Henri Bertin

Foam Mobility in Heterogeneous Porous Media

Foamed-gas injection is a promising technique for achieving mobility control and diverting fluid to low permeability strata within heterogeneous porous media. However, the factors most important for diversion have not been stated and explored definitively. Gas mobility in the presence of foam depends critically on foam-bubble size; bubble size may vary with permeability, porosity, surfactant type and concentration, and the velocity of liquid and gas. This paper adopts a local equilibrium, scaling perspective to describe quantitatively foamed-gas mobility within heterogeneous porous media. Conventional and percolation network scaling ideas are employed. A new closed form expression for the fraction of mobile gas within a foam is derived using statistical network concepts. Additional equations indicate, for instance, that porosity plays an important role in setting gas mobility because it reflects the relative abundance of foam germination and termination sites per unit volume of porous media. Liquid velocity is also important because gas mobility is inversely proportional to this factor.

Oil recovery by steam injection: three-phase flow effects

An experimental study has been conducted to investigate three-phase flow effects on oil recovery during a steam flooding process (in the case of nondistillable white oil). A laboratory setup has been developed to simulate field conditions. The experiments were performed using a linear model packed with sand. The first step of this work consisted in a hot water flooding, the results of which showed an increase in oil recovery and a reduction in residual oil saturation when increasing temperature. The same core, previously flooded by hot water, was flooded again by steam. In this case, we obtained an additional oil recovery that was attributed to three-phase flow effects rather than a contribution of vaporization/condensation effects. To check this hypothesis, we performed the same experiment, but at the last stage we replaced steam by nitrogen. The experimental results showed that the additional oil recovery after nitrogen injection was basically independent of the temperature, and comparable to the one obtained after steam injection. Finally, the experimental results have been compared with numerical results, for both hot water and steam injection.

Transient aqueous foam flow in porous media: experiments and modeling

Abstract Gas injection into reservoirs can be used to increase oil recovery. However, the viscosity and density differences between the injected and displaced fluids can lead to low sweep efficiency. To overcome mobility control problems, gas can be injected in the form of foam to increase its apparent viscosity and improve reservoir sweep efficiency. Our study is focused on transient aqueous foam flow in homogeneous porous media. The experimental apparatus designed for this study consisted on an unconsolidated porous medium, saturated by surfactant-laden water, where nitrogen is injected at a constant flow rate. Pressure drop along the core was monitored, while 2D saturation measurements were performed using a γ -ray attenuation technique. The experiments were analyzed in terms of breakthrough time, liquid recovery, pressure drop evolution along the core, and gas saturation profiles. First, we studied the influence of surfactant concentration. Second, for two fixed values of the surfactant concentration, we studied the influence of gas flow rate. The experiments were interpreted using a foam simulator, including a classical Darcys law model coupled with a foam bubble population-balance equation to model generation, destruction, and convection of gas bubbles along the porous medium. Physical parameters describing generation and coalescence of foam lamellae have been optimized by a sensitivity study.

Two-phase flow in heterogeneous porous media III: laboratory experiments for flow parallel to a stratified system

Two-phase flow in stratified porous media is a problem of central importance in the study of oil recovery processes. In general, these flows are parallel to the stratifications, and it is this type of flow that we have investigated experimentally and theoretically in this study. The experiments were performed with a two-layer model of a stratified porous medium. The individual strata were composed of Aerolith-10, an artificial: sintered porous medium, and Berea sandstone, a natural porous medium reputed to be relatively homogeneous. Waterflooding experiments were performed in which the saturation field was measured by gamma-ray absorption. Data were obtained at 150 points distributed evenly over a flow domain of 0.1 × 0.6 m. The slabs of Aerolith-10 and Berea sandstone were of equal thickness, i.e. 5 centimeters thick. An intensive experimental study was carried out in order to accurately characterize the individual strata; however, this effort was hampered by both local heterogeneities and large-scale heterogeneities.The theoretical analysis of the waterflooding experiments was based on the method of large-scale averaging and the large-scale closure problem. The latter provides a precise method of discussing the crossflow phenomena, and it illustrates exactly how the crossflow influences the theoretical prediction of the large-scale permeability tensor. The theoretical analysis was restricted to the quasi-static theory of Quintard and Whitaker (1988), however, the dynamic effects described in Part I (Quintard and Whitaker 1990a) are discussed in terms of their influence on the crossflow.

Two types of transient phenomena and full relaxation macroscale model for single phase flow through double porosity media.

Darcys flow of a weakly compressible fluid through double porosity media is studied in the framework of the homogenization theory. In previous papers, various classes of single-phase flow have been detected with various determination of the effective permeability tensor for each class. In this paper, the full model including transient phenomena is developed, where the macroscale momentum balance equation represents a modification of Darcys law with a nonequilibrium term. The effective permeability tensor appears to be nonstationary and is changing during the system evolution in time. Three relaxation times characterize the transient transformations of each component of the macroscale flow velocity.This effect is superposed with the second relaxation phenomenon caused by the exchange flow between dense blocks and the highly conductive matrix. The relaxation times for the effective permeability and for the exchange flow are shown to have different orders.All relaxation parameters are explicitly determined through solutions of cell problems.

Two-phase calculations and comparative flow experiments through heterogeneous orthogonal stratified systems

Abstract Experimental and theoretical results for two-phase flow in vertically stratified systems, the flow being normal to the strata, are presented. The experimental study is focused on the following points: (a) the initial oil-drainage process and the evolution of he water distribution during the capillary equilibrium process, and (b) the time evolution of the saturation fields during waterflooding experiments. Saturation fields were measured using a γ-rays attenuation system. The physics of two-phase flow through vertically stratified porous media can be analysed by a large-scale averaging method. This methodology is described briefly; reference is made to previous publications for detailed presentation. The water-flooding experiments were interpreted using the large-scale averaging method, first in the quasi-static case, second using a simplified closure problem taking into account dynamic effects. The results show a better agreement between experimental and theoretical results when dynamic effects are taken into account.

Experimental Evidence of the Double-Porosity Effects in Geomaterials

Double-porosity is an important characteristic of microstructure in a large range of geomaterials. It designs porous media with connected fissures/fractures or aggregated soils. The origin of double-porosity can be natural or/and it can result from mechanical, chemical or biological damage. The presence of double-porosity can significantly affect the behaviour of geomaterials. In this paper we provide an experimental evidence of the double-porosity effects by performing laboratory experiments. Series of tracer dispersion experiments (in saturated and unsaturated steady-state water flow conditions) in a physical model of double-porosity geomaterial were carried out. For the comparative purposes, experiments of the same type were also performed in a singleporosity model medium. The results clearly showed that the double-porosity microstructure leads to the non-Fickian behaviour of the tracer (early breakthrough and long tail) in both saturated and unsaturated cases.

Two-phase flow through orthogonal composite cores with wettability heterogeneity

The objective of this study is to perform and interpret oil-brine displacements in composite cores made up of sandstone blocks of the same permeability but opposite wettability. The experimental procedure consists of cutting cubic segments from a homogeneous water-wet sandstone core, one block out of two being silanated to become oil-wet. The composite cores were constructed by rearranging the blocks together. The waterflooding experiments are interpreted using the large-scale averaging method (Quintard and Whitaker, 1988). Large-scale petrophysical properties (relative permeabilities and capillary pressure) were computed from the local-scale properties measured on isolated samples. A 1D numerical simulation is then performed, using the large-scale properties, and results are compared to the experimental data.

Experiments and numerical simulations of fluid flow in a cross layered reservoir model

Abstract This paper reports on studies of two-dimensional local saturation development in a cross layered reservoir model. Numerical simulations and experimental studies have been performed on a heterogeneous reservoir model consisting of three blocks of porous material with capillary and permeability contrasts connected at a dip angle of 45°. The physical reservoir model measured 22 cm × 5 cm × 5 cm and was composed of blocks of Vosges sandstone alternating with Aerolith-10, an artificial sintered porous medium with high porosity and permeability. The physical properties, porosities, permeabilities, capillary pressures, and end-point saturations of the blocks composing the heterogeneous medium were measured independently on isolated samples. A series of oilfloods and waterfloods were performed, and dynamic two-dimensional saturation fields were measured by gamma-ray attenuation. After drainage, during a no-flow state at low water saturation, we observed a redistribution of fluids near the boundaries of permeability contrasts due to capillary pressure differences between the blocks. The two-dimensional saturation fields recorded during the low-rate waterfloods showed a different behavior in different layers due to the contrasts of permeability and capillary pressure. Recovery efficiency by waterflooding isolated samples does not necessarily predict local recovery in composite models. Good reproducibility was obtained by performing different experiments with the same boundary conditions and petrophysical properties. Two-dimensional numerical simulations performed with the full-field commercial simulator ECLIPSE confirmed the observed experimental behavior. However, the simulated recovery from each block did not match the experimental results. We concluded that two-dimensional local saturation information in larger scale three dimensional reservoir models significantly improves the interpretation of the recovery mechanisms in heterogeneous porous media.

An Experimental Investigation of the oil Recovery in the Transition Zone of Carbonate Reservoirs Taking Into Account Wettability Change

Abstract It is estimated that 60% of the world’s remaining oil is held in carbonate reservoirs. Due to its moderate permeability, the transition zone can extend over a hundred meters and therefore contain a significant amount of STOIIP. The water-oil displacements behavior is not always well understood, especially when it occurs in the transition zone where capillary effects are dominant and both phases are mobile. The oil trapping and the rock wettability in this zone appear to be two key features to deal with. They must be studied as a function of parameters such as initial oil saturation, oil characteristics, rock properties etc. There is very little experimental data available in the literature that describes these features. This study focuses on relative permeability and residual oil saturations during drainage and imbibition in carbonate reservoirs. Steady-state core floods were performed with crude reservoir oil on outcrop limestone cores, some with moldic porosity, over a very large range of initial oil saturations. Cores were aged with crude oil before the imbibition process to allow wettability change at the initial oil saturations. Two main types of limestone have been studied: with unimodal or bimodal pore size distributions. The two types of limestone cores exhibit very different responses to wettability alteration for the same oil/brine system while almost identical mineralogy. We attributed these differences to the vuggy structure of the Estaillade limestones, which might promote oil-wettability. The inspection of the water relative permeability curves show that water wettability decreases as Soi increases, i.e. as the elevation above the contact increases, for the two types of limestones. Therefore it is not correct to derive imbibition scanning Kr curves from the bounding Kr curve at high Soi, while assuming that wettability is constant. Hysteresis is observed for both the oil and water relative permeability curves as a function of saturation Non monotonic evolution of Sorw as a function of Soi has been observed for the limestone with bimodal pore size distribution. This behavior is ascribed to the combined effect of increasing fraction of micro porosity being filled by oil initially as well as wettability variation as Soi increases. On the other hand, Sorw increases monotonically as Soi increases, for the limestone with unimodal pore size distribution. The comparison between the experimental relative permeability curves and the ones derived from simple hysteresis models show that neglecting the variation of wettability along the transition zone leads to erroneous values in oil saturations thus on oil recovery.