Arthur H. Thompson

The microgeometry and transport properties of sedimentary rock

Abstract This monograph describes recent progress in modelling the transport properties of sedimentary rock. Statistical descriptions are applied to the pore-space geometry and to the transport processes involving pore fluids. Fractals are used to quantify the pore geometry at length scales shorter than grain size. Percolation theory is applied to fluid flow. The permeability can be expressed in terms of a single effective pore diameter measured from mercury injection capillary pressure. This permeability relation is valid for essentially all porous rock and for a broad class of porous media. Mercury injection provides a powerful caliper of the geometry of a percolation cluster in a pore-space and supplies new information about pore space correlations and dynamics of fluid displacements. The statistical description of fluid transport in porous media has analogues in disordered electronic and magnetic materials. Future work may make substantial use of such analogues to solve more complex problems of direct...

The verification of the existence of TiS2

Abstract The intrinsic electronic properties of TiS 2 are currently under some debate. It has not been conclusively demonstrated if TiS 2 is a semimetal or a degenerate semiconductor. We have thoroughly studied this problem by first characterizing the material composition and then determining the electronic properties. Precision x-ray diffraction, mass density, and chemical analysis have been used to characterize TiS 2 . Trends in the Ti x S 2 series of nonstoichiometric compounds have been monitored by intercalation, scanning electron microscope, magnetic susceptibility and electron transport measurements. We conclude from the total body of data collected that TiS 2 exists as a stoichiometric compound and that its semimetallic properties are intrinsic.

Transition metal phosphorus trisulfides as battery cathodes

Abstract The transition metal dichalcogenides, such as TiS 2 , have been reported to perform well as cathodes in ambient temperature lithium batteries. It has been found that the layered, transition metal phosphorus trisulfides also exhibit electrochemical activity. Nickel phosphorus trisulfide will react with more than four lithium resulting in a cell with a theoretical energy density double that of titanium disulfide.

Field tests of electroseismic hydrocarbon detection

Geophysicists, looking for new exploration tools, have studied the coupling between seismic and electromagnetic waves in the near-surface since the 1930s. Our research explores the possibility that electromagnetic-to-seismic (ES) conversion is useful at greater depths. Field tests of ES conversion over gas sands and carbonate oil reservoirs succeeded in delineating known hydrocarbon accumulations from depths up to 1500 m . This is the first observation of electromagnetic-to-seismic coupling from surface electrodes and geophones. Electrodes at the earth’s surface generate electric fields at the target and digital accelerometers detect the returning seismic wave. Conversion at depth is confirmed with hydrophones placed in wells. The gas sands yielded a linear ES response, as expected for electrokinetic energy conversion, and in qualitative agreement with numerical simulations. The carbonate oil reservoirs generate nonlinear conversions; a qualitatively new observation and a new probe of rock properties. The...

Hydrodynamic dispersion and pore geometry in consolidated rock

Experimental measurements of the dispersion of tracer particles in flow through natural porous media are compared with a percolation model. The experiments show that tracer dispersion is a sensitive function of the width of the pore‐size distribution as measured by mercury capillary pressure. Measurements of capillary pressure (or electrical conductivity) are used to estimate the geometric correlation length of the dominant flow path in the rock. Percolation theory is used to derive a power‐law relationship between the correlation length and the ratio of the dispersivity to the average grain size. The experimental value of the power‐law exponent is in agreement with the theoretical prediction. Measurements on samples containing a residual saturation of wetting epoxy show no significant change in dispersion behavior. This result mediates against dispersion models requiring trapping in dead‐end pores. Tracer concentration profiles exhibit anomalous long‐time tails in two cases. In carbonate rocks, we associate long‐time tails with macroscopic permeability heterogeneities. In sandstones, long‐time tails occur in samples with a very narrow pore‐size distribution. These samples may have permeability heterogeneities as a result of defects in the packing density. In the limit of low flow velocity, the long‐time tail disappears, suggesting a convective mechanism associated with flow heterogeneities at a millimeter‐or‐larger scale.

Minimum Saturations and Buoyancy in Secondary Migration

Percolation theory, it is often argued, requires a minimum nonwetting phase saturation of approximately 15% for hydrocarbon migration; but field measurements usually fail to find residual oil on the pathway taken during hydrocarbon migration from a source to a reservoir. We use numerical simulations and experiments to show that percolation theory, when applied to the process of oil invading a pore space, leads to the conclusion that field-scale saturations in secondary migration can be on the order of 1% or less. Our capillary invasion experiments on Berea Sandstone and numerical simulations of fluid invasion on networks show that the minimum saturation for flow of the nonwetting phase decreases as the reciprocal square root of the linear size. This result applies to cyli drical samples that have height equal to diameter. Our numerical simulations include the effects of sample aspect ratio, buoyancy, and pore-size distribution. All the numerical results reduce to a single relation between threshold saturations and sample size normalized by a function of the pore-size distribution. We find that a pore-size distribution that has many more small pores than large pores, as is typical in rocks and soils, substantially reduces the influence of buoyancy on threshold saturations. The common practice of using uniform (flat) pore- size distributions to simulate rocks overestimates the effects of buoyancy. Experiments show that for larger samples, the permeability at threshold for flow is higher than conventionally expected. In a typical geological situation, this h gh permeability is large enough to carry oil to a reservoir over geologic time at saturations of less than 1% of the pore volume. Our laboratory permeability and saturation experiments confirm the expectations of percolation theory, including the fractal dimension of the first invasion path. Size-dependent saturation is the prediction of invasion percolation theory. The percolation model is applicable to the secondary migration problem, as well as to migration of gas in reservoirs, migration of gas or fluids from radioactive waste repositories, and migration of nonaqueous-phase liquid pollutants in groundwater.

Intercalation and lattice expansion in titanium disulfide

The temperature coefficient of expansion has been measured for the a and c axes of titanium disulfide, and of its intercalates with a metal, lithium, and an organic base, s−collidine. The anisotropy in the expansion coefficients is related to the bonding in the structure.

Intercalation of organometallic compounds into layered transition metal oxyhalides

Abstract The syntheses of the new intercalate compounds FeOCl[(EtMe 4 Cp) 2 Fe] 0.16 , VOCl(CoCp 2 ) 0.16 , and TiOCl(CoCp 2 ) 0.16 are reported. Their structures are found by X-ray powder diffraction to be qualitatively the same as those of the previously reported complexes FeOCl(CoCp 2 ) 0.16 and FeOCl(FeCp 2 ) 0.16 . Results of 57 Fe Mossbauer and magnetic susceptibility studies on the latter two compounds are reported, and shown to be consistent with electron transfer from the metallocene to the host upon intercalation.

Electromagnetic-to-seismic conversion: A new direct hydrocarbon indicator

We present novel methods that directly detect hydrocarbons based on conversions between electromagnetic and seismic energy. We first introduce the subject and then discuss the experimental methods in three field tests. Next, we present the results of the tests and then end with a few model results and thoughts about future applications.

Electrochemical studies of lithium intercalation in titanium and tantalum dichalcogenides

Abstract Electrochemical intercalation studies of lithium in TayTi1-yS2 and 2H-TaS2 reveal two phase formation in the tantalum-rich materials. These results supply evidence for the collective distortion of the host and guest and provide an explanation for the observance of very narrow voltage-composition relations in some intercalation cathodes. The Li/2H-TaS2 couple is an example of both two-phase and single phase product formation in a single intercalation compound.