Listing 1 - 7 of 7 |
Sort by
|
Choose an application
This project focusses on the initial implementation of the new CSMP-GEMSnumerical code, designed for combined fluid flow (CSMP) and reactive transport modelling (GEMS), hence this code can suitable for prediction fluid distributions, temperatures as well as fluid and mineral compositions resulting from water-rock interactions. Although this new code is promising (especially regarding the level of complexity) furthertesting is needed, especially with regard to the combination of hydrologic non-isothermal fluid flow with dynamic permeability and fracture flow. Also the extrapolation of the models with respect to natural system needs to be examined further. Herein lies the innovative aspect of this projects: creating a model that combines a natural complex geometry in combination with realistic porosity and permeabilitychanges in a hydrothermal system and applying this to a natural system.To this end, the Latemar carbonate platform (Italy) was chosen. This region is ideal for testing the codes capacity to model the geometric evolution of the dolomitization (and hence of the dolomitizing fluid) asit contains different lithologies, with each their specific porosity andpermeability, which are cross-cut by fractures and dikes. Furthermore, there is still some debate concerning the nature of the dolomitizing fluid, giving us the opportunity to examine to what extend the code can determine the source of dolomitization.More specifically, this project will be divided into three major parts. The first part will mainly focus on fluid composition and will attempt to determine the source and conditions of dolomitization. The second part will focus more on the geometry of the fluid flow by incorporating the fracture and dike distribution pattern, as well as permeability and porosity changes into the model. The third part will largely depend on the findings of the two previous parts. For now, the idea is to shift the focus towards magmatic intrusion and the resulting effects on the related hydrothermal fluid flow and hence, the effects on the carbonate system.
Choose an application
The discovery of complex continental carbonate reservoirs in the South Atlantic (Brazil and Africa) rift-sag lacustrine basins has generated considerable industrial and scientific interest. One of the most common and promising reservoir lithotype described in the so-called "Pre-Salt" interval is characterized by shrub structures. Searching for analogues, the shrub morpho-types from Tivoli travertines (Central Italy) seems to be a candidate, since they display petrographic features and pore-morphologies remarkably similar to the Pre-Salt reservoir rocks. The shrubs from Tivoli also call attention by their laterally very flat and continuous layers, mapped over hundred meters, with local packages of more or less 40 m thick. They possess the dimensions of a small reservoir petroleum field.To better understand and characterize the shrubs from Tivoli and their pore network, a 2D and 3D multi-method and multi-scale workflow was worked out, in which the sedimentology and geochemistry is first studied and subsequently the pore network is accessed. Understanding complex variations in pore geometry within different lithofacies is the key to improve reservoir description and exploitation. In fact, variations in pore geometrical attributes define distinct flow zones (hydraulic units) with similar fluid-flow characteristics.The shrubs from Tivoli are mainly characterized by their branching texture, however, they are very variegated. By analyzing them petrographically and by using 3D micro computer tomography (µCT) images, it was possible to distinguish 6 shrub morpho-types, named: narrow dendriform shrubs, wide dendriform shrubs, fili dendriform shrubs, arborescent, arbustiform and pustular shrubs. Their textures (morphologies, size, size sorting and packing) greatly vary, however petrographic analysis showed that they are monotonous in relation to their mineralogy and basic fabrics. They are 100% calcite, and are constituted of peloidal micritic aggregates, always surrounded by a very thin coating of sparry calcite cement. Rarely, they possess a crystalline habit. The presence of these sparry calcite cements that surround the shrubs, influences the quality of the reservoir, because it shields micro-porosity, which is present in the center of the shrub, from meso- and macro-porosity surrounding the shrubs.The travertine shrub structures from Tivoli are interpreted in the present study to have developed in very shallow extensive waterlogged, slightly inclined flat areas, changing laterally into a slope system with crusts as the main lithotype. Shrub morphologies likely reflect specific (micro-)environments that are controlled by water flow rates, evaporation and microbial activity. Under high flow conditions, CO2 degassing is the main process leading to carbonate precipitation. Consequently, dense and tightly packed morphologies will precipitate, mainly consisting of the crust lithotype. In this setting, microbes are less dominant. Moreover, dendriform shrubs, with narrow, wide and fili morphologies are interpreted to occur in settings with moderate- to low-energy water flows. Narrow dendriform shrubs reflect faster flowing conditions, with decreasing impact of flow on the morphological characteristics toward wide dendriform shrubs to fili dendriform shrubs. Slow to stagnant flowing waters are more characteristic for the arborescent, arbustiform and pustular shrubs that are possibly highly influenced by evaporation. Besides, the shrubs in the study area make up three depositional sequences that are limited by erosive surfaces.The stable C and O isotopes are also in agreement with the proposed sedimentological interpretation. The stable carbon isotope signature showed high values varying between +8.71 and +11.32‰VPDB, and stable oxygen isotope values varied between -4.97 and -8.25‰VPDB, indicating that precipitation was mainly influenced by degassing and evaporation processes. The very high C stable isotope signatures and the shrub fabrics that are mainly composed of micritic peloidal aggregates suggest that microbes mediated also the carbonate precipitation. The 87Sr/86Sr ratio signatures pointed out that the Mesozoic limestones of Central Italy served as the main source rock. Besides, the presence of Sr, S, Na and Ba obtained by elemental analysis, suggest that the fluids also percolated the Triassic evaporites.The main pore types observed in all the shrub samples consist of intershrub and interdigit growth framework pores. Plugs yield porosities from 0.8 to 20.9 % and permeabilities from 0.001 to 5255 mD. No relationship was observed between the shrub morphologies and porosity and permeability lab measurements. However, it was observed that the shrub packing, which corresponds to the ratio between shrub width and adjacent spacing, controls primarily the porosity and secondarily permeability. In addition, shrub size sorting, defined by the complexity of the shrub sizes within a sample, controls primarily permeability and secondarily porosity. Micro-Computer Tomography imaging was used to render and evaluate the 3D arrangement of shrub morphologies, pore connectivity and porous framework. The results pointed out that shrub morpho-types can be distinguished based on their pore shape volume and possess high pore network connectivity.Therefore, an integrated methodology, including Nuclear Magnetic Resonance (NMR), Mercury Intrusion Porosity (MIP), Micro-Computer Tomography (μCT), porosity and permeability measurements, petrography and SEM analyses, was introduced to gain insight into the complex variations of the pore network within the Tivoli shrub facies. It was observed that micropores have a significant impact on the permeability by increasing the fluid pathways and tortuosity, and consequently negatively affecting the permeability. This workflow allowed observing that shrub size sorting not only controls permeability, but also pore entrances. Besides, they secondarily influence pore body sizes and porosity, while shrub packing influence primarily the pore body sizes and porosities. The study of the Reservoir Quality Index (RQI) and Flow Zone Indicator (FZI) displayed a relationship with pore parameters, and also evidenced that the amount of microporosity in the pore network negatively affects the quality of the Tivoli travertine shrub reservoir analogue. The relationship between RQI and FZI with MIP/NMR groups represents the heterogeneities of the complex travertine reservoir, and helped understanding the complexity of the pore network.The application of the Lattice Boltzmann method for permeability simulation derived from μCT images pointed out that shrub morpho-types display a relationship with porosity (µCT results), permeability (Ksim) and tortuosity, which varies according to the different depositional shrub architectures (morphology, arrangement of the branches, packing and size sorting). Furthermore, by the use of a portable hand held air mini-permeameter it was possible to quantify the permeability distribution within a reservoir with different shrub morpho-types in detail. Vertical permeability variation was very high, as well as high lateral permeability variation is observed at cm-scale. High anisotropy occurs within laminae, with larger permeability continuity in the direction parallel to the laminae. Textural heterogeneities are responsible for the high permeability variation values within laminae.The study of acoustic wave velocities showed a relationship between shrub morpho-types, pore-types and porosity. Samples with frame-forming pore-types as mouldic pores or encrusted bubbles show higher velocity values and lower porosities than samples with no frame-forming pores as vugular pores, resulting in lower velocity values and higher porosities. Besides, the analyzed samples yield lower velocities with higher porosities. In addition, the comparison of Tivoli travertine samples with Turkish and Hungarian ones showed very similar acoustic wave velocity behavior. On the other hand, the comparison with marine carbonate indicates very different compressional-wave velocity relationships with porosity.
Choose an application
The Cantabrian Zone in Northern-Spain represents the foreland of the Variscan Orogeny in the Iberian Peninsula. Post-orogenic curving resulted in the creation of an orocline, with extension and crustal thinning in the outer part of the bend and compression and crustal thickening in the inner part (Weil et al., 2000; Gutiérrez-Alonso et al., 2004). The Bodón Unit in the southwestern Cantabrian Zone consists of three thrust nappes (Forcada, Bodón and Gayo; Marcos, 1968) with stratigraphic successions ranging from Cambrian to Carboniferous in age. Several impressive dolomite bodies can be found in the formations of the Bodón Unit.The dolomite bodies are very well studied from petrographic and geochemical point of view by Gasparrini et al. (2006a & 2006b). The proposed dolomitization model implies the circulation of hypersaline and hydrothermal marine-derived brines by thermal convection. However, the influence of dewatering shales and clay mineral transitions is most likely underestimated in this model (M. Gasparrini/R. Swennen, pers. com.).The first goal of this research project is to fine-tune the model postulated by Gasparrini et al. (2006a & 2006b) by using different methodological approaches. A petrographical and geochemical study of the San Emiliano Formation (the siliciclastic formation suspected to have influenced the dolomitization) will be conducted. Also, a volumetric study of this formation and of the dolomite bodies will be performed as to estimate their relative volumes. The application of Mg isotope geochemistry will be studied. A proven influence of the San Emiliano Formation can lead to a conceptual model on the influence of dewatering shales in dolomitization, a model that could be applied to other dolomite occurrences worldwide.As a second goal, the fine-tuned dolomitization model will be used to interpret and explain the variation of geochemical and petrophysical characteristics in the structurally controlled hydrothermal dolomite bodies. Most carbonate sedimentologists assume a certain variation of characteristics in these bodies (e.g. Warren, 2000), however, a study on this topic is seldom included. The main aim of this study is thus to map these variations and try to understand the parameters that result in the variations. There will be a strong focus on mechanical stratigraphy (as to include both matrix and fracture porosity) and overdolomitization. Well-exposed outcrops of structurally controlled dolomite bodies in the Bodón Unit will be chosen to perform detailed and systematic geochemical and petrophysical sampling. In the scope of this second goal, carbonate clumped isotope thermometry will be applied. The predictability of porosity and permeability variations within dolomite bodies can lead to optimized exploration methods, not only for the gas and oil industry but also for geothermal energy and CCS purposes.
Choose an application
Choose an application
Recently huge oil-accumulations were found near the coasts of Brazil and Angola. This discovery represents one of the largest one over the last 30 years! The reservoir rock, containing the oil, is dominated by travertine. You may know travertine as a building stone of the Colosseum in Rome or as the snow white rocks of Pamukkale in Turkey. Travertine can be compared with the calcification in your water boiler, but than in nature and on a much bigger scale. Only few is known about the characteristics and genesis of this type of rock. Consequently the extraction of oil from travertine could lead to unpleasant surprises… Therefore scientists recently started to study these kind of deposits. This study investigates two boreholes that were drilled in the Lapis Tiburtinus travertine formation near Tivoli (Italy). Emphasis is on the characteristics of the water from which the travertine was formed, as some scientists claim that the water can contain information about the past climate! Additionally we want to investigate where the fluids actually came from. Stable isotope analysis in the rocks can give us a lot of information about these fluids. The ratio of heavy and light isotopes in travertine compared with the ratio in a reference material can show variations due to specific processes. For instance rock formation from hot water will lead to incorporation of a larger amount of light oxygen isotopes (16O) in the crystal structure relative to the heavy oxygen isotopes (18O), than is the case in colder water. Consequently the oxygen isotope ratios measured in travertine can tell us something about the evolution of the fluid temperature through time. The oxygen and carbon stable isotopes can, however, also be influenced by organic interference and evaporation. Investigation with microscopic techniques has been carried out to acquire more information about which processes dominantly affected the stable isotopes. The carbon stable isotopes and the ratio of 87Sr/86Sr can tell us something about the source of the water. To learn more about the formation process of the travertine in time, U-Th dating cannot be used in this formation, so OSL (Optically Stimulated Luminescence) dating is carried out. In the lab, quartz and feldspar grains are exposed to light for the first time since thousands of years, whereas the grains release a specific amount of built up energy. Measuring this energy gives us theoretically the age of the last moment that the grain saw light, e.g. during sedimentation of the grain and covering by other grains in a river, thousands of years ago. Based on a combination of all these data we came to some important conclusions. Concerning OSL dating, the measurements should be performed on feldspars instead of quartz, as the expected ages of the travertine are too high for the quartz to record. Another finding is that a large part of the water came from deep below the travertine formation, with interaction with limestones at temperatures up to 200°C! Also an important component of rainwater was present, that has cooled this warm water. We calculated that the temperature of the travertine forming water has fluctuated between 21°C and 33.5°C through time. The fascinating conclusion is that these temperature fluctuations through time can be associated with alternations of (cold) ice ages and (warm) interglacial periods: the travertine formation has recorded climatological information from the past in its stable isotopic composition!
Choose an application
Oil and gas naturally occurs in the subsurface, in reservoirs that are composed of different rock types or lithologies. To be able to extract these hydrocarbons, certain properties of the subsurface rocks must be known, i.e. porosity and permeability. Porosity is defined as the volume of void space within a rock, typically expressed as a fraction or a percentage. Fluids or hydrocarbons are usually stored in the void spaces within the rock structure. Permeability describes the ability of such fluids to flow through rocks. These properties vary depending on several factors such as the process of deposition, composition, and post depositional processes such as diagenesis. Determining these properties for reservoir rocks is not as straightforward as it may seem, especially since its expensive to obtain samples of subsurface rocks that can be at a depth of a few kilometers. The discovery of oil fields within continental carbonate deposits (a calcareous rock type that originates on land) in the Campos basin, offshore Brazil is a perfect example of this. Unlike the more common reservoir rocks such as sandstone or marine carbonates, continental carbonates are characterized by a very complex pore structure. Therefore, the relationship between porosity and permeability in continental carbonates is not as well defined. This led to extensive studies of reservoir analogues such as quarries or outcrops on the surface of the earth that approximate the characteristics of subsurface reservoirs. Defining the flow properties of a rock is a time consuming and expensive process, which is why several geologists have tried to define this relationship through more convenient methods. Several successful approaches have been made in describing the relationship between porosity and permeability in rock types with a simple pore structure, such as sandstone and marine carbonates. This done by linking the geometry of the pore structure such as dominant pore sizes(DOMsize), pore complexity (PoA (2D) or SSA (3D), shapes and pore orientation to permeability. Similarly, this study focuses on defining the link between the geometry of the pore structure and permeability in continental carbonates. This is done by obtaining similar pore geometry parameters in both a 2D and 3D aspect. The 2D analysis is done through a digital image analysis (DIA) technique conducted on thin section images of rock samples, while in 3D these parameters are obtained by micro-computer tomography(microCT). The main goals of this study are to define the relationship between the previously mentioned pore geometry parameters and permeability, compare the findings of this research to previous work conducted on less complex pore structures, such as that of sandstones or marine carbonates and lastly, to compare the feasibility of using 2D digital image analysis in comparison to 3D microCT analysis. The results obtained in this study reflect certain similarities and differences. The relationships between the pore geometry parameters such as dominant pore sizes(DOMsize) and complexity of the pore space (PoA(2D) or SSA(3D) is present, however the relationship between pore geometry parameters and permeability is not as distinct in continental carbonates in comparison to less heterogenous lithologies, such as sandstone and marine carbonates. Furthermore, the results obtained via 3D microCT analysis provided more accurate descriptions of the pore structure and lead to better results in comparison to 2D DIA.
Choose an application
Fine-grained sedimentary formations are investigated in numerous scientific fields, e.g., asa host formation for a deep geological repository for high-level radioactive waste, as cap rocks for oil reservoirs or CO2 geosequestration, or as potential economic resources in case of shale gas extraction. The permeability characteristics of these geological strata are important to assess theirability to act as a long-term effective barrier. However, apart from some gross parameters (such as hydraulic conductivity etc.), such characteristics are difficult to measure because of the nanometer-sized porosity structures and complexinterconnectivity. SCK recently developed a versatile technique to measure the diffusion coefficient of dissolved gases in low-porosity materials. The method was validated on Boom Clay samples, and up to now diffusion coefficients for He, Ne, Ar, Xe, CH4, C2H6 and H2 have been measured. The precisionof the obtained diffusion coefficients ishigh (< 10% uncertainty) compared to other existing techniques. Most recent results show that an exponential relationship exists between the kineticdiameter of these gases and the measured effectivediffusion (De). An equal relationship exists between the kinetic diameter of these gases and their self-diffusion coefficient in water D0.The ratio of D0 over Deff is called the formation factor, F. It is believed that this factorcan be linked to structural propertiesrelated to the permeability of the material. One of the objectives of this PhD is to investigate if information on the permeability/structure of the material can be obtained by measuring the diffusion coefficient ofgases.Another objective of this PhD proposal is to verify whether similar relationships between kineticgas diameter and effective diffusion coefficient exist for other low permeability materials. The diffusion coefficient of other gases can then be predicted based on their kinetic diameter. For this objective, we will investigate rocks of interest both for radioactive waste disposal (Callovo-Oxfordian, Opalinus Clay) and for oil industry and shale gas mining.
Listing 1 - 7 of 7 |
Sort by
|