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82nd EAGE Annual Conference & Exhibition
- Conference date: October 18-21, 2021
- Location: Amsterdam, The Netherlands
- Published: 18 October 2021
201 - 250 of 1137 results
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Synchroextracting S Transform and its Application in Seismic Time-Frequency Analysis
More LessSummaryNon-stationary analysis is always a challenging task because its frequency content changes as time goes. The S transform is widely used to characterize the time-varying features of a non-stationary signal. However, the resolution of S transform subjects to the Heisenberg Uncertain Principle, resulting in energy diffusion in the time-frequency (TF) plane. To overcome this drawback, we develop a new time-frequency analysis method called synchroextracting S transform (SEST).
By employing a synchroextracting operator (SEO) in the S transform, the SEST provides a time-frequency distribution with excellent concentration.
Differing from the synchrosqueezing transform (SST) by gathering the time-frequency coefficients near the instantaneous frequency (IF) trajectory, the SEST only retains the coefficients most related to the time-varying features of the analyzed signal. Hence, the SEST produces a sparser time-frequency representation (TFR) with a high resolution while allows for signal construction. We validate the proposed method with synthetic examples and compare the result with existing methods. Then, real data examples also illustrate its effectiveness in delineating more distinct channels in the horizon slices.
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Importance of Continuous Monitoring: Case Study of Shallow Co2 Injection at the Csiro In-Situ Laboratory Site
Authors K. Tertyshnikov, L. Ricard, K. Michael, A. Avijegon and R. PevznerSummaryDesigning CCS projects from the concept to commissioning and post-closure time requires a significant effort to ensure its safety over its entire life. Developing a monitoring system that observing the evolution of the injected fluid and provide assurance of its permanent containment under the ground is an integral and principal part of every such project. We have demonstrated the importance that these systems should account not only for observing the injected mass but also utilised to continuously monitor the operational activities to be able to deliver early warning for any potential incidents. The results are obtained during the CSIRO In-Situ Laboratory CO2 controlled-release experiment in Western Australia.
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Integration of Reservoir, Rock Physics, Seismic, and Geomechanical Modelling for Co2 Injection In Carbonate Reef Reservoir
By Y. NuwaraSummaryCarbonate reef reservoir is a very important reservoir in oil and gas industry worldwide. However, the challenge of studying carbonate reservoir lies on the complexity of its facies distribution and pore structures, which makes it having almost unpredictable properties if not thoroughly examined. The application of CO2 Enhanced Gas Recovery (EGR) to increase gas productivity from carbonate reservoir is also currently on the business. In the purpose of dealing with carbonate complexities, an interlinked study of reservoir simulation, rock physics, seismic modelling, and geomechanical analysis is developed. The study is also applied in the decision-making for monitoring of EGR activity to ensure its safety. A case study of CO2 injection pilot project in Gundih depleted gas field in Indonesia, is used for the implementation of this study. The result is pleasing, allowing us to comprehend more about the physical process of EGR and reservoir monitoring in carbonate reef type.
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A Closed Formula for True-Amplitude Overburden-Generated Interbed De-Multiple
Authors M. Dukalski and K. de VosSummaryOften the goal of seismic processing is to obtain an accurate image of the target, which, when buried under a strongly scattering overburden, might require internal de-multiple. Traditionally this involves knowledge of the multiple generation mechanism and invoking elementary scattering principles to arrive at a Jakubowicz’s de-multiple formula. Here we propose using a similar approach and de-construct the total reflection response in terms of transmissions and reflections of overburden and target regions, without making any other assumptions about the underlying physics. We then solve this expression for the reflection due to the target only and express it in terms of the total reflection response and appropriate temporal truncation operators. This way we obtain a closed formula for true-amplitude overburden-generated internal de-multiple. The key to obtaining the final result is a derivation of the inverse transmission generator using a set of coupled Marchenko-type equations. We show how approximations of this formula correspond to some well-known approaches.
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Predict Formation Water Salinity of Ultra-Low Permeability Reservoirs with Complex Wettability Based on Adjacent Mudstone Information
More LessSummaryTest data show that formation water salinity varies greatly in the study reservoirs with complex wettability. The common methods to predict formation water salinity have failed, which brings great difficulty to predict reservoir oil saturation. Therefore, assuming formation water salinity of sandstones is approximately equal to bound water salinity of adjacent mudstones, stable parts of adjacent mudstones are firstly selected to acquire resistivity and interval transit time. Secondly, compaction correction of interval transit time is completed. Then, a novel method of determining formation water salinity based on adjacent mudstone information is proposed by cross plot of resistivity and corrected interval transit time, which can be used to predict formation water salinity under different conditions (0 - 20 g/L, 20 - 40 g/L, 40 - 60 g/L and larger than 60 g/L). Finally, formation water salinity of 106 wells is predicted, and plane distribution contour map of the study area is drawn in combination with other 69 formation water salinity analysis data, which is helpful to study the accurate selection and plane distribution laws of formation water salinity. It provides a feasible solution for formation water salinity prediction in ultra-low permeability reservoirs with complex wettability, which can be applied universally.
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Approximation of Infrastructure Effects on Marine Csem Data
Authors J. Park, T.I. Bjørnarå and A. RomdhaneSummaryIn this abstract, we present an efficient approximation method, with which we simulate the effects of the seabed pipeline via line-segment (volume-less) finite element (FE), and validate the method in comparison to a full 3D FE numerical solution. It is seen that we can determine a certain region in a computational model where the approximation method provides inaccurate results (only very close to pipeline). The response calculated in such regions should be excluded e.g. from CSEM data inversion.
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Mechanism and Management of Seismicity in Depleting Gas Reservoirs
Authors H. De Pater and C. BerentsenSummaryGas reservoirs in different regions have induced seismicity, with magnitude up 4.5. We review cases in Southern France, western Canada and the Netherlands.
The detailed mechanism is not well understood, but two factors appears to be critical: compaction and faulting of the reservoirs. A plausible explanation has been proposed as differential compaction where part of the compaction energy remains stored at reservoir compartment boundaries, which can be released in seismic slippage. Although details, such as the role of pore pressure in the fault zone and fault properties are poorly understood, the differential compaction mechanism is confirmed by geomechanical modeling. Some examples of these models will be used for illustration.
These fields have been produced with varying rate, which correlates with seismicity, but the cumulative seismic moment is shown to be just a function of depletion. This provides a simple prediction of seismicity after about 50% depletion has occurred. Since seismicity only depends on compaction, there is little scope for management of seismicity: only pressure maintenance appears to be a viable solution. This can be accomplished by injection to preserve the mass balance or by shutting in gas fields.
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Automatic Horizon Extraction Method of Seismic Data Based on Plane Wave Similarity
Authors J. Li and L. GuochangSummaryBecause of the complexity of the underground structure and the low signal-to-noise ratio and strong noise interference of the original seismic data, it is often unable to correctly pick up the seismic horizon, and the selection of initial control points in the past horizon tracking methods is basically purely manual, which is time-consuming and labor-consuming. In order to solve these problems, this paper proposes a more accurate and automatic algorithm for seismic horizon tracking, which is especially suitable for discontinuous reflection data including faults and noises. First, the selection of initial control points is optimized to realize automatic correction and reduce manual operation; then, the local slope and similar slope are calculated by plane wave similarity technology, and the influence proportion of slope information at fault is controlled by weight parameter, and the smooth regularization term is introduced to reduce the impact of noise. In the least square system, iterative solution is carried out to realize automatic horizon tracking. The results of synthetic and field data processing show that the method has strong adaptability and high stability.
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Synthesis of Multiple-Free Plane-Wave Responses
Authors G.A. Meles, L. Zhang, J. Thorbecke, K. Wapenaar and E. SlobSummarySeismic images provided by Reverse Time Migration can be contaminated by artefacts associated with the migration of multiples.
Multiples can corrupt seismic images producing both false positives, i.e. by focusing energy at unphysical interfaces, and false negatives, i.e. by destructively interfering with primaries. Multiple prediction / primary synthesis methods are usually designed to operate on point source gathers, and can therefore be computationally demanding when large problems are considered. Here, a new scheme is presented for fully data-driven retrieval of primary responses to plane-wave sources. The proposed scheme, based on convolutions and cross-correlations of the reflection response with itself, extends a recently devised point-sources primary retrieval method for to plane-wave source data. As a result, the presented algorithm allows fully data-driven synthesis of primary reflections associated with plane-wave source data. Once primary plane-wave responses are estimated, they are used for multiple-free imaging via standard reverse time migration.
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National Data Repositories As Platforms For Success in the Energy Transition
By A. RoustiauSummaryThe energy transition requires the transformation of the energy sector from a fossil fuel based world towards a carbon emission free environment. Decarbonisation requires urgent actions on a global scale to reduce CO2 emissions and stimulate renewable energy. The role of E&P structured NDRs should therefore, in this context, be critically reviewed: do business drivers exist to maintain and adapt them to support and stimulate the required shift in the energy demand?
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Fault Leakage Rates Estimated In-Situ: Implications For Fault Seal Evaluation
By C. WibberleySummaryThis presentation examines the main controls on Darcian leakage through fault seals and investigates the evaluation of hydrocarbon column heights in such cases. Firstly, case studies are used to illustrate how fault seal permeability may be estimated in-situ from aquifer compartmentalisation data, improving on existing algorithms currently based mainly on empiric relationships.
Secondly the quantitative estimation of hydrocarbon column heights is investigated from the dynamic interplay between charge rates into the trap versus seal leakage rates. A particular consideration is placed on the geometric and petrophysical properties of the leak paths, such as across-fault flow through a fault zone barrier or up-fault conduit leakage. Finally, a consideration is made of the relative importance of aquifer hydrodynamics and dynamic hydrocarbon flow on controlling hydrocarbon contacts.
It is concluded that both hydrodynamic flow in the aquifer, and dynamic charging and leaking of hydrocarbons in an active petroleum system, can control hydrocarbon column heights trapped against a seal. Whilst an understanding of the pressure distribution is critical to prospect evaluation in such settings, sensitivity to the geometric parameters of the trap and charge / leak pathways such as fault conduits remains a key uncertainty in the quantitative analysis.
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Thrust Fault and Sub-Thrust Imaging in the Taranaki Basin With Least-Squares Tilted Orthorhombic Q-RTM
More LessSummaryThe Taranaki Basin is one of New Zealand’s largest basins. Initially forming as a Cretaceous rift basin, it has over 400 exploration and production wells. Early basin history is characterized by extensional fault blocks, and as basin evolution continued, thrusting and inversion associated with the convergent active margin set up trapping mechanisms for petroleum accumulations. Recent fault blocks within shallow Plio-Pleistocene sediments exhibit strong azimuthal anisotropy. Without considering this effect, seismic imaging in the area suffers structural discontinuity and fault misplacement. Below these fault blocks, it is challenging to image the thrust system and sub-thrust structures due to poor illumination from strong velocity variation around the thrust.
To overcome these challenges, we focused on two major aspects. First, we built a tilted orthorhombic (TORT) velocity model to handle the strong azimuthal anisotropy in the overburden. At the time, we only had access to narrow-azimuth (NAZ) data, thus we derived the TORT parameters through scanning based on stack and gather responses. Second, we applied least-squares (LS) TORT Q-RTM to honor azimuthal anisotropy and compensate for poor illumination from the complex velocity. We observed significant imaging uplifts compared with the vintage data that subsequently provided an improved geological interpretation.
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Lithology of a Mixed Siliciclastic-Carbonate-Evaporite System: Triassic Jialingjiang Formation, Sichuan Basin, China
More LessSummaryHigh-quality three-dimensional seismic data acquired in Sichuan Basin, southwestern China, offer an opportunity to map complex lithologies in a mixed siliciclastic-carbonate-evaporite system in the Lower Triassic Jialingjiang (T1j) Formation. The formation consists of siliciclastics, limestone, dolostone, anhydrite, and salt, which consist several source-reservoir-cap assemblages in the area.
Lithologies in the T1j Formation change rapidly in the vertical direction, forming different interbed patterns. In the meantime, the lateral extend of lithology is complex. This vertical and lateral distribution makes it difficult to predict lithology by single seismic attributes. Therefore, principle component analysis (PCA) was applied to tens of seismic attributes to extract useful information. The first three components contain most lithology information preserved in seismic attributes, which were used to correlate with lithology content calculated by core-calibrated wireline logs. Correlation coefficients of the three seismic components with lithologies are higher than those of individual seismic attributes. Different assemblies of end-member lithologies were selected from anhydrite, siliciclastics, tight dolostone, limestone, and salt to perform PCA. Lithologic content distribution of individual end members was shown by color-blending method to map the lithology mixture.
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The Sealing Capacity of Multi-Stage Extensional Abutting Faults in the Bohai Bay Basin, China
More LessSummaryBohai Sea area has experienced complex tectonic evolution including the multi-stage extension which has led to the development of abutting faults system. And the formation of abutting faults has been demonstrated to significantly contribute to the hydrocarbon accumulation in the fault block traps, while strong hydrocarbon productivity heterogeneity has appeared in lots of drilling practices, and hydrocarbon leakage was the main reason for some drilling failure. Comprehensive analysis and comparison combining the 3D seismic and well data reveal that the evolution level of abutting faults determining the degree of leakage in fault intersection, time interval between charge and leak determining the effective charging timing, difference of stress among faults resulted from oblique extension of pre-existing faults determining the magnitude of transpressional stress are all related to the sealing ability of abutting faults. The height of trapped hydrocarbon column derived from drilling data in the structures with abutting faults of Bohai Oilfield has excellent correlation with the sealing ability analysis based on the above three factors, which proved that this method has good application prospects in the petroleum exploration of similar structures.
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Influencing Factors of Sand Production Pressure Difference in Naturally Fractured Reservoir
SummaryThe Keshen block is a fractured tight sandstone gas reservoir in Tarim Oilfield. The porosity is around 6% to 10%. The permeability varies from 0.1 to 1mD. The fractures of sandstone are developed . During development of this block, 49 wells have sand samples collected, which accounts for 53% of existing wells. Due to sanding, 9 wells have had to be shut-in for a long term, which is 34.6% of sand production wells. Moreover, there are more production wells in the Keshen block that face sand production issues every year. Early research has found that excessive production pressure difference is the direct cause of sand production. Based on this, through analysing production data of more than 40 wells in the block, comparing rock mechanical parameters, and numerical simulation, this paper uncovers the main influencing factors of sand production pressure difference: development of natural fractures, reservoir stimulation, and tail pipe material.
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Discontinuous Galerkin Finite Element Method Using the Modified Ade Cfs-Pml for Seismic Wave Modeling
More LessSummaryAbsorbing boundary condition (ABC) is required at the computational boundary to absorb the outward propagating waves when simulating seismic wave propagation in an unbounded space. At present, there are few papers about PML for modal discontinuous Galerkin finite element method (DG-FEM), especially unsplit PML. In this abstract, we modify the ADE CFS-PML (auxiliary differential equations complex frequency shifted PML) with new auxiliary variables. Because the ADE CFS-PML equations are first-order partial differential equations, they can be solved by the same numerical scheme used in the inner domain regardless of time-marching scheme. Furthermore, compared with standard ADE CFS-PML, our method’s auxiliary differential equation is easier to be solved. The modified ADE CFS-PML is applied to modal DG-FEM and it performs well. The results are compared with the analytical solutions obtained by generalized reflection and transmission (GRT) coefficient method, and it shows that our method is reliable and stable.
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Water Flood Optimization Opportunity in Pad Well in Greater Burgan
Authors K. Al-resheedi, E. Hussain and S. RajanSummary• The successful campaign of the data acquisition for the Wara water flood project resulted in better understanding of the impact of the water flood.
• PNC data confirmed water migration and identified areas of swept in some parts of the field including a planned Pad with producers, this allowed the team to be proactive and convert the PAD producers into injectors to support some of the nearby producers
• SBHP information established areas of depletion in parts of the Greater Burgan field along with increase in pressure due to water injection excellence
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Unlocking the Cretaceous Petroleum Systems of the Norwegian Sea
Authors A. Wenke, G. Boonen Ferreira, S.A. Bullimore, S.A. Clark, M. Dörner, P. Embry, M. Erdmann, J.O. Hansen, M. Inthorn, L.M. Johansen, O.S. Kløvjan, R. Kyrkjebø, U. Mann, A. Orlovs, E. Rein, B. Rafaelsen, A.E. Ryseth, M. Roudot, B.J. Schmidt, E. Stavrou, O. Thießen, C. Vandré, J.H. van Koverden and J. ZweigelSummaryThe Mid-Norwegian segment of the Norwegian Continental Shelf, between 62° and 67° N, includes a Berriasian to Paleocene basin fill of >12.5 km thickness. The area of deposition covers several major basins and sub-basins, including the Møre and Vøring basins and adjacent terraces. Although the area contains the large Ormen Lange and Aasta Hansteen gas fields, the discovery density in post-Jurassic strata is not comparable with the Jurassic petroleum play on the Halten-/Dønna terraces.
To fully re-assess the Cretaceous petroleum system of the Norwegian Sea, an integrated petroleum system analysis study was performed including i) source rock evaluation, ii) top-down petroleum systems analysis, iii) petroleum systems modeling and iv) migration and charge analysis. Three rich source rock formations have been proven, indications for five additional source rock formations related to Cretaceous OAE collected. Regional petroleum-source correlations identified the presence of oils and condensates of pre-Albian, Cenomanian/Turonian and post-Turonian origin. The study shows that the volumes of expelled hydrocarbons and thus the YTF oil volumes are underestimated in the area. The Cretaceous petroleum systems study results were finally implemented in recent exploration strategies and proven by new discoveries on the Norwegian Continetal Shelf.
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Prediction of Knn-Based Gas-Bearing Distribution for Tight Sandstone Reservoir
More LessSummaryGas-bearing prediction of tight sandstone reservoir is difficult since the relationship between gas-bearing property and its seismic response is nonlinear. However, machine learning methods provide the potential for solving the issue. One main limitation of some intelligent methods is imperfect in interpretability, which makes the gas-bearing prediction questionable. This study introduces an improved kNN method to predict gas-bearing distribution based on a known database made from borehole-side seismic traces and the corresponding interpreted gas-bearing curves obtained from the measured well-logs. The method can output gas-bearing probability approximated by the occurrence frequency of gas-bearing samples in the first k samples which are the most like data to be predicted. Compared with outputting kNN classification results, outputting probability results can reserve the valid information. The method has a simple principle and strong interpretability. No network needs to be trained. It does not rely on big data. A numerical model designed based on petrophysical parameters in a field work area is used to test the method. The result demonstrates that the method is good at characterizing the reservoir morphology and location. When applied to the field data, the gas-bearing prediction distribution is basically consistent with the geological law of the work area.
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North West Europe High Impact Exploration: Activity Levels, Performance and Failure Analyses Since 2015
By G. BagleySummary• Between 2015 and 2019, 69 high impact (HI) exploration wells were completed in seven offshore basins across NW Europe with 2019 seeing the highest levels of high impact exploration in the region in the last 12 years
• Over the last five years this activity has led to the discovery of seven commercial discoveries, giving a commercial success rate (CSR) of 10%, comparable to the global success rates for frontier exploration over the same period.
• A further 26 wells resulted in discoveries which are currently seen as being non-commercial resulting in a technical success rate (TSR) of 38% over the period.
• 37% of the prospects are considered to have failed due to potential charge failure, 35% due to poor or absent reservoir and 7% due to trap failure.
• 23% of prospects in frontier and emerging basins fail for charge / migration related reasons compared to 10% in mature and maturing basins. Failure rates dues to reservoir and trap are similar across different play maturities.
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High Resolution Mega Mapping: A New Approach Towards Improved Structural Understanding
Authors G. Hoetz, M. Bouchingour, Y. Beaucaire and L. JanssenSummaryMerging multiple seismic time interpretations whilst honouring maximum spatial resolution allows the construction of optimised structure maps which combine the advantages of extensive coverage whilst preserving great detail where available. EBN has identified the need for detailed structural information originating from seismic data for both regional prospectivity studies and prospect specific analyses targetting hydrocarbons as well as geothermal energy. Regional scale coverage is needed to better understand fault systems in their broad tectonic context whilst the subtle detail is required to understand observations at field or at well scale, e.g. fault-cut outs and fault juxtapositions.
The aim of the HiRes Mega mapping project is to improve resolution of subsurface structure maps at key horizon levels, to better image existing fields, potential traps and associated fault systems. These grids are also suitable as input for time-depth conversion to obtain HiRes depth maps.
As the HiRes seismic time grids originate from many different surveys and/or processing versions, a fully functional automated Petrel workflow has been developed to efficiently calibrate and merge the different grids, a task which can be rather complex, time consuming and error prone if undertaken manually.
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Overpressure Transmission Through Igneous Intrusions: An Unrecognized Drilling Hazard in Volcanic Affected Basins?
Authors N. Schofield, S. Holford and A. EdwardsSummaryIn situ overpressures in sedimentary basins are commonly attributed to disequilibrium compaction or fluid expansion mechanisms, though overpressures in shallow sedimentary sequences may also develop by vertical transfer of pressure from deeper basin levels, for example via faults. Mafic sill complexes are common features of sedimentary basins at rifted continental margins, often comprising networks of interconnected sills and dikes that facilitate the transfer of magma over considerable vertical distances to shallow basinal depths. Here we document evidence for deep sills (depths >5 km), hosting permeable systems that may have allowed transmission of overpressure from ultra-deep basinal levels. We suggest that transgressive, interconnected sill complexes, may represent a previously unrecognized mechanism of transferring overpressures (and indeed hydrocarbons) laterally and vertically from deep to shallow levels in sedimentary basins, and that they represent a potentially under-recognized hazard to both scientific and petroleum drilling in the vicinity of subsurface igneous complexes.
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Two-Dimensional Cross-Gradient Joint Inversion of Gravity and Magnetic Data by a Sequential Strategy
Authors M. Tavakoli, A. Nejati Kalateh and M. RezaieSummaryThis study tries to model an already approved potash source by cross-gradient joint inversion of the available gravity and magnetic data via a sequential strategy. The target source has been located in NW Iran.
Different geophysical methods generally have different inversion systems. Especially they may differ in model parametrization and inversion algorithm. Thus, combining these different systems and yet including the nonlinear cross-gradient constraint in a joint inversion framework might be a big challenge. By decoupling gravity inversion, magnetic inversion and the cross gradient minimization, the proposed algorithm tries to avoid these challenges.
At first the efficiency of the algorithm and developed code is shown by joint inversion of noisy synthetic data. There is an improvement of the cross-gradient joint inversion results over the separate inversions both for synthetic and field data.
The density and magnetization models obtained for field example are in high concordance with available geological information, the drilling results, and previous studies. Specifically, there is a significant improvement in magnetization model affected by more trustable density model via the cross-gradient constraint.
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Nanoscale Assessment of Sandstone Wettability During Redox Treatment by Atomic Force Microscopy (Afm)
Authors S. Yesufu-Rufai, A. Georgiadis, S. Berg, F. Marcelis, M. Rucker, J. Van Wunnik and P. LuckhamSummaryA key step in de-risking chemical enhanced oil recovery (cEOR) projects is to assess the incremental recovery for the field of interest in customised laboratory experiments that mimic conditions within target reservoirs. Any deviation from these conditions, as is oftentimes the case, leads to discrepancies which call the reliability of laboratory results into question, thereby affecting the economics of the cEOR projects. Concerning iron-bearing formations, one approach is to treat samples with a reducing fluid in order to mimic native reservoir redox conditions. In this study, investigations into the effect of a solution of the reducing agent, Sodium Dithionite, in brine on surface wettability were performed using Atomic Force Microscopy (AFM) to quantify interactions between model crude oil components and an iron-bearing sandstone under varying redox conditions. Results show that the adhesion of the oil components to the sandstone surface decreased in the order -NH2 (∼70%) > -COOH (∼36%) > -CH3 (∼3%) on introduction of the reducing fluid, potentially providing a basis for deployment in core floods to ascertain the suitability of cEOR procedures.
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Flow Diagnostics for Naturally Fractured Reservoirs: A Case Study
Authors V. Spooner, G. Douglas, S. Geiger and D. ArnoldSummaryFlow diagnostics can rapidly approximate the reservoir dynamics and can be used for screening ensembles of models prior to production forecasting.
We have applied our recently extended dual porosity flow diagnostics to the Teapot Dome, a naturally fractured reservoir in the US. We have demonstrated using flow diagnostics for ensemble screening and fast optimisation studies.
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A Source-to-Sink and Reservoir Quality Prediction Workflow: The Offshore Nile Delta
Authors L. Fielding, L. Davies and S. FieldingSummaryWe outline a novel source-to-sink workflow for utilising hinterland datasets to predict reservoir quality and distribution in frontier exploration regions, and apply this methodology to a case study in the Nile Delta.
This source-to-sink example uses datasets otherwise overlooked in the exploration process and reduces the reliance on more speculative inputs such as paleogeographic reconstructions and paleoclimate modelling. The workflow provides quantitative predictions with percentage certainties, allowing explorers to understand the degree to which results can be relied upon.
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Natural Fractures and Sedimentology of a Heterogeneous Reservoir: The Valdemar Field, Danish North Sea
Authors A.C. Glad, M.J. Welch, F. Amour, H. Nick and O.R. ClausenSummaryThe Valdemar Field (Central Danish North Sea) is a heterogeneous reservoir, with a high abundance of natural fractures, producing from chalk units within the Lower Cretaceous Upper Hauterivian–Lower Albian Tuxen and Sola Formations. The Lower Cretaceous stratigraphic interval in the Danish North Sea is characterized by chalk, argillaceous chalk, marlstones and claystones with hydrocarbons trapped in the chalk reservoir units. The reservoir (chalk) sediments are characterized by high porosity and low matrix permeability, but the presence of natural fractures strongly influences the flow properties by enhancing the effective permeability, and ultimately increases recovery. Several types of natural fractures are recognized on core scale, and some of these form a potential hydrocarbon pathway as they can significantly enhance the natural permeability in the reservoir. This is a first study that conducts a detailed analysis of natural fractures in the Valdemar Field, and relate them to stratigraphy and facies. Furthermore it is considered whether certain fracture types occur more frequent in specific stratigraphic intervals. It is investigated whether the fracture-facies relationship can enhance hydrcarbon recovery.
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Sustainable Management of Ghana’s Sanitation Using the Reim Model
By V. DanquahSummaryThe United Nations 17 sustainable development goals is a plan that seeks to achieve sustainable development of the planet earth and its people. Achieving the SDGs by 2030 will require more and better financing, a renewed focus on implementation to improve the lives of those hardest to reach, significant improvements in data collection and analysis.
In order to achieve sustainability, strategies must be developed so that resources are only used at a rate which allows them to be replenished so that they will continue to be available, while at the same time emissions of waste are confined to levels which do not exceed the capacity of the environment to absorb them.
However, the world's population is growing at an alarming rate. This has raised a number of environmental concerns.
As the population grows, the generation and management of solid and liquid waste becomes crucial. Municipalities and Metropolitan areas need to put policies in place that will deal with waste collection in a sustainable way.
This paper presents a proposal to improve the planning, collection and treatment of solid and liquid waste using sophisticated methods of waste management in the form of regulation, education, investment, and motivation (REIM).
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Experiences with Machine Learning and Deep Learning Algorithms for Seismic, Wells and Seismic-to-Well Applications
Authors H. Jaglan, G. Kocsis, A. Lakhlifi and P. de GrootSummaryHere we present our experience with the standard machine learning and the more advanced deep learning workflows in three different application domains: seismic interpretation, well data analysis, and integrated seismic-to-well inversion. Seismic interpretation is discussed on the basis of two deep Convolutional Neural Network (CNN) examples: a modified U-Net based fault prediction and a LeNet-5 based seismic chimney prediction. For the well data and integrated seismic and well applications, we present log-to-log and seismic-to-log prediction experiments with various standard machine learning algorithms (e.g. Random Forest, Deep MLPs and XGBoost).
We conclude that machine learning and deep learning algorithms add value in all subsurface applications we studied. However, we learned that deeper and bigger does not necessarily mean better, i.e. we do not always need “deep learning”. For example, for log-log prediction, standard machine learning algorithms already do a good job as they can work well with the typical small amount of log data present for training – unlike the deep learning models, which require more data. In the case of the seismic chimney cube, the conventional shallow network result was preferred by the interpreter over the deep learning result, which was considered to be perhaps more accurate but less interpretable.
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Receiver Deghosting with Blended Data Using Sparse Inversion
Authors J. Cao and G. BlacquièreSummaryIn marine acquisition, the strong reflectivity of the sea surface results in ghost wavefields at the source and the receiver side. The removal of these ghost wavefields is a well-known data preprocessing step to improve the image resolution. Simultaneous source acquisition, or blending, which allows for a temporal overlap between shot records, has been proposed as a method for substantially reducing the acquisition cost while improving data quality. The effect of the blended data on the receiver degosting has not been well investigated. We propose to carry out receiver deghosting on blended seismic data (i.e., prior to deblending) using sparse inversion. Synthetic data example demonstrates the validity of this approach.
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Generalised Algorithm and Implementation of Topography Within Finite Difference Wave Solvers
Authors E. Caunt, R. Nelson, F. Luporini and G. GormanSummaryPartial differential equation solvers based on the finite-difference method have for many years been a keystone of seismic processing and modelling applications, commonly found in practical migration and full-waveform inversion methods. Sharp density contrasts within the computational domain have potential to introduce numerical error: problematic when introducing topography to a seismic model. Including a simple step change in density to approximate an air layer compromises both stability and numerical accuracy, often requiring smoothing of the contrast, and inducing both first and second order errors in space. Topography can instead be implemented via an immersed boundary conforming to the surface. This is achieved by extrapolating the wavefield across the boundary to find solution values at necessary external nodes. As this process is confined to the pre-processing step, it has negligible effect on the computational cost of the simulation.
Devitoboundary is a tool in its early stages of development, intended to compliment Devito as a user-friendly means of including immersed boundaries in practical applications. 3D immersed boundaries can be constructed from irregularly sampled topography point clouds, via Delaunay triangulation coupled with a 1D extrapolation scheme. The result is a stable, error-free boundary which can be readily integrated with Devito models.
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Inverse Scattering for Schrödinger Impedance Equation and Simultaneous P-V Inversion in Layered Media
More LessSummaryIn this presentation, we formulate the Schrödinger impedance equation of oblique incidence for acoustic wave equation in layered media and solve the related inversion scattering by the GLM (Gel’fand-Levitan-Marchenko) theory. Based on the GLM impedance solutions, we developed two inversion methods for the recovery of velocity-density simultaneously. In addition to the use of reflection amplitude, traveltime information of reflection arrivals is also utilized for inversion based on the focusing principle. Numerical tests demonstrate the validity of the theory and method. In addition, we compare a few available approaches of acoustic inverse-scattering and conduct a simple stability analysis.
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Diffraction Imaging in North-Western Poland, a 3D Land Seismic Case Study
Authors M. Podolak, W. Kobusinski, T.J. Moser, D. Gierszewska and T. SolarskiSummarySeismic diffraction imaging (DI) is applied to a 3D seismic survey acquired in the Trzebiatow Faulted Zone of West Pomerania located in the Permian Basin, North-Western Poland. 3D seismic data underwent Kirchhoff Pre-Stack Depth Migration (PreSDM) in offset domain, then extended to angledomain full-azimuth (FAZ) CRAM PreSDM, and finally DI applied as a development experiment on a 3D sub-volume. The DI was targeted to provide details of the complex network of faults. Another technical objective was the application of DI to increase structural resolution with respect to standard seismic imaging. Comparison of the novelty result and the standard images is discussed. Of the several advantages of the novelty imaging, a couple proved to be particularly valuable for geologists. Both, existence of faults, and positioning of events are key to the development assessment of the reservoir structure and were solved.
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Organic Geochemistry and Hydrocarbon Generating Potential of the Miocene Bongaya Formation in the Onshore Pitas Sabah
Authors N.A.F. Md Nor Azam, K.A. Mustapha and M.H. HakimiSummaryIn this study, the coals and shales sediments of Miocene Bongaya Formation have been evaluated for their source rock potential using geochemical methods. Bongaya Formation consisted of sandstones interbedded with carbonaceous shales that occur in isolated basins on top of older sediments such as Crocker, Kudat and Chert-Spillite Formation. The results were used to characterize organic geochemical properties of coals and shales in the formation of determining their thermal maturation, organic richness, and quality of organic matter. Pyrolysis, bulk analysis as well as petrographic analysis were also performed on the samples. Based on geochemical and pyrolysis results, the samples suggest that Bongaya Formation is a dominant Type III kerogen with minor Type II kerogen shown mainly gas prone with minor oil generative potential. The formation also indicates a good and rich source rock but with a low thermal maturity level measured from both optical analysis and Tmax value.
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Evaluating Point Set Distance Measures for 2D Seismic Analysis
Authors R. Ferreira, M. Oliveira and E. Vital BrazilSummaryRecently, many works have investigated the use of texture features to support tasks such as seismic image retrieval, classification and clustering. These works aim to assist geoscientists in different applications by reducing the time, cost and potentially increasing the accuracy of the results. Our previous work indicated that for the texture-based retrieval of seismic images with different sizes, point set distance measures outperformed the classical rescaling approach which distorts the patterns and structures found in a seismic dataset. In this work, we consider a scenario in which we have many 2D seismic datasets and we want to run a quick in situ analysis to understand the diversity in the datasets and to cluster them according to their similarities. In our experiments, we investigate 6 point set distance measures on 12 seismic surveys comprising 304 seismic datasets. The results indicate that point set distance measures may be more suitable for the comparison of in situ datasets, showing a gain of 53% in comparison to the rescaling approach.
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Derisking Marine Seismic Survey Feasibility in Shallow Waters
Authors E. L’Arvor, E. Blancart and F. TisserandSummaryFor Oil & Gas exploration projects close to shore or in shallow waters, bathymetry is needed for:
- De-risking seismic survey operations,
- Assessing how to perform seismic acquisition : towed streamers or Ocean Bottom Surveys (OBS),
- Defining survey shape and suitable line directions.
However, some of these potential exploration areas might have only sparse bathymetry data either no bathymetry at all and planning a standard bathymetry survey or airborne bathymetric LiDAR survey is not always possible at the seismic survey feasibility stage.
To mitigate this, Total E&P has started using Satellite Derived Bathymetry (SDB) technics as an alternate solution for providing, within the time frame and when feasible, derived depth data as an intermediate product/deliverable for a first assessment of survey areas.
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Shallow Water Hi-Resolution Combined Streamer and Ocean Bottom Hybrid Seismic Acquisition in the Middle East
Authors J. Wallace, M. Adnan, D. Sturko and P. FontanaSummaryThe Arabian Basin contains some of the world’s largest fields and has a long and successful track record of exploration and production.
To maximize field potential, E&P companies are embracing the latest innovations, leveraging new technology to improve sub-surface knowledge through advanced seismic acquisition and processing techniques.
Until 2019, the case study, outlined in this abstract, was covered by 2D seismic exploration lines and focused 3D surveys acquired in the 1990s. Ocean bottom cable data was acquired over “Field One” and towed streamer over “Field Three”.
Both datasets had been reprocessed a number of times, with the most recent performed approximately 10 years after acquisition.
However, the inherent limitations in the legacy data had now been reached and there was a requirement for new seismic to be acquired.
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The Effect of the Pseudo-Spherical Wave to the Reflectivity
More LessSummaryIn real seismic surveys, seismic wave propagates in the form of spherical wave and plane wave is the approximations of spherical wave in the far-field and for high frequencies. The traditional seismic processing and interpretation methods based on the plane wave theory are not exact. Studying the characteristics of reflected spherical wave can develop more accurate wave theory. In this paper, a two-layer model with a high-velocity upper layer is built to analyze the characteristics of spherical reflected wave. Tests show when the incident angle reaches a certain level, there will be an irregular wave, the pseudo-spherical wave. This irregular wave is always comes after the reflected spherical wave and has a great influence on the reflectivity. This discovery is firstly proposed by our work and has enriched our understanding of wave propagation theory and will have important guiding significance for further study on wave phenomena.
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Interbed Multiples Attenuation using 3D Complex Wavelet Transform
More LessSummaryWe propose an innovative method to attenuate multiples using 3D complex wavelet transform which transform 3D seismic data into orientation and scale domain while the original axis are still kept. The proposed method applies the transform on 3D volumes of individual migrated common offset and partial stack volume of selected offsets respectively under assumption that prestack depth/time migration is carried out using primary velocities and aligns the primary’s events within common image gathers. In the transform domain, the individual offset is filtered according to the partial stack. Therefore, multiple including the interbed multiples are attenuated while signals are enhanced. The proposed method has been tested using synthetic data sets and applied to 3D field data sets. The results demonstrate that the new method attenuate multiples and the image of reserves gets significantly better recovery than traditional methods, especially for near offsets.
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3-D Gravity Data Sparsity Inversion with Discrete Cosine Transform Compression
More LessSummary3-D Gravity Data Sparsity Inversion With Discrete Cosine Transform Compression
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Triassic Play Analysis in the Northern Dutch Offshore
Authors L. Hanemaaijer, M. Kortekaas and K. Van OjikSummaryThe Triassic play in the northern Dutch offshore remains underexplored. The Triassic reservoirs in the area are relatively thin, resulting in smaller prospective volumes with respect to the southern North Sea, which makes standalone development unlikely to be economical. A Play Based Exploration (PBE) approach enables prospects to be evaluated, risked and drilled on a portfolio level. Interdependent risks between prospects can unlock significant parts of a prospective portfolio when prospects which provide the highest value of information are drilled with success. In this study, four Common Risk Segment (CRS) maps are created for the Triassic play in the northern Dutch offshore. These CRS maps are stacked and result in a Composite CRS (CCRS) map which allows for the identification of sweet spots of the Triassic play. The CRS maps are created using a split risking method, where the risk is split into shared and non-shared risk. This is an essential step to enable prospect dependency analyses and assess the value of information of the prospects.
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An Experimental Study of the Effect of Gravity on Foam in Fractures
More LessSummaryIn this study, to investigate how gravity affects foam in fractures, we carry out seven sets of foam-scan experiments on three glass model fractures (model A, model B and model C) with a hydraulic aperture of 78, 98 and 128 microns respectively. We compare the behaviour of foam in the models placed horizontally and vertically. We find that stable foam is created and reaches local equilibrium in all horizontal-flow experiments in 3 models. Foam gets weaker as the hydraulic aperture of fracture becomes larger. In sideways flow experiments, the effect of gravity on foam stability is less in model A. As the hydraulic aperture increases, the effect of gravity is more pronounced. Due to gravity, drier and coarser foam propagates at the top of the fractures, wetter and finer foam along the bottom. Foam is stable during the sideways flow experiments in model A and B, at all foam qualities. In model C, foam breakage alternates with re-generation near the top at foam qualities larger than 0.94. It is concluded that the application of foam in vertical natural fractures (meters tall and tens of meter long) with an aperture up to hundreds of microns is problematic.
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Elastic Gaussian Beam Migration in Tilted Transversely Isotropic (TTI) Media
More LessSummaryAs elastic Gaussian beam migration has the advantages of Kirchhoff migration and wave equation migration that can process the multicomponent seismic data, we propose an elastic ray tracing systems for multi-component wave and apply it to elastic Gaussian beam migration to achieve an elastic Gaussian beam migration algorithm in anisotropic media for multi-component seismic data. According to the previous studies, we derive the anisotropic forward and backward extrapolation and imaging formula of vector wavefield by using Green tensor characterized by elastic dynamics Gaussian beam on the basis of 2D Kirchhoff-Helmholtz integral for elastic wave in anisotropic media. We also migrate the crosstalk between different waves by introducing a weight function. Compared with the traditional method based on scalar wave, it does not need to separate the wave field which indicates its suitability for real seismic data processing. Meanwhile we propose a correction method by sign function to solve the polarity reversion of qp and qsv wave. Numerical examples of subsag model and thrust model in TTI media show that the method proposed in this paper is accurate and effective.
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Application of Geomechanically-Based Fracture Models to a Fractured Chalk Field, Offshore Denmark
Authors M. Welch, M. Luthje and K. PetersenSummaryWe have developed a method of created geomechanically-based Discrete Fracture Network models by simulating the nucleation and propagation of natural fractures over geological time, based on linear elastic fracture mechanics and subcritical fracture propagation theory. In this presentation we apply the method to the Kraka field offshore Denmark, which comprises a fractured chalk reservoir developed over a salt pillow. We calculate the magnitude and orientation of the horizontal strain experienced during development of the salt structure by backstripping, and use this as input to the fracture propagation model. We compare the results with fractures interpreted on borehole images from 5 horizontal wells, as well as lineations observed on ant-tracked seismic data, and find a good match in both orientation and fracture density.
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Offshore Madagascar: Reducing Risk Through Integrated Fieldwork and Seismic Interpretation
Authors T. Beal, M. Enfield and G. SchultzSummaryLarge structures and potential stratigraphic traps are known to be present in the deep-water offshore of Madagascar. However, due to the lack of well penetrations in the area, it is difficult to accurately predict the presence and distribution of play elements (reservoir, source and seal) in these offshore basins. The application of ground-truthed sequence stratigraphic and tectono-stratigraphic analysis, incorporating the increasingly well-constrained tectonic and oceanographic evolution of the Indian Ocean ( Davis et al., 2016 ; Reeves, 2017 ), provides a framework which can be utilised in risk reduction of the offshore basins. We highlight how key events in the break-up of Gondwana, the separation of India-Seychelles and Madagascar, and subsequent shifts in spreading in the Indian Ocean can be directly linked to reservoir presence, quality and provenance, as well as the distribution of potential source rock intervals.
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Hydrocarbon Potential of the Malvinas Basin, Southern Argentina
Authors M. Reynald and R. JamesSummaryThere is plentiful evidence to suggest that the Malvinas Basin is the most prospective of the underexplored basins in the Argentine South Atlantic, a conclusion reflected in the choice of acreage acquired by companies during the previous licensing round. However, exploration in the Malvinas Basin is not free of risk. Analyses conducted by the service company indicate that chief among these are likely to be the presence of structural or stratigraphic traps within the migration fairway and whether traps will have sufficient closures to contain economic quantities of hydrocarbons. The blocks licensed in the northernmost part of the Malvinas Basin might not fall within the fairway for hydrocarbon migration away from the kitchen area in the south. The blocks in the southern part of the study area are adjudged to be more prospective and contain the possibility of a syn-rift play analogous to the productive Tobifera Formation play in the adjacent Austral Basin.
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Facivaz - Full Azimuth Differential Seismic Facies Analysis Technology for Predicting Oil Saturated Fractured Reservoirs
More LessSummaryThis work presents a novel technology for azimuth-dependent facies analysis (Facies Analysis versus Azimuth - FACIVAZ) to improve the prediction of hydrocarbon-saturated permeable fractures in terrigenous carbonate reservoirs. The analysis is performed in the depth domain, along highresolution, full-azimuth angle domain common image gathers created by a special Local Angle Domain (LAD) imaging system. The amplitude and phase preservation obtained by this imaging system is crucial to the proposed analysis. Prior to the facies analysis, the general orientation and intensity of the target fracture systems are analyzed and characterized by azimuth-dependent velocity and amplitude analyses (VVAZ and AVAZ) performed along these LAD gathers. The remaining effect of the azimuth-dependent absorption and dispersion is then detected and further related to the rate of the oil-saturated fractured reservoirs. The examples presented in this work show the effectiveness of the proposed FACIVAZ technology in accurately predicting the distribution of seismic facies in target production areas associated with oil-saturated fractured reservoirs, in an active oil field in Western Siberia. The results highly agree with the corresponding facies characteristics measured in the boreholes along the reservoir area, and therefore serve as valuable information for further drilling of new wells.
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An Assessment of the CO2 Fate at Smeaheia, A Potential Large-Scale Storage Site in Norway
Authors P. Orsini, D. Ponting, D. Stone and B. NazarianSummaryField scale simulation studies are presented for the Smeaheia storage prospect, to assess storage capacity, CO2 distribution, long-term CO2 dissolution and temperature effects. The reservoir selected for storage has pressure communication with a neighbouring fault block, where hydrocarbon production will be ongoing when storage takes place. A sensitivity analysis is carried out to quantify how this depletion affects the storage capacity. Long term simulations up to 20,000 years are also reported to model the evolution of structural, residual and solubility trapping over time. Finally, temperature effects on the CO2 plume distribution are investigated.
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Wavelet-Based Coherency Functional for Velocity Analysis of Seismic Reflection Data
More LessSummaryThis work presents a new coherency functional based on the Continuous Wavelet Transform for the velocity analysis of seismic reflection data. In particular, it discusses the efficacy of the wavelet-based functional when the analysis is performed on non-stationary seismograms. The new functional is defined in the first part of the abstract instead, the second part discusses the application of the method on a synthetic and on a field example. Both experiments are characterized by the occurrence of weak and strongly attenuated sub-basalt reflections buried in the noise and, as in the field example, obliterated by multiples. The velocity spectra computed by the wavelet-based functional, are compared with those obtained by the standard Semblance functional, and by the unconventional highresolution functional of Complex-Matched Semblance.
The results show that the proposed functional, named Wavelet Semblance, is more efficient than the standard Semblance and the Complex-Matched Semblance since it is able to take into account the occurrence of non-stationary signals allowing to detect the weak attenuated reflections (i.e. sub-basalt reflections). In addition, the method produces velocity spectra with a higher resolution and it is robust against random and non-random noise.
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Benefits of Forward Stratigraphic Modelling in Geostatistical Reservoir Characterization
Authors A. Fournillon, S. Bou Daher, E. Marfisi, N. Hawie and M. CalliesSummaryThe lateral continuity and vertical connectivity of facies are important uncertainties in reservoir characterization that influence fluid-flow behavior during hydrocarbon production. Based on geological concepts, forward stratigraphic modelling (FSM) is an efficient tool to reduce these uncertainties, should it be to define new drilling targets or develop accurate and usable static and dynamic models for field development.
This presentation illustrates a suggested workflow that integrates FSM with geostatistics to provided a better lateral and vertical representation of reservoir facies heterogeneity.
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