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Third EAGE/SBGf Workshop 2016
- Conference date: 06 Apr 2016 - 07 Apr 2016
- Location: Rio de Janeiro, Brazil
- ISBN: 978-94-6282-180-4
- Published: 06 April 2016
1 - 20 of 22 results
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A Reliable Analysis of Azimuthal Related Information for Fracture Detection
Authors A. Canning, A. Malkin and Y. WeissAzimuthal seismic analysis is an important step in the analysis chain of seismic data in carbonates and shales. However, the azimuthal information derived is very sensitive to many aspects of the data and of the analysis process. In this paper we define the concept of reliability, a measure of the quality of the azimuthal analysis, analyze some of the major factors affecting it, and show our approach to how a reliable analysis should be performed and presented.
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Wave Equation Migration Improvements - Towards Reliable Quantitative Seismic Interpretation of the Pre-salt Play
More LessStructural imaging in subsalt environments has been a major challenge for the geophysical industry in the last decades. Thanks to the tremendous improvements in acquisition, processing, model building and migration technologies, structural imaging subsalt has reached a quality level that allows today to go further and to exploit amplitudes of subsalt migrated images. For this purpose and in order to correctly handle the complexity of the wave propagation, wave equation migration methods have become the standard algorithm for subsalt environments and have largely contributed to the improvements of structural imaging subsalt. But amplitude fidelity of those migrated images is still a challenge that can be today overcome by the recent improvements added to these methods: I/ the ability to compute accurately and efficiently common image gathers, II/ the derivation of true amplitude image conditions and III/ the efficient implementation of preconditioned least squares migration. We will describe and illustrate theses improvements in the presentation.
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Reliable Seismic Amplitudes in Sub-salt Imaging Through Wave Equation Inversion
More LessTo mitigate the irregular illumination problem in the subsalt area, we propose a wave equation reflectivity inversion (WEI) method. The method poses depth imaging as least squares problem with explicit computation of the Hessian through the use of point-spread functions. WEI not only removes the illumination imprint on the seismic amplitudes, it also enhances the wave number content, improving the overall resolution of the migrated image. We will show how applying WEI ensures that reliable amplitude can also be extracted in sub-salt/pre-salt areas. Compared to a conventional migration, WEI recovers the amplitudes in the subsalt shadow zone and improves the sharpness of the reflectors.
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Impact of Geodynamics on Diagenetic By-products - An Input to Petro-acoustic Modeling of Pre-salt Carbonates
Authors A. Virgone, M. Masini, E. Gaucher, G. Massonnat and M. PellerinDiagenesis of the atypical presalt carbonate deposits is controlled by hydrothermal CO2-rich fluids circulation. In low CO2 pressure conditions, most of the reservoirs are plugged by Mg-clays (no reservoir). When the CO2 pressure is increasing, the Mg-clays can be leached and replaced by dolomitic rhombs, creating a good reservoir network. Precipitation of siliceous cement is also a by-product of the presence of the CO2, mainly in cooler areas. All these different fluids/rock alterations steps can be fossilized at different stages observed on thin sections. In-house coupled stratigraphical and diagenetical forward modeling of continental carbonates has been launched. First results are very promising and let possible to model carbonate springs in aerial conditions, which was not possible with the current forward modelling tools. This integrated approach will be used to experiment different geological scenarios (sedimentological and diagenetical) as imput to forward seismic modelling for derisking exploration and appraisal of the pre-salt play.
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Rock Physics Modeling of Diagenetic Processes of Pre-salt Carbonates
Authors J.M. Codo and F. FournierThe acoustic properties of carbonate reservoirs are strongly controlled by pore space architecture resulting from both depositional and diagenetic processes. As a consequence seismic inversion in highly diagenetized sedimentary systems such pre-salt non-marine carbonates requires first a quantification of the mineralogic, pore volume, pore geometry and fluid effects on acoustic impedance. In addition such a poro-elastic modelling approach must be coupled with the characterization and quantification of the diagenetic processes controlling the pore space architecture and mineralogy in order to constrain the seismic inversion and to compute geologically realistic models of carbonate reservoirs in 3D.
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Dispersion and Attenuation Measurements on a Bimodal-porosity-oolitic Limestone
Authors J.V.M. Borgomano, L. Pimienta, J. Fortin and Y. GuéguenDispersion and attenuation measurements have been performed on an oolitic limestone from Lavoux. This limestone comes from a Dogger outcrop, is pure calcite, and exhibits a bimodal porosity with intragranular microporosity and intergranular macroporosity. Total porosity and permeability of the sample were measured to be respectively around 23% and 10 mD. To measure the elastic-moduli dispersion and attenuation over a wide-frequency range, we used two stress-strain methods: hydrostatic and axial oscillations. The triaxial cell used allows for low-frequency measurements (0.004 Hz to 100 Hz), and ultrasonic-velocity measurements at high frequency (1 MHz). The sample was measured under three-different-saturating conditions: dry, water and glycerine. The results show no dependence to effective pressure, which is related to the absence of cracks in the limestone. Moreover, the transition from drained to undrained regimes has been successfully measured under glycerine-saturated conditions (around 1 Hz). It corresponds to a strong dispersion (~50%). The undrained-elastic moduli are consistent with Biot-Gassmann’s theory. A weak dispersion is observed (< 12%) between the undrained-elastic moduli and the ultrasonic results that remains to be further investigated.
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3D Modeling of Carbonate Rock Porous Media and Estimation of Petrophysical Parameters
Authors T.M.G. Silveira, W.G.A.L. Silva, P. Couto and J.L.D. AlvesPre-salt carbonate reservoirs represent a great opportunity for the Brazilian technological development and for national and international companies that are involved in oil industry. This giant discovery consists of heterogeneous carbonate rocks found underneath a layer of salt with variable thickness (around 2.000 meters) and spread over very large areas. Due to its huge complexity, understanding their petrophysical parameters and flow properties is fundamental and a major challenge. To overcome the difficulties, the concept of Digital Rock Physics (DRP) has been explored as a methodology that complements the traditional experimental analysis of rock samples. DRP allows to image real rocks in three-dimensional with high accuracy and resolution and to perform several virtual simulations. This papers aims to present a method that was developed to reconstruct porous systems and estimate porosity and specific surface area from coquinas samples, analogue carbonates samples to Brazilian pre-salt.
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Proposed Workflow to Incorporate Stratification within Salt Section Using Velocity and Seismic Attributes
Authors M. González, F. Gobatto, A. Maul, L. Falcão, G. González, L.C. Oliveira, T. Meneguim and P.J. AmaralBeyond time-to-depth conversion purposes, building a more realistic seismic velocity model is fundamental to provide proper inputs for seismic processing and imaging, quantitative seismic interpretation, illumination studies, geomechanical analysis, facies studies and uncertainties analysis. The Pre Salt reservoirs in the Brazilian offshore (Campos and Santos basins) are plays underlying a structurally complex area due to multiple factors, as the presence of the salt section above them, imposing several challenges regarding the amplitude response. Therefore, it makes necessary the evolution of the standard way to build velocity models, including a strong geological approach, in order to consider specific characteristics, as stratified layers inside the referred salt section, once it should influence the quality of the seismic response and its usage for reservoir characterization involving property distribution. For that reason, a new methodology is presented, based in a recursive workflow, to generate a robust geologic velocity model. This model is improved in every cycle step and each result becomes a new input for the next one. It takes into account the lithological heterogeneity of the salt section and the position of the stratifications to better represent the seismic velocities in the subsurface.
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Inversion of Multicomponent Seismic Data for VTI Medium Using the Globalized Nelder-Mead Optimization Algorithm
Authors N.R.C.F. Zuniga, E.C. Molina and R.L. PradoThe velocity analysis is a fundamental step of seismic reflection, and can be performed fitting the calculated hyperbolic curve to the observed one. The conventional seismic where it is studied PP wave reflection events (hyperbolic events) have some limitations to imaging through gas clouds. The joint P and S wave processing presented better results than the conventional seismic. However, a PS wave reflection event and the effects of a stratified medium can generate a nonhyperbolic event, what demands the use of multiparametric approximations which can characterize the nonhyperbolicity of an event. An analysis was accomplished aiming to evaluate the efficiency and the complexity of different approaches used to execute the velocity analysis of a stratified media with a limestone reservoir saturated by gas. The analysis was considered an inverse problem according an optimization criterion. Studying the complexity of the objective function we could determine the one which take more time to execute the inversion routine. Then, with the analysis of the residual travel-time we could identify the best curve fitting and the most efficient approximation to perform the velocity analysis of the model.
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Ocean Bottom Nodes Ultrasonic Physical Experiment
Authors E.S. Silva, R.S. Stewart, N.D. Dyaur and A.A.S. SobrinhoThe current efforts in the hydrocarbon industry have been concentrating in maximize oil and gas production from existing fields as the task of find new reservoirs becomes expansive and difficult. Hence, converted-waves are used in partnership with P-waves for a more complete understanding of reservoirs’ properties and geometrical arrangement. One example of it is in the marine exploration, where high quality and complete data are obtained by the Ocean Bottom Nodes (OBN) survey. In this work we have conducted 4C ultrasonic physical model seismic surveys to simulate the OBN method and study the converted waves from the sea bottom. The main objective of this study is to investigate the multiple converted waves through the usage of the OBN technology. In this stage, we have performed imaging in a carbonate layer with OBN data converted waves and the seismic processing. In addition, we measured the carbonate rock properties, studied the reflection and transmission coefficients for the model interfaces and computed the vertical resolution for the vertical and horizontal modes and the data dominant frequency. The median connected porosity for the carbonate in the model was estimated by the fluid saturation in the rock. The whole experiment and simulations were made at the Allied Geophysical Laboratory (AGL) at the University of Houston, Texas.
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Reducing Drilling Risk and Cost through Integration of Seismic and Real-time Well Data
Authors J. Mathewson and C. EsmersoyThere is always uncertainty involved in drilling a well, arising from incomplete knowledge of the subsurface. Before drilling starts an earth model in the vicinity of the well is normally produced using available information relating to geology, rock properties, stresses, pressures and temperatures from surface seismic data and nearby well data. Based on the earth model a drilling plan is made, including the well’s trajectory, casing points and other specifications. However, the model is often quite uncertain because there is a lack of information in the vicinity of the well, and this uncertainty can lead to increased drilling costs and environmental and safety risks. A recent development that can reduce drilling uncertainty combines surface seismic data with LWD log information to produce a more reliable picture of geology and pressure distribution ahead of the drill bit. Tests of this method indicate that it is effective for reducing uncertainty about subsurface structure (e.g. fault location uncertainty) and providing better estimates of pore pressure. A blind test is shown demonstrating the accuracy of pore pressure predictions made using this method.
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Digital Rock Physics from Santana Formation, Araripe Basin
Authors A. Vidal, J. Soares, L. Medeiros, I. Borges, G. Raposo and A. BarbozaX ray digital rock physics is a nondestructive technique, that enable the rock physic properties quantification and characterization. The method is based on the x ray absorption from each material, depending on the material density and the chemical components. Tomography methods are commonly used by medicine, but their application is coming together with geosciences since their discovery. The cross sections coming from the gray scale can be edited by many ways, depending on the study object. The sections integrations obtained by this method, allows a 3D projection by the material used. The image processing is made by computer systems to obtain qualitative and quantitative results quickly and efficiently.Through this stage develops a job that was applied to computed microtomography technique of X-ray mainly focused on the pores tortuosity study in carbonate rocks from Santana Formation, Araripe Basin. In this way, assist in the investigation of potential reservoirs. The data obtained by this technique is integrated and compared with petrophysical analyzes in a laboratory.
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Simulating Carbonate Dissolution with Digital Rock Physics
Authors J.P. Pereira Nunes, B. Bijeljic and M.J. BluntThe increase in CO2-injection activities for Capture Carbon and Sequestration (CCS) and Enhanced Oil Recovery (EOR) is pushing the industry and the academia to explore the implications of rock-fluid interactions in full-scale development projects of carbonate reservoirs. Some of the questions are: Do reactions occur at rates that make a substantial impact on petrophysical properties? Are they relevant for CCS and/or oil recovery? How do they impact monitoring strategies? Carbonate reservoirs are notoriously difficult to characterize. Their abrupt facies variations give rise to drastic changes in the petrophysical and mechanical properties of the reservoir. Such heterogeneity, when further associated with variations in rock mineralogy due to diagenetic processes, results in a challenging scenario to model from the pore- to the field-scale. Micro-CT imaging is one of the most promising technologies to characterize porous rocks. The understanding of reactive and non-reactive transport at the pore scale is being pushed forward by recent developments in both imaging capability - 3D images with resolution of a few microns - and in modelling techniques – flow simulations in giga-cell models. We present a streamline-based pore-scale simulation method to predict the evolution of petrophysical properties of carbonate cores subjected to CO2 injection at reservoir conditions.
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Coupling Forward Stratigraphic and Diagenetical Modeling as Input to Seismic Simulations of the Presalt Play
Authors G. Massonnat, M. Pellerin and C. PlanteblatTOTAL R&D has developed a new approach to improve the understanding of the relations between geology and geophysics in presalt carbonate rocks. This approach is multi-disciplinary and integrates measurements and knowledge of carbonates at all scales, from grain to seismic scale, from low to high resolution. The core of the scientific problematic is to interlock sedimentology, stratigraphy and diagenetic processes together with rock physics and geophysics in a both forward and inverse sense.
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De-risking Reservoir Quality and Presence through Seismic Inversion and Rock Physics Analysis in Brazil's Pre-salt Carbonates
Authors K. Azbel, O. Rodina, G. Baechle, W. Gouveia, D. Gracioso, F. Nogueira, P. Wang and R. Centenoand rock facies with a profound effect on permeability; the presence of non-reservoir rocks; limited seismic detectability of fluid signal in the rigid carbonates; and seismic data quality issues caused by the complex heterogeneous overburden. In order to address most of these challenges an integrated quantitative seismic interpretation workflow as been applied through detailed well data analysis grounded by calibration on the core and thin section scale, followed by rock physics modelling, interpretation of carbonate and non-carbonate facies, AvO-inversion, and facies-based reservoir characterization – all integrated to enable generation of 3D reservoir property cubes. The workflow also included fluid evaluation, forward modelling, and direct hydrocarbon detection (DHI) in areas where fluid signal may be detectable on seismic.The study’s interdisciplinary data reconciliation also helped improve our understanding of geological factors that control deposition of pre-salt carbonates, their elastic properties, and seismic response.
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Lessons Learned From Examples of Reservoir Seismic Characterisation in Pre-salt Context
Authors G. San Miguel, P.E. Barrallon, Q. Villeneuve, T. Teillet, L. Dubois and J.M. KluskaSeismic reservoir characterization within the pre-salt carbonate context faces two challenges. One is that the data quality, resolution and amplitudes reliability might not be good enough to let classical approach working. Second is that although Ip-Porosity or Ip/Is- Ip laws are often used to interpret the seismic as a porosity or a geological facies indicator of the reservoir, carbonate rocks rarely follow a simple relationship. That being said, seismic is the main tool for the petroleum explorationist and should be used to derisk presalt exploration or optimize appraisal campaigns. Well will expose some lessons learned from different approaches that we used in seismic reservoir characterization in the pre-salt domain.
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Integration of Lithological Data for Advanced Seismic Inversion
Authors M.A.C. Kemper, M. Abel, L.F. De Ros and J. HansfordRecent advances in seismic inversion have made it possible to integrate geophysical Elasto-Facies Associations (EFAs) into a more sophisticated workflow that allows for improved reservoir characterization. However, performing inversion still requires well data for the calibration of low frequency input models. Innovative solutions are therefore required to provide sufficient input data in areas where only low quality well data is available, if at all. A new workflow is proposed for the integration of data from additional sources in order to provide an improved facies-aware seismic inversion, flexible enough to support a range of data types to constrain the low frequency model inputs, yet robust enough to honour geological and geophysical properties. This revolutionary method offers the potential make more precise reservoir characterization accessible in spite of well data limitations.
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Diagenetic Considerations and Geophysical Pore-type Characterization in TS Carbonate Reservoirs
Here, we show the processes carried out and results of a diagenetic process analysis and geophysical characterization of pore types in Jurassic and Cretaceous carbonates in the TS oil field, Gulf of Mexico. In order to make predictions, we carried out a rigorous petrophysical evaluation and used borehole image interpretation, core analysis and thin section observations. This information was used in the construction of rock physics models that consider various arrangements of pore shape and fracture concentration. Once the physical links between the micro structural properties (type and shape of the pores) and elastic properties were established, we proceeded to make connections with attributes obtained by seismic inversion processes. These connections were formed using a probabilistic approaches where the results are volumes of intercrystaline porosity, dissolution porosity and fracture porosity.
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Quantification of 4D Seismic Response in Pre-salt Carbonates via Time Shift Analysis
Authors M.M. Costa, E.P. Silva, M.S. Santos and G.F. VasquezHeterogeneity and stiffness of pre-salt carbonates challenge the detectability and interpretation of production effects to be monitored via 4D seismic, making prior modelling crucial in a more comprehensive and robust understanding of the anomalies. In this paper we computed the time shift response for selected scenarios of fluid substitution (oil by water or gas) and pressure changes (depletion or overpressure) for two types of pre-salt rocks (microbial carbonates and coquinas). High amount of CO2 dissolved in the oil has been considered. Sensitivity of elastic moduli to effective pressure were obtained by experiments on core plug samples and revealed to be a facies dependent phenomenon, with major velocity variations for coquinas. Fluid substitution using well log data also showed higher anomalies in coquinas, since this was the most porous facies and with the higher recoverability of the reservoir. Due to the thickness of the reservoir, including aquifer, time shifts showed to be susceptible to detection, and a solution for reservoir monitoring.
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Acoustic Properties of Continental Carbonate Rocks - Controlling Factors, Analytical and Numerical Simulations
Authors J.B. Regnet, K. Anoukou, K. Danas, J. Fortin, Y. Gueguen and M. PellerinThe complex nature of carbonate rocks is a major challenge when interpreting seismic data for subsurface characterization. Understanding the relations between sonic velocity and carbonate rock type is one of the keys to interpret data from seismic sections or from acoustic logs. Studies have shown that elastic properties of carbonate rocks are affected by many parameters such as dominant mineralogy, rock fabric, pore type and shape, porosity, and pore fluid, making it difficult to attribute changes in seismic expression to any one parameter. Continental carbonates gained interest following the discovery of the supergiant field in the post- and pre-salt deposits in offshore Brazil, as they account for a large portion of the deepwater production. The genesis of continental carbonates is generally associated with physico-chemical and biological precipitation of carbonates, coupled with a strong influence of clastic mineralogical inputs. This results in a complex mineralogical mixing, associated with a wide heterogeneity of pore types due to the intense diagenetic overprint potential of carbonate deposits (cementation, dissolution, recrystallisation, dolomitisation...). With that in mind, we propose insights on the controling factors of elastic properties in a continental carbonate dataset, analogue of the brazilian pre-salt deposits. An applicable model based on the effective medium theory is proposed and discussed regarding the experimental results, and try to account for the wide variability of the elastic properties. In addition, a numerical estimation of elastic properties is carried out on virtual microstructures generated by a random sequential addition (RSA) algorithm.
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