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79th EAGE Conference and Exhibition 2017
- Conference date: June 12-15, 2017
- Location: Paris, France
- Published: 12 June 2017
61 - 80 of 1073 results
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Evaluation of Nonlinear Approaches for Surface Microseismic Processing
Authors G.C. Michaud, C. Fliedner, A. Gendrin, T. Probert and A. OzbekSummaryIn the context of surface microseismic processing, a nonlinear stack method, the phase weighted nth root stack, was evaluated and benchmarked against linear stack. From a synthetic analysis, the parameter choice was evaluated to improve the detectability of small amplitude microseismic events. The choice and impact of small exponent values for the nonlinear stack method were confirmed on one stage of a multiwell, multistage hydraulic fracturing in the Marcellus shale formation. Compared to the linear stack, up to 30 % more events were detected and located for this data example.
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Reconstruction of the Near-Offset Gap in Marine Seismic Acquisition Using Radon-Domain Interferometric Interpolation
More LessSummaryWe demonstrate that interferometric interpolation implemented in the Radon domain can be used to fill the missing near-offset traces in marine data. We demonstrate the effectiveness of this method on synthetic data and a real towed marine dataset from the Baltic Sea. We compare the results obtained by Radon-domain interferometric interpolation with those from conventional interferometric interpolation. It is clear from this comparison that Radon-domain interferometric interpolation performs better than the conventional interferometric interpolation method when the acquisition geometry is irregular and the source-receiver aperture is limited.
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Resolving and Understanding Observed Azimuthal Anisotropy — A Case Study
Authors C.L. Smith, P. Reddy, A. Glushchenko, P. Vasilyev, P. Bilsby, A. Maycock, J.E. Vargas, Y.P. Utami and D. SturkoSummaryThis case study demonstrates that the regularization of single-sensor, single-source (S4) seismic data along discrete azimuth directions with regular source-detector distance intervals (radial domain gathers) can provide enhanced imaging through azimuthal velocity analysis, and deliver inversion-ready datasets with improved noise attenuation. A holistic workflow is presented that is tailored both to improve the final image quality, and to enable azimuthal amplitude variation with offset and azimuth (AVO/AVOAz) analyses, leading to the derivation of intrinsic rock property attributes leading to better reservoir management decisions & drilling plans. A prestack depth migration approach provides compensation for the overburden effect and improves resolution at the zone of interest by removing the effects of heterogeneities in the velocity field, which can be misinterpreted as azimuthal anisotropy.
The 2016 processing sequence of a dense, broadband 3D land seismic survey in Abu Dhabi supports the understanding that azimuth-rich S4 acquisition geometries can provide advantages over conventional techniques (such as the use of receiver arrays or narrow-azimuth surveys) for the imaging, fracture characterization, and reservoir management of very subtle low-relief structures, in particular shedding light on the complex geological environments of carbonate reservoirs in the Middle East.
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Frequency-dependent Azimuthal Effects on P-Wave Reflections from a Thin Layer
Authors Z. Jin, M. Chapman, X. Wu and G. PapageorgiouSummaryThis paper examines the impact of anisotropic dispersion on P-wave reflections. We show a modest effect on the amplitude and large effect on the phase, the latter of which could be mistaken for azimuthal velocity variations. We present a Bayesian inversion based on a forward modelling technique aimed at recovering layer thickness, fracture density, and fracture length in a thin-layer example. Our results show that the large-scale fractures can be clearly distinguished from microcracks despite the presence of interfering reflections, provided we have a sufficiently accurate background velocity model.
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A Study on the Regularization of OVG Data and the 3D Visualization Method
More LessSummaryOVG (Offset vector gathers) data is unable to be used for interpretation directly, although it is generated from wide-azimuth high-density acquisition through OVT (offset vector tile) migration and contains the anisotropic information. For getting visual 3D gather display and randomly extracting gather profiles and slices on the basis of OVT migration data, an offset-azimuth domain 5D interpolation method is proposed in this paper. By interpolating through rectangular rotation data regularization (RRDR) firstly instead of the conventional fan-shaped data regularization, it overcomes the shortage of the uneven folds between far and near offsets, improves the fidelity of data before and after the regularization, achieves the cylindrical display of OVG gather as well as the random extraction and display of the common offset gather, common azimuthal gather and time slices. It lays a good foundation for prestack anisotropy interpretation.
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Hysical Modeling Study of Seismic Responses of Fractured Zones With Varied Fracture Densities and Fracture Swarms
More LessSummaryThe seismic response characteristics caused by fracture parameters are the basis for fracture prediction and further analysis of tight fractured reservoir, and must be given great weigh and analyzed precisely. We mainly analyzes the seismic responses of fractures on post-stack sections in different azumuths, and the fractures include fracture swarms and fractures zones with varied fracture densities. The size of fractured zones and fracture swarms we simulate here is from dozens of meters to hundreds of meters which is unusual in physical modeling. The conclusions are as follows: The fractured zones with obvious boundaries have strong response of string of beads on the blank geological background of the thick bed. Fracture swarms piercing through multi-layers have characteristics of scrambled reflection, energy attenuation, wider events, the distortion and fault of events, most of these characteristics are weak reflection, these characteristics are azimuthal.
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MCMC Inversion of Offshore West Africa AVA Data
Authors G.M. Hoversten, A. Royle, J. Chen and D. MyerSummaryWe define the Bayesian posterior probability distribution in terms of the data likelihood, the prior distributions of unknown parameters, the prior distribution of lithology indexes and the prior distribution of data signal to noise. The prior distribution of lithology indexes is represented as a 3D Markov random field where the cell to cell coupling is parameterized using 3D Kriging parameters of angles and ranges. We show that the resulting PDFs of the geophysical parameters (Acoustic Impedance, Vp/Vs, and density) can be non-Gaussian (multi-modal).
We compare the MCMC inversion predictions of oil in place (OIP) and net-to-gross (NTG) to an industry standard work flow of simultaneous (SI) elastic joint inversion followed by Bayesian inference for porosity prediction. For the data set considered, which is representative of most West Africa data sets, the sampling based MCMC algorithm provides superior prediction of lithology and porosity, the two parameters that drive drilling decisions. Comparisons at two blind wells show that the MCMC NTG and OIP predictions are ∼ 5x better, in terms of % error, than the SI workflow. In this example an industry standard SI algorithm and workflow would significantly underestimate the OIP, which could have significant impact on a prospect’s viability.
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Application of a Markov Chain Monte Carlo-AVA Inversion Algorithm for Reservoir Characterization in Offshore Nile Delta
Authors M. Aleardi, F. Ciabarri and B. GarceaSummaryWe propose a formulation of Amplitude Versus Angle (AVA) inversion in terms of a Markov Chain Monte Carlo (MCMC) algorithm, and we show its application for reservoir characterization and litho-fluid facies prediction in a gas-saturated reservoir in offshore Nile Delta. A linear empirical rock physics model is used to link the petrophysical characteristics (porosity, water saturation and shaliness) to the elastic attributes (P-wave velocity, S-wave velocity and density), whereas the non-linear exact Zoeppritz equations are used to relate such elastic properties to the observed AVA responses. The exact Zoeppritz equations allow us to take advantage of the long offset seismic acquisition and thus to consider a wide range of incidence angles (between 0 and 60 degrees) in the inversion. The proposed algorithm, at the expense of a relatively high computational cost, reliably estimates the posterior probability distributions of the sought parameters, taking into consideration the uncertainties in the prior information, the uncertainties in the estimated rock-physics model and the errors affecting the observed AVA responses. The match between the predicted properties and the well log information demonstrates the applicability of the proposed method and the reliability of the results.
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Uncertainty Estimation of Inverted Elastic Parameters in Shale Reservoirs - A Case Study of Vaca Muerta Formation
Authors A.P. Kautyian Ziyisyian and F.G.E. SpäthSummaryIn shale formations, elastic characterization is key in deriving petrophysical and geomechanical properties, and the estimation of lateral variations in elastic parameters allow to identify good reservoir conditions for hydrocarbon production (sweet spots). To measure the lateral heterogeneity in the Vaca Muerta formation (VM), well logs were analyzed in the central part of the basin. This study shows that the lateral variation in Zp and Zs is about 28% and 24% respectevily, while the change observed in Vp/Vs and rho is less than 5%. The methodology to estimate the uncertainty in the inversion process involves synthetic seismic modeling and inversion for Zp, Vp/Vs and rho. Inverted parameters are compared to the model. To establish the dependandce of the inversion result with the quality of seismic data, different factors are tested: S/N, Angle Range and the number of partial stacks. Zp has the smallest relative error (less than 15%) and the highest correlation (above 0.9) for the entire Angle Range tested. The inversion of Vp/Vs has an acceptable relative error (less than 20%) when the angle range is above 40° and the S/N is higher than 9dB, for 3 stacks. For an angle range below 50° rho is not inverted.
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Well Tie Challenges in Southern Chad
Authors J. Wanstall and C. SandanayakeSummaryThis paper explores the impact of near surface noise on the ability to perform synthetic well ties to 3D land seismic data over a producing field.We conclude it is essential to understand the content of a seismic stack before embarking on well ties. Even more critical when poor quality data allows for a multitude of plausible tie solutions. If a single reflection boundary dominates ones well tie, one must be very sure its angle dependent characteristics are understood. Far from being an academic exercise, the product of this work included substantially altered time-depth functions utilised in time-depth conversion. It subtly changed the assignation of many critical surfaces in a field that consists of multiple stacked producing units. It altered our understanding of the phase of the seismic data. It also set hard limits on which reservoir properties could plausibly be derived from the seismic data in its current form whilst hinting that if the near surface induced noise could be effectively treated, lithological characterisation from seismic data is technically possible.
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Using AVO to Evaluate a Thin Pay - A Norwegian Case Study - An Update
Authors B. Paternoster, P.-O. Lys, V. Marlot and M. VedvikSummaryRecent progresses in seismic acquisition have paved the way for renewed prospect evaluations. In this paper, we present the example of a Palaeocene-aged prospect offshore Norway. It was identified several years ago but seen as non-economical.
A new broadband seismic dataset was used to re-interpret the prospect. AVO-based methods helped tackle the main difficulty associated to the poorly constrained geometry of this low relief prospect. Presumably, the seismic response of the prospective pay-interval results from the interference between a top hydrocarbon sand and an interpreted fluid contact within the massive sand body.
Nominally, this interval is thinner than seismic resolution. Taking advantage of the different AVA behaviors of these interfaces, top and base pay could be picked independently. Top reservoir was revisited shallower than previously and thickness estimated clear of tuning. Furthermore, the way amplitudes at a selected angle tune as a function of un-tuned thickness allowed de-risking the nature of the fluid fill in comparison with nearby oil and gas fields.
Finally, the well that was subsequently drilled proved the picking strategy right. The discovery confirmed the interpreted oil fill. This paper is an update of the original paper presented at the 76th Conference in Amsterdam.
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Avaz Analysis for Weak Azimuthal Anisotropy and Thin Layers: Case Study From the Lower Paleozoic Shale Play in Northern Poland
Authors M. Cyz and M. MalinowskiSummaryWe present application of Amplitude versus Azimuth analysis (AVAz) for weak anisotropy (1–2 %) and thin layers (up to 25 m) case for Lower Paleozoic shale play in Northern Poland. Feasibility study using synthetic AVAz response indicated that we could expect detectable azimuthal signature given the expected low crack density only in the wet case (fluid-filled fractures), but luckily liquid phase is observed is studied area. We applied AVAz analysis on large, wide-azimuth 3D seismic survey after full-azimuth (non-sectored) pre-stack depth migration. AVAz results were then compared with volumetric seismic attributes giving correlation in major fault zones. Furthermore results were corroborated by available well data: XRMI image logs giving confirmation of acquired AVAz azimuths and by cross-dipole sonic logs confirming anisotropy level.
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Stress Prediction Technology Based on AVAZ Inverison and its Application in Sichuan Basin of China
More LessSummaryIn this paper, we mainly talk about stress prediction technology, it has proven to be important and effective for shale gas evaluation and development. We use pre-stack AVAZ inversion to predict stress field, it is carried on pre-stack azimuthal gathers with constrained wells. A slight modification was made on the basis of Shaw’s (2004) equation in order to obtain elastic parameters such as P-wave impedance, S-wave impedance and fracture weakness from inversion. The stress indicator like DHSR (Differential Horizontal Stress Ratio) can be further estimated with P-wave impedance, S-wave impedance and fracture weakness. This work could help geophysicists and engineers better understand where engineer “sweet spot” is and guide well deployment. This method is applied in real data of Sichuan Basin, it shows that the result of stress prediction is effective and reasonable.
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A Robust FWI Method for Model Updating in High Contrast Bodies
Authors T. Martin, G. Pendred, J. Vermeulen, M. Bell and P. MellarSummaryWe present a robust method for Full Waveform Inversion (FWI), enabling the recovery of long-wavelength features of a velocity model. By using both transmitted and reflected waves the dynamically weighted FWI gradient enables high-resolution model building deeper than those achieved by diving waves alone. This reduces the dependency on long offset data acquisition.
The FWI approach uses a sophisticated regularization scheme to stabilize the inversion space. This methodology, which forms an extra constraint on the objective function, overcomes some of the limitations of the inversion in the presence of high contrast bodies. The implementation uses the split Bregman method, making it efficient and accurate.
We demonstrate the benefits of using the new gradient and regularization scheme by presenting the results on an intra-volcanic reservoir velocity model build from the Faroes-Shetland Basin.
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Application of Advanced Velocity Model Building and Migration Technology On Offshore North Africa Marine Dataset
Authors M. Pouget, C. Beigbeder, F. Gamar-Sadat, H. Prigent, M. Drubigny, L. Zerrouki and J.-M. MaillartSummaryIn recent years there has been tremendous progress made on the seismic migration and velocity model-updating technology to achieve better resolution and higher positioning accuracy, thus providing more valuable information to reduce exploration risk. In a dataset from offshore North Africa, the velocity model building is challenging due to a highly faulted geological setting and the presence of gas hydrates in the shallow overburden. Furthermore the image resolution beneath these diffracting and absorptive bodies is poor if we do not compensate for the resulting attenuation. This case study illustrates how a combination of sophisticated velocity update technologies, such as full waveform inversion and the latest tomography developments, together with Q-prestack depth migration, can achieve high quality seismic imaging.
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Risk Reduction On the Ivory Prospect Via Geologically Constrained Non-Parametric Inversion and Bayesian Uncertainty Estimation On a Fault-Bounded Reservoir
Authors J. Raffle, T. Earnshaw, J. Fruehn, S. Greenwood, J. Singh, C. Hagen, R. Felicio, D. Sassen, Z. Luo, S.I. Forsund, M. Ackers, L. Aamodt and I.F. JonesSummaryThe Ivory discovery lies within the Nyk High, located in the north-eastern part of the Vøring Basin, which has been tectonically active in several phases. The main challenge in mapping the extent of the Ivory discovery has been seismic imaging at the crest of structures bound by major faults (e.g. fault shadow effects), together with depth conversion uncertainty and a poor well to seismic tie. To address the uncertainties associated with these issues, a new Pre-Stack Depth Migration was run using a dataset re-processed with the latest demultiple and deghosting technology. From this final migrated volume, structural uncertainty was then estimated using a Bayesian statistical analysis of the tomographic resolution matrices in conjunction with prior uncertainty estimates.
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Multiphysics Earth Model Building Via Simultaneous Joint Inversion of Seismic and Gravity Data for Faulted Thrust-Belt Imaging Challenges
Authors M. Speziali, A. Pawson, M. Mantovani and L. MasnaghettiSummaryThe integration of independent geophysical data sets allows reducing the risk and increasing the confidence when exploring complex geological settings, therefore maximizing the return on acquisition investment. In this context, gravity data are a successful candidate for the integration with seismic data, because of the limited acquisition cost and the excellent petrophysical similarity observed between velocity and density.
The maximization of the benefits attainable from combining multiple geophysical data sets is achieved when a quantitative approach, such as the simultaneous joint inversion (SJI), is implemented. Moreover, the integrated approach should be consistently applied throughout the whole geophysical processing and imaging sequence, encompassing time processing, near surface characterization and depth imaging.
The fulfillment of both the aforementioned conditions is desirable for solving complex geophysical challenges, such as faulted thrust-belt imaging, as discussed based on a case study from southeast Asia.
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Reconstruction Chronostratigraphy in Carbonate Reservoirs Surrounding Wrench Fault Zone of RMKS, Sakala Subbasin, East Java Basin, Indonesia
Authors M.S. Indah, M. Natsir, D. Kadar and J. SetyowiyotoSummary- Complex carbonat and Kujung contain oil and gas for exploration show at exploration well
- Complex Kujung reservoir domain for reservoir characterisation based on fossil absolute, vuggy & fracturing, and sedimen structure data core
- oil and gas prospective resources finding for 1 TCF and 1,68 BBOE
- System Track including for TST 1, HST 1, TST 2, HST 2, TST 3, HST 3
- Marker chronostratigraphy inclusing SB 0/34 MA, MFS 0/33 MA, SB 1/32 MA, MFS 1/30,5 MA, SB 2/28 MA, MFS 2/26 MA, SB 3/23 MA, MFS 3/ 22.3, SB 4 /21,5 MA
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Sequence Stratigraphy, Depositional Environment and Numerical Stratigraphic Modelling of the Orphan Basin (NL, Canada)
Authors P. Jermannaud, E. Le Guerroué, J. Pitz, T. Pichot, D. McCallum, I. Atkinson, V. Mitchell and R. WrightSummaryA sequence stratigraphic analysis coupled with a 3D forward stratigraphic model was performed in the Orphan Basin (NL, Canada). It aimed at understanding the sedimentary and stratigraphic infill of the basin and to define potential plays.
The basin sequence stratigraphic architecture was initially defined using two composite 2D seismic sections. This stratigraphic framework was then applied in 3D space using the complete seismic and well dataset to create eight (8) conceptual Gross Depositional Environment (GDE) maps.
The conceptual GDE were then numerically tested using the 4D forward stratigraphic modelling tool DionisosFlow™. The model allowed the paleoenvironment interpretation to be greatly refined, and the lateral and vertical extension of potential reservoirs on the shelf margin and within large turbiditic complexes to be identified. Transgressive intervals were highlighted to be favorable to the deposition and preservation of organic-rich sediments.
The 3D stratigraphic grid results were used to assess the exploration geological risk, considering reservoir/seal presence and effectiveness. Sand and shale distribution in the 3D stratigraphic model is available laterally and vertically in terms of Net sand, Net to Gross and as a minimum continuous thickness. Reservoir / seal couplets, defining plays, were risked (Common Risk Segment mapping) with accurate spatial definition.
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Albian Clastic Prograding System in the Dunga Field (Western Kazakhstan) From Regional Understanding to Prospectivity
Authors M. Dujoncquoy, A. Arvidsen and P. HillockSummaryThe Lower Cretaceous series of the Mangyshlak Basin in Western Kazakhstan mainly consists of clastic sediments characterizing continental to marine depositional environments. The overall basin records at that time a large wavelength subsidence without major faulting, involving eustasy as the main controlling factor on sedimentation. The lower to middle Albian interval in the Dunga license is characterized in seismic by a set of well-imaged clinoform geometries prograding from East to West at the base, passing upwards to more sub-parallel and horizontal reflections. The clinoform sequence in the lower section is interpreted to represent a shoreface/delta environment. The upper interval is interpreted as an extensive aggrading offshore to shoreface environment. The complex stratigraphic architecture of this clinoform system creates lateral and horizontal facies changes, increasing the chance of stratigraphic traps with internal reservoir-seal pairs. The Albian play has initially been proved by Maersk Oil in 2012, and further prospectivity is supported by the indications of hydrocarbons identified on wireline logs and mudlog data. A geological model has been constructed based on seismic interpretation of geometries, facies analysis from multiple wells and core data in order to better understand the remaining prospectivity within this sedimentary system.
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