The effect of wettability, stress, and temperature on the saturation and cementation exponent of the Archie equation

The 1.5 inch diameter Temco cell was setup, tested, and calibrated for the purpose of investigating the simultaneous effect of stress and wettability on the saturation and the cementation exponents of the Archie equations. In addition to the Temco cell, an electric circuit was built, tested, and calibrated for glass bead sample resistivity measurement by using the four-electrode technique, known to be immune from contact resistance effects. Glass beads were 180 to 250 μm in diameter and were cleaned with surfactants, rinsed with distilled water, and dried in an oven overnight. This treatment was performed to make sure that the beads were water wet. To make the glass beads oil wet, the water wet beads were treated by an asphaltic crude oil and then flushed with pentane and naptha to remove the non-polar fraction initially in the crude. For resistivity measurements, the beads were packed dry in the cell and vacuum saturated with 30,000 ppm (NaCl) brine solution. Porosity was measured from the volume of water injected, after correction for dead volume (non-pore volume), in the equipment. Repeat runs at different wettability and loading conditions were made to measure reproducibility. The confining axial stress and the radial stress were controlled independently, and the change in porosity and resistivity was measured with increasing stress (from 300 to 5000 psi). Values of saturation exponents were computed based on two saturation points which are 100% water saturation and irreducible water saturationPetroleum and Geosystems Engineerin

Critical Reynolds number for nonlinear flow through rough-walled fractures: The role of shear processes

This paper experimentally investigates the role of shear processes on the variation of critical Reynolds number and nonlinear flow through rough-walled rock fractures. A quantitative criterion was developed to quantify the onset of nonlinear flow by comprehensive combination of Forchheimer's law and Reynolds number. At each shear displacement, several high-precision water flow tests were carried out with different hydraulic gradients then the critical Reynolds number was determined based on the developed criterion. The results show that (i) the Forchheimer's law was fitted very well to experimental results of nonlinear fluid flow through rough-walled fractures, (ii) the coefficients of viscous and inertial pressure drops experience 4 and 7 orders of magnitude reduction during shear displacement, respectively, and (iii) the critical Reynolds number varies from 0.001 to 25 and experiences 4 orders of magnitude enlargement by increasing shear displacement from 0 to 20 mm. These findings may prove useful in proper understanding of fluid flow through rock fractures, or inclusions in computational studies of large-scale nonlinear flow in fractured rocks

Chapter 14 Electrical Properties of Soils

This chapter discusses the electric and electromagnetic methods that are used to evaluate the electrical properties of soils. Electric techniques exploit the flow of a steady-state current in the subsurface, while electromagnetic methods rely on the phenomenon of electromagnetic induction and the wave character of the electromagnetic field. The electrical techniques and associated properties are: (a) spontaneous potential methods in which the formation of water resistivity is determined; (b) resistivity methods in which the apparent resistivity can be calculated using Wenner, Schlumberger, and dipole-dipole arrays; and (c) specific conductivity methods in which the soil-specific conductivity is calculated by incorporating in the analysis of soil geometric factors, such as fabric anisotropy, tortuosity, resistance to solid matrix, bulk fluid phase, and electric double layer. Various parameters that influence the measured electrical properties are also presented, such as the nature of the soil composition (particle size distribution, mineralogy), soil structure (porosity, pore size distribution, connectivity, and anisotropy), moisture content, temperature, concentration of dissolved species in the pore-solution, wet-dry cycles, age of contaminants, and mineral formation due to biodegradation. Finally, the extraction of aquifer hydraulic properties such as porosity and hydraulic conductivity, from the measured electrical properties is discussed

Dielectric Properties of Fluid Saturated Rocks

The objective of this dissertation is to study the effect of wettability, clay content, water saturation and salinity on the electrical properties of hydrocarbon bearing rocks. The frequency range of interest is 10 Hz to 10 MHz. Measurements were made for the impedance of both fully and partially saturated rocks using the four-electrode method and for fully saturated rocks using the two-electrode method. These measurements include both clean and shaly sand samples. For fully saturated rocks, the dielectric constant is found to increase with the clay volume fraction, the cation exchange capacity and the electrochemical potential of the rock samples. It is found to decrease with increasing salinity, frequency, permeability, and porosity. Neither stress, nor wettability appear to significantly influence the dielectric constant of fully brine saturated Berea cores. Empirical correlations between the dielectric constant, frequency, permeability, cation exchange capacity, and porosity are presented for tight gas sands used in this study. These correlations provide a means of estimating important petrophysical parameters such as the permeability and the clay content from a non-destructive complex impedance sweep of tight gas sands fully saturated with brine. A lower critical frequency is found to characterize the geometry of the pore space. For partially saturated rocks, the dielectric constant appears to depend linearly on water saturation above 0.1 MHz and to have a power law dependence on water saturation below 0.1 MHz. This frequency appears to be the limit below which the resistivity index was invariant to frequency and at which all experimental runs displayed a peak in the reactivity index. Wettability effects were pronounced below 10 KHz. The effects observed experimentally are explained on the basis of the Generalized Maxwell-Wagner Theory. It is shown that the model presented by Lima and Sharma agrees quantitatively with the measured effects of porosity, clay content, saturation, grain size, and frequency. The Lima-Sharma theory for modeling the complex impedance of partially saturated shaly sands has been inverted. This inversion allows a log analyst to use low ( lMHz) complex impedance data from well logs to calculate reservoir petrophysical parameters such as water saturations in the virgin formation and in the flushed zone, porosity, clay volume fraction, clay surface charge density, and grain size.Petroleum and Geosystems Engineerin

Predicting the cation exchange capacity of reservoir rocks from complex dielectric permittivity measurements

Dimensional analysis was performed to understand the physics of ionic dispersion in reservoir rocks and to identify the factors influencing the cation exchange capacity (CEC) of these rocks. Dimensional analysis revealed the existence of a general relation independent of the unit system between two dimensionless groups denoted as the cationic dispersion number [Formula: see text] and the conductivity number [Formula: see text]. The former group [Formula: see text] stands for the ratio of the CEC to the electrical double-layer dispersion. The latter group [Formula: see text] represents the ratio of the low-frequency ionic conductivity to the high-frequency electronic polarization. Complex dielectric permittivity measurements on 121 water-saturated sandstone and carbonate rock samples were used to validate the dimensionless groups. In retrospect, dimensional analysis was useful in identifying variables influencing the CEC of hydrocarbon rocks. In particular, these variables consist of rock porosity [Formula: see text], specific surface area, and five other parameters of the Cole-Cole function, which describes the frequency dependence of the complex permittivity of rock samples in the range 10–1300 MHz. The Cole-Cole function parameters are [Formula: see text], which is a characteristic relaxation time; [Formula: see text] is the so-called spread parameter; [Formula: see text] is the real DC conductivity of water-saturated rocks; and [Formula: see text] and [Formula: see text], which are the real numbers representing the static and the high-frequency dielectric permittivities of the water-saturated rock, respectively. A general regression neural network (GRNN) model was developed to predict the CEC of shaly sandstones and carbonate rocks as a function of the variables identified by the dimensional analysis as essential in predicting the CEC. The CEC prediction capability of the GRNN model has been tested with a blind data set, and it has been compared with the CEC prediction capability using a nonlinear regression model developed in this study and using a linear regression model available in the literature. The GRNN model outperformed both of these empirical models. With the GRNN model, it is possible to obtain reliable quantitative estimates of the CEC of shaly sandstone and carbonate rocks using nondestructive frequency-dependent dielectric permittivity measurements that are rapid, economic, and accurate. In return, accurate and fast estimates of the CEC are useful in many petroleum engineering applications. They can be used to identify clay types and can also be used to quantify the volume of hydrocarbon in shaly sands using well-log resistivity data. The results of this study represent a major advantage for formation evaluation, wellbore stability analysis, and designing stimulation jobs. </jats:p

Explaining the comparative perception of e-payment: role of e-shopping value, e-payment benefits and Islamic compliance

Purpose This study aims to examine three factors affecting the comparative e-payment perception, namely, perceived e-shopping value, e-payment benefits and Islamic Sharia compliance. It verifies an original model explaining the comparative perception of e-payment as a tool to pay online purchases. The newly integrated variables are the perceived compliance of the e-payment with Islamic Sharia, as a moderator, and the perceived e-shopping value, as a predictor. This investigation also tested the mediating role of e-payment benefits between perceived e-shopping value and e-payment comparative perception. Design/methodology/approach A questionnaire was distributed, via an online survey, to professional and personal networks of Master students who have spread the survey link to their social media groups. This procedure resulted in 185 valid observations. Findings Results show that the comparative perception of e-payment systems, as opposed to cash on delivery, is explained directly by e-payment benefits and indirectly by e-shopping value. The comparison of the model paths based on the perceived compliance to Islamic Sharia showed that this variable is non-significant as a moderator. Originality/value The verified model and paths of this study have not been covered yet, namely, the direct and indirect effects of e-shopping value. Thus, their verification constitutes the main originality of this article. Besides, the verification of the moderating role of compliance to Islamic sharia has not been verified in prior studies about e-payment. </jats:sec