Clay Volume Fraction Research Articles

Ground‐penetrating‐radar‐assisted saturation and permeability estimation in bimodal systems

Near‐surface investigations often require characterization of vadose zone hydraulic parameters. Conventional sampling or borehole techniques for estimating these parameters are costly, time consuming, and invasive, all of which limit collection of hydrogeological data at a spacing needed for detailed site characterization. Incorporation of two‐ or three‐dimensional densely sampled geophysical data with conventional hydrological data increases the amount of data available for the characterization and thus has the potential to significantly improve the hydraulic parameter estimates over those obtained from borehole data alone. The hydraulic estimation procedure can be greatly improved by incorporating dielectric information potentially available from ground penetrating radar (GPR), a noninvasive, high‐resolution geophysical method. The procedures for collecting and processing GPR data in the format needed for the proposed estimation technique are relatively new and still a topic of research; our method requires as a starting point the ability to estimate dielectric constants from GPR data. Numerical experiments were performed to investigate the general utility of the GPR‐assisted estimation technique under a range of conditions. Three bimodal systems were investigated, each system being composed of a sand facies together with another facies with a larger clay volume fraction; each facies was defined using characteristic values of clay content, porosity, and permeability. Using dielectric information and petrophysical relations, degree of saturation and intrinsic permeability values at each location within the three systems were identified. For bimodal systems, a dielectric constant measurement corresponds to two possible values of saturation and intrinsic permeability at each location; single values of saturation and intrinsic permeability were estimated from these values using the principle of maximum likelihood. Results from case studies demonstrate that a combination of GPR data with conventional borehole data significantly improves the estimates of saturation and has the potential to improve the estimates of permeability over those obtained from well bore data alone. The proposed method should be especially advantageous for vadose zone characterization in areas favorable for GPR data acquisition, where detailed hydraulic parameter information is required but the drilling of numerous boreholes is prohibited.

Neutron Scattering Study of Vermiculite−Poly(vinyl methyl ether) Mixtures

A four-component clay−polymer−salt−water system, consisting of n-butylammonium vermiculite, poly(vinyl methyl ether), n-butylammonium chloride, and heavy water, was studied by neutron scattering. The volume fraction of clay in the system and the salt concentration were held constant, at r = 0.01 and c = 0.1 M, respectively, and the volume fraction of polymer v was varied between 0 and 0.04. The addition of polymer, up to v = 0.04, had no effect on the phase transition temperature between the tactoid and gel phases of the clay system. However, even for v values as low as 0.001, the clay plates in the gel phase were more parallel and more regularly spaced than in the system without added polymer. In the gel phase, the lattice constant along the swelling axis of the clay colloid decreased exponentially as a function of the polymer volume fraction, from 12 nm at v = 0 to 8 nm at v = 0.04. In the tactoid phase, at T > 14 °C, the c-axis lattice constant in the crystalline regions was equal to 1.94 nm at v = 0 a...

Water saturation and permeability from resistivity, dielectric, and porosity logs

An analytical approach previously proposed to model the electrical properties of shaly sands has been adapted to obtain the cementation exponent (m), the water saturation [Formula: see text], and the shaliness distribution from electromagnetic and porosity log measurements in an oil well. Shaliness is described by the clay volume fraction (p) and by the clay type parameter [Formula: see text] in the sand. For a shale‐coating structure these parameters can be related to the exchange cation density [Formula: see text]. Based on an equivalent flow regime inside this granular model, a Kozeny‐Carman type equation has been derived, expressing the intrinsic permeability (k) of the medium in terms of a porosity‐tortuosity factor [Formula: see text] and of the parameter [Formula: see text]. The power‐law derived expression shows that k decreases with the amount of clay, not only because a high [Formula: see text] implies a narrowing of the pore channels, but also because it modifies the hydraulic tortuosity of the medium. This new equation has been statistically tested with extensive petrophysical laboratory data for different types of sandstones and satisfactorily applied to core and log data of an oil well from Potiguar Basin, Rio Grande do Norte, Brazil.

The Influence of clay content, salinity, stress, and wettability on the dielectric properties of brine‐saturated rocks: 10 Hz to 10 MHz

Complex impedance measurements have been performed on 14 shaly sand samples, Berea sandstone, and Ottawa sand‐bentonite packs in a frequency range of 10 Hz to 10 MHz, using both the two‐ and four‐electrode techniques. Measurements have been conducted at an effective radial stress varying from ambient pressure to 4000 psi for brine‐saturated oil‐wet and water‐wet samples. The dielectric permittivity is found to correlate with the clay volume fraction, the cation exchange capacity, and electrochemical potential of the rock samples and to depend strongly on the salinity of the brine used. Stress and wettability are shown to have a small influence on the dielectric constant of fully brine‐saturated rocks. A lower critical frequency is found to characterize the geometry of the pore space. Empirical correlations between the dielectric constant, frequency, permeability, cation exchange capacity, and porosity are presented for the shaly 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 nondestructive complex impedance sweep of shaly sands fully saturated with brine.

Ultrasonic compressional and shear velocities in dry clastic rocks as a function of porosity, clay content, and confining pressure

SUMMARY For clastic silicate rocks sampled from a Rotliegendes well core the velocities up and us were obtained at 10 pressures up to 300MPa using a pulse-transmission technique. The porosities of all rocks (57 sandstones, 26 siltstones, five claystones) ranged from 0.01 and 0.15 by volume fraction, and the clay content varied from less than 0.01 to 0.88 by volume fraction. Both velocities increase with pressure. In the low-pressure range the rate of increase is large, non-linear and is greater for up than for us. Above 120 MPa both velocities increase linearly. Velocities, porosity, and clay content were fitted by least-squares regression for pressures of 8, 24, 60, 120, 200, and 300 MPa. The fractional effect of porosity and clay on the velocities for dry clastic silicate rocks can be described (above 120 MPa) by u = A - B# - CCluy, where v is the velocity of the P-wave or S-wave, # is the volume fraction of pores, and Clay is the volume fraction of clay. From this it is possible to obtain pressure-dependent velocity functions u = a +pb - c exp (-dp), where u is the crack-free velocity, linear in porosity and clay, b is the velocity slope under high pressure, u - c is the zero-pressure velocity, and d is related to closure of cracks.

Ultrasonic velocity and attenuation in aqueous kaolin dispersions

Near field measurements of ultrasonic compressional wave attenuation (α) and velocity ( c) in aqueous kaolin clay dispersions are presented. The dependence of these parameters on the clay volume fraction (in the range 0 to 0.3) and frequency (in the range 1 to 5 MHz) is examined. The velocity measured has been compared with the theoretical expressions due to Urick, Ament, and Gibson and Toksőz. It is shown that when particle size and ultrasonic viscous skin depth are of similar magnitude, the particle eccentricity must be taken into account to reconcile theory and experiment. Predictions for the volume fraction dependence of attenuation due to Urick, Hovem, and Gibson and Toksőz have been compared with the experimental data. The Urick theory and the low frequency approximation of Hovem's expression show qualitative agreement with the experimental data up to a solid volume fraction of about 0.1 and 0.3, respectively. At high frequencies, when the viscous skin depth is small relative to particle size, the application of a correction function to the Stokes' drag force on the suspended particles greatly improves the agreement between experiment and the Gibson and Toksőz theory.

Rheology of oil in water emulsions with added kaolinite clay

This paper deals with the rhelogical measurements of oil in water emulsions with added kaolinite clay. The percent oil concentration, solids-free basis, was varied up to 70% by volume. The volume fraction of clay was varied up to 0.2 based on the total volume. The clay/emulsion mixtures displayed shear thinning behavior. Yield stress was observed, and its value increased with clay volume fraction and with oil concentration. The shear stress versus shear rate data could be fitted by the Casson model for low oil concentrations (below 40%) and by the Herschel-Bulkley model for higher oil concentrations. On the basis of the experimental data, a correlation was developed to evaluate the relative viscosity of the clay/emulsion mixtures, where the relative viscosity was defined as the ratio of the viscosity of clay/emulsion mixtures to that of emulsions alone. A viscosity equation was also developed for calculating the viscosity of clay/emulsion mixtures.