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Abstract The objective of our work was to carry out a petroleum geological study regarding migration routes, hydraulic trapping, occurrence of potential reservoir rocks and spatial distribution of pressure and reservoir properties in a petroleum-bearing basin. Our work was based on an integrated geological and hydrogeological research on Late Miocene-Early Pannonian formations in the basin, particularly focusing on deep-water turbidites. We used the (hydro)geological model based on the results of this work as a key input for building a hydrodynamic model with which we could later assess the natural flow system and hydrodynamic conditions of the area studied. Reconstructing the depositional environment types and the related lithological type units enabled us to estimate petrophysical and hydrogeological parameters in little-known areas of the basin. Based on these approximations a more reliable hydrodynamic model was built. The model enabled us to determine the main directions of petroleum migration and to approximate the relative timeframe of hydrocarbon entrapment. We also identified possible areas for hydraulic trapping of HC's which were verified by exploration results. Using our model we are also able to predict the spatial distribution of pressure in the basin with special regards to the severity of overpressure. The results of hydrodynamic modelling demonstrate several practical applications:Predicting the spatial distribution of pressure and especially overpressure is of global importance from interrelated economic, technical and HSE aspects. The determination of migration pathways is of crucial significance from the exploration point of view. The presented method can be powerful in both well-explored mature areas and less-known territories and is independent of scale, there are numerous examples of successful application at both regional and local scale. Geological setting The focus of this study is a sub-basin of a larger neogene basin. When the basin was formed, the surroundings uplifted therefore intensive erosion was taking place and the erosional products (sediments) were transported by rivers towards the lowlands and started to fill-up the basin so a deltaic depositional system formed. Accordingly the succession above the pre-miocene basement starts with suspension-originated basal marls which are followed by distal and proximal turbidites that have a continuous transition to the deltaic sediments. Figure 1. shows a NE-SW seismic section from the area. Turbidites are indicated by a hummocky, clinoform internal reflection pattern and onlap reflection terminations on the basement highs. The deltaic sediments can also be seen clearly on the section.
ABSTRACT: The following introduces a simplified model to concurrently represent strata deformation and steady fluid flow in a porous medium as a result of underground mining. The model is based on a coupled finite element formulation where elastic deformation controls changes in fluid hydraulic conductivity of a fractured medium idealized as a porous equivalent. Coupling is steady state and neglects the influence of seepage forces. The model is compared with a case study to reveal that changes in strata conductivity are strongly related to the intensity of the mining effect. The greatest modification of hydraulic conductivities is found to occur within the caving or severely fractured zone. 1 INTRODUCTION High productivity longwall mining is becoming increasingly popular for mining uninterrupted and near horizontal coal seams. Despite high productivity, this high extraction ratio method is subject to problems related to excessive subsidence and aquifer dewatering. To address these problems and to examine the alternative of mining with narrow and less disruptive panels the following analysis is completed. Other researchers have investigated the flow regimes present around underground mines (Owili Eger, 1975; Booth, 1984) using numerical methods. Of interest is representing the post mining hydraulic regime that develops with the changing stress and displacement field. This field develops in a transient manner as compressive stresses develop undrained fluid pressures in response to the migrating face. This transient behavior has been reported by Walker (1988) but is of less consequence to the resulting terminal groundwater regime than the steady (long term) displacement field that is manifest. In an attempt to quantify the long term influence on the groundwater regime, the following numerical analysis, comparing the effect of different mining geometries, is completed. 2 FINITE ELEMENT MODELING A finite element model is developed to represent permeability enhancement in deforming strata containing natural fractures. Deformations throughout the elastic body induce changes in aperture of individual fractures that may drastically change permeability distributions. 2.1 Governing equations The following development is restricted to two-dimensional elasticity with concurrent fluid flow. Within the solid phase, strains are expressed in terms of displacements through the relations where e?? are components of the solid strain tensor and Ui and Uj are displacements in the X1 and X2 coordinate directions, respectively. 3 MODEL VERIFICATION The validity of the proposed model may be best illustrated by direct comparison with field measurements taken around a developing longwall panel. 3.1 Site specification The mine is located in West Virginia. For the purpose of simple validation, only the in- situ conditions of most concern are provided. Hydrogeology: The shallow water bearing strata present over the site exhibit perched or semi-perched aquifers as controlled by interbedded shale units of low relative conductivity. Decreasing permeabilities recorded with depth suggest the dominance of secondary porosity in determining conductivity magnitudes. Water level fluctuations in the shallow aquifers are primarily attributed to the steep topography. Water levels in strata deeper than 400 feet (122 m) below the surface remained fairly constant throughout the pre-mining period.
SUMMARY: Ground subsidences caused by cave-in can be avoided by. rockbolting or hydraulic filling of shallow underground caverns under the busy downtown of Eger. Reinforced caverns are suitable to multi-purpose utilization. Abandoned, partially collapsed caverns are filled with sand to stop or reduce further surface subsidences. The improved technology is the cheapest one, and both traffic and peoples everyday life are not disturbed by the work. ZUSAMMENFASSUNG: Die Beseitigung von zusammengehen des Kellers verursachten Bodesenkung en in der Innerstadt Egers ist mög1ich mit Ankerausbau oder mit Spuelversatz. Die mit Ankerausbau verstarkte Kellern kann man fuer viele zwecken benutzen. Bei durch Spuelversatz mit Sand gefuellten verlassenen und teilweise zusammengebrochenen Kellern sind die weitere Bodensenkungen beseitigt. Diese ausgeprobte Technologie hat sich als billigsten Verfahren erwiesen. Ein weitere Vorteil war dass die Anwendung dieser Technologie beeinflusste den Verkehr und das tagliche Leben in der Innenstadt nur minimal. RESUME: Les affaissements du sol, provenants des ecroulements des caves au centre de la ville Eger, peuvent etre elimines par boulonnage ou remblayage hydraulique. Les caves, reinforcees de soutenement par boulons d''ancrage sont utilisables pour plusieurs de destinations. Au cas du remblayage hydraulique par gres des caves abandonnees ou partiellement rupturees, les affaissements renouveles sont exclus. Cette technologie essayee est la plus economique, et ni la circulation ni la vie quotidienne des habitants n''etaient incommodees par les travaux. INTRODUCTION Eger is a dynamically growing town in Northern Hungary, having a historically important inner district. Under this beautiful baroque downtown an interconnected network of cellars and tunnels has developed through the 17th and 18th centuries. Even if the whole length of this network is not completely known, it is probably longer than 100 km. These under- ground caverns have rather different size, shape configuration and depth. Most cellars /90 %/ were excavated in rhyodacite tuffs, the rest are found in fresh-water lime-stones and calciferous sandstones. Cellars are partly abandoned in a ruinous condition. In the depth of 12–15 m, most abandoned caverns are flooded due to heavy rainfalls or the failures of the water supply pipelines. The heavy traffic of the downtown and the higher and heavier buildings accelerate the cave-in of the abandoned and flooded caverns. The last ten years have brought a great number of abrupt ground subsidences over the tumbled cellars, making unsafe both the traffic and some of the historic buildings. Civic design and reconstruction is also restricted due to the uncertain underground circumstances. It appeared that this oppressing problem had been too serious to be solved by full exploitation of local vesources. Recognizing this situation, an Inter-departmental Coordination Committee were set up to elaborate a plan to stop these dangerous circumstances.
Abstract. In the Gifhorn trough E of Hanover (see fig. 1 l), gr ès quartzeux d'Aalénien qui sont interstratifi és à une orthoquartzites of upper Aalenian age are the main pay s érie épaisse d'argiles illitiques gris-foncées. Des rehorizons. They are embedded in a thick series of dark cherches de la structure géologique, appuyées par des grey, marine illitic shales. Structural investigations, sup- mesures de la porosit é et la diagenèse des argiles ainsi ported by shale porosity and diagenesis studies as well que par des interpr étations de sonic logs ont fourni une a s interpretations of sonic logs, enabled the reconstruc - histoire détaillée de la subsidence et formation des t ion of the history of subsidence and trap-development. pièges. The time of oil accumulation has been determined by II a été possible de déterminer les époques de I'accumusand diagenesis measurements in combination with cub- lation du p étrole par la combinaison de diagrammes sidence diagrams of the wells. The diagenesis of quartz d'abaissement avec une étude de la diagenèse du quartz. depends mainly on the overburden pressure and is inter - Avant tout elle dépend de la pression et est interrompue r upted by the oil accumulation. Therefore it indicates the par l'accumulation du pétrole. Ainsi elle montre la plus m aximum depth of burial before oil accumulation (fig. 5). grande subsidence jamais atteinte avant l'accumulation O nly a minor relationship exists between geological du p étrole (fig. 5). h istory and properties of the degasified oils. The light Tandis que les caract éristiques du p étrole ne dépendent hydrocarbons, however, increase considerably with the que peu de l 'histoire des r éservoirs et ainsi refl ètent les depth of burial (e. g. bubble points: 141 +3140 p.s.i.a.; roches-mère largement homogènes, les hydrocarbures methane: 0,17+26,9 weight % of reservoir hydrocar- l égers déterminés par des mesures d'autoclaves sont en bons; fig. 1 O). Probably, the migrating hydrocarbons have forte augmentation avec la profondeur de la subsidence been uniformly rich in natural gas. In most reservoirs, (par ex., augmentation des bubble points de 9.9 à 220 at however, much of the gas has been lost by selective dif - et de la teneur en méthane de 0.17 à 26.9 poids % des fusion, which was controlled by the porosity of the cover hydrocarbures dans les r éservoirs; fig. 1 O). shales during accumulation of oil. The connection bet- En conséquence, les HC migrant vers les pièges étaient ween the loss of the light hydrocarbons and surface gas uniform ément riches en gaz. Aux réservoirs, il yavait une survey is stressed. perte de gaz par diffusion sélective, contr ôl ée par la The migration in the Gifhorn through was confined to the porosit é des argiles superposé