- Home
- Conferences
- Conference Proceedings
- Conferences
82nd EAGE Annual Conference & Exhibition - Workshop Programme
- Conference date: October 18-21, 2021
- Location: Amsterdam, Netherlands / Online
- Published: 18 October 2021
45 results
-
-
Geological Uncertainty Quantification: A Futile Attempt in the Absence of a Decision Context
More LessSummaryIn most extractive industries, understanding geological uncertainty is key to making good decisions. In addition, the decisions should serve our goal of extracting economical amounts of resources. With this description, building the most realistic geological model should not be the goal. Instead, our goal should be to build models that support good extraction decisions. Yet, we rarely discuss the link between uncertainty models and their usefulness. We devote substantial efforts to gathering information and building sophisticated subsurface models but significantly less to exploring their economics and usefulness. If, for example, we make the same petroleum drilling decision irrespective of the granularity of the uncertainty model, then the time and effort spent on developing such sophisticated models have been in vain.
-
-
-
Acoustic versus Elastic 3-D FWI: a Case Study at the East Pacific Rise 9ºN
Authors M. Marjanovic, R. Plessix and A. StopinSummaryFull Waveform Inversion (FWI) has become a standard tool for imaging subsurface. Although the acoustic formulation of the wave equation in FWI has been commonly used, excluding the elastic effect could have a significant impact on the inversion results. To quantitatively evaluate the contribution of the elastic approach, we compare acoustic and elastic 3-D FWI applied to a 3-D seismic data set from the East Pacific Rise (EPR) 9°50’ N, collected in deep-marine setting. After conducting a number of tests, we suggest a simultaneous, multi-parameter inversion using frequencies below 7 Hz for both acoustic and elastic approach. The resulting residual from the elastic case is 10–15% lower than that for the acoustic case, suggesting that the elastic approach explains the observed data better. Furthermore, the final compressional velocity model of the subsurface using the two approaches differ significantly, not only in velocity magnitude but also suggest different geological interpretation. We argue that the results obtained from the elastic modelling are geologically more plausible and more reliable image of the subsurface at the EPR.
-
-
-
Incorporating Probabilistic Petrophysical Information into Elastic Full Waveform Inversion
More LessSummaryElastic full waveform inversion (EFWI) augmented with petrophysical information defines a high standard for velocity model building, as it delivers high-resolution, accurate and lithologically feasible subsurface models. The technique enhances the benefits of using an elastic wave equation over the acoustic implementation while constraining the inverted models to geologically plausible solutions. We derive elastic models of subsurface properties using EFWI and explicitly incorporate petrophysical penalties to guide models toward realistic lithology, i.e., to models consistent with the seismic data as well as with the petrophysical context in the area of study. This methodology mitigates several issues related to EFWI, as it reduces the high non-linearity of the inverse problem, mitigates the artifacts created by interparameter crosstalk, and prevents geologically implausible earth models. We define this penalty using multiple probability density functions (PDFs) derived from petrophysical information, such as well logs, where each PDF represents a different lithology. We demonstrate that the combined FWI objective function establishes a more robust foundation for EFWI by explicitly guiding models toward plausible solutions in the specific geological context of the exploration problem, while at the same time reducing the misfit between the observed and modelled data.
-
-
-
Subset 3D Geological Modelling for Petroleum Reservoir Estimation
Authors E. Pakyuz-Charrier and J. KeetleySummaryObtaining a reliable understanding of the geological structures at depth is essential in offshore Petroleum exploration scenarios. 3D geological modelling software such as GeoModeller may be used to answer this need. GeoModeller uses an implicit fully 3D modelling engine, the structural data is used directly to construct the volumes and surfaces with a cokriging interpolator. Geological formations are then topologically sorted using a binary (Erode/Onlap) stratigraphic pile. As both the input data and the modelling engine – through measurement errors and simplifications, respectively – are inherently imperfect, the end result of the modelling process is necessarily uncertain. A range of Monte Carlo Uncertainty Propagation (MCUP) methods have been developed over the last decade to provide the community with means to estimate uncertainty. In this paper, Intrepid Geophysics explores MCUP methods and their application to Oil & Gas reservoir estimation with the unique constraint of using MCUP methods to reduce uncertainties and propose alternative scenarios in a hybrid driven environment.
-
-
-
The Role of Minimum Phase in Internal Multiple Removal
By M. DukalskiSummaryGiven true-amplitude pre-processed data, Marchenko equation based methods could remove all overburden-borne internal multiples without the adaptive subtraction. The method hinges on calculating an inverse transmission response, however in many practical cases to find a solution, one is required to provide a part of it on input. This requirement can be lifted by invoking minimum phase - a mathematical property familiar to many geophysicists, yet normally not associated with a de-multiple workflow. Here we discuss the state of the art, challenges and road ahead for minimum phase enriched internal de-multiple. In particular we focus on the differences in minimum phase reconstruction between single input single output (1.5-D single mode) vs multiple input multiple output systems (everything else).
-
-
-
Realistic Uncertainty Estimation in an Integrated Geostatistical Seismic Property Modeling
More LessSummaryGeostatistical Seismic property modelling is about taking all available prior information and measurements into account. Evidently, one very important and valuable piece of information is the seismic data, which has extensive lateral coverage compared to the sparse information provided at well locations. Using Bayesian inference, we can incorporate a variety of data and expert knowledge to obtain predictions that are more realistic.
At the same time, using multiple realizations we are taking into account overall uncertainties including both variance and bias ( Moradi Tehrani 2016 ) that give us a handle to estimate and mitigate risk and make informed decision.
As there is no single right answer, the answer depends on the question. If we know our objective, then we can get the answer. In this case, we can also estimate how reliable the answer is.
By analyzing the realizations through ranking, we can determine the range of possible answers. Ranking relies on defining an objective criterion that captures the key characteristic of interest.
This approach is powerful for realistic uncertainty estimation and therefore provides a sturdier foundation for making informed decisions.
-
-
-
Elastodynamic Marchenko Method: Advances and Remaining Challenges
Authors C. Reinicke, M. Dukalski and K. WapenaarSummaryMarchenko methods aim to remove all overburden-related internal multiples. The acoustic and elastodynamic formulations observe identical equations, but different physics. The elastodynamic case highlights that the Marchenko method only handles overburden-generated reflections, i.e. forward-scattered transmitted waves (and so-called fast multiples) remain in the data. Moreover, to constrain an underdetermined problem, the Marchenko method makes two assumptions that are reasonable for acoustic, but not for elastodynamic waves. Firstly, the scheme requires an initial guess that can be realistically estimated for sufficiently-simple acoustic cases, but remains unpredictable for elastic media without detailed overburden knowledge. Secondly, the scheme assumes temporal separability of upgoing focusing and Green’s functions, which holds for many acoustic media but easily fails in presence of elastic effects. The latter limitation is nearly-identical to the monotonicity requirement of the inverse scattering series, indicating that this limitation may be due to the underlying physics and not algorithm dependent. Provided that monotonicity holds, the aforementioned initial estimate can be retrieved by augmenting the Marchenko method with energy conservation and a minimum-phase condition. However, the augmentation relies on the availability of an elastic minimum-phase reconstruction method, which is currently under investigation. Finally, we discuss a geological setting where an acoustic approximation suffices.
-
-
-
When Do We Need Elastic Waveform Inversion for Velocity Model Building? Marine and Land Examples
Authors C. Pérez Solano, G. Chang, R. Plessix, K. Bao, A. Stopin and X. WangSummaryFull waveform inversion is a widespread data-fitting technique commonly used for velocity model building. In this context, the target input data are low-frequency transmissions and post-critical reflections in a long offset range. These seismic data, associated to diving waves, are highly sensitive and therefore can be used to retrieve the P-wave velocities of the subsurface. However, according to the diffraction theory, the transmission data can be influenced by shear parameter variations in the subsurface which create tuning and interference effects at the low frequencies, notably when the variations are large and occur inside the first Fresnel zone. The elastic interference challenges the applicability of an acoustic waveform inversion approach in a global manner, and despite its relatively low computational costs and practicality, its results have proven mixed. We discuss marine and land seismic data examples, from the Gulf of Mexico and the Middle-East, where elastic waveform inversion provides compelling results superseding the acoustic waveform inversion results.
-
-
-
3D Elastic FWI for Land Seismic Data: A Graph Space OT Approach
Authors W. He, R. Brossier and L. MetivierSummaryIntegrating surface wave information is challenging for land seismic full waveform inversion. Cycle-skipping of surface waves can easily occur due to their highly dispersive and oscillating properties. While this issue can be mitigated using wider basin objective functions, a more severe difficulty is related to the unbalanced amplitude distribution between surface waves and body waves. The energetic surface waves dominate the objective function and drive the inversion to update only the shallow structure. The contribution from body waves is masked and the deep structures are not recovered. In a recent study, we have shown how an optimal-transport based function can help mitigating this issue, providing naturally a better balance between events (KR-OT). Here, we apply a newly introduced OT based misfit function, relying on a graph space approach (GS-OT), in this framework of elastic FWI for land data. GS-OT better handles cycle skipping than KR-OT. We show here that it also helps to balance the amplitude of seismic events. We design a practical workflow based on the GS-OT misfit function, coupled with an on-the-fly source estimation wavelet and a Gaussian-time window strategy. The method is applied to a synthetic case study from the SEAM II Foothill model.
-
-
-
Reconstruction of Quantitative Variable Density Acoustic Reflectivity in the Context of Velocity Model Building
Authors M. Farshad and H. ChaurisSummaryThe quality of focusing panels (Common Image Gathers) plays a fundamental role in the construction of the macro-model via image domain techniques. Recent works demonstrated that iterative least-squares migration is recommended for obtaining reliable focusing panels: this ensures relevant tomographic macro-velocity updates. In practice, iterative least-squares migration needs to be accelerated through suitable pre-conditioners such as pseudo-inverses of the forward modelling operator. The pseudo-inverses are currently limited to the constant density acoustic case. In this paper, we first discuss the impact of density variations on focusing panels, and then propose an approach to quantitatively reconstruct two acoustic parameters. The main ingredient is the Radon transform. From an extended reflectivity (single iteration), we apply the Radon transform to reconstruct the inverse of the bulk modulus and the density perturbations in the physical domain, while preserving the data fit. We validate our approach on the Marmousi-II dataset, demonstrating that the proposed approach is an efficient alternative to the more expensive least-squares migration. As expected, there is a leakage between the inverted two parameters.
-
-
-
Uncertainty Quantification Enhancement by Combining Data of Varying Accuracy and Precision
Authors J. Chautru, H. Binet, P. Masoudi, S. Rodriguez and M. PapouinSummaryA common issue in Depth conversion and Volumetrics calculation is the estimation of the range of variation of important reservoir parameters, like structural closure depth or reservoir volumes, which are often poorly estimated. For example, the GRV and hydrocarbon volumes in most of the developed reservoirs are found to be closer to the P90 than to the P50 determined at the exploration phase, which means that the range of variation is underestimated.
Combining data sources of varying precision and accuracy such as seismic data, CCAL, SCAL or logs, which correspond to different scales, is a difficult issue. It requires appropriate mathematical tools, like the ones provided by Geostatistics. This paper details the geostatistical techniques than can be used for calculating geological models and quantifying the associated uncertainty. Focus is put on the role played by input data accuracy and precision in the final estimation of GRV and hydrocarbon volumes range of variation, accounting for the varying accuracy and precision that are manageable in practice. This allows decision makers to take the most appropriate decisions concerning the field development. The methodologies and results are illustrated with a simplified modelling based on a real dataset, emphasis being put on structural modelling.
-
-
-
Assessing and Communicating Geological Model Uncertainty
Authors A.K. Turner and M. BianchiSummaryAn overview of recent alternative procedures for assessing and communicating the multiple sources of uncertainty in geological models
-
-
-
Extending the Potential of Acoustic Optimal Transport FWI in the South of Oman
Authors S. Shutova, D. Carotti and O. HermantSummaryBroadband land WAZ acquisitions provide the ideal data for land FWI thanks to low frequencies and long offsets. While acoustic FWI has been successful in the north of Oman, the complex near-surface geology and the presence of strong velocity contrasts in the south of Oman better fits with the use of elastic propagation to obtain an accurate velocity model. In this paper we discuss the challenge of improving acoustic land FWI results in the south of Oman, thus avoiding the use of elastic FWI, which is still prohibitively expensive for deriving high-resolution velocity models. The key success factors for this acoustic land FWI study were proper pre-processing of the input seismic data and the use of an Optimal Transport objective function to mitigate cycle skipping issues.
-
-
-
The Use of Multi-Scattered Energy in Imaging and Velocity Model Building
Authors T. Alkhalifah, Q. Guo, G. Wang and Z. WuSummaryMultiples and multi-scattered seismic recorded energy are often ignored or suppressed in imaging and inversion applications. This happens because they tend to appear weak in our recorded data and they also violate the linearity clause, complicating their treatment. On the other hand, they carry valuable information that allows for better illumination of the Earth and better velocity model building. We will share those features through our generalized internal multiple imaging strategy, as well as incorporating multi scattered energy in Full waveform inversion. The results demonstrate the ability of multi-scattered energy to better image the subsurface, as well as yield a better velocity models.
-
-
-
Quantification of Effective Permeability Uncertainty Estimation on Geothermal Aquifer Scale
Authors M. Verberne, R. Dalman, J. Breunese, B. Van Kempen and K. GeelSummaryThe economic extraction of energy from geothermal systems and hydrocarbon reservoirs rely largely on production rates, which in turn is largely reliant on the permeability. The effective permeability of a reservoir is often inconsistent with the local (borehole) permeability leading to high rate of economic failures. This mismatch is caused by heterogeneities related to e.g. permeability contrasts, faulting and other types of low permeable barriers such as lateral facies changes, these are notoriously hard to capture in permeability estimation.
This study empirically tests several analytical methods to estimate the effective permeability on a production system scale for a suite of geological facies and permeability distributions representative for the Netherlands deep subsurface. Ultimately we construct a toolbox of optimal techniques for determining the accuracy and precision distribution for permeability for a suite of genetically related reservoir types. Thereby allowing a significantly improved estimation of effective permeability and subsequently derisking pre- and postdrill evaluations of both geothermal and hydrocarbon projects.
-
-
-
An Overview of Marchenko Methods
Authors K. Wapenaar, M. Staring, J. Brackenhoff, L. Zhang, J. Thorbecke and E. SlobSummarySince the introduction of the Marchenko method in geophysics, many variants have been developed. Using a compact unified notation, we review redatuming by multidimensional deconvolution and by double focusing, virtual seismology, double dereverberation and transmission-compensated Marchenko multiple elimination, and discuss the underlying assumptions, merits and limitations of these methods.
-
-
-
Data-Driven Internal Multiple Elimination Applications Using Imperfectly Sampled Reflection Data
Authors J. Brackenhoff, J. Van IJsseldijk and K. WapenaarSummaryWe consider reflection data that have been subsampled by 70% and use Point-Spread-Functions to reconstruct the original data. The subsampled, original and reconstructed reflection data are used to image the medium of interest with the Marchenko method. The image obtained using the subsampled data shows artifacts caused by internal multiples, which are eliminated when the original and reconstructed data are used.
-
-
-
Including Internal Multiples in Imaging and Velocity Updating: Potential and Limitations
Authors E. Verschuur and Y. SunSummaryIn many areas around the world the impact of internal multiples on seismic data can be strong, due to large subsurface contrasts. There is a choice of removing these multiples in advance and apply primaries-only imaging. Such a method often requires densely sampled data, especially for Marchenko-based approaches. If data sampling is coarser, an image-driven approach can be adequate, where the Earth model is used as a constraint in the inversion. Such an approach is followed by full wavefield migration (FWM) and joint migration inversion (JMI), where the subsurface is parametrized by reflectivity and a velocity model. In this way, internal multiples, together with transmission effects, can be handled and an imprint-free image is ideally obtained. In this paper, the potential and limitations of this approach will be analyzed.
-
-
-
Predicting Internal Multiples by Inversion Based Imaging
Authors M. Davydenko and D.J. VerschuurSummaryTo handle internal multiples in imaging can be done via data-driven procedures (e.g. Marchenko-based multiple removal) or via an image-driven process that includes an option to model internal multiples from the reflectivities. The advantage of data-driven methods is that it can utilize the physics implicitly available in the data, while the image-driven method has to make this physical model more explicit via an image, which may create some leakage. However, a main advantage of the image-driven approach is that it is very insensitive to coarse source sampling, while data-driven methods requires dense data. The aspect of coarse sampling and its effect on the final multiple suppression effects of the image-driven approach is demonstrated.
-
-
-
Target-Oriented Elastic Parameter Models Estimation from Surface Seismic Data Uusing JMI-res
Authors A. Garg and E. VerschuurSummaryElastic full waveform inversion (FWI) has the potential to provide a high-resolution velocity model by inverting all wavelengths of the subsurface structures. However, due to the associated computational costs and non-linear coupling between different elastic parameters, it is only applied for low frequencies, especially in a full elastic 3D fashion. Mostly, high-resolution elastic parameter models are only required within the limited area of the earth subsurface. Therefore, high-resolution elastic-FWI for full bandwidth can also be restricted to a target area. With this concept in mind, we present reservoir-oriented joint migration inversion (JMI-res) using both a numerical and a field data example. It first reconstructs the localized elastic data at the reservoir depth (local impulse responses) and then use this as input for elastic-FWI for the area of interest. In addition, the redatuming step of JMI-res correctly account for the overburden-related multiple scattering. Thus, the localized elastic data is of high-resolution and free of overburden artefacts, while avoiding a complete elastic FWI for the whole medium.
-
-
-
A New Role for Adaptive Filters in Marchenko Equation-Based Methods for the Attenuation of Internal Multiples
By M. StaringSummaryWe have seen many developments in Marchenko equation-based methods for internal multiple attenuation in the past years. Starting from a wave-equation based method that required a smooth velocity model, there are now Marchenko equation-based methods that do not require any model information or user-input. In principle, these methods accurately predict internal multiples. Therefore, the role of the adaptive filter has changed for these methods. Rather than needing an aggressive adaptive filter to compensate for inaccurate internal multiple predictions, only a conservative adaptive filter is needed to compensate for minor amplitude and/or phase errors in the internal multiple predictions caused by imperfect acquisition and preprocessing of the input data. We demonstate that a conservative adaptive filter can be used to improve the attenuation of internal multiples when applying a Marchenko multiple elimination (MME) method to a 2D line of streamer data. In addition, we suggest that an adaptive filter can be used as a feedback mechanism to improve the preprocessing of the input data.
-
-
-
General Overview of Advanced Internal Multiple Attenuation Prediction Methods and Workflows
Authors F. Xavier de Melo and C. KostovSummaryThis work takes a close look at practical aspects when performing a complete internal multiple attenuation workflows. Along with advanced methodologies constantly adopted to improve the internal multiple prediction outcome, bridging the gap between the recorded multiple within the adaptive subtraction stage of the workflow requires understanding of the processing goals, the requirements of later processing stages, careful and meticulous quality assurance criteria and finally extensive parameter testing. Depending on the subsurface complexity and field maturity, different techniques and workflows are being applied to maximize the attenuation internal multiples while preserving underlying primary reflections.
-
-
-
Multiples: Towards a Toolbox Perspective on Assumptions, Challenges and Options (an Invited Presentation)
Authors F. Xavier de Melo, J. Wu and F. Xavier de MeloSummaryIn this work we will touch on the fact that all seismic methods have assumptions and prerequisites. Understanding these assumptions is an important step to: (1) help understand what is needed to make a processing method effective, (2) define the role the seismic processing method could play in the seismic processing toolbox, when it would be the appropriate and indicated choice, and when to seek another option and (3) help understand what is behind the breakdown and failure of the algorithm. Embracing that all internal multiple prediction methods (attenuation and elimination) have advantages and limitations according to external environmental factors and physical assumptions, we encourage collaborative research whose goal would be to understand under what circumstances the Marchenko approaches and ISS methods might be the indicated and appropriate toolbox choice for removing multiples.
-
-
-
Structural characterization and Diagenetic Study of Mineralized Fractures in Paleo-Geothermal Systems – the Geneva Basin
Authors M. Perret, M. Gasparrini, S. Omodeo-Salé, L. Guglielmetti, A. Moscariello and V. TelesSummaryGeothermal exploration in low- to medium-enthalpy settings, such as sedimentary basins, is gaining increasing interest worldwide. This local source of heat and/or electricity appears as a durable and sustainable energy source. The present project aims to reduce uncertainties and risks linked to the occurrence of cementation in potential geothermal reservoirs and to reconstruct paleo-fluid circulation conditions.
A multidisciplinary approach combining the study of paleo-geothermal systems and the active present ones is used in the Geneva Basin (Switzerland and France). The workflow consists in : 1) a characterization of the structural framework of faults and fractures in an exhumed fossil geothermal system (Mont Vuache); 2) a petrographic study of the diagenesis of fractures (cementation, dissolutions) to infer the origin of paleo-fluids (timing, temperature, pressure, composition) and their circulation conditions in natural conduits of the fractured reservoirs; 3) fluid-rock interaction simulations to verify the thermodynamic validity of conceptual models related to diagenetic processes at the origin of cements, and to evaluate the volumes and spatial distribution of cementation.
This paper focuses on mineralized fractures (veins) sampled in cores at depths between 300 and 3050 metres, as well as in outcrops in the Mont Vuache, South-Western area of the Geneva Basin.
-
-
-
A Modular Wavefield Inversion Process, Including Internal Multiples, Transmission and Converted Waves
Authors E. Verschuur and L. HoogerbruggeSummaryOver the last two decades the full waveform inversion (FWI) method has established itself as one of the main methods for seismic velocity model estimation. However, due to its computational expenses its full 3D application is limited to the lower frequency range, especially with the extension to the elastic situation in mind. Therefore, we need additional full waveform tools for velocity updating that is more geared towards broadband reflection data, e.g. via reflection waveform inversion. The nice feature of migration-based methods is that the sampling requirements are only dictated by the Nyquist sampling criterion. Extending the reflection tomography to include converted waves can in principle be done at the same spatial sampling as the PP reflection inversion, especially in a marine environment. The proposed full wavefield migration and joint migration inversion methodology is based on the building blocks of one-way propagation and reflection/transmission at both sides of a discontinuity. This method can be used to effectively estimate velocity model and images without multiples cross-talk imprint. Furthermore, this approach can also be naturally extended to include converted waves, with the ability to reduce converted wave cross-talk and actually use it to estimate a consistent P/S reflection image and P/S-wave velocity models.
-
-
-
Enhancing Internal Multiple Prediction by Using the Inverse Scattering Series
Authors J. Wu, Z. James Wu, F. Xavier de Melo, C. Lapilli and C. KostovSummaryWe report several factors to enhance the application of the inverse scattering series method for internal multiple prediction to field data. Firstly, there are challenges related to data conditioning in the inverse scattering series method. In addition to other data conditioning steps, we introduce an efficient data regularization strategy by applying nearest neighbor search and differential move out to accommodate various acquisition situations. Secondly, improving the model’s quality is always preferable and significant. The strategy includes correctly incorporating the 3D source effect and obliquity factor to enhance amplitude fidelity in terms frequency spectrum and angle information. Thirdly, the cost is another challenge for the method. We apply the angle constraints over the dip and opening angles to reduce the computational cost without compromising the model’s quality, and propose an automatic solution for parameterization. Fourthly, the segmented prediction by limiting the range of the multiple’s generator can benefit the subsequent adaptive subtraction. We will illustrate all these points with a field-data example in the presentation.
-
-
-
Marchenko Multiple Elimination
More LessSummaryMarchenko methods compute a focusing function for a receiver at the acquisition surface and a virtual source in the subsurface. Computing the focusing function requires subsurface information. The method has been modified to operate at the acquisition surface. The focusing function becomes a fundamental wave field as known since many decades. These can be computed from the up- and down-going parts of the data without any subsurface information. The up- and down-going parts can be obtained from up-down decomposition, or from up-down decomposition of the data followed by free surface multiple removal and wavelet deconvolution. The primary reflection dataset is obtained from applying the fundamental wave field to the data, or directly from the up-going part of the fundamental wave field. In the first option, the obtained primary reflections are the same as in the data, with all transmission effects and possibly the source ghost and source wavelet. In the second option, the obtained dataset is a primary reflection impulse response where the amplitudes have been compensated for transmission effects.
-
-
-
Internal Multiple Attenuation: Using the Low Frequencies to Protect the Primaries
Authors P. Hugonnet, F. Haouam, L. Vivin, T. Rebert, A. Pica, S. Leroy and A. El EmamSummaryHorizontally layered geological media are challenging for the modeling and subtraction of multiples. As both the primaries and the multiples are flat, it is very difficult to adaptively subtract a model of multiples while preserving the primaries. A model of primaries, if available, can be used together with the multiple model to perform a simultaneous adaptive subtraction and to protect the primaries. We propose herein a method to build primary models by considering that in some geological contexts characterized by fine layering, the internal multiples are virtually absent from the lowest frequency part of the data; therefore, a blind deconvolution algorithm is used to restore a full band from this low frequency part. The validity of this approach is demonstrated on onshore field data from Kuwait.
-
-
-
Using Dempster-Shafer Theory to Model Uncertainty in Petrophysical Interpretation
By F.M. MiottiSummaryThe analysis of the uncertainty is a key element of the reservoir characterization because it provides effective support in ranking potential plays and contributes to reduce the risk of unproductive drilling. Various approaches are detailed in the technical literature: some studies addressed the uncertainty of petrophysical parameters through joint inversion of geophysical attributes ( Miotti et al. 2018 ) while other methodologies exploited the stochastic framework to model the uncertainty of reservoir parameters, ( Bachrach 2006 ). This study leverages the Evidence Theory or Dempster Shafer (DS) theory ( Helton 2009 ) to rank the potential reservoir zones through evidential intervals. The presented workflow shows how the log measurements can be combined together through the DS theory to identify and rank the reservoir play in the well. The procedure is tested on a well log dataset to assess the robustness of the methodology. The workflow outcomes are then validated through a comparison with the benchmark petrophysical interpretation.
-
-
-
CSEM Search for Geothermal Water for Combined Heat and Power
Authors A. Ziolkowski and P. StoffaSummaryGeothermal energy is under-used in the energy strategies of many countries. Groundwater is the obvious means to move heat from depth to the surface for use in combined heat and power plants. If the water temperature at depth (normally > 3 km) is greater than 100 °C, it vaporises at atmospheric pressure, releasing 2,260 kJ/kg. This is a huge resource. The problem is to locate hot water in subsurface reservoir rocks before drilling. We present a new approach to find hot subsurface groundwater using controlled-source electromagnetics (CSEM). EM propagation in conducting media satisfies the diffusion equation, not the wave equation. There are no identifiable arrivals associated with travel paths defined by ray theory and there is no theory to enable the diffusive responses from different source-receiver pairs to be combined to increase signal-to-noise (S/N) ratio. We propose that the time-domain impulse responses obtained from broad bandwidth CSEM data be transformed into equivalent waves, which may then be processed using seismic methods to increase S/N and yield high-resolution 3D images of conducting bodies down to 4 km depth. Using the analytic response of an impulsive current dipole source in a full space, we show that the required transformation is feasible.
-
-
-
GPOS Evaluation for Geothermal Projects in the Netherlands
More LessSummaryEvery subsurface project has the risk of failure or disappointment if the predictions made by the subsurface evaluation team are incorrect. In some cases the reality is so much different from the expected that no production is possible or allowed. This is well known for hydrocarbon wells, but also in geothermal projects prediction errors are possible that could result in a total write off of the well or the project. To cater for these risks a fit-for-purpose GPOS evaluation scheme for geothermal projects has been developed within EBN. A consistent GPOS evaluation will help EBN to determine the correct usage of funds in its mission to explore for and accelerate the use of geothermal energy in the Netherlands. Five subsurface aspects are seen as the main parameters determining the technical success of a geothermal project in the Netherlands: Aquifer, Permeability, Fluid Compatibility, Temperature and Connectivity.
-
-
-
Acoustic FWI for Salt and Sub-Salt Update from Simple Initial Models
Authors C. Wang, P. Farmer, C. Calderon, I. Jones and J. BrittanSummaryWe will show our newest FWI technology that allows us to start from simple velocity model and push acoustic FWI as far as we can for salt and sub-salt update.
-
-
-
Visualisation of Uncertainty in Voxel Models of the Shallow Subsurface of the Netherlands
Authors J. Stafleu, D. Maljers and J. GunninkSummaryTNO – Geological Survey of the Netherlands builds and maintains a national 3D voxel model of the shallow subsurface. Each voxel contains the following properties: (1) the stratigraphical unit the voxel belongs to; (2) the lithological class that is representative for the voxel; and (3) a set of probabilities of occurrence for each of the lithological classes that may be present in the voxel.
The probabilities of occurrence provide us with a measure of model uncertainty. The probabilities of an individual voxel can be displayed in a bar graph. Similar displays are possible in visualizations of virtual boreholes. However in 2D and 3D visualizations it is no longer possible to show all probabilities in a single view: the user will always be presented with one probability at a time.
To solve this problem, Wellmann and Regenauer-Lieb (2012) proposed to use information entropy as a measure of uncertainty in 3D models. The information entropy of a voxel is a single value ranging from 0 to 1 that can easily be calculated from each of the probabilities of lithological class. Based on this concept, we added two measures of uncertainty to the model: one for lithological class and one for stratigraphical unit.
-
-
-
Uncertainty of the Geological Framework Model of the Netherlands
Authors W. Dabekaussen and H.J. HummelmanSummaryTNO – Geological Survey of the Netherlands builds and maintains models of the shallow subsurface of the Netherlands, up to a depth of about 500 m below mean sea level. Various property models, for instance populated with lithological or hydrological parameters, rely on a national stratigraphic framework model to constrain interpolation of borehole information. With increasing interest in the uncertainty of subsurface models, there is a need for accurate quantification of the uncertainty of the stratigraphic framework model. This is not an easy task, as geological modelling tends to rely heavily on expert geological knowledge to help interpolation of structures from sparse borehole information. It is shown that a mixed approach using cross-validation and kriging variance can be used to accurately estimate model uncertainty of the stratigraphic framework model. The next challenge will be how to visualize this uncertainty and to quantify how the uncertainty of the stratigraphic framework model will propagate into that of derived property models.
-
-
-
What Can the High-resolution Velocities from Full-Waveform Inversion Offer for Seismic Interpretation?
Authors J. Mann-Kalil, G. Duval and A. RatcliffeSummaryWe present a wide range of full-waveform inversion (FWI) velocity model build case studies from around the world, but highlight these from an interpreter’s point of view and show how the accuracy and resolution in the FWI velocity field can be used to de-reisk and enhance the geological interpretation. Additionally, we highlight that increases in compute power and algorithm efficiency allow FWI to be regularly run on large, basin-scale areas, and also that recent advances in FWI technology are allowing deeper updates, and ever more accurate velocity models, to be obtained.
-
-
-
Play-Based Exploration and Development Plan for Geothermal Energy in the Netherlands
Authors F. Vinci, J. De Jager, J. Schellekens and C. LeoSummaryThe presented ‘Play-based Exploration and Development Plan for Geothermal Energy in the Netherlands’ provides an up-to-date overview of how and where geothermal heat can be developed safely, responsibly, sustainably and cost effectively.
To reach this goal, a play-based portfolio approach was adopted, allowing to extract best value from available information and to guide further exploration steps. Using current knowledge, Common Risk Segment (CRS) maps of the six main aquifers of the Dutch subsurface were generated. However, since the deployment of geothermal heat is not only influenced by subsurface geology, but also by local heat demand and presence of heat networks, CRS maps were integrated with this type of surface data. As a result, the presented Exploration and Development Plan brings together in one map subsurface knowledge, heat networks and heat demand, opening to a new world for understanding, steering, planning and budgeting for long term geothermal development.
This makes it a valuable source of information not only for geoscientists, but for also for regional governments, civil society organizations and commercial operators that have to make choices between the development of geothermal heat or applying other renewable sources.
-
-
-
Modelling of mineralisation in Geothermal Projects: a Stirred tank Approach
Authors A. Hussain, N. Khoshnevis, B. Meulenbroek, H. Bruining, A. Reerink and K. WolfSummaryMineralisation in geothermal projects is an important issue. The precipitate ensuing from mineralisation within the doublet restricts the flow path of the water. Consequently, more energy is wasted on the process. Thus, mineralisation in a geothermal reservoir may result in additional costs and thereby reduces the project’s economic return.
But, modelling precipitation and dissolution over the complete doublet in a connected manner can be challenging when attempting to account for all physical and chemical processes. This involves among others the mineralisation reactions coupled to the heat and mass transport equations in surface facilities and porous media.
Here we model the mineralisation in a volume of produced water as a function of time, accounting for the decrease in pressure and temperature, and model the reactions based on a kinetically controlled approach. PHREEQC allows us to model the amount and composition of the mineralization over time. We find that precipitate formed in the heat-exchanger consists mainly of Pyrolusite, Barite and Calcite. Barite, Chalcedony and Quartz are the main minerals to be formed downstream of the heat-exchanger, but upstream of the reservoir.
-
-
-
Elastic Versus Acoustic Asymptotic Extended Born Inversion for Marine Acquisition Surveys
Authors M. Farshad and H. ChaurisSummaryWave-equation based asymptotic Born inversion was originally developed for pure acoustic media. Recently, the applicability of approximate Born inversion has been extended to variable-density acoustic and elastic media, all assuming marine towed-streamer data. Even if only pressure waves propagate in the water layer, we study the impact of elastic effects: we compare the elastic and acoustic imaging results based on the asymptotic pseudo-inverse Born operator. We conduct two numerical experiments, for a simple layered model and part of the 2004 BP salt model. Numerical results illustrate the superiority of the elastic inversion compared to the acoustic version, especially due to converted waves around the salt interface.
-
-
-
Deployment of Machine Learning Solutions to Production Seismic Processing
By R. HeggeSummaryOnce machine learning solutions have proven themselves in a research environment, they generally need additional work before they can be used in production.
-
-
-
Growing up: On Productizing Sub-Surface Machine Learning Workflows
By J. LimbeckSummaryIn this presentation we cover the main pillars of the strategy we are following in Shell that allows more rapid movement from data science proof of concepts to the deployment stage where value for the business is generated. Where applicable, the concepts are illustrated with examples.
-
-
-
Deriving High Fidelity Velocity Model using Acoustic Full Waveform Inversion
More LessSummaryIn this abstract, we present the results of dynamic matching full waveform inversion (DMFWI) applied to various data sets from different geological settings. DMFWI is an acoustic algorithm and concentrates on inverting the kinematic difference while minimizing the impact of amplitude. With proper constraints, this algorithm is effective in inverting for highly accurate velocity models.
-
-
-
Incorporating Probabilistic Petrophysical Information into Viscoelastic Full Waveform Inversion
More LessSummaryFull waveform inversion (FWI) augmented with petrophysical information enhances wavefield-based velocity model building. In regions of shallow low-velocity anomalies, estimating accurate and lithologically feasible viscoelastic models is crucial for accurate seismic processing and imaging. However, inverting for velocity and attenuation models simultaneously is a challenging task because of the severe interparameter crosstalk between these parameters. We derive viscoelastic models of subsurface properties using viscoelastic FWI and explicitly incorporate petrophysical penalties to guide models toward realistic lithology, i.e., to models consistent with the seismic data as well as with the petrophysical context in the area of study. This methodology mitigates artifacts created by interparameter crosstalk, and prevents geologically implausible earth models. We define this penalty using multiple probability density functions (PDFs) derived from petrophysical information, such as well logs. In order to formulate the penalty term, we build each PDF considering spatial distribution patterns in the petrophysical data. With a realistic synthetic example, we demonstrate that the combined inversion objective function establishes a robust foundation for viscoelastic FWI by explicitly guiding models toward plausible solutions in the specific geological context of the exploration problem.
-
-
-
Three-dimensional Elastic Model Building from Ambient Noise Seismic: a Case Study from Southern Oman
Authors M. Danilouchkine, A. Adwani, R. Plessix, F. Ten Kroode, Q. Al-Siyabi, F. Ernst and O. Al DroushiSummaryIn many areas in the Middle East the presence of large vertical variations of lithologies gives rise to strong multiples and mode conversions of primary P-wave reflections and leads to difficulties in imaging the subsurface. An accurate model of the subsurface is highly desirable
to circumvent this problem. In this paper we present a successful attempt to model building, based on elastic Full Waveform Inversion (eFWI) and ambient noise seismic interferometry (ANSI). An unorthodox deployment of the latter technology on continuously acquired land data made it possible to extract the ground roll and to subsequently invert it in the frequency range up to 1.2 Hz. The study was conducted using the real 3d seismic dataset, acquired in the Southern Oman. The obtained low-resolution elastic model extends to a depth of 4 km, captures the major velocity contrasts in the shallow and deep subsurface, and conforms well with interpreted subsurface interfaces.
-