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79th EAGE Conference and Exhibition 2017 - Workshops
- Conference date: 12 Jun 2017 - 15 Jun 2017
- Location: Paris, France
- ISBN: 978-94-6282-219-1
- Published: 12 June 2017
41 - 60 of 144 results
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Seismic Uncertainty and Ambiguity
Authors K. Mosegard, A. Zunino, N. Frandsen and P. ChristiansenThe link between seismic data and subsurface properties suffers from an intrinsic ambiguity, i.e., that many reservoir models fit the same data within the noise. In some pathological cases, this may cause biases in the interpretation of the structure of the earth models used in exploration and reservoir management. Inversion techniques for large seismic data sets encountered in the oil industry are well established and are assumed to be reliable. Although this is generally true, thanks to integrated knowledge from geology and other geophysical data, there is, in some cases, still a significant risk that traditional approaches may end up finding only part of the models which can explain the observed data, overlooking potentially different scenarios and, moreover, hampering a correct uncertainty quantification. This phenomenon is often observed in practice when different inversion contractors arrive at significantly different results from the same data sets. The impact of the unavoidable non-uniqueness should be assessed when performing inversion of seismic data. We investigate the magnitude of the ambiguity problem in seismic modelling of chalk reservoirs by explicitly taking ambiguity into account in the inverse problem. Our study is based on a careful selected test case from the the Danish North Sea sector.
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Multiphysics uncertainty analysis and considerations: a toolkit for interpreters
By M. MantovaniThe non-seismic employment operates a hypothetical reduction of the geophysical equivalence. Traditionally, the mutual agreement imposed to the properties is supposed to reduce the degree of freedom in shaping the final model of the earth. Nevertheless, in many cases, it is difficult to quantify how much influence the non-seismic data has on the reduction of the geophysical ambiguity. The presentation attempt to exemplify one instance of a typical situations of velocity determination with seismic-only solvers, and provide some reference number for estimating the geophysical equivalence reduction and the decrease of the uncertainty of results in the occurrence of seismic and non-seismic data.
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Tomographic model uncertainties and their effect on imaged structures.
Authors M. Reinier, J. Messud, P. Guillaume and T. RebertWe demonstrate a recently developed method for computing tomography model uncertainties and mapping them into the migrated domain. After the final tomography, the method generates a series of equi-probable velocity model perturbations within a standard deviation confidence level. This allows computing standard deviation-like attributes for velocity and anisotropy parameters and for key horizons. An application to West of Shetland dataset highlights the interest of the estimated uncertainties.
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Anisotropic Earth model building and some sources of uncertainty in the results
By O. ZdravevaAnisotropic earth model building (EMB) is a challenging task: even when we use best-quality modern workflows with non-seismic data and information to better constrain the problem, results are inherently non-unique. Methods for quantifying the uncertainty of earth models for seismic imaging exist and their successful application has been demonstrated in the past. All of them assume that the available model is a close representation of the true earth and is accurate enough, i.e. it explains at least all available seismic and borehole data. In addition, they rely on some extra knowledge and information for the area under investigation to be brought in to form some priors. This abstract discusses and illustrates the EMB sensitivity and uncertainty associated with: (1) the absence of enough complementary to surface seismic measurements; (2) inaccuracy in salt geometry and subsalt velocities, and (3) Q-compensation methods and parameterization. It emphasizes the need to validate earth models thoroughly before conducting uncertainty analysis and, if needed, to further update the models and ensure all limitations and assumptions of the data conditioning and EMB validation are factored into the priors for further uncertainty analysis.
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Uncertainty estimation by probabilistic first arrival time tomography using Markov Chain Monte Carlo sampling
Authors A. Gesret, J. Belhadj, T. Romary, M. Noble and N. DesassisWe present several applications of probabilistic first arrival time tomography by Markov Chain Monte Carlo sampling dedicated to uncertainty estimation. In the first part, we introduce a new velocity model parameterization based on Johnson-Mehl tessellation that allows applying probabilistic approach to typical seismic refraction data. We also present results of the tomography to a real data set recorded in the context of hydraulic fracturing and illustrate how the velocity model uncertainties can be properly taken into account when locating seismic events.
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Model uncertainty analysis for de-risking seismic image accuracy
Authors A. Bell, L. Russo, T. Martin and D. van der BurgWith exploration moving towards areas of increasing geological complexity, reservoir evaluation is often based on the interpretation of a single seismic image. Recovering a suitable velocity model employed in pre-stack depth migration plays a crucial role in the creation of this image on which economic evaluations are drawn. Typical depth imaging projects provide final velocity model attributes and their associated seismic image. The amount of uncertainty associated with this image is poorly understood; the only quantitative measures of reliability are provided through analysis of volumetric residual move-out and by comparison with available auxiliary data. We aim to address this situation by using the same tomography method we use to derive the model parameters. The workflow allows us to establish the resolution of the tomography, in establishing the model parameters. It also enables us to determine the recoverable degree models may be perturbed prior to the tomography. Using the workflow in conjunction with these criteria we generate a population of solution models which equally conform to the observed data. We then analyse the variance of this model population to derive confidence attributes to assign to both the target model and its associated seismic image.
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Complexity in common image gather behaviour in offshore continental settings arising from velocity model building and imaging choices.
Authors G. O'Brien, M. Igoe, J. Doherty, P. Matrice and R. MecklenburghCommon image gather complexity arising from uncertainties in the subsurface velocity model feeds into exploration risk through degradation in seismic attributes and facies prediction. In off-shore continental settings where the overburden is geologically complex, the seismic wavefield exhibits complex behaviour when propagating through such highly varying geological structures which impacts the resultant seismic images and attributes. Using a representative synthetic model, the imaging choices and velocity model uncertainties are explored in light of maximizing facies prediction using seismically derived attributes.
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What mistakes are we making while interpreting salt? Could FWI help?
Authors J. Dellinger, A. Brenders, X. Shen, I. Ahmed, J. Sandschaper and J. EtgenModel studies indicate that our conventional salt-interpretation workflow, consisting of cascaded sequences of flooding with either salt or sediment velocities, migration, and picking, produces two distinct types of velocity errors: 1) small but ubiquitous positioning errors of the margins of the salt, and 2) large “chunky” errors where salt boundary reflections were grossly misinterpreted. Full-Waveform Inversion might be a solution, but to achieve success may require new kinds of data, improved algorithms, or most likely both.
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Reduction of depth uncertainties using common offset RTM (COR) Gathers
Authors S. Liu, G. Rodriguez and F. HaoSubsalt velocity estimation has presented significant challenges in the past. Ray based methods suffer from poor S/N ratios that results from sparse ray coverage beneath salt bodies. The use of common offset RTM gathers (COR) has been shown to decrease uncertainties in subsalt residual moveout estimation, which can more reliably be used by tomographic algorithms to invert for more accurate velocity estimations. Furthermore COR gathers have been shown to improve salt velocity estimations in areas with sediment inclusions. Better ties to well information (sonic logs, formation markers) have validated the improved resultant velocity models.
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Post-Migration Processing and Imaging in the Local Angle Domain
By Z. KorenIn many areas of interest, the available seismic data combined with the most advanced seismic modeling/imaging tools, well information, potential field data, and geological and geophysical constraints, are still not sufficient to uniquely determine the complexity of subsurface geological media. There has been a continuous effort to enrich these data components in order to converge to a minimum set of plausible geological models that can be considered throughout the O&G exploration, development and production stages. The reliability of seismic imaging in complex geological areas depends on many factors. One of the most important is the ability to use the available recorded seismic data to illuminate subsurface image points from a wide range of directions and opening angles/azimuths between the incident and scattered waves. This multi-dimensional illumination challenge mainly depends on the density and extension of the seismic acquisition system and on the complexity and accuracy of the inverted subsurface geological model. Moreover, seismic imaging is classified into many categories, depending on the specific goal at each stage. For example, structuraloriented imaging for locating large scale potential reservoirs significantly differs from high-resolution imaging at the reservoir for fracture detection. In this work I demonstrate the advantages of using a novel multi-dimensional local angle domain (LAD) system for enriching information from the available recorded seismic data in order to obtain more reliable information about continuous and discontinuous subsurface target objects. In particular, I’ll briefly demonstrate the potential of using the mapped seismic data for different post-migration processing/imaging solutions: velocity model updating and re-migration, amplitude correction, accounting for illumination, geometrical spreading, and absorption/dispersion (Q-correction), in-situ data reconstruction, and specular/diffraction imaging.
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Seismic matching pursuit decomposition based on the attenuated Ricker wavelet dictionary
More LessThe wavelet dictionary is the critical part for the matching pursuit decomposition of seismic traces. In this study, considering the effects of the wave‐attenuation we develop a new wavelet atom based on the traditional Ricker wavelet, and thus form a new dictionary—the attenuated Ricker wavelet dictionary. Based on the proposed dictionary, we use the orthogonal matching pursuit to decompose an input seismic trace into a set of components, each of which can establish the relation between the quality factor Q and the spread time of the wavelet atom. Then we can derive the Q model of the underground medium by smooth algorithms. By compensating the amplitude attenuation of each decomposed wavelet atom, the input seismic trace can be compensated. We test our algorithm with a synthetic trace and a field seismic profile preliminarily, the seismic wave‐attenuation can be well compensated and the resolution is improved.
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Towards Realistic Synthetic Models of Middle East Carbonate Reservoirs for Evaluating Reservoir Engineering Workflows
Authors A. Darishchev and D. GuérillotThis paper proposes building realistic synthetic models of carbonate reservoirs typical of those frequently occurring in the Middle East, particularly in the State of Qatar. Based on published data, these models represent the Upper Jurassic Arab C and D reservoirs which are among the most abundant and economically important. They are well studied and most of the reservoir data is available in literature. In these models, the rock and fluid properties are based on actual fields. Developing and upgrading these models with partners and sponsors will lead to advanced reservoir engineering workflows for enhancing oil recovery, screening and benchmarking various innovative scenarios of field development and uncertainty assessment. This stimulates effective collaboration, knowledge and expertise sharing and establishes better practices in carbonate reservoir engineering.
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Combining seismic and petrophysics to improve facies proportions modeling
Authors J. Chautru, H. Binet and M. BourgesA new workflow to propagate expected Facies proportions from wells into the 3D space is proposed, considering seismic data as stronger constraints than a simple drift or auxiliary variable in cokriging calculations. The idea is to combine seismic attributes transformed into Porosity, calibrated to well data, with the Porosity distribution per Facies determined from core plugs and Porosity logs. The workflow is made of two steps, the first one corresponding to calculations at seismic vertical scale, the second one being a resolution enhancement at well data scale (between 1 meter and 1 foot). In the first step, well data are obviously averaged at seismic vertical scale for ensuring consistency between the different data sources. At this vertical scale, the average Porosity at a given location in the reservoir is obtained from a mixture of already defined Facies, which expected proportions are related to the Porosity distribution inside each Facies. The distribution of expected Facies proportions at any point is calculated, ensuring that the average Porosity calculated from seismic attributes at that point is honoured. Then, the vertical evolution of Facies proportions is calculated at a sub-metric scale, from well data and the local average proportions previously determined.
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Core Tests and Field Case Studies of Successful and Unsuccessful Low-Salinity Waterfloods from Four Oil Fields
Authors V. Khisamov, V. Akhmetgareev and T. ShilovaThe aim of the work is to define successful and unsuccessful cases of low-salinity waterfloods (LSW) and to determine the incremental recovery if compared with high-salinity water injection. Four oil fields have been studied. Double-coreflood tests showed: a) fines: three-fold decrease of water relative permeability (krw) for the Pervomaiskoye field and five-fold decrease for the Bastrykskoye field; b) wettability alteration in carbonates: three-fold reduction of residual oil saturation (Sor) for the Romashkinskoye field; however, no changes were noted for the Arkhangelskoye field. 3D models of the fields were built and history matched. To simulate salinity-dependent effect of fines migration and wettability alteration, options of krw and Sor decrease were used. Field performance analysis showed that LSW resulted in increase of incremental oil recovery by 3.5% in the Pervomaiskoye field, but in the Bastrykskoye field, the LSW effect was negligible. Analysis of two LSW pilots in the Romashkinskoye field showed improvement of the incremental oil recovery by 2.7% due to LSW, while LSW pilot in the Arkhangelskoye field was unsuccessful. For sandstones, LSW into aquifer yields no positive effect, nor does it at the initial and final stages of reservoir development. For carbonates, the effect depends on viscosity of oil.
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Application of Nanoparticles in Adsorption Reduction of Polymer in Chemical EOR Processes, Experimental Approach
Authors S. Mellat and M. JamialahmadiThe implementation of tertiary Enhanced Oil Recovery methods is required due to the huge amount of oil retained in the reservoir at the primary recovery stage. Polymer flooding has proved to be an effective chemical EOR method which improves sweep efficiency and increases recovery; however, one of the major problems that can make polymer flooding inefficient and economically infeasible is polymer adsorption on the rock surface. Applicable methods which can reduce polymer adsorption in carbonated porous media have not yet been widely investigated. In this paper, the effects of adding nano silica and nano alumina on adsorption-reduction of polymer in Partially Hydrolyzed Polyacrylamide (PHPA) solutions were experimentally studied. Adsorption density of six test points was calculated based on the calibration curve generated in accordance to the solution electrical conductivity. Also, the Critical Micelle Concentration (CMC) was determined (1580 PPM at 28 C). The results show the adsorption density decreases by 16% in presence of nano silica and 24% in presence of nano alumina and therefore, the addition of nanoparticles into the polymeric solutions remarkably reduces the polymer concentration loss.
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Effect of Wettability Alteration on Production Improvement in Gas Condensate Reservoirs: a Review Paper
Authors M. Sheydaeemehr, I. Shafiei Sarvestani and M. PasdarWettability alteration is a novel approach in gas condensate reservoirs by altering the wettability of the reservoir rocks from strongly liquid wetness to preferential gas wetness or intermediate-wetting by treating them with chemicals that it's effects has been proved in lab scale. Both gas and condensate cumulative productions are improved significantly after the wettability alteration. The effect of wettability alteration on gas-condensate production improvement is more pronounced in the intermediate-wetting state. Wettability alteration could significantly increase well productivity at relatively low cost because only the near well region needs to be treated. In this paper, a review of recent studies on effects of wettability alteration on gas and condensate production improvement in gas condensate reservoirs has been presented.
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Salt deformation history and salt related structures signification ,offshore Golf of Gabes,Tunisia
Authors H. Ghuedifi, I. Hamdi Nasr, M. Hedi Inoubli, N. Barhoumi and et al.Regional seismic profile shows salt walls predominance on the Golf of Gabes which is flanked by elongate minibasins. The overburden and the underlying sub-salt basement become welded together which means that salt layer is completely removed , Salt welds forms may are in response to complete evacuation of salt materials due to salt movement or to viscous flow and dissolution , in consequence the salt growth may be still stopped at the actual stage. The rim basin between the salt walls reveal an important subsidence history of the basin .The Salt diapir in the study area is characterized by an upward-converging sides and antithetic crestal faults which can be the result from levelling movements that reduce structural relief due to salt growth according to Cloos(1928) and Dennis and Kelley (1980)or the consequence of salt welds formation. Thickness variation of geological strata toward the salt diapir reveals evidence about synsedimentary activity.
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The fracture prediction in M carbonate oilfield
By Y. NieM carbonate oil field is located in Zagros low angle belt. Having experienced multi-period tectonic movement, the fracture system and the fracture scale of the belt are extremely complex. The structural fracture has formed the good reservoir space. Therefore, the reservoir fracture prediction is the key to effectively develop the M carbonate reservoir. According to the characteristics of M carbonate reservoir, this paper puts forward a set of fracture prediction methods based on the post-stack and pre-stack seismic data. Firstly, we apply post-stack seismic data to simulate stress field and analyze the fracture-developed zones quantitatively; secondly, apply AVAZ analysis to pre-stack seismic data and identify fracture density as well as the orientatation. Finally, reasonably verify the result of fracture by production wells. This research leads a detailed analysis for fracture reservoirs in the studied area, which in turn unveils the fracture development rules and spatial distribution characteristics. Therefore, it provides a certain guide for future oil and gas development.
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Experimental investigation of oil-water two-phase slug flow in inclined pipes
More LessThis paper conducted an experiment to investigate the oil-water two-phase slug flow characteristics in inclined pipe for the inclination angle of +10º, +20º and +30º. The flow photographs and oil hold-up were obtained from the experiment.
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Numerical Modeling of Carbonated Water Injection into Oil Reservoirs Using Buckley-Leverett Theory Considering the Capillary Pressure
Authors M. Ahmadi, D. Zendehboudi and D. JamesThe Buckley-Leverett theory is broadly employed in the upstream oil industry. This theorem suffers from the assumption of zero capillary pressure. This paper develops the Buckley-Leverett theory where the capillary pressure is taken into account. This modification on the original form of the Buckley-Leverett equation can extend the applications of this theory towards more accurate results in terms of fluid dynamics in porous media. This work considers a water-oil system with two different boundary conditions; including, constant carbonated water injection rate and constant bottom-hole pressure that simulate real conditions of Carbonated Water Injection (CWI) operations for oil reservoirs. The two-phase numerical modeling of CWI is performed using the MATLAB® software through the Implicit Pressure Explicit Saturation (IMPES) method. Parametric sensitivity analysis is conducted where the effects of the different parameters (e.g., mobility ratio, injection rate, fluids and rock characteristics, time step, and grid size) are studied on the CWI performance, numerical dispersion, and round-off errors. In this work, a black oil simulator is developed where the wettability, capillary pressure, and relative permeability are extensively investigated. This research aims to further understand the CWI processes in oil reserves in terms of recovery mechanisms and practical implications.
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