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ABSTRACT Mine models incorporate geological, geotechnical, and rock mechanics principles to offer a 3D distribution of the principal stresses within the rockmass. Information that can independently confirm and calibrate these models is essential to offer reliable tools to the industry. Event mechanisms have long been used in earthquake seismology to infer the orientation of principal stresses assuming quasi-static stresses. This study evaluates the conditions under which the stress tensor can be derived from event mechanisms in a mining environment. Advantage is taken of the microseismic array at Goldex mine, Quebec. The array comprises 4 triaxial and 22 uniaxial accelerometers covering a volume of 450 x 250 x 120 m. A total of 544 reliable seismic moment tensor solutions for events occurred between February and May 2009 are retained for analysis. The results indicate that the mechanism solutions exhibit a high variability in both the type of fracture components and the actual fault-plane geometry. The most significant clustering of these solutions appears related to the development blasts. These blasts cause a significant reorientation of the stress tensor in a volume adjacent to that of the advancing cave front. It is further shown that the highest homogeneity in the orientation of the moment tensor solutions is obtained for events closely located in time and space with respect to each other. 1. INTRODUCTION Underground mine design and development rely heavily of the modeling of the stress distribution and redistribution within the rock mass. Mine operations change rapidly the underground conditions, and implementing changes to the mine model is often far from trivial, requiring time. Meanwhile, direct stress measurement data is very limited, making difficult an independent testing and evaluation of the mine model proposed by rock mechanics. The seismic moment tensor (SMT) provides the orientations of the principal strain axes, which are related to the local ST components (magnitudes and orientations) through the Hook’s law. In earthquake seismology, stress tensor (ST) inversion based on fault-plane orientations obtained from seismic moment tensor (SMT) solutions was pioneered by [1]. He demonstrated that the only constraint imposed on ST orientation by a fault-plane solution is that the largest principal ST axis lies in the quadrant defined by pressure (P) axis of the SMT. Some seismological studies use an average P-axis direction as equivalent to the direction of the largest principal stress. Formal algorithms for ST inversions were developed by [2, 3]. The most recent algorithm, based on a Bayesian approach to ST inversion, was introduced by [4]. Despite the long development history of ST inversion from seismological data, it remains work in progress. This is due to the intrinsic ambiguity of fault-plane solutions obtained from SMT inversions, as well as to the assumption of uniform (quasi-static) ambient stress field within the volume or region where the SMT data set was collected. ST inversion of SMT solutions for mining induced seismicity is even more challenging. In the mining environment, along with problems mentioned above, conventional assumptions, like the main and intermediate ST or SMT principal axes pointing downward [4] are not obvious.
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Information Technology > Artificial Intelligence > Representation & Reasoning > Uncertainty > Bayesian Inference (0.48)
- Information Technology > Artificial Intelligence > Machine Learning > Learning Graphical Models > Directed Networks > Bayesian Learning (0.48)
ABSTRACT: A third-order asymptotic solution in Lagrangian description for nonlinear water wave propagating over a sloping beach is derived. The particle trajectories are obtained as a function of the nonlinear ordering parameter ε and the bottom slope α to the third order of perturbation. This solution enables the description of wave shoaling in the direction of wave propagation from deep to shallow water, as well as the successive deformation of wave profiles and water particle trajectories prior to breaking. A series of experiment are conducted to investigate the particle trajectories of nonlinear water wave propagating over a sloping bottom. It is shown that the present third-order asymptotic solution agrees very well with the experiments. INTRODUCTION The motion of a fluid particle within a propagating surface wave may be described by either observing the fluid velocity at a fixed position or the trajectory of a particle that is carried along with the flow. It is also well known that the Eulerian description for a free surface can always be expressed in Taylor series at a fixed water level, which implicitly assumes that the surface profile is a differentiable single-valued function. In the Lagrangian approach, however, the surface elevation is specified through the position of a surface particle, i.e., a particle whose vertical parameter is equal to zero. Unlike an Eulerian surface, which is given as an implicit function, a Lagrangian form is expressed through a parametric representation of particle motion. Hence, the Lagrangian description is more appropriate for limiting the free surface motion, whereas this unique feature cannot be represented by the classical Eulerian solutions (Biesel, 1952; Naciri and Mei, 1993; Chen et al., 2005, 2006 and Buldakov et al., 2006). The first water wave theory in Lagrangian coordinates was obtained by Gerstner (1802) who assumed the flow possesses finite vorticity.
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.50)
- Data Science & Engineering Analytics > Information Management and Systems > Artificial intelligence (0.34)
Abstract The use of production data to increase the reliability of production forecasts of a field is limited, especially in early development, when there are fewer observed data and then a significant uncertainties raise. An alternative to improve the quality of the model is the use of saturation and pressure maps obtained from time-lapse seismic. The incorporation of this information has not been explored in reservoir engineering studies and has great potential for reducing uncertainties caused by lack of information and complexity of oil fields. Recent work indicates that the best way to use this information to calibrate reservoir numerical models is to convert it into saturation and pressure. Thus, this study aims to derive, from time-lapse seismic attributes, distributions of saturation and pressure in oil reservoirs. This paper presents a methodology to estimate saturation and pressure maps simultaneously through an inversion process constrained by engineering data. These maps information are then combined with production data in a global objective function aiming at improving an integrated history matching procedure. This methodology is applied in a modified model of the "Namorado Field" (Campos Basin, Brazil), that has geological faults and high permeability channels. It was also necessary to apply an empirical modeling of the rock bulk modules regarding pressure variations, which improved the reservoir acoustic sensitivity and allowed, together with the engineering data constraints, to derive these maps. It was possible to identify the main structures that can influence fluid flow trends in the reservoir and significantly reduce time consuming and increase the reservoir behavior predictions reliability. As major contributions of this study are the development of a methodology able to provide saturation and pressure trends regarding time-lapse information and engineering data constraints to the overall process and its quantitative application in an integrated history matching procedure.
- Geophysics > Time-Lapse Surveying > Time-Lapse Seismic Surveying (1.00)
- Geophysics > Seismic Surveying (1.00)
- South America > Brazil > Rio de Janeiro > South Atlantic Ocean > Campos Basin > Garoupa Cluster > Namorado Field (0.99)
- South America > Brazil > Campos Basin (0.99)
- Reservoir Description and Dynamics > Reservoir Simulation > History matching (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- (2 more...)
- Information Technology > Modeling & Simulation (0.95)
- Information Technology > Artificial Intelligence > Representation & Reasoning > Optimization (0.47)
Abstract Seismic data incorporation in reservoir simulation models history matching (HM) studies has been continuously growing. 4D seismic data, in contrast with well production data, can provide a very good scenario of fluids arrangement along reservoir. In this work we describe how 3D and 4D seismic data gathered in acquisitions performed in Campos Basin was incorporated in Marlim Sul deep water field geological model reconstruction and in assisted HM (AHM). It is taken advantage of both 3D and 4D seismic data in several stages of the study, for instance, in the construction of a new porosity – most influential in impedance – model by using a methodology based on the inversion of synthetic seismic (calculated by petro-elastic model) in porosity through an optimization process that aims to reduce the difference between observed and synthetic impedance, and when defining influential parameters based on fluids displacement registered by seismic signal, by using a technique based on the creation of transmissibility multipliers parameters regions that considers the fluids displacement shown in 4D signal. Another relevant point is the use of information from reservoir and 3D seismic data when weighting the 4D data in the objective function. Combining the above mentioned techniques with the knowledge of the field – supported by the 3D seismic data – which allowed, for instance, identification of faults – where fault transmissibility multipliers were used as parameters in the HM process – a fairly good agreement on the observed well and seismic production data was achieved. HM studies using AHM tools have been shown a much more time-efficient technique when compared to manual HM. The incorporation of 4D seismic data can considerably improve the HM quality by improving the reservoir description, once it increases the ability of describing fluids arrangement and pressure distribution. The techniques successfully applied in the Marlim Sul field HM support these conclusions.
- Europe (1.00)
- South America > Brazil > Rio de Janeiro > South Atlantic Ocean (0.35)
- Geophysics > Time-Lapse Surveying > Time-Lapse Seismic Surveying (1.00)
- Geophysics > Seismic Surveying (1.00)
- South America > Brazil > Rio de Janeiro > South Atlantic Ocean > Campos Basin > Marlim Sul Field > Macae Formation (0.99)
- South America > Brazil > Rio de Janeiro > South Atlantic Ocean > Campos Basin > Marlim Sul Field > Lago Feia Formation (0.99)
- South America > Brazil > Rio de Janeiro > South Atlantic Ocean > Campos Basin > Marlim Field > Macae Formation (0.99)
- (15 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Four-dimensional and four-component seismic (1.00)
- Information Technology > Modeling & Simulation (0.95)
- Information Technology > Artificial Intelligence > Representation & Reasoning (0.46)
Abstract During the last decade, a large amount of data has been collected for a field development project, located in a challenging geological area, deepwater offshore West Africa. It was necessary to create a database including these different data types, which represents the purpose of the work presented here. In order to integrate, visualize and query this database for the project needs (geohazard assessment, layout optimisation, etc), ESRI ArcGIS was selected as the appropriate analysis tool. The aim of this paper is twofold: to explain how the data was organized into an efficient GIS project and to highlight its principal applications. Firstly, the GIS project is organized into several thematic geodatabases. Each geodatabase corresponds to a field survey and its internal organization resulted from a complex approach. A geodatabase includes several feature datasets, which, in turn are composed of multiple feature classes. An attribute table with enhanced information was created for every data type. This offers a solution for data query using spatial analysis and map algebra. Secondly, the data visualization and integration allows the identification of possible geohazards and, further, their possible impact on the field development. The advantage of this GIS project is that it can be used in all the steps of the field development. This can help decision making related to the optimization of the field layout and the definition of targets for future site investigations. Moreover, the interface being user-friendly; it can be manipulated even by non-specialist project users. In conclusion, this GIS project is being considered as a reference for future projects dealing with wide diversity and large amount of data. Introduction During the last decades, oil and gas industry targets moved from shallow to deepwater challenging environments. Consequently, the planned infrastructures are often located in geohazard-prone areas. This is the case of the study area, located on the continental slope offshore West Africa. In order for the seabed and sub-seabed field infrastructures to be safely installed in this complex geological environment, desk top studies, various reconnaissance surveys and specific studies have been performed over a period of 10 years. Consequently, the associated large amount of data provided by different contractors needed to be integrated and visualized, taking into account the variable data formats and geodetic parameters. The Geographic Information System (GIS) globally recognized as the most efficient tool for data compilation, organization, management and integration (Noll IV et al., 2010; Varnell et al., 2010; Turner and Bell, 2010) was selected as the appropriate tool for this study. Figure 1 portrays a typical programme of an offshore development and the relationship between data gathering and GIS construction.
- Africa > West Africa (0.81)
- North America > United States > Texas > Harris County > Houston (0.16)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Management > Asset and Portfolio Management > Field development optimization and planning (0.96)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.85)
- Information Technology > Artificial Intelligence > Representation & Reasoning > Information Fusion (0.41)
- Information Technology > Artificial Intelligence > Representation & Reasoning > Spatial Reasoning (0.34)
Amplitude variation with angle (AVA) inversion is performed on the top Utsira Sand reflector at the Sleipner field, North Sea, Norway. This interface is of particular interest because of the accumulation of injected from a point deeper in the Utsira Sand. The focus is on the postmigration processing of angle gathers together with the actual inversion procedure. The processing treats amplitude extraction, offset-to-angle mapping, and global scaling in detail. Two algorithms are used for the inversion of AVA data, one that assesses uncertainties and one fast least-squares variant. Both are very suitable for this type of problem because of their covariance matrices and built-in regularization. In addition, two three-parameter approximations of the Zoeppritz equations are used. One is linear approximation and the other is quadratic. The results show significant signals for all three elastic parameters, but the substitution of brine by using Gassmann’s equation indicates that the contrasts in S-wave impedance and density are overestimated. For the contrasts in P-wave impedance the results are in agreement with the fluid substitution. A simple sensitivity analysis shows that the offset-to-angle mapping and the damping factor in the inversion are the most plausible explanations of the discrepancy.
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Utsira Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Block 15/9 > Sleipner Field > Draupne Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Block 15/8 > Sleipner Field > Draupne Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Block 15/6 > Sleipner Field > Draupne Formation (0.99)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic modeling (1.00)
- Information Technology > Data Science > Data Mining (0.46)
- Information Technology > Artificial Intelligence > Representation & Reasoning (0.46)
- Information Technology > Artificial Intelligence > Machine Learning > Learning Graphical Models (0.46)
Surface-wave methods are quite popular for site characterization in geotechnical earthquake engineering. Among these techniques, a particular role is taken by passive methods for their ability to yield information on the low-frequency range and consequently on large depths. One such passive method, the refraction microtremors (ReMi) technique, has been proposed as a simple alternative to 2D-array techniques to estimate surface-wave dispersion by using linear arrays of geophones. The technique owes its name to the use of widely available instruments also adopted for seismic refraction. The basic hypotheses underlying ReMi are that noise is distributed isotropically in azimuth or is aligned exactly with the array. These conditions often are not met, and in most cases they are not verified because such analysis requires an accurate approach to data processing that is rarely applied. We have developed an algorithm that verifies ReMi’s basic hypotheses by analyzing experimental data. In addition, we have proposed an algorithm to identify the lowest apparent velocity on the ReMi spectra, thus avoiding interpretation problems.
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Information Technology > Data Science (0.50)
- Information Technology > Artificial Intelligence > Representation & Reasoning (0.46)
We present a rank reduction algorithm that permits simultaneous reconstruction and random noise attenuation of seismic records. We based our technique on multichannel singular spectrum analysis (MSSA). The technique entails organizing spatial data at a given temporal frequency into a block Hankel matrix that in ideal conditions is a matrix of rank , where is the number of plane waves in the window of analysis. Additive noise and missing samples will increase the rank of the block Hankel matrix of the data. Consequently, rank reduction is proposed as a means to attenuate noise and recover missing traces. We present an iterative algorithm that resembles seismic data reconstruction with the method of projection onto convex sets. In addition, we propose to adopt a randomized singular value decomposition to accelerate the rank reduction stage of the algorithm. We apply MSSA reconstruction to synthetic examples and a field data set. Synthetic examples were used to assess the performance of the method in two reconstruction scenarios: a noise-free case and data contaminated with noise. In both cases, we found extremely low reconstructions errors that are indicative of an optimal recovery. The field data example consists of a 2D prestack volume that depends on common midpoint and offset. We use the MSSA reconstruction method to complete missing offsets and, at the same time, increase the signal-to-noise ratio of the seismic volume.
- North America > United States (0.46)
- North America > Canada > Alberta (0.29)
- Information Technology > Artificial Intelligence > Machine Learning (0.46)
- Information Technology > Software > Programming Languages (0.34)
- Information Technology > Artificial Intelligence > Representation & Reasoning > Spatial Reasoning (0.34)
Our aim is to understand the stress-dependent seismic anisotropy of the overburden shale in an oil field in the North West Shelf of Western Australia. We analyze data from measurements of ultrasonic P-wave velocities in 132 directions for confining pressures of 0.1–400 MPa on a spherical shale sample. First, we find the orientation of the symmetry axis, assuming that the sample is transversely isotropic, and then transform the ray velocities to the symmetry axis coordinates. We use two parameterizations of the phase velocity; one, in terms of the Thomsen anisotropy parameters α, β, ɛ, δ as the main approach, and the other in terms of α, β, η, δ. We invert the ray velocities to estimate the anisotropy parameters α, ɛ, δ, and η using a very fast simulated reannealing algorithm. Both approaches result in the same estimation for the anisotropy parameters but with different uncertainties. The main approach is robust but produces higher uncertainties, in particular for η, whereas the alternative approach is unstable but gives lower uncertainties. These approaches are used to find the anisotropy parameters for the different confining pressures. The dependency of P-wave velocity, α, on pressure has exponential and linear components, which can be contributed to the compliant and stiff porosities. The exponential dependence at lower pressures up to 100 MPa corresponds to the closure of compliant pores and microcracks, whereas the linear dependence at higher pressures corresponds to contraction of the stiff pores. The anisotropy parameters ɛ and δ are quite large at lower pressures but decrease exponentially with pressure. For lower pressures up to 10 MPa, δ always is larger than ɛ; this trend is reversed for higher pressures. Despite the hydrostatic pressure, the symmetry axis orientation changes noticeably, in particular at lower pressures.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.57)
- Oceania > Australia > Western Australia > Carnarvon Basin > Exmouth Basin (0.99)
- North America > United States > South Dakota > Williston Basin (0.99)
- North America > United States > North Dakota > Williston Basin (0.99)
- North America > United States > Montana > Williston Basin (0.99)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
Assessing the effectiveness of elastic full-waveform-inversion (FWI) algorithms when applied to shallow 2D structures in the presence of a complex topography is critically important. By using FWI, we overcome inherent limitations of conventional seismic methods used for near-surface prospecting (acoustic tomography and multichannel spectral analysis of surface waves). The elastic forward problem, formulated in the frequency domain, is based on a mixed finite-element P0-P1 discontinuous Galerkin method to ensure accurate modeling of complex topography effects at a reasonable computing cost. The inversion problem uses an FWI algorithm to minimize the misfit between observed and calculated data. Based on results from a numerical experiment performed on a realistic landslide model inspired from the morphostructure of the Super-Sauze earthflow, we analyzed the effect of using a hierarchical preconditioning strategy, based on a simultaneous multifrequency inversion of damped data, to mitigate the strong nonlinearities coming from the surface waves. This strategy is a key point in alleviating the strong near-surface effects and avoiding convergence toward a local minimum. Using a limited-memory quasi-Newton method improved the convergence level. These findings are analogous to recent applications on large-scale domains, although limited source-receiver offset ranges, low-frequency content of the source, and domination of surface waves on the signal led to some difficulties. Regarding the impact of data decimation on the inversion results, we have learned that an inversion restricted to the vertical data component can be successful without significant loss in terms of parameter imagery resolution. In our investigations of the effect of increased source spacing, we found that a sampling of 4 m (less than three times the theoretical maximum of one half-wavelength) led to severe aliasing.
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling > Seismic Inversion (1.00)