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First EAGE Workshop on Evaluation and Drilling of Carbonate Reservoirs
- Conference date: October 4-6, 2017
- Location: Potsdam, Germany
- Published: 04 October 2017
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Depositional Cycles Within The Upper Kharaib Formation Of An Abu Dhabi Oilfield
Authors S.N. Ehrenberg, S.W. Lokier, L. Yaxin and R. ChenSummaryThe fact that reservoir sub-zones (previously suggested to be fourth-order parasequence sets) are defined by dips in the porosity log profiles, reflecting increased stylolite frequency, indicates that these boundaries are diagenetic in character. Nevertheless, the correlation of these features over tens to hundreds of kilometers indicates an underlying depositional control. We suggest that the link between sea level and diagenesis is depositional clay content, which facilitates stylolitic dissolution. Profiles of bulk-rock alumina analyses in the studied cores tend to confirm higher clay contents at the sub-zone tops. Possible factors promoting clay influx onto a carbonate shelf during falls in sea level include increased stream gradients and a more humid climate, causing greater rainfall and higher weathering rate.
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Comparison Of Open Fractures In Ca2 Carbonates From Outcrop And Well, Using Laser Scans, Image Logs, And 3D Stress
Authors I. Becker, P. Wüstefeld, B. Koehrer, W. Jelinek and C. HilgersSummaryUnderstanding the fracture patterns of carbonate reservoirs reduces uncertainties in reservoir characterization. This study integrates outcrop and well data to evaluate their comparability in fracture characteristics with a focus on Zechstein Ca2 (Stassfurt Formation) carbonates in the Southern Permian Basin, N-Germany. We identified a suitable outcrop on the SW margin of the Harz mountains, which can be used as an analog to an operated naturally-fractured Zechstein (Ca2) carbonate gas field, some 130 km further to the NW, with a similar depositional environment (upper slope) and lithology (dolomite).
Using our newly developed automated workflow, we derive fracture data from terrestrial laser scanning (LiDAR) in addition to manually measured ones, and compare fracture orientations and –frequencies to results from subsurface fracture analysis. Furthermore, we determine the dilation tendency of those fractures based on the regional stress field and thus, their potential to reactivate and contribute to the flow potential within the reservoir.
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Modeling Of Normal Net Stress Effect On Fracture Relative Permeability And Its Effect On Oil Recovery From Fractured Car
Authors A.Y. Rozhko, S. Jonoud, O.P. Wennberg and M. NaumannSummaryIn this work, we investigate the effect of alteration of fracture total permeability, relative permeability and capillary pressure with the change of normal net stress (due to fluid injection or depletion), on estimated oil recovery factor from fractured carbonate reservoir. The numerical experiments are performed in two steps: first, we predict two-phase fluid-flow properties of fracture for different levels of normal effective stress using our in-house geomechanical model; and second, we study the effect of normal net stress in the reservoir on oil recovery factor, using conceptual simulation models and a commercial simulator.
Our main conclusions of this study:
- Oil recovery and water production in fractured carbonate reservoirs is controlled by, not only the fracture permeability (and other matrix related parameters), but also fracture rock curves.
- Complex behavior of fluid flow in fractures cannot be captured only by varying fracture permeability. Shape of relative permeability and its dependence on the effective stress have a significant impact on flow of water vs. oil.
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Upgrading Of Carbonate Classifications By Digital Image Analysis And Multivariate Statistics
By E. KieferSummaryCarbonate classifications and petrophysical rock typing are popular in reservoir characterization, core-log-calibration, seismic inversion, and petrophysical modeling for reservoir simulation. They rely on visual comparison charts and semi-quantitative estimations. This paper outlines the potentials of advanced digital image analysis tools in combination with agglomerative hierarchical cluster analysis (AHC) to define rock types. This approach has been tested in a tight oil reservoir using more than 500 petrophysical plug measurements and petrographic thin section analyses from 6 wells. The case study resulted in 11 rock types, which clearly seperate in terms of porosity, permeability and density.
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Mysterious Palaeozoic Carbonates In Nordland Ridge-Application Of Multi-Disciplinary Approach To Subsurface Data
Authors P. Farzadi, J. Garland, S. Morgan, J. Stilling and L. ChiariottiSummaryThe carbonate package of Upper Permian (Zechstein) age in Mid-Norway is underexplored. Sedimentological analysis of the four wells that penetrated this interval confirm the model of platformal carbonates located on depositional highs and more restricted carbonates deposited within the basins. Only one intriguing well situated on the Nordland ridge exhibits +250 m of heavily dolomitised carbonates carrying no clues about depositional settings. The original depositional character of these unusual foliated dolomites is a mystery and their coarse nature along with other evidence is indicative of fault-related hydrothermal activity. In order to gain insight into the internal heterogeneity and architecture of the Upper Permian carbonates, advanced sedimentological and geophysical technologies deemed necessary. The geological information extracted from the outcome of these technologies in particular analysis on IsoMetrix high resolution 3D seismic is far more diagnostic than conventional reflection seismic data interpretation. An Upper Permian carbonate play may be matured further only by utilizing these advanced technologies.
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Chemical EOR In Carbonates - Reservoir Analogs For Core Flood Experiments
Authors F. Schulze, H. Bullien, S. Reimann, N. Schleifer, P. Aurin and G. OetterSummaryCore flood experiments under reservoir conditions are a sensible step between laboratory trials and field tests. An evaluation cycle of suitable surfactants for enhanced oil recovery (EOR) from defined carbonate reservoirs in Middle East (high temperature, high salinity) is demonstrated: reservoir and analog characterization, flooding experiments on selected analogs and finally, test of selected surfactants and original Middle East core material.
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The Prediction Of Reservoir Quality Through The Effect Of Diagenesis To The Porosity Evolution Of Carbonate Rocks In Won
Authors I. Akmala and J. Gaby TiaraSummaryThis research was conducted in Wonosari Formation because those carbonate rocks making up good representatives as analogue because it has been suffered diagenesis intensively. The research methods by stratigraphic measurement in the field. Rock samples were prepared for thin section analysis and pororsity measurement. The main object which is investigated are lithofacies, diagenetic products (such as cemen type, mineralogy and other products that may be encountered such as paleosoil, karst and caliche), pore type and porosity. Diagenetic history of carbonate rocks in Wonosari Formation will be understood by the result identification of diagenetic product and the interpretation of diagenetic processes.
Early Hypothesis, carbonate rocks of Wonosari Formation experienced some diagenetic process in marine, burial and meteoric conditions in early stages, then continued to burial diagenesis until exposed to the surface and has suffered meteoric diagenesis till now. Based on diagenesis history that has been explained, carbonate rocks of Wonosari Formation would have increasing or decreasing of porosity quality. The significant porosity reduction occurred by cementation process, whereas the significant porosity enhancement occurred by the dissolution process. This dissolution process as a diagenesis product with huge potential as an oil and gas reservoir.
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Microscopic Sweep Efficiency In Fractured Carbonate Reservoirs - Use Of Micro-Scale Models To Study Matrix Fracture Inter
Authors S.J. Jonoud, O.P.W. Wenneberg, A.R. Rozhko, M.N. Naumann, F.L. Lapponi and Å.H. HaugenSummaryEffect of small scale parameters on micro sweep efficiency in fractured carbonate reservoirs is studied. Parameters with most significant impact are listed and effect of those are taken into account using different upscaling techniques.
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Application Of At Bit LWD Resistivity And Drilling Dynamics Measurements In Early Pre-Salt Reservoir Detection, Deepwater
Authors R. Cremonini Baptista, J. Gripp, C. Vieitez, D. Neto, C. Nunes and J. SalazarSummaryBrazilian deep water pre-salt reservoirs are located over 200 km from the coastline and 5000 m below sea level, with 2000 m water depth. To reach these oil rich limestone reservoirs, operators drill more than 1000 m of siliciclastic and limestone rocks before encountering the 2000 m thick salt layers. Before entering the reservoir, there is an intermediary borehole section, usually of 17 ½” size, drilled through the salt. Casing has to be set inside competent formation (anhydrite or limestone) with minimal reservoir entrance to guarantee wellbore stability.
Combining local geoscience expertise and high technology drilling services, the drilling operation is optimized to identify changes in drilling dynamics and to perform proper formation characterizations, where resistivity at the bit technology enhances the geological interpretation for an effective and accurate decision while drilling. Such technologies have been successfully applied, minimizing operational risks and reservoir entrance.
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Hybrid Drill Bit Technology Significantly Improves Build Up Rate Capabilities Of Multiple RSS Tools
Authors M.G.O. Omar, M.B. Bushehri, A.M.G. Makki, T.U. Uno, W.M.A. Agawani and R.K.D. DixitSummaryWith an objective to shorten directional intervals, operators place greater demand on higher build up rates. The section just before the pay zone involves the most intensive directional work, pushing rotary steerable systems to their capability limits. This paper focuses on a particular interval of hard and soft interbedded carbonates that provides a significant challenge for conventional Polycrystalline Diamond Compact (PDC) bits to provide consistent build up rate and good borehole quality on rotary steerable systems. Throughout the paper we demonstrate the engineering process of designing a bit to increase build-up rate capabilities of rotary steerable systems and improving drilling efficiency through interbedded carbonate formations.The optimized hybrid bit and BHA combination eliminated drilling vibrations in intervals where extreme vibrations were witnessed with conventional PDC bits, significantly increasing drilling efficiency. Improved torsional stability reduced the load on the directional tools improving the ability to achieve the required doglegs. In softer shale where RSS with conventional PDCs had to control parameters while using maximum steer force to achieve target dog legs of 7°/100ft, the hybrid bit was able to achieve 10°/100ft while utilizing only 70% of the steer force. The hybrid technology proved to be successful with both push-the-bit and point-the-bit RSS systems.
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Assessing Reservoir Potential Of Devonian-Carboniferous Carbonates In The Dutch Subsurface
Authors B. Jaarsma, L.J. Heijnen and E.A. RosendaalSummaryAnalysis of a regional dataset of (old and new) wells and seismic data in the Dutch subsurface, in comparison with nearby outcrops and with analogue carbonate systems elsewhere have yielded new, more positive, insights into the original reservoir development and the possible present-day range in reservoir quality of the underexplored Devonian Kyle Limestone and the Dinantian Carbonates. Large variations are present, both between the two systems and within the Dinantian Carbonates. These insights support predictions of reservoir quality in these strata. At the same time, the results of modelling of variations in seismic character of these carbonates, as a function of composition, porosity, pore fill and overburden properties, can be used in the reprocessing and interpretation of existing seismic and in the acquisition of new seismic data. This will be part of a nation wide study into the potential of Ultra Deep Geothermal projects in carbonate reservoirs.
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Heterogeneities of Carbonate Ramp Reservoirs - Characterization and Modelling of a Shoal Outcrop Analogue (Mid-Triassic)
Authors A. Petrovic, T. Aigner and M. PontiggiaSummaryIn order to improve the understanding of sedimentological heterogeneities on varies scales, from micro-scale thin section to macro-scale correlations, a joint project was initiated between the University of Tübingen (Germany) and ENI S.p.A. This outcrop study focused on the characterization and modelling of the largest and thickest wedge (wedge 3) of the Quaderkalk Formation. The Middle Triassic Quaderkalk Formation in SW Germany composed of four lithostratigraphic separated bioclast-rich wedges and represents an outcrop analogue for sub-seismic scale carbonate ramp reservoirs. Facies range from mud-rich, low-energy offshoal (non-reservoir facies) to bioclast-rich, high-energy shoal (potential reservoir facies), deposited on an epeiric carbonate ramp. Instead of a continuous facies belt, tens of kilometres-scale correlations indicate several separated high-energy shoal areas forming a shoal complex “mosaic”, which is controlled by a cycle architecture. Integrating all data of an intensive field study, two 3D facies models were produced: (1) a 30 × 30 km model to simulate the large-scale facies pattern and (2) a more detailed 10 × 10 km small-scale model to simulate internal shoal reservoir heterogeneities. The results highlight the importance of realistic geological, especially sequence-stratigraphic input in order to optimize the simulations of carbonate shoals.
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The Upper Jurassic In Southern Germany - A Carbonate Aquifer For Geothermal Exploration
Authors U. Steiner and K. BeichelSummaryThe Upper Jurassic Malmian in the Southern Germany Molasse Basin developed in the last 15 years to an increasingly intensive used carbonate reservoir for producing geothermal energy. The over 20 geothermal wells (reaching depths of up to 5.000 m TVD) which were investigated by ERDWERK, provide a significant amount of information to optimize the future exploration strategies. (3D-) seismic data, drilling parameters, cuttings, geophysical logs as well as outcrop analogues studies allow for conclusions to be drawn concerning the lithofacies, diagenesis, carstification, geodynamic anomalies and strucural framework of the carbonate reservoir, which are the drivers for the inflow zones and so the overall productivity of the geothermal wells. The study presents results from the structural and facies analysis of the Malmian carbonate reservoir and exhibits the requirements for a decision-making workflow for an optimal exploration.
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Organic-inorganic Interactions During Reactive Fluid Flow in Carbonates
Authors H.M. Schulz, N. Schovsbo, R. Wirth, A. Schreiber and W. van BerkSummaryThe talk will present results about organic-inorganic interactions leading to porosity formation due to migration of source-rock-derived corrosive fluids through carbonate reservoirs. Two aspects will be covered: (i) detectable processes at the nanometer scale by imaging techniques, and (ii) generic hydrogeochemical modelling results of porosity creation at a play scale (from source rock to reservoir).
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Characterisation Of Natural Open Fractures In Carbonates Using X-Ray Computed Tomography -Examples From Shetland Group I
Authors O.P. Wennberg, L. Rennan, B. Graham Wall, S. Jonoud and A.Y. RozkhoSummaryA large proportion of carbonate reservoirs contain natural open fractures, which have a significant impact reservoir fluid flow and ultimate recovery. In this study, high resolution X-ray computed tomography (µCT) has been used for imaging, interpretation and analysis of open fracture in carbonate in true 3D. The samples are form the Shetland Group in the Gullfaks Field, which has produced oil since late 2012. The µCT data shows that the tensile fractures occur as calcite veins or are partly filled with calcite cement. Fractures tend to be most frequent in low porosity parts of the formation, and bioturbations also have a significant effect on the shape, orientation and occurrence of fractures. The µCT gives the detailed geometry and aperture distribution of the fractures in 3D.
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A Novel Micro-Fracture Tool Design For Directional Hydraulic Fracturing Pilot Test
More LessSummaryThe benefit of directional hydraulic fracturing technique is to enable operators to control hydraulic fracture orientation to maximize oil recovery. Due to complex stress distribution near the borehole, hydraulic fracture patterns in the formation are very difficult to predict.
Formation tester dual packer module was recognized as a successful pilot test tool for micro fracturing, it can quickly obtain downhole formation fracturing breakdown and propagation pressure. In order to test directional hydraulic fracturing patterns, the authors of this paper have designed a new formation tester packer probe module to enable it to do oriented injection of fluids into the formation and enable it to do directional hydraulic fracturing. Besides the directional hydraulic fracturing operations, the new packer probe can monitor hydraulic fracture pattern generation in the formation in real time by monitoring the voltage of sensor buttons mounted on it. Through the analysis and inversion of the azimuthal formation resistivity, the directional hydraulic fracture azimuth and re-oriented radius can be estimated. Finally, the optimized directional angle for fracturing can be estimated by cycling through different orientations of directional hydraulic fractures and measuring the resistivity of each.
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