This paper presents horizontal well test design and interpretation methods. New analytical solutions are developed, which can be easily handled by a desktop computer, to carry out design as well as interpretation using semi-log and log-log analysis. These analytical solutions point out a distinctive behavior of horizontal wells which is :- At early time, a circular radial flow in avertical plane perpendicular to the well.- At late time, a horizontal pseudo-radial flow. Each type of flow is associated with a semi-log straight line to which semi-log analysis has the adapted. The horizontal pseudo-radial flow takes into account a pseudo-skin depending on system geometry which is a priori defined and estimate Practical time criteria are proposed to determine Practical time criteria are proposed to determine the beginning and the end of each type of flow and provide a guide to semi-log analysis and well test design. We study the behavior of uniform flux or infinite conductivity horizontal wells, with wellbore storage and skin. The homogeneous reservoir is infinite or limited by impermeable or constant pressure boundaries. pressure boundaries. A method is also outlined to transform all our solutions for homogeneous reservoirs into corresponding solutions for double porosity reservoirs. 1 - Introduction The first horizontal producing wells yielded extremely positive results These results made it necessary to study flow around a horizontal well with a view to practical applications : test design and interpretation. The purpose of this study is to provide, with a horizontal well configuration a way :- to decide upon whether a test has to be made ornot : will the test help to obtain the requiredinformation ?- to optimize test time, if necessary : test mustbe long enough to be interpreted.- to interpret the test performed usingapplicable methods. The simplest and most significant analytical approach is first described in this paper. It relates to the transient behavior of a well with no wellbore storage C and no skin S, with a uniform flow (flow per unit length is the same everywhere in the well). Then the wellbore storage, the skin and the effect of the boundaries of the reservoir are taken into account, leading to a practical approach applicable to most real cases. The transposition of these solutions to infinite conductivity wells is described.

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The safety of acid gas geological storage is to a large extent controlled by the capillary properties of the caprock. This low-permeable (e.g., clayey) porous media usually saturated with water acts as a capillary barrier to the underlying stored acid gas, provided its water-wettability is preserved and water/acid gas interfacial tension (IFT) is high enough. The displacement or capillary breakthrough pressure, above which the stored acid gas intrudes into the caprock, is directly related to those two interfacial properties. Water/acid gas IFTs have recently been thoroughly characterized. However, little is known on the effect of acid gases (CO2, H2S and their mixtures) on the water-wettability of caprocks. We present an experimental setup and procedure for measuring contact angles on mineral substrates in the conditions of geological storage. Measurements have been carried out in a range of pressures extending up to 150 bar, both with CO2 and H2S, and with mineral substrates representative of caprock minerals such as quartz and mica, as well as with a substrate sampled from the caprock of a depleted gas reservoir. We observed that the wettability alteration of mica is moderate in the presence of dense CO2, but pronounced in the presence of dense H2S. In contrast, the wettability of quartz and of the 'real' caprock substrate is not altered by dense CO2 or H2S. In addition to those substrate- and acid gas-dependent wettability effects, the much lower water/acid gas IFTs as compared to water/hydrocarbon gas IFTs are responsible for a loss in capillary-sealing potential of a given caprock when a hydrocarbon gas is replaced with acid gas, especially when the acid gas is rich in H2S. This potential, as evaluated by the displacement or capillary breakthrough pressure, should be determined very carefully when planning an acid gas geological storage operation. 1. Introduction As an increasing number of H2S-containing (sour) gas reservoirs are being exploited around the world, there is a growing interest for injecting and storing in geological formations the H2S rich-acid gas that is separated from the (sour) natural gas in gas processing plants. For instance, acid gas disposal in geological formations has been practised over the past 15 years in Western Canada, where more than 3 Mt of H2S and 3 Mt of CO2 have been injected, with a maximum up to 83% of H2S in one of the 40 storage sites (deep aquifers or depleted hydrocarbon reservoirs; Bachu, 2007). The reinjection of H2S-rich acid gases in massive quantities is currently being considered in some reservoirs such as the Kashagan oil field in the North Caspian Sea. These reservoirs usually contain CO2 along with H2S as associated gases, which are both separated in the gas plant. The injection of the resulting acid gas stream in a geological formation is interesting for the two following reasons:to avoid atmospheric emissions of CO2, andto avoid H2S desulphurization through the Claus process, which has many drawbacks, both environmental and economical (Abou-Sayed et al., 2005). The implementation of this option on a large scale requires a proper assessment of the effects induced by the presence of acid gas on the integrity of the formation. This assessment is the subject of many research studies, mostly conducted in the context of CO2 geological storage. A large part of this effort addresses the different possible leakage mechanisms by which CO2 may escape from the geological formation where it is stored. This effort needs to be extended to acid gases containing significant amounts of H2S.

Résumé -Injectivité du CO 2 dans les stockages géologiques : programme et principaux résultats du projet ANR GéoCarbone-Injectivité -L'objectif du projet GéoCarbone-Injectivité était de définir une méthodologie pour étudier les phénomènes complexes intervenant aux abords des puits lors de l'injection de CO 2 . La méthodologie proposée s'appuie sur des expérimentations interprétées numériquement à l'échelle de la carotte afin de comprendre (modélisation physique et lois de comportement) et de quantifier (paramétrisation des outils de simulation) les différents mécanismes susceptibles de modifier l'injectivité : les interactions roche/fluide, les mécanismes de transport aux abords du puits d'injection et les effets géomécaniques. Ces mécanismes et les paramètres associés devront ensuite être intégrés dans une modélisation à l'échelle métrique à décamétrique des abords du puits d'injection. Cette approche a été appliquée pour l'étude d'une injection potentielle de CO 2 dans la formation géologique du Dogger du Bassin Parisien, en relation avec les projets ANR GéoCarbone. Abstract

fr -joelle.hy-billiot@total.com -virgile.rouchon@ifpen.fr -gerard.mouronval@total.com -marc.lescanne@total.com veronique.lachet@ifpen.fr -nicolas.aimard@total.com * Corresponding authorRésumé -Une méthode géochimique pour la surveillance d'un site pilote de stockage de CO 2 : Rousse, France. Approche combinant les gaz majeurs, l'isotopie du carbone du CO 2 et les gaz rares -Ce papier présente la caractérisation géochimique des différents gaz, naturels et anthropogéniques, impliqués dans un pilote de stockage de CO 2 en champ de gaz naturel appauvri (Rousse, France). Dans ce pilote, le CO 2 est produit par oxycombustion d'un gaz naturel transformé en gaz domestique à l'usine de Lacq. Ce CO 2 est transporté dans un pipeline de 30 km de longueur jusqu'au réservoir de gaz appauvri de Rousse. Les gaz produits à Rousse avant injection de CO 2 , le gaz commercial de Lacq et le CO 2 résultant de l'oxycombustion ont été échantillonnés, ainsi que les gaz situés dans un puits de surveillance (à une profondeur de 45 m) et les gaz du sol situés au voisinage de Rousse. Pour tous ces échantillons, la composition en gaz majeurs, la signature isotopique du carbone ainsi que l'abondance et signature isotopique des gaz rares ont été déterminées. Les compositions gazeuses du gaz naturel de Rousse sont comparables à celle du gaz domestique de Lacq avec le méthane comme composé principal et la fraction C 2 -C 5 et CO 2 comme gaz résiduels. Les gaz des sols reflètent typiquement des mélanges entre l'air (pôle pur) et le CO 2 d'origine biogénique (avec des teneurs maximales de l'ordre de 9-10 %), tandis que les gaz présents dans le puits de monitoring reflètent typiquement la composition de l'air sans excès de CO 2 . Le gaz de Rousse et le gaz domestique du site de Lacq ont une composition isotopique δ 13 C CH 4 égale à -41,0 ‰ et -43,0 ‰ respectivement. Le CO 2 injecté sur Rousse a une composition isotopique δ 13 C CO 2 égale à -40,0 ‰ à la sortie de la chambre d'oxycombustion, tandis que la composition isotopique δ 13 C CO 2 des gaz des sols est comprise entre -15 et -25 ‰. Le gaz naturel de Rousse et le gaz domestique du site de Lacq sont tous les deux enrichis en hélium, appauvris en néon, argon et krypton par rapport aux valeurs de l'air (standard naturel). Le procédé de combustion produit un CO 2 enrichi en hélium, hérité du gaz domestique de Lacq, et une composition en néon, argon et krypton reflétant celle de l'oxygène produit par l'unité de séparation d'air. En effet, le néon est appauvri relativement à l'air, tandis que le krypton est enrichi de 10 fois, résultant de la séparation cryogénique des gaz rares au sein de l'unité de séparation d'air. Les gaz rares des échantillons de sols ont une composition équivalente à celle de l'air. À partir de ces résultats, les compositions des pôles purs impliqués dans le site pilote de stockage de CO 2 montrent que les compositions en gaz rares produits par le procédé d'oxycombustion sont suffisamment

Prior to any CO 2 geological storage operation, the caprock's ability to prevent CO 2 leakage must be carefully assessed. This ability is primarily related to the caprock's pore structure and to the interfacial properties of the caprock and the fluids in place, namely the brine that imbibes the caprock and the CO 2 stored in the underlying reservoir. This paper reports an experimental effort to characterize some of these parameters, using as a working example the carbonate-rich caprock and reservoir conditions of the Rousse depleted gas field in the South-West of France, where an estimated 120000 tons of CO 2 will be injected during two years. The parameters examined are: (i) the caprock wetting behavior in the presence of CO 2 , (ii) the caprock intrinsic (single-phase) permeability, (iii) the CO 2 breakthrough (or displacement) overpressure, i.e., the minimum pressure difference between CO 2 and brine required for CO 2 to penetrate and flow through the brine-saturated caprock, and (iv) the caprock effective permeability to CO 2 after breakthrough. The latter two parameters are indicative of, respectively, the caprock's capillary sealing efficiency and CO 2 leakage rate once breakthrough has occurred.The main observations and results are as follows. (i) The water-wet character of the Rousse caprock in the presence of CO 2 in storage conditions is confirmed through a series of contact angle measurements on substrates. (ii) Single-phase (brine) permeability coefficients measured in steady-state conditions are extremely small and strongly sensitive to the effective stress, i.e., to the difference between the confining pressure and the pore fluid pressure. They do not exceed 20-25 nanodarcy (10 -21 m 2 ) for effective stresses below 4 MPa, and 1 nanodarcy for effective stresses in the range of 10 MPa and above. (iii) Gas breakthrough in two different brine-saturated caprock samples, using either CO 2 or N 2 as the displacing gas phase, occurs in one sample for a CO 2 overpressure in excess of 7.6 MPa, and in the other sample for a N 2 overpressure in the interval of 4.5-6 MPa. In the latter sample, the effective permeability to N 2 after breakthrough is extremely low, below 1 nanodarcy; some "aging" effects are observed upon subsequent resaturations with brine and CO 2 breakthrough experiments, with a CO 2 breakthrough overpressure lower than expected and an increasing effective permeability to gas, yet still lower than 2 nanodarcy after two consecutive brine resaturations and CO 2 breakthroughs.

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