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Collaborating Authors
Oil & Gas
Summary We develop an efficient method to calculate the broadband seismic illumination and resolution. The point spreading function of seismic image contains the full information for illumination and resolution analyses. Physically, it is the image of a point scatter. Therefore we can obtain the illumination information by calculating the point spreading function. We develop a method to better calculate the point spreading function. The scattered waves from background structure are eliminated, Noise from higher-order interscatter multiples are investigated and properly avoided. By converting the point spreading function to the wavenumber domain, methods for illumination and resolution analyses in angle domain are also discussed. Introduction Migration image is one of the most important processing techniques that map the reflection data to the target to generate the subsurface image. Due to limited acquisition aperture, complex overburden structure and target dipping angle, the migration often generates a distorted subsurface image. Seismic illumination and resolution analyses provide a quantitative description on how the above mentioned factors will cause the image distortion. These analyses are vital in obtaining true reflection image, AVA analysis, reservoir characterization as well as seismic survey design and processing quality control. Traditionally, seismic illumination and resolution analyses are performed by ray or one-way propagator based methods (Gelius et al., 2002; Lecomte, 2008; Xie et al., 2005, 2006; Wu et al., 2006). To simulate the acquisition system, the wavefield needs be extrapolated from all sources and receivers to the subsurface. Angle decomposition needs be conducted locally in the model space to construct the angle domain illumination. The related computation is extremely intensive. To be practical, the illumination analysis is often conducted under a single (usually the dominant) frequency and with limited number of sources and receivers. Recently, the full wave equation based RTM has become the industry standard. To be consistent with this trend, the broadband, full-wave based illumination analysis method should also be developed.
Summary We present results of application of stress field inversion on microseismic monitoring data. We inverted regional principal stress directions from the source mechanisms of microseismic events induced by hydraulic fracturing in a shale reservoir. We compare results of stress inversion from several groups of microseismic events and inversions. We compare inversions using source mechanisms inverted from manually picked amplitudes and automatically inverted source mechanisms. We show changes in the stress field orientation based on subset of dataset created according to observed type of source mechanisms and depth of microseismic events. The resulting stress fields are stable, highly similar and consistent with regional stress field. We get maximum regional stress in the vertical direction, which is typical for most of sedimentary basins, and maximum horizontal stress oriented approximately 75° from the direction of the drilled wells. The fact that we obtained the regional stress indicates that the regional stress determined the source mechanisms of induced microseismic events and we use Mohr diagrams to determine most likely fault planes of these events. Introduction Microseismic monitoring is considered to be a crucial tool for observing and mapping reservoir response to hydraulic fracture stimulation. Locations of microseismic events determine basic information about fracture geometry such as direction of fracture propagation, its length and height. Recently, an advanced fracture characterization using source mechanisms of induced microseismic events is also routinely provided (Baig and Urbancic, 2010). Locations and source mechanisms allow other advanced characterization such as discrete fracture network (Williams-Strout et al., 2010) and stress orientation. Observed mechanisms are dominated by shearing (Stanek and Eisner, 2013; Rutledge et al. 2013). Each source mechanism of a shear event represents an (micro)earthquake with two potential fault planes and slip on these planes. According to a type of stress regime in the source area we observe different types of source mechanisms (Anderson, 1942) radiating specific directional dependent pattern of seismic waves (Aki & Richards, 1980). We use the waveforms of seismic waves to determine source mechanisms. The source mechanisms enable us to invert the most suitable stress field orientation which is consistent with the slippage on the fault planes determined from source mechanisms
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.70)
Summary The characterization of geomorphic features such as fault plane geometries and slickensides can reveal intricacies of fault displacement as well as the forces that formed the fault. Fault plane geomorphic features such as grooves, ridges, and steps, which are normally observed in outcrops, are apparently scale independent and can be extracted by detailed fault interpretation on 3D Seismic data. Strain not only affects the fault plane, but also extends into the rock volume (Matonti et al., 2012) and can be inferred in different ways through direct observation of features in the rock (Van der Pluijm and Marchak, 2004). This study proposes that strain can also be inferred by observation of features within the fault plane geomorphology and that given the proper conditions, these geomorphic features can be interpreted within seismic data. Introduction A fault is a fracture on which slip develops primarily by brittle deformation processes. Faults control the distribution of economic resources by controlling the permeability of rocks and sediments, properties which, in turn, control fluid migration (Van der Pluijm and Marshak, 2004). Faults surfaces play important roles in the petroleum system, functioning as hydrocarbon migration pathways or as structural seals (Metwalli and Pigott, 2005). Very few comprehensive structural studies have been conducted utilizing advanced seismic attribute analysis combined with fault plane geomorphology. Of these studies, even less have been made available to the general public. Fault characterization is a crucial issue in reservoir exploitation, because faults can behave either as hydraulic seal or as conduit. This research is focused on data from a producing Middle Eastern oil field. The Middle East accounts for an estimated 47.9% of the world’s proven oil reserves (BP, 2014). Many of the world’s giant and super-giant fields have been discovered in Middle Eastern countries. There are 47 supergiant fields (proven and probable recoverable reserves > 5,000 MMboe) and 194 giant fields (500-5,000 MMboe proven and probable reserves) that have been discovered within the Middle Eastern counties that line the Eastern Tethyan Margin (Marlow et al., 2014). Due to confidentiality agreements, disclosure of the exact field or location is restricted.
- Asia > Middle East > Israel > Mediterranean Sea (0.24)
- Asia > Middle East > Iraq > Diyala Governorate (0.24)
- Geophysics > Seismic Surveying > Surface Seismic Acquisition (0.55)
- Geophysics > Seismic Surveying > Seismic Interpretation (0.54)
Summary Imaging diffracted waves can provide useful information about complex subsurface geology and fracture networks. Separation of diffractions from typically more intensive reflected waves can be based on specularity, which measures deviation from Snell’s law. Here, we analyze two formulations of specularity and their applicability to diffraction processing for anisotropic media. We show that the most common definition of specularity, originally introduced for pure modes in isotropic media, remains valid for both pure and converted waves in arbitrarily anisotropic models. The other formulation operates directly with the difference between the slowness projections onto the reflector for the incident and reflected waves. Testing on a VTI (transversely isotropic with a vertical symmetry axis) diffraction ramp model demonstrate that both formulations produce satisfactory results for anisotropic media with appropriate tapering of the specularity gathers. Introduction Diffractions are caused by heterogeneities with linear dimensions smaller than the seismic wavelength. They can provide valuable information about complex subsurface features such as small-scale faults, fractures, pinch-outs, karst, and rough edges around salt bodies (Landa, 2010). Diffractions are treated as noise during conventional seismic processing, which is designed for enhancing and imaging of reflected waves. The main challenge in utilizing diffractions is separating them from reflections, which typically dominate surface seismic data. Khaidukov et al. (2004) separate diffractions in isotropic media by applying focusing and defocusing operators. Fomel et al. (2007) operate on poststack time sections to separate diffractions using plane-wave destruction filters and perform isotropic velocity analysis based on a measure of focusing. Imaging with diffractions can potentially provide higherresolution seismic sections (Khaidukov et al., 2004), which can be combined with conventional reflection-based images for improved interpretation (Sturzu et al., 2013; Khaidukov et al., 2004; Moser and Howard, 2008). Kozlov et al. (2004) apply a weighting function, based on the Fresnel zone around the specular reflected ray, to the Kirchhoff integral to suppress reflections during isotropic migration. However, constructing such weights for anisotropic media is cumbersome. Moser and Howard (2008) propose to define the weigting function using another approach (called "specularity"), which measures the deviation from Snell’s law at the reflection point. This approach is employed by Sturzu et al. (2013) to create "specularity gathers" for efficient separation of diffraction and reflection energy (Sturzu et al., 2013). Although specularity ignores the Fresnel zone contribution to the reflections, specularity gathers overcome this problem and provide an efficient method for diffraction separation.
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.35)
Summary This paper provides: (1) a brief overview of the current status of multiple attenuation in the petroleum industry; (2) recent progress for marine and on-shore plays; (3) open issues and pressing challenges and (4) a plan to address those high priority challenges and recent progress towards that goal. Introduction The demand for new and improved capability in removing multiples is driven by the portfolio of the petroleum industry and by current and anticipated future exploration trends. For example, the industry moved to deep water roughly 30 years ago. With that move, highly effective multiple-removal methods that were being applied industry-wide suddenly bumped up against their statistical assumptions, when applied to deep water plays, and failed. Since then, the overall industry trend to explore in progressively more complex and remote areas, with ill-defined and difficult-to-estimate subsurface properties motivates the search for capabilities that will not require subsurface information. Methods for multiple removal that require various forms of subsurface information include, e.g., stacking, F-K and Radon filters, and Feedback demultiple methods. The inverse scattering series provides the opportunity to achieve all processing objectives directly and without subsurface information. The current inverse-scattering-series (ISS) internalmultiple- attenuation algorithm has a unique capability to predict the exact phase (time) and approximate amplitude of all internal multiples, at once, automatically, and without subsurface information. These properties separate the ISS internalmultiple- attenuation algorithm from all other methods, and make it the high-water mark of current internal-multiple effectiveness. That is, those ISS properties and strengths are what all other current demultiple methods (e.g., Feedback loop methods, modeling and subtracting multiples, and filter methods) do not possess (e.g., Hung et al. (2014); Kelamis et al. (2013a); Luo et al. (2011); Ferreira (2011)). Carvalho (1992), Carvalho andWeglein (1994), Ara´ujo (1994), Ara´ujo et al. (1994), Weglein et al. (1997), and Weglein et al. (2003) developed ISS free-surface-multiple elimination algorithms and internal-multiple attenuation algorithms. Field-data applications demonstrated their effectiveness. Several marine and onshore data examples are noted below.
- Asia > Middle East > Saudi Arabia (1.00)
- Asia > Middle East > Yemen (0.93)
- Africa > Sudan (0.93)
- (3 more...)
Detection of Salt-dome Boundary Surfaces in Migrated Seismic Volumes Using Gradient of Textures
Shafiq, Muhammad A. (Center for Energy and Geo Processing (CeGP) at Georgia Tech, King Fahd University of Petroleum and Minerals) | Wang, Zhen (Center for Energy and Geo Processing (CeGP) at Georgia Tech, King Fahd University of Petroleum and Minerals) | Amin, Asjad (Center for Energy and Geo Processing (CeGP) at Georgia Tech, King Fahd University of Petroleum and Minerals) | Hegazy, Tamir (Center for Energy and Geo Processing (CeGP) at Georgia Tech, King Fahd University of Petroleum and Minerals) | Deriche, Mohamed (Center for Energy and Geo Processing (CeGP) at Georgia Tech, King Fahd University of Petroleum and Minerals) | AlRegib, Ghassan (Center for Energy and Geo Processing (CeGP) at Georgia Tech, King Fahd University of Petroleum and Minerals)
Summary Salt domes, an important geological structure, are closely related to the formation of petroleum reservoirs. In many cases, no explicit strong reflector exists between a salt dome and neighboring geological structures. Therefore, interpreters commonly delineate the boundaries of salt domes by observing a change in texture content. To stimulate the visual interpretation process, we propose a novel seismic attribute, the gradient of textures, which can quantify texture variations in three-dimensional (3D) space. On the basis of the attribute volume, we apply a global threshold to highlight regions containing salt-dome boundaries. In addition, with region growing and morphological operations, we can remove noisy boundaries and detect the boundary surfaces of salt domes effectively and efficiently. Experimental results show that by utilizing the strong coherence between neighboring seismic sections, the proposed method can delineate the surfaces of saltdome boundaries more accurately than the state-of-the-art detection methods that label salt-dome boundaries only in twodimensional (2D) seismic sections. Introduction The evaporation of sea water leads to the deposition of salt. Because of the lower density, salt grows upwards and commonly penetrates into surrounding rock strata, which forms an important diapir structure, salt domes. Salt domes are mostly impermeable and can seal petroleum and natural gas with surrounding strata. To localize petroleum reservoirs around salt domes, experienced interpreters need to accurately label saltdome boundaries in migrated seismic data. With the dramatically growing size of collected seismic data, however, manual interpretation is becoming time consuming and label intensive. To speed up interpretation efficiency, in recent years, interpreters have been utilizing computer programs to interactively delineate salt-dome boundaries. With the supervision of interpreters, the computer-assisted interpretation is feasible. Since the formation process determines the textures of geological structures in migrated seismic data, salt domes and their surrounding strata commonly have distinctive textures. To characterize the texture difference between the two sides of salt-dome boundaries, current computer-assisted salt-dome detection methods were proposed based on graph theory and image processing techniques. Lomask et al. (2004) represented seismic sections as weighted undirected graphs by defining vertices and edges as pixels in seismic sections and the connections of arbitrary two pixels, respectively. The weights of edges are determined based on intensity and position difference of pixels. Using the normalized cut image segmentation (NCIS) method, seismic sections can be partitioned into two parts along detected salt-dome boundaries. The NCIS-based method was later enhanced in Lomask et al. (2007) and Halpert et al. (2009). However, the main disadvantage of NCIS-based methods is their high computational complexity. Therefore, Halpert et al. (2010) employed a more-efficient graph-based segmentation method, referred to as "pairwise region comparison" (Felzenszwalb and Huttenlocher, 2004), in the detection of salt-dome boundaries
Summary A novel particle swarm optimization (PSO) method for discrete parameters and its hybridized algorithm with multi-point geostatistics are presented. This stochastic algorithm is designed for complex geological models, which often require discrete facies modeling before simulating continuous reservoir properties. In this paper, we first develop a new PSO method for discrete parameters (Pro-DPSO) where particles move in the probability mass function (pmf) space instead of the parameter space. Then Pro-DPSO is hybridized with the single normal equation simulation algorithm (SNESIM), one of the popular multipoint geostatistics algorithms, to ensure the prior geological features. This hybridized algorithm (Pro-DPSO-SNESIM) is evaluated on a synthetic example of seismic inversion, and compared with a Markov chain Monte Carlo (McMC) method. The results show that the new algorithm generates multiple optimized models with the convergence rate much faster than the McMC method.
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
Summary We develop a new tool for initial seismic migration-velocity model building based on a recent gravity inversion method. This method consists of an iterative algorithm that provides a 3D density-contrast distribution on a grid of prisms, the starting point being a user-specified prismatic element called "seed". By means of this technique of planting anomalous densities, we are able to interpret multiple bodies with different density contrasts. Therefore, the method does not require the solution of a large equation system, which greatly reduces the computational demand. Once the geometry of the anomalous-density body is known, we can extract the skeleton of the inverted body and fill each prism with a velocity consistent with the presumed geology. Starting at this velocity model, the next step is to perform a migration velocity analysis (MVA). The result of MVA can then, in turn, be used to improve on the geometry for the gravity inversion. This joint processing and interpretation can be considered as an alternative way to improve the knowledge of complex structures. For example, the image quality of salt structures and sub-salt sediments obtained by reflection seismic is almost always limited by the effects of wavefield transmission, scattering and absorption. Simple synthetic examples show the capacity of the proposed velocity-model-building algorithm to generate initial velocity models for depth-migration velocity analysis, including those for specific geological targets. Introduction Time and depth migration are to fundamental processes in seismic imaging that are regularly applied to seismic data. For their success, high-quality velocity models are indispensable. However, automatic and/or efficient velocity-model construction tools are still a challenge. Most present-day model-building techniques are iterative procedures that improve a starting model based on intermediate results. Examples for new algorithms for time-migration velocity analysis based on prestack time migration (PSTM), which bypass the conventional CMP-based velocity analysis, are presented in Fomel (2003), Schleicher et al. (2008), Schleicher and Costa (2009), Coimbra et al. (2013a,b, 2014) and Santos et al. (2014a). While time migration is more robust and tolerant to velocity errors, methods acting in the depth-domain are more precise. Prestack depth migration (PSDM) techniques are capable of imaging more complex structures including lateral velocity variation and dipping reflectors (Liu and Bleistein, 1995; Liu, 1997). This is so because depth migration is highly sensitive to the velocity model (Zhu et al., 1998). Its strong dependence on a precise velocity model makes PSDM an interesting tool for velocity analysis (Abbad et al., 2009; Mulder and ten Kroode, 2002; Al-Yahya, 1989). On the other hand, a more accurate velocity model is required for its application, which almost always increases the computational cost. This, in turn, leads many researchers to search for alternative methods.
- North America > United States > New Mexico > Eddy County (0.40)
- Europe > Portugal > Coimbra > Coimbra (0.25)
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
Is a Steel-Cased Borehole an Electrical Transmission Line?
Aldridge, David F. (Sandia National Laboratories) | Weiss, Chester J. (Sandia National Laboratories) | Knox, Hunter A. (Sandia National Laboratories) | Schramm, Kimberly A. (Sandia National Laboratories) | Bartel, Lewis C. (Carbo Ceramics Inc.)
Summary Under certain restricting assumptions, an electrically energized steel-cased geologic borehole may be modeled as an electrical transmission line. Current waveforms are obtained by solving the governing telegraph equation in the frequency-domain, followed by numerical inverse Fourier transformation. Electric current pulses propagating along the borehole undergo progressive amplitude loss and waveform distortion with distance, arising from leakage of current into the surrounding geology. A major modeling uncertainty involves the proper boundary condition to impose at the end of a borehole transmission line. Introduction There appears to be increasing interest in utilizing a steelcased geologic borehole as a giant source electrode for electromagnetic (EM) exploration purposes. The casing, energized either at/near the wellhead or at a deep downhole point, provides a high conductivity pathway for electric current to enter a large subsurface volume. Moreover, high amplitude current can be delivered close to a geophysical feature of interest near the borehole, such as a hydraulic fracturing stage. The present situation motivates further examination of the current-carrying characteristics of a steel-cased borehole. Several investigators (Kaufmann, 1990; Kaufmann and Wightman, 1993; Schenkel and Morrison, 1994; Wait, 1994, 1995; Bartel, 2014) have studied the problem of electric current flow in a coaxial cylindrical geometry consisting of fluid, casing, and cement, and surrounded by layered geology. The primary focus has been on logging formation resistivity through casing, and a direct current (DC) assumption is often adopted. In this study, we use the electric transmission line analogy originally developed by Kaufman (1990) to calculate full bandwidth time-domain current waveforms along a cased borehole surrounded by a homogeneous geology. More than 80 years ago, Schelkunoff (1934) provided a derivation of the (frequency-domain) transmission line equations directly from Maxwell’s equations expressed in cylindrical coordinates. A major assumption involved circular symmetry of both medium parameters and sources, and hence of the generated EM wavefields. Thus, the transmission line representation of a current-carrying borehole applies strictly to a vertical well penetrating horizontal layered geology. It does not apply to a well tracking horizontally within a deep geologic formation.
- Energy > Power Industry (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.48)
Summary We propose an efficient and accurate plane wave reverse time migration (RTM) imaging condition using frequency domain plane wave Green’s functions. The proposed imaging condition can be applied in anisotropic media, as well as in isotropic media. Based on the discrete Fourier transform (DFT), a procedure is developed to extract frequency plane wave Green’s functions from time domain wave fields that include anisotropy. The rapid expansion method (REM) is implemented for the decoupled P wave equation in an acoustic vertical transversely isotropic (VTI) medium to compute time wave fields. Only plane wave Green’s functions need to be computed for imaging, which leads to a fast migration scheme. Furthermore, the proposed imaging condition can generate ray-parameter common image gathers (CIGs). Therefore, the migration approach can be a useful tool for anisotropic parameter analysis. The proposed method is demonstrated to be efficient and effective through one synthetic example. Introduction The RTM (Baysal et al., 1983; McMechan 1983; Zhang and Sun 2008) is a powerful tool for imaging complex subsurface areas. In areas where the effect of anisotropy cannot be ignored, isotropic wave propagation used for RTM may result in mis-positioning of structures. The acoustic transversely isotropic (TI) media, including VTI and tilted transverse isotropy (TTI), have been proven to be good approximations for many subsurface areas. Implementing RTM under VTI (Du et al., 2008; Liu et al., 2009; Pestana et al., 2012; Zhou et al., 2006a) and TTI (Zhan et al., 2012; Zhang and Zhang 2008; Zhou et al., 2006b) assumptions have been shown to recover structures correctly in anisotropic media. In this study, we first derive the plane wave imaging condition using plane wave Green’s function for double plane wave (DPW) dataset with the Born approximation (Bleistein et al., 2001; Stolt and Weglein 2012). Tatalovic et al. (1990) introduced the DPW transform and DPW imaging in coupled ray-parameter and frequency domain. DPW full waveform modeling was introduced and implemented by Sen and Frazer (1991) and Sen and Pal (2009). Stoffa et al. (2006) implemented DPW migration by computing vertical delay time for plane wave components with the aid of asymptotic ray theory (ART). DPW-based time domain RTM (Zhao, Stoffa, et al., 2014) and frequency domain RTM (Zhao, Sen, et al., 2014) were also realized.