Search

Summary Ion exchange and dissolution/precipitation processes are of considerable concern when aqueous fluids are injected into reservoir sandstones, as in waterflooding or alkaline flooding or in well treatments. This paper describes a flow model that takes into account several ion exchange equilibria and the precipitation/dissolution of carbonates and hydroxides. Its validity is tested through simulations of laboratory experiments dealing with brine and alkali injection. Some insights into the effects of ion exchange and precipitation on flow properties are given.

Mineral-alkali interactions have received considerable attention in the recent literature dealing with enhanced oil recovery techniques and clay stabilization treatments. One of the critical factors to be considered is alkali consumption. Alkalinity decrease occurs through several mechanisms, which are ion exchange, precipitation, reaction with crude oil components, and dissolution of minerals. This paper describes the dissolution process. An original kinetic model is proposed to describe the alkaline dissolution of a clayey sandstone. This model is based first on results concerning quartz dissolution/condensation processes. It is also based on new experimental data, which demonstrate the inhibiting effect of aluminum and, as the reaction proceeds, the precipitation of an aluminosilicate whose the chemical composition has been determined. From these data, a kinetic scheme has been conceived in which adsorption of different chemical species is assumed to occur onto solid surfaces. These species play a more or less important role according to the extent of the reaction. In the mechanisms considered, the argillaceous fraction of the rock provides silicon and aluminum which inhibit the dissolution of the matrix while silicon coming from quartz interferes with clay attack. The kinetic model depicts the coupling of elementary dissolution processes and calculates dissolved silicon and aluminum. It has been tested for various operating conditions, providing initial reaction rates for quartz and clay. Results emphasize the definitive advantage of carbonate compared to other alkaline chemicals owing to the relative low pH of solutions, which is particularly favorable for promoting inhibition by aluminum and, as a general rule, for reducing mineral dissolution.

In the implementation of enhanced oil recovery processes by chemicals, the use of alkaline agents may be recommended. In order that these techniques be efficient, transport of alkaline additive from injection wells to production wells has to be ensured. That means a correct evaluation of the consumption of the alkaline agent which results from ion exchange and dissolution phenomena. This work deals with the study of mineral dissolution by contact with alkaline solutions in flow-type and batch experiments. The former ones are conducted until steady-state conditions are reached. In both experiments, dissolution is evaluated by the measurement of silicon and aluminum in solution. Sand, mixture of sand and kaolinite, natural sandstones are considered. Additionally, the modeling of the above experiments is made, based upon a kinetics scheme valid for the quartz dissolution condensation mechanism, which was recently proposed by S.D. Thornton. This scheme has been extended for describing clayey sandstone dissolution. The experimental results which are presented in this paper, were not found in agreement with the above scheme. The given interpretation relies upon the effect of the alkali-clay reaction products, on the dissolution of minerals. Besides, the study gives some insights into the effect of pH, temperature and rock composition on alkaline dissolution. The above numerical model has been used to predict alkaline slug propagation at field scale and the relevant alkaline consumptions. Practical consequence for the implementation of this process are examined.

Abstract One of the critical factors to be considered when using alkaline additives in enhanced oil recovery processes is alkali consumption. The mechanisms that control alkalinity decrease are ion exchange, precipitation, reaction with crude oil components, and dissolution of minerals. The aim of this paper is to describe the alkaline dissolution process in sandstone reservoirs. An experimental approach was followed to identify the key features of the process. Various operating conditions were investigated concerning temperature, nature of the alkaline agent and rock mineralogy. The attack proceeds through the adsorption of silicon and aluminum species on solid surfaces, and the adsorbed species play a more or less important role according to the extent of the reaction. Precipitation of an aluminosilicate was observed, and its chemical composition was determined from the interpretation of effluent compositions and ESCA analysis. Kinetic equations were deduced and tested, providing initial reaction rates for the quartz matrix and the associated clay fraction. These equations emphasize the coupling of elementary dissolution processes, the role played by the clay fraction in over-all alkali consumption and the inhibiting effect of the new aluminosilicate formed. A reservoir simulator was designed, which combines the detailed reaction chemistry and the flow properties. This model gives some new insight into the impact of kinetic phenomena on the propagation of alkaline additives at a reservoir scale. Introduction Many alkaline flooding field tests have been undertaken over the last twenty years, which have revealed that alkali injection is not a simplistic method but requires careful project design and monitoring techniques(1). Profitability of these field tests was not clearly established. One reason why conventional alkaline floods have been so discouraging is the lack of mobility control during alkali injection. Another reason is that low caustic soda concentrations required for obtaining low interfacial tensions prevent propagation of alkali because of its consumption by ion exchange and dissolution precipitation processes. It is, therefore, essential to identify the occurring mechanisms and to be able to estimate properly the amount of alkali loss by rock reactions. We can expect from this evaluation a better optimization of me process, i.e. the choice of the most appropriate type and concentration of alkali to obtain a high oil recovery efficiency. This paper concerns the dissolution process. There is a controversy concerning the way of approaching the problem. Same workers consider that, on account of the high residence times of the alkaline fluids in the reservoir during a field application, the system can be described by assuming that thermodynamic equilibrium is reached in each point of space(2,3). Calculation of pH breakthrough time is then made by using solubility products data for minerals typically encountered in sandstones as well as for new minerals that could appear during the alkaline dissolution(4). Other authors deduce from laboratory experiments that dissolution is kinetically limited(5,6). In that case, this limitation is liable to affect the pH front propagation and consequently reduce the alkali consumption, even at field times scale.

Quelle que soit la conjoncture economique, le procede de recuperation assistee du petrole par injection d'agents tensio-actifs necessite une mise en oeuvre tres elaboree pour tirer le meilleur parti des produits et donc pour franchir le seuil de rentabilite. Il apparait par ailleurs que son champ d'application doit etre etendu aux conditions de reservoir couramment rencontrees, notamment les fortes salinites, par l'utilisation de structures chimiques adaptees. Pour reduire les pertes de tensio-actifs par adsorption sur la roche, et par suite, preserver l'efficacite du fluide micellaire, deux techniques sont etudiees a l'Institut Francais du Petrole. L'une d'entre elles consiste a reduire l'adsorption en augmentant le pH de la formation a l'aide d'agents alcalins. Dans l'autre methode, les molecules adsorbees sont remises en solution par un agent desorbant ajoute a l'eau de chasse. L'extension du procede aux gisements sales est illustree avec une famille de tensio-actifs qui ont un comportement prometteur dans ces conditions, les sulfonates d'olefines alpha. Il apparait que l'efficacite interfaciale de ces produits ne doit pas etre seule prise en compte, mais egalement la solubilite, la stabilite chimique, le comportement rheologique et l'adsorption sur les surfaces minerales.

Les problemes d'acidification des reservoirs greseux sont abordes en introduisant une grandeur cinetique caracteristique du milieu a stimuler appelee reactivite dont la determination est necessaire pour l'interpretation complete des courbes de reponse a l'acide; ce concept de reactivite prend en compte la morphologie du milieu poreux (dimension et forme des- grains, distribution des mineraux), et les constantes de vitesse de dissolution des differentes especes mineralogiques. Les effets de l'acidification sont evalues en etablissant une relation liant la porosite, la permeabilite et la reactivite; cette relation est independante des conditions de l'experience : debit, concentration et volume d'acide injecte. Par ailleurs, un modele mathematique de l'acidification a ete concu et mis au point en geometrie radiale et unidimensionnelle. Ce modele, alimente par les donnees tirees de l'experience, restitue de maniere tres satisfaisante l'evolution des proprietes petrophysiques du milieu ; son application a la geometrie radiale (cas de l'operation de chantier) conduit a des recommandations sur la procedure a adopter en fonction des caracteristiques de la formation.

This paper describes an enhanced oil recovery (EOR) model involving use of chemical additives. The model is as general as possible in light of present phenomenological knowledge. It takes into consideration diffusion, exchanges between fluid phases, exchanges between fluids and solids, and convection (including gravity, relative permeabilities, viscosities, interfacial tensions (IFT's), and mobility reduction by polymers). Its main properties are (1) three-phase flow (aqueous, oleic, and microemulsion); (2) that each phase can be represented by a mixture of seven components; (3) overall flow is one dimensional (1D), but the sections of space considered may be constant or variable; and the porous medium may be heterogeneous. In addition to its compositional nature, which is required for describing changes in phase properties, the model must also account for ionic environment, loss of chemicals, and capillary number distribution. For these reasons, it differs from conventional multicomponent models. It is designed for simulating any EOR problem involving the addition of suitable chemicals to fluids to be injected continuously or in successive slugs. The model has been tested successfully by two-phase flow, four components (water, oil, polymer, and surfactant plus alcohol), and Winsor Type I environment experiments. It can be adapted to more and more complex phenomenological situations, depending on availability of data.

The objective of this study is to identify the mechanisms governing the propagation of alkaline solutions in a definite field case where mineralogical and petrophysical properties have a particular influence on the selection of the proper alkaline agent. In the first part, the divalent ion removal process is studied by means of flow experiments under different operating conditions, giving more or less importance to precipitation mechanism. Results are examined with the help of ion exchange isotherms and salt and hydroxide solubility data. Consequences on flow properties are discussed. In the second part, hydroxide breakthrough times are compared for two alkaline agents, i.e. carbonate and metasilicate, and a mathematical model, based on ion exchange and chemical equilibria of species in solution, is used for the interpretation of results. The relationship between rock mineralogy and hydroxide consumption is discussed.