Adrian Cerepi

Pore microgeometry analysis in low-resistivity sandstone reservoirs

Abstract The objective of this work is to analyse the pore microgeometry and its effect on petrophysical properties in six low-resistivity sandstone reservoirs by combining a 2D quantitative petrographic image analysis (PIA) and 3D petrophysical tools. The classic petrophysical tools enable the measurement of different classic reservoir properties such as specific surface area, average pore diameter, pore size distribution, macroporosity and microporosity, capillary pressure versus saturation, pore chamber–pore throat diameter ratio, electrical properties and permeability. The petrographic image analysis quantifies pore microgeometry in more than four orders of magnitude, from submicron to millimeter scale. Chloritic low-resistivity sandstones show dual porosity structure defined as chloritic texture. The pore microgeometrical parameters measured by petrographic image analysis allow one to model different reservoir properties such as capillary pressure, permeability and electrical behaviour. The results obtained in these models show that pore microgeometry plays an important role in the physical properties of low-resistivity sandstone reservoirs.

Petrophysical properties of porous medium from Petrographic Image Analysis data

Abstract Petrographic Image Analysis (PIA) is a well-established rapid two-dimensional (2D) method to quantify pore and solid space in reservoirs and different porous materials. This paper aims to describe a method of characterization and quantification of petrophysical properties in carbonate pore systems using Petrographic Image Analysis over more than three orders of magnitude, from a submicron to a millimeter scale. We integrated two kinds of multiscaled digital image: the transmitted-light-colored petrographic images which allowed us to characterize the macroporosity; the Back-Scattered Electrons (BSE) grey level images which gave us information about microporosity. This technique enabled us to measure different classical petrophysical properties such as pore area, specific surface area, average pore diameter, distribution of pore size, pore shape factor, macroporosity and microporosity. We used image parameters in order to obtain the model of capillary pressure curve versus saturation (Pc–S). On the other hand, using empirical equations of permeability derived from Carman–Kozeny expression and a bundle of capillary tubes model, we were able to calculate the permeability of carbonate pore systems from different image parameters. The same petrophysical parameters were directly measured on core through classical three-dimensional petrophysical techniques (3D), such as Hg-injection porosimetry, permeametry and the BET technique. Finally, we compared the values different petrophysical properties of carbonate pore systems, obtained from 2D image analysis (PIA) and 3D classical petrophysical techniques.

Analyse quantitative de l'hétérogénéité de la fracturation : application aux carrières souterraines

Abstract The quantitative analysis of fracturation heterogeneity from Geographic Information System (GIS) has become very important for the modelling of underground quarries stability, the reservoir properties deduced from fracturing and their consequences on the groundwater run-off. This paper aims to give a method of quantitative analysis of fracturing in three underground limestone quarries of Gironde. More than 1000 fractures were measured, mapped and numbered. The heterogeneity analysis and the fracturing connectivity are based on the spatial distribution of geometrical parameters of each fracture, such as: openness, length, direction, orientation, spatial distribution of different fracture classes and connexity. To cite this article: A. Cerepi, C. R. Geoscience 334 (2002) 163–170.

Electrical behaviour of saturated and unsaturated geological carbonate porous systems

This chapter discusses the theoretical principles of the complex resistivity, the electrical behavior of a saturated and unsaturated porous medium, and electrofiltration phenomena. The chapter provides the physical properties of different samples. The experimental setting and the conclusions are also presented in the chapter. More than thirteen carbonate samples were investigated to measure classic electric parameters in saturated and unsaturated geological carbonate porous systems. The values of the cementation factor m range from 1.55 to 2.49. The dolomitic crystal texture shows the highest value. The electrical behavior of the carbonate porous system in an unsaturated medium is investigated from the saturation exponent n . The highest values of n are obtained for a dolomite crystal carbonate while the lowest values of n are obtained for a mudstone-wackestone texture. The values of the chargeability factor M range between 0.19 and 0.5, and they depend on the brine/gas saturation of the carbonate porous system, carbonate textures, and the salinity of brine in a porous medium.

Modelisation and circulation of fluids in geological porous systems. images analyzing and mercury porosimetry

The principal object of this article is the description and the development of a software which makes it possible to simulate in real time the circulation of a fluid in a porous rock. We obtain not only rock parameters (porosity, radius of pores connection), but we also observe the progression of the fluid in the rock (phenomenon of deflation). In the second time we explain the first results which we obtained with these simulations then we will compare these results 2D with the data 3D of porosity per mercury injection to allow us to establish a link between porosity image 2D and the data 3D.

CO2-Vadose and DEMO-CO2 Projects: Two Complementary Projects about Geochemical Monitoring during CO2 Leakage

Carbon capture and storage site (CCS) are subjected to specification relative to security towards population but also toward the environment. As consequences, it has been suggested that a maximum of 0.01 % per year of CO2 leakage would be the maximum amount of CO2 tolerated to leak from a CCS site (White et al., 2003; Oldenburg et al., 2003). Therefore geochemical tools have to be developed to monitor and detect CO2 leakage from the near surface and the shallow unsaturated zone (vadose zone). They must have the potential to precisely detect and quantify leaks, and discriminate natural signal from anthropogenic ones.The aim of this study is to understand the attenuation mechanism in the carbonate vadose zone and to estimate the processes of transport and reaction. This works describes the results of a release experiment in the shallow surface of the vadose zone.

Characterization and modelling of argillaceous porous medium by compressional and shear acoustic waves

This chapter focuses on the characterization and modeling of argillaceous porous medium by compressional and the shear acoustic waves. The prediction of effective porosity and elastic moduli in mixed phases depends on volume fractions and the elastic modulus of each phase as well as their geometrical combination. With volume fractions specification, it is only possible to predict the mixed upper and lower elastic moduli bounds. The results showed that the clay compaction evolution and the water drainage cause density increase. It is observed that clay is initially put in suspension in water and then arranges itself progressively to raise a laminated structure. The ultimate stage of compaction tends to form a mineral block of a much reduced porosity, in which anisotropy tends to disappear. Taking into account of geometrical structure, and Reuss and Voigt formulations, it is possible to express clays bulk and shear moduli. To use the good values for mineral elastic moduli, it is advisable to have a good reliability about the clay mineralogy for a given depth. Clay mineralogy determination could be done with two methods—X-Ray diffraction on plugs, and gamma ray spectroscopy.

Effect of Pore-Lining Chlorite on Petrophysical Properties of Low-Resistivity Sandstone Reservoir

Chlorite bearing sandstones usually give low resistivity signals, and are thus erroneously identified as non pay zones, even if they exhibit good preserved porosities at depth. The purpose of the paper is to provide petrophysical and mineralogical laboratory measurements, that help improving the log interpretation in these sandstones. The main results, obtained on a selection of reservoir cores, for sandstones having an amount of chlorite between 3 and 11 wt-%, are (1) the cementation index and saturation exponent (m and n) have values lower than the common 2 values, n frequently around 1.5. These low values have been carefully checked in order to avoid experimental artefacts. (2) Cationic Exchange Capacities (CEC) and Specific Surface Area (SSA) have low values, as expected from the clay structure. (3) the distribution of pore throats is bi- or tri-modal, with a large contribution of microporosity. The interpretation suggested by these results is that the amounts and distribution of microporosity associated to pore lining clay is the key of the chlorite sandstones electrical behavior. The values of CEC or SSA are too low to fully explain the low values of saturation index n. Use of these low values in log interpretation has the effect of increasing the evaluation of oil in place. Advantages of a multi-disciplinary approach for better evaluation of such complex argillaceous sandstone reservoirs is highlighted.