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80th EAGE Conference and Exhibition 2018
- Conference date: June 11-14, 2018
- Location: Copenhagen, Denmark
- Published: 11 June 2018
81 - 100 of 1073 results
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Global Exploration Discoveries and Industry Outlook
By A. LathamSummaryThis paper reviews global discovery trends in conventional oil and gas exploration and considers the outlook for the industry. Key changes to the scale and nature of industry exploration programmes are summarised. These include the characteristics of companies involved, likely scale of investments expected, play types in favour and implications for the sector’s long-overdue return to profitability.
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Guyana’s First Deepwater Discovery
By M. CousinsSummaryThe Liza discovery in the Guyana Basin marked the opening of a new and significant deepwater oil provenance.
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The SNE Discovery Offshore Senegal - Moving a Frontier Basin to Emergent
By E. HathonSummary“In 2014 Cairn Energy operated the first deep water wells offshore Senegal in the MSGBC basin. Both the FAN-1 and SNE-1 wells were basin-opening discoveries, encountering light oil and gas in both basinal and platform settings. SNE-1 was the largest global oil discovery in 2014, and is currently estimated to hold 2C reserves of over 550 million barrels of recoverable oil and 1.3 TCF gas. These frontier discoveries demonstrate how careful analysis of available data pre-drill can illuminate opportunity, mitigate risk and lead to success in moving a basin from frontier to emergent.
The SNE field has been defined by eight exploration and appraisal wells. Hydrocarbons are contained within a combination structural and stratigraphic trap. Two Albian-age reservoir zones have been designated: the shallower S400 Series and the deeper S500 Series. Both zones are turbidites deposited in a slope to toe-of-slope setting. The maximum extent of the field is 350 square kilometers, with a 100 m column of 31o API oil. The SNE Field has now been fully appraised and is moving towards final investment decision (FID). A phased development is planned, with a target plateau of 75,000–125,000 bopd with subsea infrastructure tied back to an FPSO.”
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Delivering Success in the Mauritania Senegal Basin
By T. HendersonSummaryThe recent success in the Mauritania Senegal Basin by Kosmos and BP has demonstrated a world-class hydrocarbon province with a significant discovered gas resource and substantial follow-on potential. It is the largest new petroleum system opened in the last 15 years along the Atlantic Margin outside of Brazil, with 25 TCF of gas discovered and 50 TCF de-risked (pmean). With an acreage position of roughly 50,000 square kilometres and only 7 wells drilled to date, much of the acreage position remains underexplored. Two drilling campaigns have been conducted. The first campaign was completed in 2016 resulting in the Tortue, Teranga and Marsouin discoveries. The second campaign, which began in early 2017, yielded further success with the world’s largest discovery of 2017, the Yakaar discovery. The second drilling campaign will be completed in early 2018 with the Requin Tigre well in northern Senegal.
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Giant Regional Play Fairways from Modern Seismic Data
Authors K. Rodriguez and N. HodgsonSummaryA new deep water exploration trend has emerged as a number of key wells drilled recently in North West Africa have started to open the door to a low risk play that has achieved stunning success to date and looks set to draw the industry into exploring a new play type down on the basin floor. Previous to this Petrobras’s discoveries in Brazil’s Sergipe basin have shown that not only can the deep water be incredibly rewarding, with fast development opportunities, but it is also rich in oil. Recently, Exxon’s discoveries in Guyana have highlighted the great potential in stratigraphic traps, while the Ranger discovery has highlighted the positive role of magmatism in the development of petroleum systems.
Regional petroleum systems evaluation of an extensive 2D seismic database with global coverage has been carried out in order to identify future exploration frontiers. Modern seismic, smarter geoscience models and enhanced drilling techniques, will open frontier areas to explore new play fairways never accessible before: the base-of-slope and basin floor fans of the South Atlantic, where prospect resource potential is created and determined by plate scale geometries, Guyana stratigraphic analogues and the multiple play types offshore Somalia to name but a few.
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Reactivation of Fault Zones due to Thermo-Poroelastic Stress Changes
Authors T. Meier and T. BackersSummaryThis work investigates numerically by means of the Finite Element Method (FEM) the influence of a) homogeneous poroelastic medium, b) a heterogeneous poroelastic medium containing small-sized defects, and c) a hydraulic fracture within a poroelastic medium on the stability of a fault system during simultaneous depletion and injection.
Since the mechanism of fault slip are a matter of research, this modelling campaign aims at investigating the size of a possible reactivated area on the fault system. The size of the reactivation is related to Amonton’s law that governs fault reactivation as soon as the ratio of the shear (⊤) to normal (σn) stress acting on a fault exceeds the friction coefficient (µ) of the fault (see for example Moeck and Backers 2011 ). The size of the reactivated area can then be related to moment magnitudes through empirical correlation (e.g., Wells and Coppersmith 1994 ). This approach assures a conservative measure of possible earthquake magnitudes by employing numerical methods linked with statistics.
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Reservoir Strain Changes from 4D Time-Strains
By H. KlemmSummary“Time-lapse seismic surveys have proven extremely valuable to guide reservoir management decisions. Changes in seismic reflection amplitudes can provide information on fluid contact movements or pressure changes, whereas variations in travel-times of seismic signals can provide information on geomechanical effects such as reservoir compaction, overburden strain and subsidence. Here, we present a new methodology to obtain reservoir strain changes via geomechanical inversion of seismic time-lapse time-strains. If a linear pressure-strain relationship is assumed, the volumetric strains can be translated into reservoir pressure changes. We demonstrate the method on an example from the Danish North Sea and discuss some observations.”
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Stress Prediction and Evaluation of Heterogeneous Reservoir
More LessSummaryWe proposed a new approach for stress prediction and evaluation of heterogeneous reservoir. New azimuthal P wave equation in form of Young’s modulus, Poisson’s ratio and crack density and Differential Horizontal Stress Ratio (DHSR) formula expressed by Poisson’s ratio and crack density which reflects the reservoir stress property were derived. Then, pre-stack angle gathers of different azimuth angle were applied to execute AVAZ inversion for elastic parameters and crack density. We utilized the inverted Poisson’s ratio and crack density to estimate DHSR. The real data application showed that stress predicted result agreed with geology deposition property and the new drilled well interpretation. The novel approach can offer reliable and convenient stress evaluation evidence for heterogeneous reservoir.
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Dynamics of Stick-Slip Sliding Induced by Fluid Injection in Large Sandstone Block
Authors V. Oye, S. Stanchits, N. Seprodi, P. Cerasi, A. Stroisz and R. BauerSummarySafe geologic sequestration of CO2 is important to decrease the concentration of greenhouse gases in the atmosphere. However, the injection could increase the underground pore pressure and potentially induce sliding of critically stressed faults. We report results from a laboratory test where fluid injections close to an artificial interface of ∼1m length were observed to induce sliding. During the injection, the pore pressure at the injection point reached up to 6.2 MPa and after shut-in, it dropped down to almost zero. However, about 10 minutes later, a sudden sliding of the interface (stick-slip motion) was recorded. Two types of acoustic emission (AE) signals were detected: short bursts and long-lasting oscillations (tremors). The analysis of the spatial distribution of the AE energy was applied to monitor the dynamics of stick-slip, indicating a nucleation phase of the sliding, then the rupture propagated through the whole interface with an average rupture velocity of a few m/s. The speed and the energy radiated during this event were approximately 6 orders of magnitude larger than observed during quasi-static sliding preceding the stick-slip. This observed stick-slip motion can be considered a laboratory analogue to earthquakes, and its occurrence can be related to the injection of fluids.
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Robust Non-Linear Inversion for Reservoir Deformation from Surface Displacement Data
Authors K. Bisdom, M. Cid Alfaro, K. Hindriks and A. KudarovaSummaryCompacting and expanding reservoirs cause respectively subsidence and heave at the surface which at present can be measured using different geodetic methods. Knowing the source of compaction and expansion is of large value to our subsurface operations as it aids in assessment of reservoir conformance and possible containment issues. However, measured subsidence cannot be related one-on-one to actual reservoir compaction: An inversion process is required. Due to the spatial convolution and filtering nature of the subsurface on the actual reservoir compaction or expansion problem, inversion is a complicated process.
This paper describes an iterative inversion workflow, taking full advantage of the speed of semi-analytical forward models while adhering to the actual complexity of the subsurface captured in a detailed finite element model. The iterative scheme allows for handling of the ill-posed nature of the problem. The workflow presented here shows the utility of integrating geodetic data sources to estimate reservoir volume changes. This technique has proven to add value when it comes to monitoring areal and temporal changes in the reservoir. It is relatively easy to implement as it does not require large amounts of input data and can be applied to any field where surface deformation data is available.
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How the Presence of Oil and Water Affects Chalk Mechanics at Isotropic Stresses
Authors J.S. Sachdeva, A. Nermoen, R.I. Korsnes and M.V. MadlandSummaryThis study focuses on chalk mechanics for oil and water saturated cores. Tests were carried out on four Kansas chalk cores initially saturated by 1.1 M NaCl-brine. Two cores were wettability altered by a mixture of Heidrun oil - heptane (60/40 volume ratio) and then aged for three weeks at 90°C. The wettability index was estimated from test series of equally treated cores. All four cores were hydrostatically loaded to 1.5 times above yield at 130°C and left to creep. During the first 15 days of creep the fluids in the pores were stagnant. It was followed by flooding of 0.219 M MgCl2-brine at two flow rates (0.01 ml/min and 0.04 ml/min) for different durations. It is observed that during loading with stagnant fluids inside the pores, the stiffness and strength are affected by wettability. The axial creep strain curves for different wettability cores overlap during the stagnant fluid creep period and during flooding of MgCl2-brine at both flow rates. We see that the creep curves, given that the creep stress is 1.5 times the yield stress, are insensitive to the initial wettability and oil/water saturation. Hence yield stress is the determining factor for these experiments.
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Handling Wellbore Instability in Overburden Tertiary Shales
Authors F. Ditlevsen, F. Bourgeois and M. CalvertSummaryFrom November 2015 to April 2017 nine infill wells were drilled in the Danish Tyra South East field. The geomechanical challenges experienced in the Tertiary shales while delivering these wells were much larger than anticipated. Limited reservoir compaction had induced stress changes in the overburden, not fully captured in the pre-drill models, which caused the delivery to be more challenging and the requirement of more comprehensive models apparent. A more detailed 3D geomechanical model was developed and associated to new 4D seismic observations after drilling more than half of the wells in the campaign. Also, real-time geomechanical evaluations and near wellbore 3D models were coupled to the 3D geomechanical model to further investigate the stress changes in the overburden. Two main failure mechanisms were identified to have contributed to the instability experienced; shear failure and bedding plane instability. The investigations and new modelling results showed that the minor stress changes in the overburden caused the MW strategy used to be connected to both shear failure and bedding plane instability. Minor changes to the MW strategy and better control of the mud pressure invasion into the shale would improve stability and the delivery of the sections through the Tertiary shales.
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Localization and Characterization of Hydraulically Conductive Fractured Zones at Seismic Scale with the Help of Geomecha
Authors N. Dubinya, I. Bayuk, S. Tikhotskiy and O. RusinaSummaryIn the paper an approach to develop a fracture network model is proposed. The key feature of this approach is the ability to distinguish hydraulically conductive and non-hydraulically conductive fractures. This ability is granted by modeling the fracture network with the use of rock physics methods using data based on both seismic survey data and geomechanical modeling results. Following the concept of hydraulically conductive and critically stressed fractures we carried out an analysis on fractures present in the reservoir to determine which of them are hydraulically conductive in the actual stress state. Then the fracture network was developed for these fractures applying the rock physics modeling methods. The integration of geomechanical properties of fractures into rock physics modeling provided an opportunity to predict how the conductive fracture network would alter with dynamically changing stress field throughout the reservoir development. A fracture network model was developed for an oil field in Russia and the results of well productivity analysis provided a solid basis for establishing the relationship between fracture network model parameters and well productivity. The obtained results strongly enhance the reliability of fracture network model based on geomechanical modeling results.
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Improving Quantitative Interpretation beneath Sand Injectites: A North Sea Case Study
Authors C. Leone, A. Osen, M. Cavalca, R. Fletcher and M. FerridaySummaryOverburden geological complexities such as cemented sand injectites can degrade the image quality at reservoir level, introducing errors and uncertainties for quantitative interpretation.
In this study, we employ depth domain inversion to improve amplitude fidelity and resolution beneath the injectites, and to obtain a more reliable estimation of acoustic rock properties.
The dip-dependent illumination effects caused by overburden heterogeneities are modelled by 3D deterministic operators, that are calibrated to well information to perform seismic amplitude inversion directly in the depth domain. This migration-inversion approach is an image-domain Least-Squares Kirchhoff Depth Migration.
The result is a higher-resolution image, showing better-balanced amplitudes and improved event continuity. The depth domain inversion to acoustic impedance demonstrated an increased reliability of seismic amplitudes, leading to an improved quantitative interpretation.
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Comprehensive Prestack Seismic-to-Well Tie Using Data Combination for Better Seismic Reservoir Characterization
More LessSummaryAll quantitative Seismic Reservoir Characterization workflows rely on careful seismic-to-well ties. It turns out that many Quantitative Interpretation (QI) workflows consist in linear combinations of prestack seismic data such as rotations / projections of Near / Far angle stacks or AVO intercept / gradient in their respective cross-plot domains. More sophisticated techniques such as prestack seismic inversion designed to estimate acoustic impedance and Poisson’s ratio to be further used for facies classification have a quasi-linear behavior relative to their input. Some of these combinations may reveal quite unstable so that good seismic-to-well ties of their input may not be sufficient to ensure quality results.
It is proposed here to assess the quality of seismic input not only within its measurement range but also across a comprehensive range of linear combinations of the same input.
Examples will illustrate that:
-It may be hazardous to plug real data into a linear combination derived from synthetic data analysis only.
-When scanning real data for an appropriate combination that matches a given elastic well log or even when using constrained seismic inversion results, the outcome might not genuinely represent the said elastic parameter.
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Quantitative Seismic Interpretation of a Class-1 AVO Turbiditic System Located Offshore Cote d’Ivoire, West Africa
Authors P. Alvarez, W. Marin, J. Berrizbeitia, P. Newton, F. Bolivar, M. Barrett, H. Wood and L. MacGregorSummaryThis paper presents a case study where a Class-1 AVO turbiditic system located offshore Cote d’Ivoire, West Africa, was characterized in terms of rock properties (lithology, porosity and fluid content) and stratigraphic elements using well log and prestack seismic data. The methodology applied involves, 1) the conditioning and modeling of well log data to several plausible geological scenarios at the prospect location, 2) the conditioning and inversion of prestack seismic data for P- and S-wave impedance estimation, and 3) the quantitative estimation of rock property volumes and their geological interpretation. The approaches used for the quantitative interpretation of these rock properties were the multi-attribute rotation scheme (MARS) for lithology and porosity characterization, and a Bayesian litho-fluid facies classification (SRP – statistical rock physics) for a probabilistic evaluation of fluid content. The result shows how the application and integration of these different AVO- and rock physics-based reservoir characterization workflows help to understand key geological stratigraphic elements of the architecture of the turbidite system and its static petrophysical characteristics (e.g. lithology, porosity, and net sand thickness).
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Reservoir Elastic Parameters Estimation from Surface Seismic Data Using JMI-res: A Full-Wavefield Approach
Authors A. Garg, S. Sharma and D.J. VerschuurSummaryAny target-oriented localised inversion scheme for reservoir elastic parameters is as good as the input dataset. Thus, the accuracy of the input dataset i.e. local reflection response or impulse response (virtual source-receiver response) is of utmost importance, especially when the target area is below a complex overburden. In these subsurface settings, the overburden internal multiples and associated transmission imprint obscure the local response, which in turn affects the estimated elastic parameters resolution. Here, we demonstrate a novel process called JMI-res, based on Joint Migration Inversion (JMI), to estimate the reservoir elastic parameters from the surface seismic elastic data for a complex subsurface scenario. In JMI-res, we first obtain the accurate local impulse responses at the target depth level, while correctly accounting for overburden internal multiples and then we apply a localized inversion scheme on the estimated impulse responses to get the reservoir elastic parameters. Moreover, the propagation velocity estimation is an integral part of JMI-res. In this paper, we show that JMI-res provides much more reliable local target impulse responses, thus yielding high-resolution elastic parameters, compared to standard redatuming based on time reversal of recorded data, courtesy of proper handling of internal multiples in the redatuming step.
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Bringing Broadband Data, Wavelet Extraction Methods and Inversion Together: With Surprising Low-Frequency Phase Results
Authors N. Ahmad and H. PelletierSummaryMany papers over the past few years have delved into the challenges, and subsequent rewards, of better determining the frequency content of our broadband seismic data. In this paper we will use a broadband dataset -acquired and processed - from the Northern Danish Central Graben to highlight a practical workflow that optimally extracts usable broadband wavelets for inversion purposes. Furthermore, low-frequency phase uncertainty was addressed during inversion testing yielding a surprisingly significant effect on the inversion result.
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A Depth Variant Seismic Wavelets Extraction Method for Inversion of Post-Stack Depth Domain Seismic Data
More LessSummaryDepth domain seismic data could suffer from stretch effects compared with time domain seismic data, which could cause strong spectral variation and non-stationarity. This could result in the invalidation of stationary assumption for conventional convolution model, which also causes difficulty for directly inverting the depth domain datasets for reservoir characterization. In this paper, we propose a depth variant wavelets extraction method by using the S-transformation with incorporation of a non-stationary convolution model to accommodate the spectral variation on the depth domain seismic data. The technique has been successfully applied on a field dataset for inversion for subsurface reflectivity and acoustic impedance. The inversion results show good fit with the well-log data, which have demonstrated its effectiveness on post-stack seismic data.
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Integration of Results from Two Seismic Inversion Methods – A Case Study
Authors R. Srivastava and S. MaultzschSummary“Seismic inversion results are non-unique and can suffer from various pitfalls related to prior model assumptions or seismic data quality issues. Combining results from two entirely different inversion algorithms can substantially improve the understanding of these results. In this study, we use an inversion for probabilities of litho-facies, referred to as Pcube+, together with a classical elastic inversion. Pcube+ is a Bayesian method of updating prior probability models of lithology-fluid classes defined in the elastic parameter space. Outputs are posterior probability volumes for each pre-defined lithology-fluid class. A standard elastic inversion yields elastic parameter volumes, which can subsequently be transformed into probabilities of litho-facies using classification.
Comparing results from the two methods in areas away from well control has proven valuable in this case study. The main data source for pre-defining the lithology-fluid classes in PCube+ are well logs. However, wells tend to be biased and may not represent the full elastic parameter space that is required to explain the seismic data away from wells. In these situations, a cross-check with an elastic inversion gives crucial insight into which elastic parameter distributions are required to match the seismic AVO response, so that prior models for PCube+ can be fine-tuned.”
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