Natural fractures play a crucial role in many sustainable subsurface applications, particularly in reservoirs with low primary porosity and permeability. Therefore, fracture analysis has become a fundamental aspect of geosciences, often starting with fracture interpretation from borehole image logs. It has been widely recognized that interpretations come with uncertainties; nevertheless, there is a current lack of both quantitative and qualitative understanding regarding differences among interpretations. This study aims to address this gap, by performing a statistical analysis on five interpretations of the same well, highlighting their differences and similarities. Based on the results from the analysis, a workflow was created to reduce uncertainties in fracture interpretations from image logs.

The created workflow was then applied to two wells in the Geneva Basin, Switzerland; associated with a geothermal project aiming to produce heat and electricity from the Upper Cretaceous limestone rocks. Research has shown that these rocks form a tight reservoir, and fluid flow will rely on the presence of fracture networks. In the two wells, a total of eight fracture sets were defined based on movement and relative chronology, and used to reconstruct the fracture history of the basin. This led to the identification of four Mesozoic to Cenozoic stress regimes: 1) a normal or strike-slip regime, 2) a NE-SW reverse regime, 3) a normal regime, and 4) a NW-SE reverse regime. The latter is considered the main deformation event of the region: the Late Miocene fold-and-thrust tectonics. In the Geneva Basin, this event is represented by a pair of NE-SW striking conjugates, which forms the majority of observed fractures. The fifth fracture set is believed to be fault-related and was only observed in one of the wells.

Beyond the regional implications, this study emphasizes the importance of uncertainty reduction in the early stages of fracture analysis, and its effects on establishing a reliable fracture history.

In the geothermal exploration well, NLW-GT-01, in the West Netherlands Basin, a very tight reservoir with low porosity (≤5.0%) and matrix permeability (≤ 0.1mD) has been encountered in the Main Buntsandstein Subgroup. The impact of natural fractures, which can significantly impact fluid flow in tight reservoirs, has been studied. However, there is a lack of consensus in different studies on the fracture classification.

In this study, a re-evaluation is performed of the well data of the NLW-GT-01 and VAL-01 wells. An analysis comparing core, geophysical, and image logs is performed to document the drivers and characteristics of natural fracture distribution in the WNB and investigate the geological and geomechanical parameters influencing the development of fractures in the Main Buntsandstein Subgroup.

On the core of NLW-GT-01 and VAL-01, five types of fractures are classified veins, joints, Mode II fractures, stylolites and drilling-induced fractures. The natural fractures have a dominant NW-SE strike orientation. The drilling-induced fractures and the borehole breakouts indicate a NE-SW oriented in-situ minimum stress and an NW-SE oriented maximum stress. The natural fractures are favourably oriented to be open based on their orientation compared to the in-situ stress orientation.

The fractures are associated with large-scale tectonic events. During the burial of the formation related to the extensional phase of the WNB during the Mesozoic, veins, joints, conjugate fractures, and stylolites could be formed. During the inversion of the basin in the Late Mesozoic-Cenozoic, tectonic stylolites could have been formed, and the previously formed conjugate fractures could have been reactivated.

Natural fractures are concentrated in more heterolithic intervals of the VAL-01 and NLW-GT-01 wells in both image logs and cores. These heterolithic sections display alternations of medium sandstones with silt- and claystones. The identification of more fractures in VAL-01 compared to NLW-GT-01 can be explained by the difference in basin location. VAL-01 is located in the centre of the basin where distal playa environments produced more fine-grained material alternating with coarser sands. The more proximal NLW-GT-01 is dominated by fluvial sands. The lithological variability produces Young’s and Shear modulus variability that seems to be driving increased fracture density rather than the
absolute value of the Young’s modulus causes this.

Stylolites 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 classification
scheme 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.

Subsurface 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.

Permian deposits are found in outcrops and in the subsurface of Southern Tunisia, in the Jeffara Basin. Their stratigraphic and tectonic evolution is not yet fully understood and represents the main focus of this work. Aspects of the Permian system such as, lateral extend of formations, dating and paleo environments are not well constrained. Answering these questions will impact future hydrocarbon exploration and also improve the geological understanding of Tunisia. To achieve this, seismic lines and well data of the Jeffara Basin have been re-interpreted and re-correlated.

The results of the study indicate a lagoon depositional environment for the Early Permian, a carbonate self environment for the Middle-Upper Permian successions, with dimensions of 80 square kilometers and a general east-west orientation. The thickness of the carbonate deposits reaches a maximum of 2500 kilometers to the north of the reconstituted paleoshore. A Sabkha environment has been interpreted for the Upper Permian with significant deposits of anhydrite. Structurally, it was observed that the Permian is not affected by major normal faults.

Conversely, significant folds have been identified at the seismic data, with a general east-west strike and a northwards dip. Based on the displacement of seismic reflectors, two tectonic episodes have been identified. The first is dated to the Upper Carboniferous - Early Permian and the second to the Early-Middle Triassic. Decompaction calculations indicate low subsidence rates and general stability during the Early Permian. This was followed by significantly increased subsidence rates during the Middle and Upper Permian.

The 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.

This report contains the results of the two thesis studies that finalise a combined MSc--programs of Reservoir Geology and Science Communication. The first part of the report comprises the multi-scale data (kilometers to meters scale) analysis of a) the large--scale architecture of the subsurface Daly Waters Arch which was obtained from seismic data interpretation; and b) fracture pattern characterisation by outcrop measurements and drone imagery in the Tomkinson Province. Both the Daly Waters Arch and the Tomkinson Province are located in the largely undeformed Palaeo-- to Meso--Proterozoic Greater McArthur Basin in the Northern Territory, Australia. In July 2019, a geological fieldwork was conducted in the Tomkinson Province to collect the fracture data with the drone. In this research, the Daly Waters Arch and the Tomkinson Province have been geologically linked based on seismic and fracture data. By discussing analog cases of far-field deformation, these results have been placed in a larger context of large--scale basin deformation.

The second part of the report focuses on the Netherlands, where ambitious goals have been set for the implementation of geothermal energy in the energy transition. During the gas production in Groningen, a negative social perspective towards mining operations, in general, was developed. For the implementation of geothermal energy, an approach for the communication of technical uncertainties between the initiators and the local public of a geothermal project is designed in this study. Technical uncertainties that are present in geothermal energy implementation in the Netherlands have been identified during semi-structured expert-interviews with different stakeholders in the spectrum of geothermal energy. The approach addresses guidelines for the communication of the context, the goal, the technical uncertainties present in the geothermal project, the main communicating actors, their reference frames, and the situation in which the communication process takes place.

During 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.

The primary reservoirs present in the Southern Chotts Basin, Central Tunisia, are located within Triassic, Permian and Ordovician units. They are mainly sourced by the Silurian -- Lower Devonian Fegaguira formation and its Hot Shale member. Late Paleozoic exhumation has eroded part of the Palaeozoic package, removing the Early Devonian -- Carboniferous and most of the Permian deposits in the Southern Chotts Basin. This resulted in a diachronous unconformity in the present-day stratigraphy and represents significant uncertainties. This study presents a reconstruction of the tectonic and thermal history of the Southern Chotts Basin and the subsequent impact on source rock thermal maturation, with an emphasis on the Hercynian exhumation. Implications on the petroleum systems in the basin are evaluated by means of a migration study. Investigation of adjacent analogue basins allows estimation of the amount of initially deposited sediment in the Early Devonian -- Permian. Calibration with vitrinite reflectance data minimizes exhumation uncertainties in the basin history and indicates ca. $2300$ m sediment eroded during the Hercynian phase. Subsidence analysis shows similar subsidence patterns throughout the area of interest since the Mesozoic. This argued to use a single set of high and low case initial deposition estimates, calibrated with vitrinite reflectance, in source rock maturation modelling. Source rock maturation modelling in the kitchen area indicates hydrocarbon generation occurs in two phases separated by a phase of stable maturity during Hercynian exhumation. Maturation in the kitchen area is found to currently be in the condensate -- wet gas zone. Migration modelling shows that Paleozoic generation in the northern and northeastern portion of the basin primarily sourced the present-day hydrocarbon discoveries. High capillary entry pressures in overlying Fegaguira shales forced hydrocarbons generated in the Hot Shale member to migrate downward into porous Ordovician units. Subsequently, hydrocarbons laterally migrate up-dip into local traps, where they remain trapped wherever the overlying source rock is preserved during Hercynian exhumation. The Ordovician units acts as a reservoir, and as a carrier bed to source present-day accumulation in the Triassic TAGI unit. A newly identified petroleum system primarily hosts accumulations in lower shoreface Ordovician El Atchane deposits, overlain by the Fegaguira and Hot Shales. Simulated hydrocarbon accumulations and projection of shoreface deposits throughout the area of interest mark a sweet spot area with significant reservoir potential in structural traps. Recommendations are given to further investigate the potential of this system.

The 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 geological history of the McArthur Basin (NT Australia) is poorly understood. It consists of five onshore Paleo- to Mesoproterozoic packages with mainly siliciclastic and carbonate rocks, with cumulative thicknesses up to 15km. The basin contains the world’s oldest hydrocarbons, principally hosted in unconventional reservoirs in the Wilton Package. Fluid flow in these reservoirs is related to natural, reactivated or induced fractures. Characterizing the fracture network is an important part of predicting fluid flow. This study tries to link the geological history to the generation of fractures.

The geological history needs to be better understood to characterize the fracture network. In this study seismic, well, outcrop and geophysical data are integrated to construct a cross section that links outcrops (Batten Fault Zone and Broadmere Complex) with the subsurface (Beetaloo Sub-basin). The literature in combination with the cross section is used to revise the geological history.

A fieldwork is conducted to study fracture geometries on outcrops of the Wilton Package that are analogues to subsurface fracture networks. A drone is used to image fracture pavements at an order (10²m) that is normally missed by geologists (10¹m) and satellite images (10³m). The Tanumbirini-1 well, located in the sub-basin, provides a FMI log for interpreting fractures in the subsurface. A key objective is to differentiate fractures associated with fracture drivers like regional stress, folds and faults.

This study identified two unconformities in the seismic data, corresponding to two deformation events. The Carpenteria Event between the Wilton Package and the Inacumba Group is associated with a dominantly N-S oriented stress field and the Borroloola Event within the Inacumba Group corresponds to a mainly E-W oriented stress field. Both events created their own fracture sets and are observed on outcrops and in the subsurface. The tectonic stress is σ₁ at the surface but σ_H,max in the Beetaloo Sub-basin. Fracture generation in the sub-basin happened at another stress regime than the surface outcrop analogues, making any direct comparison less reliable. Hence this study gives a prediction of the fracture density and permeability trends in the sub-basin. A conceptual model of the subsurface permeability is proposed where the permeability trend is mainly E-W oriented.

A three-dimensional geological model has been constructed of a 49 square km area in the sub-Alpine chains in the French Drôme department. The area was situated in the Vocontian Basin, which was an epicontinental sea situated at the western margin of the Alpine Tethys Ocean, between former continents of Gondwana and Laurasia. Formations of limestones and marls have been deposited over a time span of approximately 80 Ma from the Late Jurassic to the Early Cretaceous, which can be classified into eight distinct formations. This was followed by two phases of deformation. First, the counter-clockwise rotation of Iberia into Europe inducing S-N compression in this area. Second, the collision of Adria with the European continent inducing E-W compression. Both events uplifted the area by an estimated 2500 to 3000 m.
This thesis uses data collected during the second year fieldwork (course AESB2430) of the Applied Earth Sciences bachelor at Delft University of Technology. The cross sections and geological map from this fieldwork were revised where necessary. Three new cross-sections were constructed along the north, east, and west boundaries of the area for more coverage. All cross-sections were digitized using the Move software package. To check whether these were geologically feasible, they were restored to their pre-deformation state by removing the effect of faulting and folding. These cross-sections form the basis for a 1:25 000 scale three-dimensional model. Horizon surfaces were created between cross-section horizons using spline interpolation and fault surfaces using linear interpolation
Fauld displacements are removed and an unfolding is performed on the 3D model, in an attempt to reconstruct a balanced pre-deformational setting. The result is a viable model, with some inaccuracies such as gaps and overlaps between formation surfaces and slight variation s in layer thickness. The aim of this 3D model is to aid the understanding of the configuration of rocks and of the structural evolution of the area. The average shortening due to deformation for cross-sections was found to be 14.71 %. The surface reduction value of the area is found to be 8.2 푘푚 or 14.3 %.
The direction of shortening is primarily in the S-N, due to the Iberian collision, and to lesser extent in the E-W direction, due to the Adriatic collision.