39 research outputs found
Fracture characterisation in carbonate reservoirs for geothermal production
No full textSubsurface energy projects carry high risk due to the lack of data available to accurately model reservoir characteristics. There is a need for high level analysis to extrapolate subsurface data from a single point (i.e. a well). The focus of this study will be on fracture characterisation in a carbonate reservoir located within the Geneva Basin for the purposes of geothermal exploration. The goal is to use fracture characterisation techniques in the form of an OBI analysis and the use of a fracture growth model with a focus on geomechanics to predict the possible fracture growth patterns. This work will allow for a better understanding of fluid flow and permeability throughout the reservoir. As well as explore the benefits and limitations of this approach. The case study is a fractured carbonate reservoir made up of limestone and marlstone packages. To calculate the paleo stress environment, the fracture data is used to back calculate the possible magnitude of the stress field during fracture formation. This choice was made after careful consideration and comparison of the fracture data with the fault data. The output of this modelling will be a DFN with multiple layers controlled by the fracture density. This model can hopefully be used in the future for dynamic simulation to understand the impacts of these assumptions and validate with production data from the well. Applied Earth Science
Predictive mechanical model for fracture stimulation in an enhanced geothermal system (EGS) context
No full textAccepted Author ManuscriptReservoir EngineeringApplied Geolog
Geological and structural map of the southeastern Pag Island, Croatia: field constraints on the Cretaceous - Eocene evolution of the Dinarides foreland
No full textThe sedimentary succession exposed in the Northern Dalmatia Islands mainly consists of Cretaceous to Neogene shallow water carbonates, folded and imbricated within the External Dinarides thrust belt. During Cretaceous times, carbonate sediments were deposed on a heterogeneous, tectonically-influenced carbonate platform, which was then uplifted and eroded, as evidenced by a regional unconformity embracing the Late Cretaceous and Paleocene. Sedimentation resumed during the Eocene, when the area was part of the foreland basin of the Dinaric belt. With our geological and structural map of the southeastern Pag Island at the 1:25,000 scale, we refined the stratigraphic and structural setting and the tectono- sedimentary evolution of the area.Applied Geolog
Fracture Network Prediction in the Geneva Basin: A Geothermal Case Study
No full textThe aim of this study is to reduce the risk of the ongoing Geothermal exploration effort in Geneva Basin by estimating the influence of the natural fracture on the reservoir properties. A Discrete Fracture Network (DFN) was generated to resemble the fracture network in the Lower Cretaceous carbonate reservoir. The DFN modelling approach is using a novel workflow that is based on a geomechanical forward modelling simulation approach. Two 2D seismic lines and well data, including interpreted fractures using Borehole Image (BHI) log, were used to prepare the model inputs. Some results were derived from the fracture data that were also used to prepare the model inputs. In general, the fracture data have fairly constant orientation along the Lower Cretaceous interval. In this study the fractures are assumed to be formed under a single tectonic regime. However, when partitioning the fractures in different stratigraphic formations, a change in the direction of the fractures with depth is observed. This observation could be explained by the variation in rock's stiffness between different stratigraphic formations.Two techniques were used to model the subsurface fracture network: paleo-tectonic stress inversion and fracture network forward modelling techniques. The modelled DFN resembles the fractures geometry at the well location whereas away from the well the model is constrained by the subsurface fault geometry and far-field tectonic stress. Moreover, the modelled DFN consists of multiple 2 meters thick layers where each layer include a layer-bound fracture network. One of the main limitations of this approach is that it can not consider multiple tectonic regimes to simulate the fracture network. In addition, this approach requires large computational power.Applied Earth Science
Vertical Movements and Petroleum System Modelling in the Southern Chotts Basin, Central Tunisia
No full textThe southern Chotts basin (SCB), Central Tunisia, has shown hydrocarbon potential since the end of the 1980s. This basin records a complex structural history which appears decoupled at the Hercynian or Variscan unconformity. The Paleozoic series is deformed by short to medium wavelength folds (kilometres-multi kilometres scale) and by steep normal faults. The Mesozoic series is largely less deformed. The evolution of the basin through time is still a matter of debate as the preserved Paleozoic series is fragmented (e.g. affected by erosions). In this paper, we proposed a reconstruction of the vertical movements affecting the basin and an evaluation of their magnitude. Using basin modelling techniques, we provided new insights on the possible thermal evolution of the basin that might be used in the future exploration phases. This study was completed by structural restorations allowing the reconstruction of the paleogeography of the basin at the time of deposition of principal reservoir formations.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Applied Geolog
2D Modelling of a fold and thrust belt in the French Prealps
No full textDuring this thesis, 2D modelling using the MOVE software suite is performed on a fold and thrust belt in the French Prealps. The area of interest is called the Couspeau area and is 72 km2. In this area, Vocontian basin sediments deposited during the Jurassic and Cretaceous can be found. The area contains well exposed fold and thrust structures. The oldest structures begin in the West, while the younger ones can be found in the East. All thrusts strike approximately N-S. These thrusts were assumed to be formed by the second Alpine orogeny. A structural map of the area was created in QGIS version 3.12.0 using geologic maps from the BRGM and using fieldwork data from Applied Earth Sciences students collected during the AESB2430 course at TU Delft. Subsequently, four E-W orientated cross sections of the area were constructed. These sections were restored using MOVE to verify if the interpretations were geologically feasible. 2D forward modelling was then applied to discover possible types of structural mechanisms which were active in this area. Possible mechanisms include fault-bend folding and regular folding. Fault propagation folding was assumed to be a suitable mechanism, but didn’t produce satisfactory forward models. Strain circles were added during forward modelling to analyse what kind of deformation is caused by different thrusting mechanisms. The restored sections were also used to calculate the total amount of shortening in the area, and how much of this shortening was caused by folding or faulting. The total amount of shortening was 24%, from which 38% was caused by faulting and 62% by folding.Civil Engineerin
Pressure transient analysis to investigate a coupled fracture corridor and a fault damage zone causing an early thermal breakthrough in the North Alpine Foreland Basin
No full textThe heterogeneity of the Upper Jurassic carbonate reservoir (Malm reservoir) beneath the North Alpine Foreland Basin has a significant influence on the mass and heat flow processes during geothermal exploitation. Geophysical borehole data revealed that sub-seismic scale fractures and karstified fractures occur at the inflow zones of deep geothermal wells. However, pressure transient analysis (PTA) in some previous studies concluded that it is difficult to detect the influence of sub-seismic scale features, suggesting that radial flow regime is dominant. Accordingly, a regional thermal-hydraulic model adopted the equivalent porous medium (EPM) approach, homogenizing the sub-seismic scale reservoir heterogeneities; however, unable to detect an early thermal breakthrough (ETB) in a geothermal doublet located SE of Munich. We apply PTA on three buildup tests belonging to that doublet following a deterministic approach to constrain the reservoir type by interpreting the pressure derivative (PD) plots constrained by geophysical and geological data. We derive the magnitudes of the reservoir hydraulic parameters by matching the PD plots with the selected interpretation models. We find that clustered fractures have a significant influence on the reservoir hydraulics, evidenced by trough-shaped curves in the PD plots. Linear flow regime interpreted from the interference test between the two wells indicates permeability anisotropy, which may have caused the ETB. Geophysical data interpretations indicate that these fractures correspond to a coupled fault damage zone and a fracture corridor. Finally, we present a fit-for-purpose 2D discrete fracture network model utilizing the PTA results to match our analytically calibrated model. Our study offers a potential hydraulic explanation to the cause of the ETB highlighting the importance of integrating multi-scale/disciplinary data sets to improve the reliability of dynamic reservoir models, based on which, economic-related decisions are made.Applied Geolog
The Impact of Stylolite Morphology on the Mechanical Strength of Limestones and Ultrasonic Coda-Waves: Investigation using Uniaxial Compression Tests and Coda-Wave Decorrelation
No full textStylolites are rough dissolution surfaces ubiquitous in sedimentary rocks, which locally exercise a strong influence on porosity and cementation, resulting in a change in strengths and permeabilities of the host rock. Thus, these structures are important in many applications in geosciences. Yet, little research has been done to test the effect stylolites have on the strength of limestones, due to their seemingly obvious role as stress concentrators. Furthermore, there has been no research into whether the morphology of stylolites plays a role into this weakening, and to what extent. Ultrasonic monitoring using coda-wave decorrelation has shown to be effective in monitoring temporal changes in homogeneous rocks during loading tests in the laboratory. However, no research has shown that this technique can detect small changes in rock deformation for rocks with stylolites. To investigate the effect stylolites and their morphology has on the mechanical and acoustic behaviors of limestones experimentally, uniaxial compression tests with active source ultrasonic testing were performed on Treuchtlinger Marmor samples containing sedimentary stylolites and Meyrargues Limestone samples containing tectonic stylolites. Samples were grouped based on stylolite morphology using a novel classificationscheme utilizing the geometric features of 2D traces of the stylolites. Acoustic data was analyzed in conjunction with stress-strain curves, by utilizing coda-wave decorrelation, which allowed small perturbations such as microcracks and pore-collapse in the rocks to be detected. Additionally, X-ray micro-CT experiments were conducted on some samples pre and post-deformation, for greater insight into the weakening effect of stylolites. These experiments found that stylolites, for almost all samples, weaken the rock, however, this weakening effect depends on the degree of stylolite morphology. In these cores, the larger the stylolitized zone, the greater the strength of the rock, when compared to samples containing stylolites. Additionally, stylolite morphology impacts the frequency content of ultrasonic waves, whereby rougher stylolites attenuate higher frequencies during loading.Applied Geophysics | IDEA Leagu
Regional Geology and Fracture Network Characterisation of the Southern Chotts and Jeffara Basins, Central Tunisia: Implications for Petroleum Reservoirs
No full textThe Southern Chotts and Jeffara Basins are situated within the Saharan Domain of Central Tunisia, North Africa. The Southern Chotts Basin hosts reservoirs within the Triassic, Permian and Ordovician units that contain significant hydrocarbon accumulations whilst the Jeffara Basin contains outcrop analogues of the same hydrocarbonbearing formations. The basins experienced a late Hercynian shortening phase which involved the uplift of a major topographic high (Tebaga de Medenine). This high, in conjunction with a older regional high, the Telemzane Arch influenced the deposition and geometry of the Permian and Triassic units across both basins. This shortening event is characterised at the scale of hundreds of meters by EW striking folds into which the midlate Triassic and early Jurassic units are deposited. The folding is also observed at field scale (10’s meters) through small faultrelated folds in the Permian deposits of the Tebaga de Medenine. This late Hercynian phase occurs between the late Permian and early Jurassic in the basins. Fracture data collected from the upper Permian and lower Triassic units (Jeffara Basin) provides an analogue to the fracture networks at depth (Southern Chotts Basin) in the Paleozoic reservoirs. A conjugate fracture system observed in the field (from fracture pavements) corroborates with the interpretation of regional shortening in the basins. Seismic attribute analysis on depth slices in the Paleozoic reservoirs also shows the conjugate system at depth. This analysis is integrated with outcrop fracture data and FMI data from wells to create an open fold distributed fracture model of the system in the basins. This model indicates the main driver for fracture generation in the region is folding and is used to predict the fracture networks at depth. This is undertaken using discrete fracture network (DFN) modelling of the subsurface. This model is integrated with a deterministic model from the seismic time slices to create a hybrid predictive fracture model of the early Paleozoic reservoirs. Analytical aperture modelling of the fracture model demonstrates the fractures varied in openness depending on orientation and fracture length. The conjugate set orientated at 240∘and longer joints detected from seismic attributes presented the widest aperture size. These fractures in the subsurface at implications on the transmissibility of the reservoirs, especially Permian units which have low bulk rock permeability and the lower Triassic (TAGI) sequences which are susceptible to compartmentalisation
The MPS-Based Fracture Network Simulation Method: Application to Subsurface Domain
No full textNatural fractures conduct fluids in subsurface reservoirs. Quick and realistic predictions of the fracture network organization and its fluid flow efficiency from limited amount of data is critical to optimize resources productivity. We recently developed a method based on multiple point statistics (MPS) technique to produce geologically-constrained fracture network simulations. The method allows to account for the intrinsic non-stationarity of these networks by considering a multivariate input data instead of averaged distribution of fracture parameters. In addition, the method considers probability maps reflecting the influence of fracture drivers in the network variability. Consequently, the simulated fracture networks derived from the innovative MPS approach are geologically better constrained than in classical discrete fracture network modelling approaches. This paper proposes to apply this method in subsurface conditions where available data are sparsely distributed. We developed a workflow where data are gathered from wellbore and from additional sources (outcrops). These data are used to extrapolate a network around the borehole as training images and themselves are extrapolated at the reservoir scale following a geological probability map.This work also presents innovations on the way how training images and probability maps that may integrate more geology constrain than relying almost entirely on available data.Accepted Author ManuscriptApplied Geolog
