Mercury Injection Tests Research Articles

Interrelations of the petrophysical, sedimentological and microstructural properties of the Oolithe Blanche Formation (Bathonian, saline aquifer of the Paris Basin)

The Paris Basin seems a suitable location for CO 2 capture and storage given both the amount of CO 2 produced and the availability of depleted fields and deep saline aquifers. This study investigates the petrophysical properties in relation to the sedimentary and diagenetic environment of the Oolithe Blanche Formation (Middle Jurassic), a deep saline aquifer considered a potential candidate for CO 2 storage. Because of the scarcity of core data in the Paris Basin, our investigation was based on the study of field analogues in the south-east part of the Paris Basin. The Oolithe Blanche Formation (Bathonian) is 70–80 m thick. Eighteen oriented blocks were collected from three outcrops selected for the different sedimentological facies identified in the formation. Their petrophysical properties were measured: porosity, pore size distribution derived from mercury injection tests, permeability and capillary imbibition parameters. The sedimentary and diagenetic facies were defined by using optical microscopy coupled with image analysis on thin sections and SEM. The Oolithe Blanche Formation is composed of oolitic and bioclastic limestones, deposited in a shallow marine setting. Three main sedimentological facies were defined: the oolitic shoal facies, the tide dominated facies and the prograding oolitic facies. They exhibit subtle variations in composition and in the distribution of carbonate textures. Porosity, measured using the water saturation triple weight method, ranges from 6% to 34%. Permeability values are low, between 0.1 mD and 9 mD. The data from mercury intrusion porosimetry show that the distribution of the pore throat diameter is either unimodal (microporosity only) or bimodal (macro- and microporosity). Microporosity is intraparticle (intraooid) and macroporosity is interparticle and is related to dolo–dedolomitization. Variations of petrophysical parameters can be explained by the microstructure. Now, these latter results calibrated by studying field analogues must be extended to borehole data and core data to optimize our knowledge of the deep saline aquifer of the Oolithe Blanche Formation. Without such investigations, it will be impossible to estimate the suitability of this deep saline aquifer for CO 2 storage.

Petrophysical Properties of the Middle Jurassic Carbonates in the PICOREF Sector (South Champagne, Paris Basin, France)

This article, carried out as part of the PICOREF Project for the CO<sub>2<sub/> storage in the aquifers of the Paris Basin, presents an important petrophysical database from the numerous petroleum wells drilled in the PICOREF Sector (south-eastern part of the Paris Basin) between 1953 and 2001. These core data concern the three saline carbonated aquifers of the Middle Jurassic: the Oolithe Blanche and the Comblanchien formations, Upper Bathonian age, and the Dalle Nacrée formation, Lower Callovian age, that would be used for the CO<sub>2<sub/> sequestration. Located at –1230 to –1750 m sub sea in the studied sector, these carbonate reservoirs which cumulative thickness is about 150 m, outcrop in the Burgundy region, at about 80 km south-eastern the Sector where they are exploited in several quarries. The analysis of the 6800 routine measurements (porosity and permeability) gathered for this study allowed to improve the knowledge of the petrophysical properties. Special measurements (mercury injection tests) allowed to characterize the porous medium.

A New Approach for Constructing Pore Network Model of Two Phase Flow in Porous Media

Development of pore network models for real porous media requires a detailed understanding of physical processes occurring on the microscopic scale and a complete description of porous media morphology. In this study, the microstructure of porous media has been represented by three dimensional networks of interconnected pores and throats which are designed by an object oriented approach. Afterwards, the connectivity of the system has been optimized by an optimization algorithm. To validate the methodology, a network of a carbonate sample is constructed. In this model, the geometrical characteristics of the pores and throats, such as their shapes, effective radii and lengths, are selected from the image analysis of SEM picture and statistical distribution methods based on the mercury injection test results. Then the constructed network is further tuned according to laboratory measured porosity, absolute permeability and capillary pressure. Having built a flexible and detailed model, its prediction of relative permeability and saturation variation along a core plug are compared with experimental data for both drainage and imbibition phenomena. This comparison shows good matches for almost all experimentally measured data.

Pore-throat characterization in highly porous and permeable sandstones

Several methods have been developed to characterize the pore spaces in sandstone reservoirs using data on the pore-throat-size distribution obtained from mercury injection tests. The Winland equation, the threshold pressure, the displacement pressure, and Pittman's equation are mostly used for this purpose to delineate the stratigraphic traps and seals. This study examines the reliability of these methods applied to the highly permeable Nubia sandstones in their type section in southern Egypt. These sandstones are composed mainly of siliceous sandstones and constitute the main Paleozoic–Cretaceous aquifers and reservoirs in Egypt. Routine core analysis and mercury injection tests were conducted to delineate the pore network characteristics for these rocks. The relationships between helium porosity and the uncorrected air permeability from the routine core analysis, and the various parameters derived from mercury injection–capillary pressure curves were established using multiple regressions. This study indicates the high reliability of the displacement pressure at 10% mercury saturation and also reveals the apex of Pittman's hyperbole at 45% mercury saturation as a complexity apex at which the pore network becomes highly chaotic. Despite the great benefits of such types of measurements, they are not commonly used because of their high cost. This study introduces a series of empirical equations for constructing a partial pore-aperture-size distribution curve from routine core analysis for the highly permeable rocks.

Spontaneous imbibition in porous basalt mediated by microbial perturbations

The fate and transport of organic contaminants in subsurface depend on complex interactions between several system components such as fluid chemistries, geochemistry, microbiology, geology, and physical parameters. This study describes imbibition studies to assess the incipient interaction between selected hydrocarbons and pertinent mineral surfaces as a function of aqueous phase chemistry and microbiological perturbation. Microbial perturbations may have significant impact with respect to monitoring the contaminants and finding better strategies for remediation. Basalt cores used in laboratory experiments were obtained at depths of 200 to 300 ft from a test well located at the Idaho National Laboratory (INL). Thin section analysis of core samples showed that the basalt was formed from feldspar and pyroxene crystals with most of the pore space occurring as vugs. Mercury injection tests indicated a wide range of pore throat sizes through which the vugs could be accessed. All of the vugs were connected by inter/intra crystalline pores that were less than about 0.5 μm in width. Although most pore space occurs as vugs, miscible displacement tracer tests did not reveal significant heterogeneity. Base-case spontaneous imbibition tests were conducted on cores that had been fully saturated with dodecane using synthetic groundwater as the invading phase. Imbibition tests were then performed against basalt with cell-free supernatants and sonicants (diluted by synthetic groundwater) of three indigenous microorganisms, Acinetobacter genospecies, Arthrobacter globiformis and Bacillus atrophaeus that had been isolated from the test well. Waterflooding was performed on each core after imbibition testing to obtain the Amott wettability index to water. Imbibition tests show that, although the basalt/dodecane/synthetic groundwater system was strongly water-wetted, the scaled imbibition rate was much slower than previously observed for other core types such as sandstone and limestone. The production of organics obtained by waterflooding after spontaneous imbibition was close to zero, indicating that the basalt was strongly water-wet. At the same time, the water permeability by waterflooding was often extremely small at imbibition residual organic saturation. The distribution of trapped oil and its effect on relative permeability in the crystalline matrix may explain the relatively slow imbibition rates that were observed. The addition of microbial components in the invading aqueous phase resulted in higher imbibition rates and final recovery of organics than observed for synthetic groundwater.

Influence of stress-induced and thermal cracking on physical properties and microstructure of La Peyratte granite

Abstract New data are presented on the influence of thermal cracking and stress-induced cracking on several physical properties (porosity, acoustic velocity, attenuation, electrical conductivity, permeability) of a fine-grained granite from La Peyratte, France. Two sets of samples were studied: the `TC' set was made of samples in which thermal cracking was induced, the `MC' set included samples in which cracks were generated at increasing stress levels in mechanical tests. Good correlations were found between the evolution of the physical properties and the amount of damage induced. For the mechanical cracking process, we show that acoustic emissions recording was the key point in order to control in real time the evolution of the cracking processes. The strong anisotropy in the acoustic velocity data found only in the MC samples is clearly due to the anisotropy of the crack distribution, as shown by microstructure analyses and 3D reconstructions of crack networks from confocal scanning laser microscopy images. A model for the propagation of elastic waves in cracked solids was used in order to infer the crack density and the mean crack aspect ratio for the granite samples. Our results show that the aspect ratio of artificially induced cracks is significantly smaller than that of cracks in `natural' rocks. Network modelling for fluid flow in porous media was done using data from mercury injection tests and available information on the crack network geometry as input data. Although the numerical model gives the correct order of magnitude for the permeability, it could not account for relative permeability evolution with induced damage, presumably because of oversimplified assumptions in the model. All in all, our study confirms the strong control of the rock microstructure on physical properties. The data set presented in this paper might be very useful for studies on safety assessment for potential nuclear waste storage in geological environment.

Relationship of Porosity and Permeability to Various Parameters Derived from Mercury Injection-Capillary Pressure Curves for Sandstone (1)

Pore aperture size estimated from mercury injection tests has been used to evaluate seals for traps and to explain the locations of stratigraphic hydrocarbon accumulations. However, mercury injection tests are expensive and therefore not abundant. This paper develops empirical equations for estimating certain pore aperture size parameters from routine core analysis. The relationship of porosity, uncorrected air permeability, and various parameters derived from mercury injection-capillary pressure curves was established using multiple regression on a database of 202 samples of sandstone from 14 formations that range in age from Ordovician to Tertiary. These sandstone formations vary in composition and texture. A series of empirically derived equations also permits the calculation of pore aperture radii corresponding to mercury saturation values that range from 10 to 75% in increments of five. This makes it possible to construct a calculated pore aperture radius distribution curve using porosity and permeability from core analysis.

Fault-Zone Seals in Offshore Trinidad Oil Fields

Hydrocarbon columns in Pliocene sands of offshore SE Trinidad occur in 3-way closure, primarily in the footwall of normal faults. Multiple reservoir sands and numerous fault blocks result in a large number of individual hydrocarbon accumulations. Fault-plane sections demonstrate that fault sealing is unrelated to juxtaposition of intercalated shales. These fault-zone capillary seals were studied by (1) inferring their fluid-flow properties from the pattern of trapped hydrocarbons and (2) direct examination and measurement of cored faults. Buoyancy pressures for hydrocarbon columns were calculated from fluid property data for each reservoir and fault block. Buoyancy pressures range widely, increasing nonlinearly with fault displacement and percent shale in the faulted section, but do not vary systematically with stratigraphic position or depth. Small-displacement faults observed in core are narrow zones of cataclasis within porous sandstone. Mercury injection tests indicate fault-zone displacement pressures that coincide with buoyancy pressures calculated for hydrocarbon columns sealed by large-displacement faults. The agreement between measured displacement pressures and calculated buoyancy pressures indicates that (1) the reservoirs are filled to their capacity, dictated by the displacement pressure of the fault zones, and (2) the fault-zone seals are primarily the product of deformation of the sands, with some enhancement by incorporation more » of argillaceous material into the fault zones. The observed relationship between fault displacement and calculated buoyancy pressure of the hydrocarbon columns implies that fault-zone continuity is a factor that needs to be assessed in fault-zone seal analysis. « less