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Fourth Naturally Fractured Reservoir Workshop
- Conference date: February 11-13, 2020
- Location: Ras Al Khaimah, United Arab Emirates
- Published: 11 February 2020
27 results
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The Interplay between Fracture Apertures and Critical Stresses in a Naturally Fractured Carbonate Reservoir in Saudi Arabia
Authors K. Olvera Carranza and O. E. Meza CamargoSummaryThis study explores the relationship between natural fracture aperture and in situ local stresses and how their interplay define preferential direction of fluid flow in fractured carbonate reservoirs. Fracture aperture and the effect imposed by present day stresses is rarely characterized. We applied a workflow that links fracture aperture averages estimated from fractures detected by micro resistivity image logs and then we calculated shear and normal stresses on those fracture planes. Results showed that two main fracture orientations exhibit large fracture aperture and are critically stressed. The identification of these two critically stressed fracture sets was the main driver to estimate fracture permeability during the construction of the 3D reservoir fracture model. Directional patterns observed from fluid velocity data corresponds with the orientation of critically stressed facture sets. Incorporation of this workflow is improving our natural fracture prediction workflows by adding an in situ estimation of fracture permeability.
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An integrated approach to interpreting ‘poor’ seismic in a heavily faulted reservoir
Authors E. Angerer, G. Arzmüller, T. Schröckenfuchs and M. HaghighiSummaryAn integrated fault characterization study was performed as part of a comprehensive mature field redevelopment project in the Austrian Flysch reservoirs. Structural interpretation was challenging due to the complexity of the faulting and the poor quality of the available seismic data. Structural complexity is often a reason to degrade the seismic image. The seismic was reprocessed with CRS for noise reduction and CBM as an imaging method. In a close cooperation between geophysicists and interpreters seismic fault attributes were derived. The heavily faulted structure was interpreted in an inductive manner based on numerous fault crossing in the wells and the observed faults on the seismic. An structural was developed honoring all available data leading to an improvement of the geological concept of regional tectonics. Further a number of prospective yet undrilled compartments could be identified in this mature field.
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Fracture sequence in folded carbonates: a long and complex history of reservoir properties
Authors J. Lamarche, T. Kaci, L. Marié and P. RichardSummaryFractures in folded carbonate layers are sampled along a scan-line, such as an “Along Well Measure Depth”. We deciphered 11 types of brittle structures (stylolites, joints, tension-gashes, faults) which are relatively date as pre-, syn- and post folding. Brittle stages are plot on the loading path and at each step we characterize the reservoir properties and Nelson reservoir type. With burial, the reservoir would evolve from type I to type II. Then, the tectonic inversion trigger fractures and faults which increased and decreased the fracture and matrix contribution respectively The data-base is shown like a well data-set what allows challenging and calibrate the structural analysis performable from a well.
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Exploring the limits – Integrated drill cuttings analysis for fractured (basement) reservoirs
Authors T. Schröckenfuchs, A. McGeer, B. Rupprecht and E. MekonnenSummaryA thorough drill cuttings study was conducted for a fractured basement reservoir, focusing on fracture analysis. The aim of this study was to provide input to a conceptual fractured basement reservoir model, progress the understanding of lithological controls on fracturing, and to investigate how the connected hydrocarbon volume from fractures and/or potential matrix are distributed at the well scale. A thorough macroscopic cuttings screening combined with insights from all available log, production and seismic data led to a selection of 45 cuttings samples, which were thoroughly analyzed with thin section microscopy, X-ray diffraction (XRD) and X-ray fluorescence (XRF). Our study shows that cuttings can provide a valuable source of subsurface information at a low cost – also with regard to fracture description. Outcomes show that a stereomicroscopic cuttings screening proved to be most suitable for fracture frequency detection. Thin section analysis combined with geochemical measurements were crucial to understand cement generations, related fracture conductivity and porosity types. Furthermore the study highlighted the linkage between lithology/metamorphic facies/hydrothermal alteration and microfracturing along with methodology limitations such as scaling, cavings and mud additives.
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Karst conduits formed along fracture corridors in anticline hinges of carbonate units: implications for reservoir quality
Authors C. Pontes, F. Bezerra, G. Bertotti, F. Balsamo, V. La Bruna and S. De HoopSummaryThe hypogenic caves developed in carbonate units have a significant structural control but most of their features are not detect by conventional methods due to their size below seismic resolution. This contribution focuses on the structural, petrographic and geometric characterization of karst conduits in Neoproterozoic carbonates of the Salitre Formation, central part of São Francisco Craton, Brazil. We address the influence of fractures and folds on the development of karst conduits through field and laboratory analysis and the application of Light Detection Ranging to characterize cave/conduit geometry. The preliminary results indicate that the process of karstification are intensified in fractures corridors developed along fold hinges, which create fluid flow corridors in carbonate units and may change petrophysical reservoir properties.
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Characteristics and genesis of hypogenic karsts in carbonate successions: inferences for hydrocarbon and geothermal systems
Authors G. Bertotti, P. Audra, A. Auler, F.H. Bezerra, S. De Hoop, R. Prabhakaran, C. Pontes and R. LimaSummaryMultiscale karst systems, typically below seismic resolution, are important contributors to permeability but also provide significant challenges in drilling operations and in flow simulations. A substantial portion of subsurface karsts is of hypogenic origin, that is, is associated with upward movement of chemically aggressive fluids. The Morro Vermelho Karst System and Cave developed within Proterozioc shallow water carbonates and is an inspiring analog for buried hypogenic karsts. MVKS formed in association with a regional strike-slip fault. In an initial stage, deformation in the “softer” carbonates overlying more rigid quartzites and basement was accommodated by a 100s of m wide semi-ductile shear zone. Wholesale dolomitization took place and numerous dolomite-filled veins formed. With progressing strike-slip, the fault propagated upward creating an anticline parallel to the fault zone, causing the development of m-long extensional fractures, the arrival of SiO2 rich fluids in the karts and, eventually, the formation of the cave. Vertical fracture corridors and/or faults capturing deep, generally layer parallel flow are present in different settings, from foredeeps to rifted margins and are primary candidates for widespread hypogenic karst development.
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Hydrothermal silicification and dolomitization in fault system, Irecê Basin (Brazil) - implication for reservoir properties
Authors V. La Bruna, F. Bezerra, F. Balsamo, C. Menezes, G. Bertotti, J. Lamarche, P. Richard, F. Agosta and C. PontesSummaryThe carbonate rocks exposed in the Irecê (Brazil) are pervasively affected by hydrothermal silicification and dolomitization. These mineralizing events drastically changed the original petrophysical properties of the host rock. In order to understand the role played by deformation mechanisms and tectonic evolution of these carbonates on the ingression of the mineralizing fluids, we focused our study on the mineralogical, petrographic, stratigraphic, structural and geochemical characterization of the faulted Neoproterozoic carbonates of the Salitre Formation, central Brazil. In this contribution, we present the first results of a combined outcrop- to micro-scale investigation of the structural evolution of the fracture network responsible for hydrothermal silicification and dolomitization processes.
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Critically Stressed Fractures and Their Contribution to Flow – Coal Bed Methane Case Study
Authors J. Dudek, M. Kępiński, D. Podsobiński and P. RyderSummaryThe result of these works are detailed mechanical earth models for wells within the area of investigation and description of behaviour of interpreted CSF under variable stress state as well as understanding of the connectivity of natural fractures within zone subjected to fracturing treatment.
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Structural and sedimentary discontinuities control vuggy porosity formation
Authors R. Araújo, F. Bezerra, V. La Bruna and P. AudraSummaryThe epigenetic karstic systems in carbonate rocks are the result of the dissolution caused by meteoric waters during the geological time. The topic investigated in this study are the structural and sedimentary discontinuities that control the formation of vuggy porosity by epigenic fluids in carbonate units. These discontinuities include vertical fractures, horizontal and vertical stylolites and sedimentary discontinuities, such as cross stratifications. In this work, we studied these karst features in the Cretaceous carbonates of the Jandaíra Formation, Potiguar Basin, Brazil. In order to describe these discontinuities, we performed four stratigraphic columns and collected Schimdt hammer data and horizontal and vertical plugs to analyse porosity and permeability in each layer and at the boundary between layers. We also investigated diagenetic features at the thin section and electronic microscopy scales. The findings indicate that vertical fractures and vertical stylolites were dissolved together by meteoric water percolation and cross cut all the layers, which allowed the horizontal fluid flow along sedimentary discontinuities. We conclude that structural and sedimentary discontinuities control fluid flow during diagenesis and influence the development of vuggy porosity.
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Diffraction imaging of the Wisting Discovery
Authors T.J. Moser, L.M. Moskvil, E. Angerer, W. Kobusinski, M. Pelissier and J. OroszSummarySeismic diffraction imaging (DI) is applied to the Barents Sea Wisting field, using the velocity and reflection dip fields obtained from a legacy PSDM. The objective is to image steeply dipping faults. The fault definition obtained from the DI is compared to the legacy PSDM and also to a high resolution P-cable survey. The improved resolution and detectability of the fault systems by DI offer a significant added value for interpretation of the legacy PSDM as well as the P-cable.
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Fracture recognition with U-net and pixel-based automatic fracture detection
Authors W. Zhu, S. Khirevich and T. PatzekSummaryInterpretation of fractures in raw outcrop maps is a tedious and time-consuming task. A few semi-automatic or automatic interpretation methods based on image processing are available; however, they are usually sensitive to the contrast of the image that, in turn, causes under or over-interpretation of fracture geometry. A successful interpretation of fractures from a raw outcrop image requires two stages: (1) conversion of a multi-bit per pixel raw outcrop image to a binary map that preserves fracture geometry and connectivity, and (2) replacement of the binary fracture images with line segments or polylines. These two stages are fracture recognition and fracture detection, respectively. We apply the U-net architecture to recognize fractures in a raw outcrop map. When 200 training epochs are applied to our images, the training accuracy reaches 0.94, while the mean square error decreases to 0.02. The implementation of U-net yields good results for fracture recognition. We propose a pixel-based fracture detection algorithm. The algorithm can automatically interpret the fractures in the recognized binary map as line segments or polylines. By combining fracture recognition and detection, we can interpret automatically fractures in a complex raw outcrop map.
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Predicting connected fracture networks: Field validation of numerical models
Authors M. Welch, M. Lüthje and S. OldfieldSummaryWe apply the mechanically driven approach to fracture modelling of Welch et al. (2019) to two fractured outcrops, Nash Point in South Wales and Robin Hood’s Bay in NE England. We show that the local stress field developed around larger faults is a key control on the geometry of the fractures, along with layer thickness, fracture propagation rate and layer stiffness. We can use this information to predict fracture anisotropy and connectivity.
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Investigation of modeling options for numerical simulation of fractured and karstified reservoirs
Authors M.V. Machado, F. Quadros, D. Brito and R. MoraesSummaryThe present study deals with the geological modeling of a fractured and karstified outcrop. This model was applied for numerical investigation of the karst influence on fluid flow in depletion scenario and sweeping efficiency in waterflood strategy. The results show the importance of representing the karst geometry in situations of low matrix permeability and that the association with fractures, through double porosity models, enhances the deficient sweeping.
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Multi-scale investigation focusing on the lineament of the Pan-African basement ( Eastern Egypt)
Authors S. Luby, Y. Geraud, M. Diraison, M. Wicker, L. Bertrand and C. BossennecSummaryThis study focuses on the multi-scale analysis of lineaments on the pan-African base of the Arabo-Nubian shield. Several satellite images of different resolutions were used (DTM, Landsat, RapidEye, GeoEye). The lineaments measured highlight structures such as Najd-Faults (large shear zones), a dyke network and a primary fracture system. The length distribution was also analyzed and shows a power law applicable to most of the scales studied demonstrating control of large and small lineaments on the fracture network.
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Role of basement inherited structural network on heat distribution and flow pathways in rift basins
Authors C. Bossennec, Y. Géraud, L. Bertrand, R. Divies, C. Souque, L. Mattioni and I. MorettiSummaryDeeply buried sandstone reservoirs in contact with the basement are targeted in the Upper Rhine Graben for oil, gas and geothermal energy production. Here, a conceptual basin model of fluid flow segmentation within the rift blocks, reconstructed from analytical datasets on structural network and geochemical conditions on barite and carbonate fracture infills, is tested on a 2D burial modelling approach integratin the basement structure and properties.
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Collapse structures indicate karst flow corridors in carbonate units in the Salitre Formation, Brazil
Authors R. Maia and H. BezerraSummaryKarstification generated by the circulation of fluids along fracture zones leads to the formation of upward erosive features, which result in dolines. In this work, we investigate collapse structures and their relationship with flow corridors in Neoproterozoic carbonate units in the Irecê Basin, Brazil. This area has a high concentration of dolines that connect surface drains through a cryptorheic system. We used high-resolution unnamed aerial vehicle (UAV) imagery, field mapping of dolines, structural lineaments, drainage, and field measurements of bedding strikes and dips. We conclude that collapse structures along anticline fold hinges form flow corridors. These findings have implications for fractured reservoirs.
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From static evidence to dynamic reality: the role of diffuse fractures
More LessSummaryThe paper presents the case study of a carbonate oilfield offshore UAE. It shows how a multi-disciplinary approach combining a review of static data alongside dynamic information has allowed identifying the presence of diffuse fractures. The synthesis of dynamic and production data reveals the impact of the diffuse fractures on the reservoir behavior. The paper shows that the understanding of their distribution and connectivity is critical for accurate fluid flow prediction and successful field development.
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Syndepositional deformation of the Lastoni di Formin carbonate platform (Italy) from Virtual Outcrops and field studies
Authors R. Inama, N. Menegoni and C. PerottiSummaryIn recent years, the evolution of Unmanned Aerial Vehicles (UAV), together with advances in photogrammetry and Structure from Motion techniques (SfM) have enhanced the role of Digital Outcrop Models (DOM) in fracture studies, due also to the possibility to obtain accurate 3D measurements from large and inaccessible areas. In this work, we applied the Digital Outcrop Model techniques, developed by UAV Photogrammetry, to the study of fracturation of a strongly prograding carbonate buildup in the Dolomites. About 250 fault and fractures where measured from the Digital Model, and more than 400 fracture trends were collected in the field , both on the platform-top surface and in the overlying Heiligkreutz formation. Opening mode joints and neptunian dykes, orthogonal to the direction of progradation (i.e. margin parallel) were detected at seismic scale and in the field, and interpreted as early-stage fractures. Moreover, the carbonate body records two main tectonic events, which contribute to form the present-day fracture network: the Jurassic extension, forming N-S trending joints and normal faults, and the Alpine compressive phase. Syndepositional fractures are preferentially reactivated in strike-slip, showing that their orientation with respect to the stress field can influence the subsequent evolution of the fracture pattern.
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Characterising Fractured Basement Reservoirs
Authors S. Daniels, R. Holdsworth, K. McCaffrey, J. Long, R. Jones and R. WalkerSummaryFollowing the recent discovery that the storage and flow capacity of some basement reservoirs relates to both fracture and fissure capacity, we are working towards further understanding as to how and when this paradigm shift should be applied. Our current model is based upon observations from the Rona Ridge in the UK West of Shetland. Critical questions to be addressed include: How applicable is the fissure model to other basement plays (and tight cover sequences) globally? What are the relative contributions of the fractures and fissures to storage and flow, how do they inter-relate, how can they be adequately described and how might we expect the contributions to vary in different settings?
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Impact of Natural Fractures in a Predominantly Non-Fractured Carbonate field, Sabiriyah Mauddud
Authors P.D. Richard, V. Zampetti, B. Dewever, P. Schutjens, I. Hossam, C. Vemperala, C. Chen, B. Al Otaibi, N. Al Sultan, M. Al Ajmi and C. Von WinterfeldSummaryProduction from the mid-Cretaceous Sabiriyah Mauddud Formation results to a large extent from waterflood, yet field data indicate that reservoir performance is impacted by large permeability contrasts in the reservoir. High permeability (high-K) elements in the reservoir are likely the product of sedimentological and diagenetic processes as well as the structural evolution of the field. In this abstract, we concentrate on the fault and fracture components of an integrated study with included carbonate and structural geology, seismic interpretation diagenesis, geomechanics and reservoir engineering. One of the key outcomes of the study is an improved understanding of the complex High-K pathways summarized in a so-called plumbing diagram. The two first order elements for the High-K plumbing system are 1) cemented low porosity cycle tops that are sequence stratigraphically controlled and where dissolution enlarged open fractures and vugs make up flow paths and 2) fault damage zones with increased fracture density in cemented layers. While it has been observed that, statically, the reservoir is characterized by the presence of faults and fractures contributing to flow paths, from a dynamic-response point of view, the reservoir behaves overall as an unfractured reservoir.
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Oman’s thinnest oil column produced so far in a naturally fractured reservoir under GOGD
Authors C. Volery, L. Bazalgette, S. Shuaili, F. Aljiroudi, I. Kobenko, P. Almeida, A. Zahibi, S. Omairi, H. Sukaity and M. GharbiSummaryAn ambitious project recently undertaken by PDO is aiming at producing the thinnest oil column so far in a naturally fractured carbonate reservoir by cold gas oil gravity drainage.
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Integrated analysis of fracture corridors
Authors S. Viseur, J. Lamarche and B. GauthierSummaryFracture corridors are singular Mode I fracture clusters where the density of highly persistent fractures is anomalously high with a complex and unpredictable fracture architecture in 3D. In reservoirs, fracture corridors have major impacts on fluid flow. Hence, the 3D detection and modelling of the fracture networks within corridors is of paramount importance in order to restore their 3D nature from restricted 1D data sets in underground reservoirs. In this poster, we present an integrated approach of corridors combining a geometrical characterization of corridors from structural and numerical field survey and a numerical method to detect and locate the corridors from 1D data (scan lines or underground wells).
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A novel way to decipher field performance in a NFR carbonate field
By P. OlivierSummaryA novel way to decipher field performance in a NFR carbonate field.
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Comparison of Fracture Intensity Measured in Outcrop and μCT Core Plugs in a Carbonate Reservoir Analogue
Authors S. Kokkalas, R. Jones, M. Wilkinson, S. Daniels, S. Gilment and S. NizamuddinSummaryThe porosity and permeability structure of fractured reservoirs is highly heterogeneous, however typical sub-surface data are unable to quantify this heterogeneity across scales of analysis that are most relevant for fluid flow. Comprehensive analysis of outcrop analogues can provide detailed, quantitative characterisation of the fracture network to produce robust ranges of values for input to discrete fracture network (DFN) or other fracture models. We compare fracture intensities measured from 3D X-Ray Computed Micro-Tomography with those calculated from scan lines measured along 1D tape measure transects in outcrop, and from multiple virtual scan lines in 3D point cloud data acquired from terrestrial laser scanning (lidar) and digital photogrammetry. Micro-tomography is also useful to help extend understanding of fracture intensities to analysis of fracture porosity.
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Interplay of heat transport and fracture aperture in fractured reservoirs
Authors L.F.L. Torres, S. Salimzadeh and H.M. NickSummaryIn this study, the interaction among thermal-hydraulic-mechanical (THM) processes in fractured reservoirs is investigated by means of numerical experiments. Particularly, the impact of fracture geometry, the injection rate and rock matrix permeability on heat transport in such reservoirs is studied. To do this, a fully coupled thermal-hydraulic-mechanical finite element is utilised to consider non-isothermal flow through the rock matrix and fractures subjected to mechanical deformation. The resulting temperature field is observed for different scenarios considering a doublet system in which cold fluid is injected into an injection well, and hot fluid is extracted from the production well. The simulations strongly support that in fractured systems depending on fracture density and matrix permeability, the arrival time of the cold front and the extent of the cold plume vary.
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Bridging multi-scale data set for fracture characterization and their stress sensitivity evaluation in the near-wellbore region: Results from a novel workflow
Authors S. Randazzo, C. Barton, Y. Bouzida, G. Izadi, J. Tinnin, J. Franquet, S. Perumalla, E. Cazeneuve, A. Ghadimipour and G. ZhunussovaSummaryIntegrated fractures characterization is a critical for the development of unconventional carbonate reservoirs. Having relevant conceptual geological and geomechanical models tied to well data helps to optimize the positive impact of natural fractures on production so that appropriate well placement and completion/hydraulic fracture will maximize the intersection of well with target sweet spots while avoiding faults that may connect with water or H2S geohazards.
While Borehole Images (BHI), due to their high resolution, are cornerstone for providing precise data and orientation of fractures intersected by the well. Unfortunately, they have a shallow wellbore depth of investigation. While, the Patented deep shear methodology allows identification of features up to 110 feet away from the borehole and confirms fracture hierarchies and fracture bed interaction.
A data integration and 3D visualization of the BHI, DSWI, geomechanical and seismic data were analyzed in the same field. The results were very promising to bridge between the different scales of features observed. It has been instructive to validate the systematic integration within same wells. This has provided additional insight for the sub-surface team to propose hierarchical reservoir characterization models and for the engineering team to understand better the geological structures prior and post to fracking.
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Importance of diagenesis in naturaly fractured reservoirs
By E. UkarSummaryDiagenesis affects fracture properties. Fracture cements contain information about temperature, pressure, and fluid composition during and after deformation, as well as fracture timing. Cathodoluminescence (CL) imaging of fracture cements is key to unravelling the evolution of fractures, but limitations of this technique have heretofore limited our ability to image ubiquitous carbonate cements. Here I show three examples of carbonate-cemented, naturally fractured reservoirs for which recent advances in SEM-CL imaging enabled determination of fracture formation timing and/or sealing. Extensional fault zones in the Apennines contain carbonate cements precipitated in the vadose/phreatic zone during and after faulting. Fault cores show higher porosity and permeability than the host rock, but cement linings and reactivation associated with coseismic slip caused permeability reduction. In the Vaca Muerta Formation, a combination of thrust fault-bounded kinematic indicators within bed parallel veins (BPVs) and fluid inclusion microthermometry indicate BPVs formed in the Late Cretaceous, whereas bed-perpendicular fractures formed in the Paleocene. Finally, cross-cutting relationships, isotopic analyses, and radiometric dating of fracture and vug-filling cements indicate the main reservoir porosity-forming event in Ordovician carbonates of the Halahatang oilfield, Tarim Basin, occurred in the Silurian-Devonian at depths of as much as ∼1.5–2 km. Dissolution was related to fractures and faults.
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