Daniel Broseta

Capillary Alteration Of Shaly Caprocks By Carbon Dioxide

The efficiency of the CO2 geological storage process in aquifers and hydrocarbon reservoirs is controlled by several factors. In the case of reservoirs with a shaly caprock, one critical factor is the capillary-sealing potential of the caprock. This potential can be expressed in terms of a maximum storage pressure, equal to the hydrostatic pressure in the caprock plus the CO2 capillary entry pressure in the brine-saturated caprock. It is therefore controlled by the CO2-brine interfacial tension, the water-wettability of shale minerals, and the pore size distribution within the shaly rock. By means of contact angle measurements, we provide experimental evidence that the water-wettability of minerals representative of shales, such as mica and quartz, is significantly altered in the presence of CO2 under pressures typical of geological storage conditions. Those minerals, known to be strongly water-wet in the presence of oil, turn out to be intermediate-wet in the presence of dense CO2. We discuss the consequences of such wettability alteration on the maximum CO2 storage pressure, which can be converted into a maximum CO 2 height stored in the reservoir. In the case of hydrocarbon reservoirs initially close to capillary leakage, the maximum CO2 storage pressure should be only a fraction of the initial virgin pressure.

A modified rock physics model for analysis of seismic signatures of low gas-saturated rocks

In seismic applications, the bulk modulus of porous media saturated with liquid and gas phases is often estimated using Gassmanns fluid substitution formula, in which the effective bulk modulus of the two-phase fluid is the Reuss average of the gas and liquid bulk moduli. This averaging procedure, referred to as Woods approximation, holds if the liquid and gas phases are homogeneously distributed within the pore space down to sizes well below the seismic wavelength and if the phase transfer processes between liquid and gas domains induced by the pressure variations of the seismic wave are negligible over the timescale of the wave period. Using existing theoretical results and low-frequency acoustic measurements in bubbly liquids, we argue that the latter assumption of “frozen” phases, valid for large enough frequencies, is likely to fail in the seismic frequency range where lower effective bulk modulus and velocity, together with dispersion and attenuation effects, are expected. We provide a simple method, which extends to reservoir fluids a classical result by Landau and Lifshitz valid for pure fluids, to compute the effective bulk modulus of thermodynamically equilibrated liquid and gas phases. For low gas saturation, this modulus is significantly lower than its Woods counterpart, especially at the crossing of bubble point conditions. A seismic reflector associated to a phase transition between a monophasic and a two-phase fluid thus will appear. We discuss the consequences of these results for various seismic applications including fizz water discrimination and hydrocarbon reservoir depletion and CO2 geological storage monitoring.

Pseudo-component Delumping for Multiphase Equilibrium in Hydrocarbon-Water Mixtures

Abstract An analytical and consistent delumping procedure is implemented for fluids of petroleum interest containing water, non-hydrocarbon gases (such as N2, CO2, and H2S) and hydrocarbon (HC) compounds. Two sorts of difficulties are associated with these fluids: they often exhibit three or more equilibrium phases, and their thermodynamics cannot be described by conventional cubic equations of state (EoS). In this work, the Søreide-Whitson modification of the Peng-Robinson EoS, in which different binary interaction parameters are used in the aqueous and non-aqueous phases, is used. The method is successfully tested on two cases in the two- and three-phase regions: one synthetic HC/N2/CO2/H2O fluid and a “real” water/reservoir fluid.

Improved Delumping of Compositional Simulation Results

Abstract A recently developed method for pseudo-component delumping is tested for delumping the results of compositional reservoir simulation. The procedure, based on the reduction concept, is analytical and consistent and it accurately takes into account non-zero binary interaction parameters in cubic equations of state. The delumping method was implemented in a postprocessor to the commercial Eclipse reservoir simulator and successfully tested on several cases: oil and gas condensate reservoirs for depletion, lean gas re-injection, and carbon dioxide injection. The analytical delumping method based on reduction gives systematically better results than the regression-based delumping method used previously.

Help from a Hindrance: Using Astigmatism in Round Capillaries To Study Contact Angles and Wetting Layers

Round glass capillaries are a basic tool in soft-matter science, but often are shunned due to the astigmatism they introduce in micrographs. Here, we show how refraction in a capillary can be a help instead of a hindrance to obtain precise and sensitive information on two important interfacial properties: the contact angle of two immiscible fluids and the presence of thin films on the capillary wall. Understanding optical cusps due to refraction allows direct mesurement of the inner diameter of a capillary at the meniscus, which, with the height of the meniscus cap, determines the contact angle. The meniscus can thus be measured without intrusive additives to enhance visibility, such as dyes or calibrated particles, in uniform, curved, or even tapered capillaries or under demanding conditions not accessible by conventional methods, such as small volumes (μL), high temperatures, or high pressures. We further elicit the conditions for strong internal reflection on the inner capillary wall, involving the wall and fluid refractive indices and the wall thickness, and show how to choose the capillary section to detect thin (submicron) layers on the wall, by the contribution of total internal reflection to the cusps. As examples, we report the following: (i) CO2-water or -brine contact angles at glass interfaces, measured at temperatures and pressures up to 200 °C and 600 bar, revealing an effect apparently so far unreported-the decrease in the water-wet character of glass, due to dissolved salts in brine, is strongly reduced at high temperatures, where contact angles converge toward the values in pure water; (ii) A tenuous gas hydrate layer growing from the water-guest contact line on glass, invisible in transmission microscopy but prominent in the cusps due to total internal reflection.

Hydrate-Based Removal of CO2 from CH4 + CO2 Gas Streams

This chapter is concerned with CO2 separation from CO2 + CH4 mixtures by means of gas hydrates. It describes and discusses the laboratory experimentation and the metrics of CO2 separation, which define, for given gas mixture and experimental conditions, the various parameters that describe the efficiency of the capture process. A review is then presented of the few available experimental results obtained with CO2 + CH4 mixtures, emphasizing the role of additives, whether water‐soluble or ‐insoluble molecules. The chapter points out possible directions worth being pursued to enhance this selectivity, such as that consisting in forming hydrate in some moist mesoporous materials. It presents and discusses the performance indicators and some of the routes explored for improving selectivity. These routes combine the use of chemical promoters with “non‐chemical” methods investigated so far mainly for increasing the rate of formation of gas hydrate.