the main factors that may lead Archie's equation inaccurate in low and middle porosity sandstone formations. In order to build a robust relationship between the formation resistivity factor and the porosity for the low and middle porosity sandstone formations, we presented a pore-throat model (PT model) that considered the effect of pore geometry. The PT model is an effective medium model that treats the pore space as a series of a spherical pore and two throats. The spherical pore can be described by the pore radius, and the throat can be described by the ratio of the pore radius over the throat radius (the pore-throat radius ratio) and the tortuosity. We collected seventy-two core plugs from the typical low and middle porosity sandstone formation in the Ordos Basin in China, having porosity ranging from about 3–20%. Forty-seven of the samples with low clay content were chosen for laboratory resistivity measurements to validate the PT model. The core experiments and the application to the well logging interpretation indicated that the PT model provides a more convincing formation resistivity factor, while the formation resistivity factor calculated using Archie's equation is larger than that measured in the lab, especially when the porosity is relatively low. The tortuosity used in the PT model was calculated by a theoretical method and verified by a thin section analysis method. The PT model enhances the understanding of the effects of the pore geometry on the relationship of the formation resistivity factor and the porosity.

Using Least Square for Develop a New Formation Resistivity Factor Correlation and Relationship between the Salinity and the Corrosion

Formation resistivity factor (Fr),introduced by Archie , is an important parameter for electric log interpretation .It is defined as the resistivity of rock fully saturated with brine (Ro) divided by the resistivity of brine (Rw). This factor is function of porosity, resistivity, tortuosity and cementation factor, which are consequently affected also by particle size and degree of compaction .Formation resistivity factor is usually determined experimentally or by using empirical approach. During the present paper, we try to develop a new formation resistivity factor (Fr) correlation based on statistical methods, Least square, by taking into account different parameter such as brine salinity, particle size and degree of compaction. In addition, this study aims to determine the relationship between salinity and corrosion.

Formation evaluation using conventional and special core analyses: Belayim Formation as a case study, Gulf of Suez, Egypt

The present study aims to throw the light on the importance of the conventional and special core analyses in the integration with the petrographical studies for the formation evaluation of the reservoir rocks. The petrographical studies include the microfacies analysis and studying the diagenetic factors that predominated during the diagenetic history of the Belayim rock sequence in the study area. Two zones of Belayim Formation in the onshore Belayim oil field (the upper level (zone IIA) represents Hammam Faraun member and the lower one (zone IV) represents Sidri member) were studied. The measured routine core analyses data includes porosity (helium and summation fluids), density (grain and bulk), permeability (horizontal and vertical) and fluid saturations (oil and water). In addition, the formation resistivity factor, irreducible water saturation, Archie’s parameters (a, m and n), liquid permeability, relative permeability, wettability, the pore throat distribution, as well as the porosity and permeability measured under high pressure were measured as a special core analyses procedure. From the integration of the aforementioned petrographical and petrophysical studies, the Belayim Formation can be discriminated into three petrophysical facies (Facies-1, Facies-2 and Facies-3) described petrographically as (1) Facies-1 (argillaceous subfeldspathic arenite microfacies), (2) Facies-2 (siliceous quartz arenite microfacies) and (3) Facies-3 (dolomitic sublithic arenite microfacies). The petrophysical Facies-2 (siliceous microfacies) is characterized by the best reservoir properties (rank III, very good average porosity, very good permeability, fair to very good reservoir quality index (RQI) and relatively poor to good flow zone indicator (FZI), neutral to moderately oil wet and more than 75% macropores and mesopores). On the other side, samples of the petrophysical Facies-1 (argillaceous microfacies) have the lowest reservoir potential (rank VI, poor average porosity, poor to fair permeability, poor to impervious RQI and relatively poor to fair FZI and more than 50% micropores and nanopores). Therefore, it is recommended to use the conventional and special core analyses data in the integration with the petrographical studies as a good procedure for the formation evaluation and discrimination of the reservoir sequence into different flow units.

The use of artificial neural network to predict correlation of cementation factor to petrophysical properties in Yamamma formation

The cementation factor has specific effects on petrophysical properties in porous media. The accurate determination of this factor gives reliable saturation results and consequently hydrocarbon reserve calculations. Nasiriya oil field is the studied field, which is one of the giant oil fields in the south of Iraq. Five wells from NS-1 to NS-5 were studied wells. The study was made across Yamamma carbonate formation with depth interval from 3,156 m to 3,416 m. Environmental corrections had been made as per SLB charts 2005. Permeability, porosity, resistivity formation factor and cementation factor had been calculated using interactive petrophysical software. In this study, porosity, permeability and resistivity formation factor relationships to cementation factor were proposed using the artificial neural network model. This methodology provided very efficient performance and excellent prediction of cementation factor value with less than 10−4 mean square error (MSE). The results of this model showed that the cementation factor values ranged between 1.95 and 2.13. [Received: August 12, 2015; Accepted August 3, 2016]

Comment on: “Feasibility of electromagnetic methods to detect and image steam-assisted gravity drainage steam chambers” (S. G. R. Devriese and D. W. Oldenburg, Geophysics, 81, no. 4, E227–E244)

Devriese and Oldenburg (2016), abbreviated below as DO16, propose a synthetic case study aimed at demonstrating the advantages and limitations in using galvanometric- and induction-based resistivity methods to monitor the growth of steam-assisted gravity drainage steam chambers. They first simulate a simplistic case and then they apply their strategy to a more realistic geometry inspired from a case study operated by Imperial Oil. The geophysical work is based on a set of petrophysical relationships and classical regularization methods for the inverse problem. The petrophysical model used to connect the underlying physics of the problem to the geophysical observable is far from being correct, raising some questions regarding the validity of the input parameters, hence conclusions reached in the paper. The choices for the regularizers and inversion schemes are also problematic as discussed below. I start first with the petrophysical model used in DO16. Despite the claims made in DO16, equation 11 is not Archie’s law for the resistivity formation factor and cannot be found in the seminal paper of Archie (1942). It is a mix of the first and second Archie’s law with a tortuosity added to the equation without any justification. Archie’s law is an equation connecting the intrinsic formation factor to the porosity through a power law relationship. The formation factor can also be defined as the ratio of the tortuosity by the connected porosity (Pride, 1994). In their equation 11, we have both factors used concomitantly, which is not correct (see the discussion in Appendix A of Revil, 2013). Then, DO16 propose to use a Waxman and Smits (1968) equation, see their equations 12–15, to take into account the surface conductivity. Their form of the Waxman and Smits equation suffers four problems:

Application of Well Log Analysis to Assess the Petrophysical Parameters of the Early Eocene Sui Main Limestone (SML) in Kharnhak-1 Well, Middle Indus Basin, Pakistan

The petrophysical analysis of the early Eocene Sui Main Limestone (SML) has been conducted in Kharnhak-1 well for the prospect of the hydrocarbon exploration of the Khairpur-Jacobabad High, Middle Indus Basin, Pakistan. The petrophysical analysis of SML is carried out on the basis of well logs including gamma ray, spontaneous potential, resistivity, neutron, and density logs. These analyses lead to interpreting the vertical distribution of porosity and permeability in order to measure the reservoir potential of the SML. The Archie equation was used to assess the petrophysical characteristics. The SML has good porosity and poor permeability with positive correlation coefficient between the two parameters. The average volume of shale is 18%. The log signature of SML shows dominance of carbonates (limestone). The reservoir quality of the SML in Kharnhak-1 well is such that it is 77% water saturated. The porosity (x) varies inversely with formation resistivity factor (F) and compressional wave velocity (Vp). However, F and Vp are directly related with each other. Thus, the electric and elastic properties of the carbonate rocks can be influenced by postdepositional alterations, which include porosity enhancement and reduction processes respectively.

Hydro/Engineering Geophysical Parameters and Design Response Spectrum for Sustainable Development in Ras Muhammed National Park, Sinai

The Egyptian government is preparing a sustainable development master plan for the Ras Muhammed National Park (RMNP), south Sinai. Noteworthy, the scarcity of the freshwater resources and close proximity to the active seismic zones of the Gulf of Aqaba implicate geophysical investigations for the fresh groundwater aquifers and construct a design response spectrum, respectively. Accordingly, 14 VESs, hydro/engineering geophysical analysis, pumping tests, downhole seismic test, a design response spectrum for buildings, and borehole data were carried out in the study area. The unconfined freshwater aquifer was effectively depicted with true resistivities, thickness, and EC ranged from 56 to 135 Ω m, 11 to 112 m, and 1.4 to 7.1 mS/m, respectively. The Northeastern part was characterized by higher aquifer potentiality, where coarser grains size, highest thickness (112 m), high true resistivity (135 Ω m), groundwater flow (0.074 m3/day), tortuosity (1.293–1.312), formation resistivity factor (4.1–4.6), and storativity (0.281–0.276). An increase in pumping rate was accompanied by an increase in well loss, increase in aquifer losses, decrease in well specific capacity, and decrease in well efficiency. Design response spectrum prognosticated the short buildings (<7 floors) in RMNP to be suffering from a high peak horizontal acceleration and shear forces for acceleration between 0.25 and 0.35 g. Therefore, appropriate detailing of shear reinforcement is indispensable to reduce the risk of structural damages at RMNP.

Reservoir characterization of the Lower Abu Madi Formation using core analysis data: El-Wastani gas field, Egypt

The Messinian (Upper Miocene) sandstones of the Lower Abu Madi unit are the main reservoirs of the El-Wastani (EW) gas field, located in the onshore Nile Delta of Egypt. Reservoir quality is highly variable and represents the major risk in locating new delineation and development wells in the field. Four lithofacies (F1, F2, F3 and F4) are characterized based on textural attributes and sedimentary structures. Facies F4, which is a medium to coarse-grained fluvial channel sandstone, exhibits the best reservoir rock quality. Four hydraulic flow units (HFU 1 through HFU 4) were delineated in the studied wells with flow zone index (FZI) values indicative of a broad range of hydraulic properties. The cementation factor (m) value, was calculated from the inverse relationship between porosity and formation factor for EW-4 and EW-6 wells, agrees with the published values of clean sandstone reservoirs. The results of grain density analyses is close to the published value of grain density of quartz, and also supported by the results of petrographic study, where quartz is the dominant framework mineral. Generally, both the permeability and porosity can be linked to the two derived electrical properties (formation resistivity factor and electrical tortuosity) in the clastic reservoirs of the Lower Abu Madi unit. This correlation is particularly evident in the western and central parts of the study area at EW-4 and EW-6 wells, where facies F4 is dominant.

Geoelectrohydraulic parameters of shallow sandy aquifer in Itu, Akwa Ibom State (Nigeria) using geoelectric and hydrogeological measurements

Knowledge of geoelectrohydraulic parameters is paramount in the management of groundwater resource and the design and construction of safe engineering structures. Results obtained from integrated borehole-constrained geophysical analyses and interpretations, in situ measurements on water samples and laboratory analyses of aquifer units were employed in estimating the basic geoelectrohydraulic parameters such as formation factor, porosity, tortuosity, coefficient of permeability, bulk and interface conductivities. Other parameters estimated are Dar-Zarrouk parameters and transmissivities. The application of empirical and semi-empirical models in the analyses of sixteen evenly spread resistivity and hydrogeological data of sixteen nearby aquifer repositories measured in laboratory were combined with the results of in situ measurements of water samples to obtain the geoelectrohydraulic properties. The ranges of results obtained and their variations established through computations and graphical illustrations show goodness of fit when compared with other ranges and variations documented in literatures. From the results, the upper hydrogeological units have bulk resistivity range of 804–6001Ωm with mean value of 4118Ωm. The range of water resistivity and the mean are respectively 21.9–612.0Ωm and 237.7Ωm. Formation resistivity factor ranges from 9.8 to 36.7 with an average value of 21.6. The estimated range and mean values of porosity were 16.7–29.69% and 21.8%. The tortuosity values range from 1.79 to 2.48 with a mean value of 2.11. The hydraulic conductivity values of the aquifer units gave a range spanning between 3.03×10−5 (2.6) and 2.38×10−4m/s (20.60m/day) with an average value of 7.46×10−5m/s (6.45m/day). The economic aquifers have thicknesses ranging from 27.9 to 103.0m and a mean value of 63.1m. The range and the mean values of Dar-Zarrouk parameters are 9.0×10−3–3.5×10−2Ω−1 and 1.8×10−2Ω−1 for longitudinal conductance and 22,432–565,882Ωm2 and 28,6393Ωm2 for transverse resistance respectively. The transmissivity also lies between 73 and 1186m2/day with a mean value of 672.0m2/day. The deduced parameters can be used as the physical basis for predicting groundwater flow and a guide to designing geofluid flow modelling programmes in the saturated subsurface of the study area. The estimated models and spatial spread of parameters from data processing are promising and suitable for use in contaminant migration modelling. They can also be used to improve the quality of existing models in the study area.

Integrated petrographical and petrophysical studies of some Eocene carbonate rocks, Southwest Sinai, Egypt

The present study deals with the effect of petrographical aspects on the petrophysical properties of the Eocene rocks, which are represented by Thebes, Samalut, Darat and Tanka formations in Southwest Sinai, Egypt.The studied diagenetic factors have an important role to enhance and/or reduce the pore volume and governing the petrophysical behavior. The cementation and neomorphism are the main porosity-reducing factors, whereas dissolution and leaching out as well as the fossil content are the main porosity-enhancing factors.The petrophysical behavior of the studied facies has been outlined by measuring rock porosity, density, permeability, and electrical resistivity. The reservoir quality index (RQI) reveals that, the petrophysical features of the studied facies are consistent with the petrographical characteristics indicating bad reservoir properties for Thebes, Samalut, Darat and Tanka formations in the nearby subsurface extensions. Studying the petrophysical behavior indicates that, both permeability and formation resistivity factor are mostly dependent on the effective porosity and to some extent on the electric tortuosity.

Impacts of the pore- and petro-fabrics on porosity exponent and lithology factor of Archie’s equation for carbonate rocks

Archie’s parameters, including the tortuosity factor ‘a’ and the porosity exponent ‘m’, are important parameters controlling the formation resistivity factor–porosity relationship. Though, they are among the most important parameters, they are still a matter of controversy due to their dependence on many geological factors. They are not constant values, but vary greatly from facies to facies and from sub-facies to another. So, a considerable error would be assigned when the Archie’s parameters are assumed to be constant values.The present study is a trial to assign the identity of Archie’s parameters and their controlling factors. Based on the petrographical and petrophysical study for 261 carbonate core samples (representing Risan Aneiza, Halal, Bir Maghara, Rajabia and Masajid Formations, in Sinai Peninsula in Egypt), the studied samples can be grouped into three major facies types which are further discriminated into ten sub-facies; each one has its diagnostic Archie’s parameters (1.06⩽‘a’⩽8.76, and 1.19⩽‘m’⩽2.67). Petrographically, the present samples are mostly characterized by intercrystalline pore spaces, and sometimes other pore types as vuggy and vuggy channels are assigned. The closed pore spaces are assigned also, but with no effect on the conductivity properties of the studied rocks.From the present, it is achieved that, the lithology factor ‘a’ for the carbonate rocks is dependent mostly on the permeability and formation factor, as an indication for the pore channels tortuosity, as well as the porosity and mineralogy; whereas the porosity exponent ‘m’ is dependent mostly on the porosity types and values, as well as permeability and formation factor. The pore and grain elongations are other factors controlling the Archie’s parameters.In other words, the porosity exponent ‘m’, is dependent mostly on the pore fabric, whereas the tortuosity factor ‘lithology factor’ is dependent mostly on the petro-fabric, as well as the pore fabric. Dependence of Archie’s parameters on the same factors, but with varying behaviors, can be explained by an inverse proportional relationship assigned between ‘a’ and ‘m’ (r=−0.93).

The effect of a variable pore radius on formation resistivity factor

Formation resistivity factor F was introduced as the ratio of the resistivity of a rock fully saturated with conductive water to the resistivity of the conductive water based on results of laboratory measurements. It was also found that the formation factor is a function of the type and character of a formation and is related to porosity by a relationship including an exponent m. For model calculations of the formation factor, capillary channel models describing a straight tube with a constant circular cross-sectional area are frequently used. However, the pore channel radius is not constant in natural rocks.A modified capillary model that describes a straight pore channel with a radius varying between its two extreme values rt (pore throat) and rb (pore body) is presented. The proposed model can therefore explain the effect of pore shape upon formation factor and porosity. In this case, exponent m is controlled by the porosity itself and the ratio rb/rt. Different rock types have a specific position in a plot of formation factor versus porosity including a forward calculated grid for varying ratio rb/rt. Sand and gravel are characterized by low ratios rb/rt of 2.5 to 4.5, while sandstones possess intermediate rb/rt of 5.0 to 20.0. Carbonates show the greatest variability with ratios of 1.0 to 40.0.This new approach can be used to derive the ratio rb/rt from a determination of porosity and formation factor and thus enhances the understanding of pore space geometries in different formation types, which is also of importance for hydraulic conductivity.

Geohydrodynamic properties of hydrogeological units in parts of Niger Delta, southern Nigeria

We used geophysical and laboratory techniques to study the geohydraulic properties of the geological units in the Niger Delta of southern Nigeria. Our main objective was to investigate the distribution of the geohydrodynamic parameters and to establish the interrelationships among them in the study area for effective characterisation of hydrogeological units. Measurements on the core samples aided in the estimation of effective porosities. The hydrogeological units’ bulk resistivities measured from 1-D resistivity data constrained by nearby boreholes and the formation pore-water resistivities measured in the laboratory were used in computing the hydrogeological unit formation factor resistivity. Integration of field and laboratory measurements in conjunction with regression analysis of the data led to the determination of the hydrodynamic coefficients of the hydrogeological units. The graphs and the contour maps generated from the data show the variations and the interrelationships among the parameters. A theoretical model for the porosity–resistivity formation factor relation which conforms to Dakhnov’s formulation, obtained for similar sediment with different grain sizes in another geological province has been developed based on the measured data. A good approximation with error of the mean square of 2.48 and standard deviation of 1.5 was obtained between the experimental aquifer formation factor F and the predicted aquifer formation factor Fm. Generally, the results of our study reveal good correlations with similar studies carried out in literatures at different places. The juxtaposition of contour maps which show variations of geohydraulic parameters in a continuum is worthwhile. The changes in geohydraulic parameters are influenced by size of grains, magnitude of pore sizes and shapes, pore-water and formation conductivities, facies changes and anisotropy of aquifer sediments. Our results have not really shown any interaction between freshwater and saltwater within the potential aquifers despite the proximity of the salt water within the area.

Integrated Petrophysical Evaluation of a Heterogeneous Shaly-sand Reservoir: A Case Study in Nahr Umr Formation-subba Giant Oil Field, Iraq

This study presents an integrated petrophysical evaluation for Nahr Umr reservoir by highlighting a practical trustworthy approach petrophysical model for Nahr Umr reservoir in Subba oil field depending on available data. The available data include core analysis conducted on seven core samples taken from seven wells in Subba oil field and well set logs which include gamma ray, static spontaneous, neutron, sonic, density and resistivity logs. Subba oil field is a giant oil field located in southern part of Iraq about 110 km Northwest Basra. Nahr Umr formation in Subba oil field is a heterogeneous clastic reservoir. It was considered one of the most important producing clastic reservoir in southern Iraqi oil fields. The conventional petrophysical models, by using neutron- density cross-plot for lithology and porosity and Archie's equation for water saturation, can be adequate for evaluating clean sands. Usually the shaly sand formations are adhere to bad hole in shale section. Facies identification was achieved depending on core analysis data, core description data and wire line log measurements. The calculations of permeability was based on rock types identification and using available core data measurements. The generated permeability models can be used to calculate permeability for uncored intervals in all wells corresponding to each facies. Porosity was calculated using Neutron-density porosity model and Sonic model for bad hole section. Saturation model was built by utilizing the Indonesia Equation model, this model has proved its efficiency to be applied successfully for clastic Iraqi reservoirs. The petrophysical parameters were determined on a well-by-well basis. The formation resistivity factors (a, m) and water saturation exponent (n) have been derived from Pickett plot and formation water salinity. Reservoir quality calculations or net pay values are based on cut-offs values for porosity, saturation and shale volume.

Groundwater resource evaluation in the western part of Kushtia district of Bangladesh using vertical electrical sounding technique

Geoelectrical sounding, borehole litholog, and groundwater data have been used for the exploration of groundwater resources in the western part of greater Kushtia district, Bangladesh. This study aimed to delineate the boundary and the depth of aquifers, and assess their vulnerability to near-surface contaminants. Fourteen geoelectrical sounding data are interpreted and the corresponding geoelectrical logs are correlated with the available nearby horehole lithologs. Four distinct geoelectrical layers are identified within the depth of 105 m, namely thin topsoil (8.0–97.6 Ωm, 0.5–3.6 m), conductive clay-silt-sand layer (8.6–27.5 Ωm, 1.3–49.4 m), medium resistive fine grained aquifer (25.8–45.0 Ωm, 10.1–30.4 m), and high-resistive coarse grained water-bearing aquifer (35.0–64.9 Ωm, 30.0–76.9 m). The shallow aquifer (third layer) is found to occur at a depth ranging between 1.7 and 51 m, whereas the deeper aquifer (fourth layer) is found to occur within the depth between 14 and 52 m, both saturated with water. The groundwater resistivity and formation resistivity factor in the study area is found to vary from 15 to 30 Ωm and 1.93 to 2.68, respectively. The narrow low-protective layer has made the shallow aquifer highly vulnerable to surface contaminant in the study area.

Pore fabric assignment using electrical conductivity of some Albian–Cenomanian sequences in north Eastern Desert, Egypt

The electric pore fabric concept has been testified in many previous studies, mostly concerned with sandstone rock samples. The present study is a further trial to testify the reliability of the proposed concept on carbonate and clastic facies. The studied facies are representative for the Albian–Cenomanian Raha and Abu Qada Formations at the western side of the Gulf of Suez in Egypt. A total of 37 samples have been studied petrophysically by measuring electric conductivity in 3-D to rank their petrophysical potentiality and to detect their electric pore fabric. The studied samples are grouped into four facies, namely: (1) facies 1 (calcareous sandy siltstones) and (2) facies 4 (glauconitic quartz arenite) as clastic facies as well as (3) facies 2 (bioclastic limestones, and dolostones) and (4) facies 3 (clayey to sandy limestones) as carbonate facies. Porosity values of the studied carbonate facies are very good due to dolomitization and dissolution, whereas porosity values of the clastic facies are poor due to their high clay content. The formation resistivity factor values are low to medium values due to the reducing effect of the clay content and the very good porosity values. Archie’s parameters a and m are mostly related to the formation resistivity factor and to some extent to the mineralogical composition as well as the electric tortuosity. The electric pore fabrics of the studied facies are slightly anisotropic, mostly as primary depositional fabrics affected by slight foliation rather than lineation. Presence of a slight fracturing system can be revealed by assigning the minimum formation resistivity factor through the vertical direction perpendicular to the bedding plain. However, the fracturing system is still not strong enough to affect the electric pore anisotropy by increasing the electric pore lineation as a secondary fabrics’ indicator.

WITHDRAWN: Estimation of porosity, formation resistivity factor, Archie cementation factor, pore geometry factor and tortuosity for a coastal aquifer

WITHDRAWN: Estimation of porosity, formation resistivity factor, Archie cementation factor, pore geometry factor and tortuosity for a coastal aquifer

Experimental Study on the Relationship Between Reservoir Permeability and Its Formation Resistivity Factor

AbstractTo improve the evaluation of low permeability reservoirs with strong heterogeneity by using electrical logging data, it is essential to correctly understand the relation of formation permeability to its resistivity factor. In this paper, a comprehensive analysis is made on the assorted experimental data obtained from the Bohai Bay Basin, including porosity, permeability, NMR T2 spectrum, rock resistivity, mercury injection, X‐ray diffraction, casting thin sections and so on. For the same group of core samples, the relation of formation resistivity factor to permeability, average pore throat radius and reservoir quality index is further studied separately. Each result is compared to the relation of formation resistivity factor to porosity. The study reveals that the relation of formation permeability to its resistivity factor is not monotonic, and core samples with similar porosity but different pore structure quality and permeability can have close electrical conductivity. The reasonability of this phenomenon is further proved with theoretical analysis. It is also found that the difference of permeability is related to the square of the ratio of average pore throat, pore tortuosity and geometry for core samples with similar porosity and electrical conductivity.