Petroleum reservoir | EPFL Graph Search

A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence of high heat and pressure in the Earth's crust. Petroleum reservoirs are broadly classified as conventional and unconventional reservoirs. In conventional reservoirs, the naturally occurring hydrocarbons, such as crude oil or natural gas, are trapped by overlying rock formations with lower permeability, while in unconventional reservoirs, the rocks have high porosity and low permeability, which keeps the hydrocarbons trapped in place, therefore not requiring a cap rock. Reservoirs are found using hydrocarbon exploration methods. Oil field An oil field is an area of accumulation of liquid oil underground in multiple (potentially linked) reservoirs, trapped as it rises by impermeable rock formations. In industrial terms, an oil f

Les circulations d'eau dans les massifs cristallins alpins et leurs relations avec les ouvrages souterrains

The present study has been achieved within the framework of the scientific program AQUALP, supported by the EVIAN Foundation. Its theme is the study of the hydrogeology of the Alpine crystalline. The AQUALP programme consists of two co-coordinated parts : while the "source" part, lead at the Savoy University, studies natural circulation towards springs, the "work" part, which concerns this study, has focused on the interaction between civil engineering works and underground waters. The approach adopted is that of a field study during which water inflows encountered in various Alpine underground works and replaced in their geological contexts were followed up as from the discharge, the physico-chemical and the isotopic chemistry point of view. A tracer test and numerical simulations of underground flows were also undertaken. Main results The summary of the hydrogeological data in the numerous existing underground works allowed to calculate, on the basis of simple analytical solutions, the distribution of the hydraulically conductivity of the massifs crossed. These results show that the deeper one goes the more the hydraulical conductivity decreases. They bring us to specify the thickness of the decompressed zone, i.e. about 500 m. This zone strongly influences the underground flow in these massifs. Presence of mica inhibits the hydraulical conductivity in conferring a more plastic comportment to the rocks during past tectonic phases. The temperature of the water inflows encountered is a complex function of the thickness of the overlying rock and the quantity of waters circulating in the massif. Therefore it constitutes a precious indicator, during the excavating of underground works, of the presence of possible more permeable sections in formations to come. A numerical simulation of such a case has been undertaken and shows the possibility of using this tool to improve the expectation of water inflow in the work. The temperature study as well as the application of the chalcedony geothermometer to the entire of the inflow studied has shown the existence of ascending flow systems, fed by precipitation. Waters circulating in the Alpine massifs have a chemical composition strongly influenced by the reservoir rock. Chemical analyses of major and trace elements have allowed to distinguish waters issued from the various petrographies encountered. One must first of all underline the complementarity of major and trace elements analyses. The discriminating power of these two types of analyses does not apply to the same type of rocks. The major structures hydraulically conductive in crystalline Alpine massifs have been defined. One can mainly quote isolated fractures, strongly fractured and tectonised zones, kakirite zones, the decompressed zone, the down-bending zone, contacts between distinctive hydrogeological units and large metasedimentary structures. Hydraulical and physico-chemical characteristics of waters associated to each type of defined structures have been determined. These structures are straightened and induce water circulation close to the vertical, from the surface towards the work. The infiltration zones of waters determined on the basis of the orientation of major structures generally coincides with the altitudes calculated on the basis of isotopic analyses of waters (0-18). Some anomalies have nevertheless been put into evidence. They are mainly relative to circulation in the decompressed zone or in overlying Quatemary beds. Relationship between surface waters (barrier lakes or rivers) and underground works have also been put in evidence on the basis of the interpretation of isotopic results. Numerous water inflows are poor in tritium and attest of the time of transit through to the work in the order of a number of decades, in relation with the weak permeability observed in depth. These waters are often rich in sodium, because of the alteration of silicates contained in rocks. More recent waters have been encountered in shallow depths, in the decompressed zone or in association with a great geological fault. The examples of the interaction between underground works and springs are systematically linked to important water inflows in the works either through a decompressed zone of the massif, or through a particularly transmissive zone connected with the surface. These examples show that in this fissured environment, extremely divided into compartments and anisotropic, the drying up of springs is not linked with the progressive lowering of a water table along side the work but at punctual and localized inflows. A conceptual model of the hydrogeology of the Alpine crystalline is proposed in this study. It is accompanied with an interaction model between a work and the natural middle. It must help the project manager to foresee the water inflows in underground works and to adopt the optimal solution to minimize the impact of the work on water resources.

EPFL1998

Propagation of fluid driven fractures in transversely isotropic material

Fatima-Ezzahra Moukhtari

The propagation of fluid driven fractures is used in a number of industrial applications (well stimulation of unconventional reservoirs, development of deep geothermal systems) but also occurs naturally (magmatic dyke intrusion). While the mechanics of hydraulic fractures (HF) in isotropic media is well established, the impact of the anisotropy of natural rocks on HF propagation is still far from being understood. Sedimentary rocks like shales and mudstones are ubiquitous in upper earth crust which are made of fine layers which result in transverse isotropy. In the framework of continuous mechanics, these rocks are commonly modelled as a transverse isotropic media (TI). In addition, a large number of fluids used in HF are non-Newtonian. They typically exhibit a shear-thinning behavior which can be reproduced by different rheological models with varying levels of accuracy (Carreau, power law, Ellis). In this thesis, we focus on hydraulic fractures in impermeable TI media. We assume that the fracture propagates normal to the isotropy plane without any further assumption on its shape. This configuration is relevant for normal and strike-slip stress regimes where the minimum in-situ stress is horizontal. We combine a boundary element and a finite volume method with an implicit level set scheme to model the growth of three dimensional planar HF. Both anisotropy of elasticity and fracture energy/toughness are accounted for. This algorithm couples a finite discretization of the fracture with the solution for a steadily moving hydraulic fracture in the tip region. We show that the near tip elastic operator has a similar expression than in the isotropy pending the use of a near-tip elastic modulus which now depends on the local propagation direction with respect to the isotropy plane. Using this numerical model we quantify the fracture elongation as a function of both the elastic and fracture toughness anisotropies. The elongation is maximal in the toughness dominated regime. The transition of the viscosity to the toughness regime occurs faster along the arrester direction, thus promoting fracture elongation. In parallel, we report laboratory experiments of HF growth in cubic samples of slate Del Carmen under true-triaxial confinement. We were able to propagate a planar HF perpendicular to the bedding planes only when the initial stress normal to bedding was 20 times larger than the other two stresses. For both regimes, the fracture surfaces are very rough with a self-affine behavior in the direction of the bedding and a stationary state in the direction normal to bedding. We also investigate the effect of a non-Newtonian rheology on HF growth. We solve the problem of steadily moving semi-infinite HF driven by a Carreau fluid. We use a Gauss-Chebyshev method for elasticity combined with finite differences for lubrication flow and solve the resulting non-linear system with the Newton Raphson method. The solution exhibits four asymptotic regions: a linear elastic fracture mechanics (lefm) asymptote near the tip, high-shear rate Newtonian and power law asymptotes in an intermediate region and a low-shear Newtonian asymptote in the far field. For the same dimensionless toughness, the fluid lag is smaller than for a Newtonian fluid of low shear rate viscosity. We show that simpler rheological models (Ellis and power law) cannot capture the complete solution, which accounts for the full rheological behavior.

EPFL2020

Polymer nanospray interfaces for on-line electrochemically induced modifications

Tatiana Rohner

The aim of this work has been to design, and fabricate a miniaturized electrospray-type interface for mass spectrometry analysis, which allows the nebulization of solutions by applying a high potential difference between the source and the mass spectrometer. The fabrication of the nanospray emitter is based on UV-laser photoablation of polymer substrates. Thick-film channel flow electrodes can be integrated in the microfluidic system, allowing the application of a high voltage to generate electrospray from the open outlet of the microchannel. The polymer-based interface first presented is characterized by a flat edge interface. However, a V-shaped nozzle has been found to present higher stability and ease of use. This design also allows the generation of spray by applying high voltage through an electrode located in a solution reservoir, thereby inducing an electroosmotic pumping. Taking advantage of the intrinsic electrolytic behavior of electrospray, a specific electrochemically induced tagging of free cysteine residues located in proteins can be performed on-line. A p-hydroquinone buffer is used to perform a continuous infusion of protein solution. When in contact with the high-voltage microelectrode, p-hydroquinone undergoes oxidation, thereby producing protonated p-benzoquinone. The latter reacts with free cysteine residues, following a Michael-type addition. The modification of the protein can be followed thanks to MS analyses. A complete study of the mechanisms involved in the electrochemically induced tagging with hydroquinone has been carried out by cyclic voltammetry and digital simulation. The process of the tagging consists of an ECE mechanism, since the formed adduct is stabilized in the reduced state, and is thus free to be oxidized. The rate constant of the chemical reaction has been extracted, by performing cyclic voltammetry studies and modeling the whole system by digital simulations. Finite element simulations have also permitted to highlight several mechanistic aspects of the electrotagging. The nanospray interface has been modeled as a channel-flow electrode cell. After validation of the model with respect to the experimental results, kinetics and mass transport conditions have been investigated. The flow profile, as well as the kinetic rate constant, has been shown to be of great importance in the electrochemically induced tagging. The use of a sacrificial electrode as metallic ion source to generate electrospray has also been investigated. Transition metal electrodes, i.e. copper, zinc, nickel and iron, as well as silver, were used to get on-line complexation with model peptides. It has been demonstrated that the use of in-reservoir sacrificial electrode was an efficient method to generate metal ions in order to form complexes with peptides, without the addition of metallic salts. These studies have demonstrated that polymer nanospray interfaces can be advantageously used as analytical devices, together with their primary function, i.e. ionization sources for protein analyses by mass spectrometry.

EPFL2003