Diagenese en toepassing van LiDAR in reservoiranalogen-onderzoek: karstvorming in de Krijt kalkstenen van het Apulia platform en dolomitisatie van het Trias Latemar carbonaatplatform

The ever-increasing demand for energy and hydrocarbons coincides with gradual depletion of currently producing conventional oil and gas reservoirs. Therefore new exploration plays are extended to more complex oil and gas plays, such as karstified limestones and hydrothermal dolomites. Furthermore production from currently producing reservoirs is optimized by revisiting or improving the geological knowledge of these reservoirs. These two perspectives are covered in this study on dolomitization in association with magmatic processes and karstification of platform carbonates. The spatial distribution of the reservoir facies is of great importance in heterogeneous reservoirs, such as karstified limestone and dolomite. Gathering 3D high-resolution (spatial) data from the subsurface is often not possible. Outcrop analogue studies are typically used to overcome this obstacle. By studying rocks in outcrop, that are similar to the reservoir rocks, the 3D architecture of the reservoir facies can be assessed in great detail. Furthermore this allows to unravel the diagenesis of the rocks, without depending on wellbore positioning, that might miss specific but significant diagenetic features. Outcrop analogues can provide the essential 3D distribution of the reservoir facies and characteristics that cannot be derived directly from the subsurface. Furthermore outcrops can be studied at high resolution on reservoir scale (depending on the size of the outcrops).Laser ranging is applied for decades for a wide range of applications. Essentially a laser light pulse is sent and the reflected light is detected by a scanner. The time it takes between sending and detecting the pulse is used to determine the distance of an object. In recent years, advancements in LiDAR (Light Detection and Ranging) technology allow a high-resolution (mm-cm) high-accuracy (mm) 3D reconstruction of objects.In outcrop analogue studies, LiDAR scanning is used to create 3D photorealistic digital outcrop models (DOM). This is an accurate 3D digital representation of the outcrop morphology, that is coloured by projecting photographs. The application of LiDAR in reservoir outcrop analogue studies presents a whole new range of possibilities, such as virtual field trips, accurate geometrical measurements or digital access to physically inaccessible locations. Typical field measurements such as position, distance and orientation can be measured on DOMs, often with higher precision. The DOMs often correspond to reservoir scale and provide data sets that can easily be implemented in geocellular reservoir models. Quantification of geological information and subsequent interpretation obtained from DOMs both form challenges that are fairly new. Digital fieldwork on the DOM is required to gather quantitative data. Techniques have to be created or adapted to handle and interpret these new types of data.In addition to LiDAR scanning, other techniques can be used for the generation of DOMs, such as photogrammetry. A detailed comparison between LiDAR- and photogrammetry-based DOMs suggests that photogrammetry can provide high-quality and consistent DOMs. However for the applications presented here, a higher resolution and accuracy is warranted and thus LiDAR scanning is used.LiDAR scanning is applied in two reservoir outcrop analogue case studies. LiDAR based DOMs are used to derive high-quality fracture orientation data from inaccessible positions in three quarries in Apulia (southern Italy). The relation between fracturing and karstification is studied in order to compose a conceptual model of karst cavity distribution and assess the timing for karst dissolution. Furthermore dolomitization and dolomite distribution of the Latemar platform (Dolomites, northern Italy) is studied. The 3D distribution of dolomite bodies in the Latemar is analyzed on a LiDAR-based DOM. This also allows the implementation of dolomite distribution and characteristics in a reservoir model. New approaches are designed to handle and interpret this new type of data. In the subsurface of the southern Apennines and the Adriatic Sea, the karstified Apulia Platform hosts some important oil fields (respectively Val d’Agri and Rospo Mare). The study of the relationships between the sedimentary framework and the structural and tectonic evolution in several three-dimensional outcrops in Apulia is key to interpret and forecast the porosity-permeability properties in southern Italy’s time equivalent Cretaceous carbonate reservoirs. In the Apulia Platform, karstification is mainly vertically oriented and appears to be related to fracturing. The most common karst types are fracture enlargement and karst cavities in an inverse droplet-like shape that terminate into a fracture. Therefore the organization of fractures will have an important influence on karstification and a mechanical stratigraphic approach will be used.In this study, four quarries are analyzed to understand the mechanical stratigraphy and the link between fractures and karstification. Two quarries of layered sub- to intertidal limestone and two quarries in massive rudist floatstone are studied. Karstification in layered carbonates is studied in the Bisceglie and Trani quarries. In both cases, karst cavities appear to be aligned along fractures. Most fractures are stratabound and fracture density varies significantly vertically across the outcrops (mechanical stratigraphy). Most karst cavities are confined to specific sedimentary units and are aligned along fractures. In these outcrops, the relationship between karstification, fracturing and sedimentary units is assessed. In layered rocks a proportional relationship is found between karstification and fracture density of the layers (mechanical stratigraphy). Analysis of variation of fracture spacing indicates that fractures are regularly spaced and thus karstification is not associated to clusters of fractures. A typical relationship of increase in fracture spacing with respect to bed thickness is observed. Furthermore an inversely proportional relationship is identified between karstification andbed thickness. These observations have lead to a concept of fracture related karstification in layered carbonates. High fracture density mostly occurs in thin layers and causes dispersed flow of percolating meteoric fluids. In layers where fracture density is low (thicker units) fluid flow is focused into few fractures in which intensive karstification occurs. At the contact between thick units (wide fracture spacing) with overlying thinner units (narrow fracture spacing) horizontal flow paths form that are ideal inception horizons to initiate karstification along fractures. Two quarries (Barile and Cavallerizza) of massive rudist floatstone are studied. Karstification in these quarries is extensive and visibly fracture related. A thick paleosol (4-5 m) of Turonian age separates the rudist-rich Bari Limestone from the overlying layered Altamura Limestone. Several large-scale vertical fractures exist but not all are dissolution enlarged or have been overprinted by karstification. Karstification is mainly associated with fractures that crosscut the Turonian paleosol. The overlying Altamura Limestone is more intensely affected by karstification, possibly in relation to its present-day near-surface position. Fracture spacing and orientation measurements along scan lines between karst cavities indicate that fracture are regularly spaced and thus karstification is not controlled by clustered fracture corridors. Where the Turonian paleosol protects the underlying Bari Limestone from meteoric water infiltration, karstification is not controlled by fracture density but rather by fracture persistence. Only where fractures crosscut the impermeable Turonian paleosol, fluids can penetrate and karstification occurs. A thickness of five meters of this paleosol is apparently enough to shield the underlying rock.Karstification of the Apulia Platform in the Murge area is strongly fracture related. Fracture orientation data, derived from LiDAR scans, is combined with the incidence of karst cavities. Clusters of fracture orientation data could be linked to karstification. Several fracture orientation clusters are evidently affected by karstification, whereas others are not influenced by dissolution. This allows putting fracturing, tectonic history and karstification in a common timeframe. The fractures along which most of the dissolution occurred are related to the southern Apennines compression and bulging of the Apulia Platform and are probably of Pleistocene age. Furthermore bulging of the Apulia platform also caused subaerial exposure and thus formed ideal conditions for karst development. Unaffected Late-Pleistocene sediments above karst cavities imply that karstification predates deposition of these sediments. Therefore it can be concluded that the studied karst are of Pleistocene age.Structurally controlled (hydrothermal) dolomites have gained increased attention because of their potential as hydrocarbon reservoirs globally (Canada, US, Saudi Arabia, offshore Angola, Gulf of Mexico, ...). However the association of hydrocarbonreservoirs in relation to igneous and volcanic rocks has been documented frequently, these setting were previously avoided due to technical challenges. Because the (partially) dolomitized Latemar platform is located close to the Late Ladinian Predazzo Intrusion and is crosscut by numerous dikes, it forms a well-exposed reservoir analogue for these new oil and gas plays.Crosscutting relationships of different diagenetic phases indicates that matrix dolomitization in the Sciliar Formation postdates emplacement of the Predazzo Intrusion and associated mafic dikes. The dolomitizing fluid is preserved in dolomite cement in veins and brecciated zones along the dikes. The link between the dolomite cement in dikes and the surrounding matrix dolomite was confirmed by geochemistry and reservoir modelli

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