BP (United States)

It is now commonplace for 3-D data sets to be processed as partial offset volumes to exploit the AVO information in the data. However, there has been significant asymmetry in the way these volumes could be calibrated and inverted. The amplitudes of near-offset, or intercept, stacks relate to changes in acoustic impedance and can be tied to well logs using synthetics based on acoustic impedance (AI) or inverted, to some extent, back to AI using poststack inversion algorithms. However, there have been no simple analogous processes for far-offset stacks.

BACKGROUND: Colorectal cancer (CRC) remains one of the major cancer types and cancer related death worldwide. Sensitive, non-invasive biomarkers that can facilitate disease detection, staging and prediction of therapeutic outcome are highly desirable to improve survival rate and help to determine optimized treatment for CRC. The small non-coding RNAs, microRNAs (miRNAs), have recently been identified as critical regulators for various diseases including cancer and may represent a novel class of cancer biomarkers. The purpose of this study was to identify and validate circulating microRNAs in human plasma for use as such biomarkers in colon cancer. METHODOLOGY/PRINCIPAL FINDINGS: By using quantitative reverse transcription-polymerase chain reaction, we found that circulating miR-141 was significantly associated with stage IV colon cancer in a cohort of 102 plasma samples. Receiver operating characteristic (ROC) analysis was used to evaluate the sensitivity and specificity of candidate plasma microRNA markers. We observed that combination of miR-141 and carcinoembryonic antigen (CEA), a widely used marker for CRC, further improved the accuracy of detection. These findings were validated in an independent cohort of 156 plasma samples collected at Tianjin, China. Furthermore, our analysis showed that high levels of plasma miR-141 predicted poor survival in both cohorts and that miR-141 was an independent prognostic factor for advanced colon cancer. CONCLUSIONS/SIGNIFICANCE: We propose that plasma miR-141 may represent a novel biomarker that complements CEA in detecting colon cancer with distant metastasis and that high levels of miR-141 in plasma were associated with poor prognosis.

Abstract Seismic surveys generally have irregular areas where data cannot be acquired. These data should often be interpolated. A projection onto convex sets (POCS) algorithm using Fourier transforms allows interpolation of irregularly populated grids of seismic data with a simple iterative method that produces high-quality results. The original 2D image restoration method, the Gerchberg-Saxton algorithm, is extended easily to higher dimensions, and the 3D version of the process used here produces much better interpolations than typical 2D methods. The only parameter that makes a substantial difference in the results is the number of iterations used, and this number can be overestimated without degrading the quality of the results. This simplicity is a significant advantage because it relieves the user of extensive parameter testing. Although the cost of the algorithm is several times the cost of typical 2D methods, the method is easily parallelized and still completely practical.

Experimental models of acute ischemic myocardial injury indicate that the inflammatory response after the ischemic event contributes to tissue damage. This is especially apparent with reperfusion of the ischemic tissue. In such models some therapeutic strategies designed to reduce neutrophil accumulation or function have resulted in apparently beneficial effects. Although such findings are encouraging, interventions into these pathological processes using specific molecular targets will require greater understanding of specific mechanisms. Current evidence indicates that potential sites of therapeutic intervention will be found in pathways leading to complement activation, generation of lipid-derived mediators, adhesion of neutrophils to endothelial cells and cardiac myocytes, and activation of neutrophil secretory processes releasing, for example, proteolytic enzymes and reactive oxygen. Understanding the dynamic interplay between the mediators, adhesion pathways, and secretory processes that results in myocardial damage will allow a rational approach to controlling the detrimental inflammatory consequences of ischemia and reperfusion.

Abstract We make the case for Early Cretaceous transfer zones that segment the obliquely rifted Atlantic margin of southeastern Brazil. Our interpretation is based on published literature, Bouguer-corrected gravity, regional reflection seismic profiles, and well data. In the Santos and Campos basins, Neocomian rift architecture was strongly influenced by preexisting fabric and structures of the Late Proterozoic (Brasiliano orogeny). The Atlantic margin inherited an east-northeast-west-southwest orientation so that rifting was oblique to the margin. On a regional map of Bouguer-corrected gravity, a nearshore belt of positive anomalies correlates with an interpreted broad Moho uplift in the footwall of Neocomian extensional faults. Farther offshore, a second belt of positive anomalies correlates with a presalt ridge of eroded volcanic or basement anticlines covered by thin Aptian evaporites, interpreted as a failed spreading center. Intervening negative anomalies coincide with the main rift basin. All three belts show apparent offsets along linear zones trending west-northwest-east-southeast, which we interpret as transfer zones. The vergence of half rifts tends to change across transfer zones, compartmentalizing the rifted margin into subbasins. Our results have implications for the risks associated with distribution, maturation, and migration of hydrocarbons within the prolific Early Cretaceous lacustrine petroleum system of the Campos and Santos basins.

Abstract Prestack depth migration is the most glamorous step of seismic processing because it transforms mere data into an image, and that image is considered to be an accurate structural description of the earth. Thus, our expectations of its accuracy, robustness, and reliability are high. Amazingly, seismic migration usually delivers. The past few decades have seen migration move from its heuristic roots to mathematically sound techniques that, using relatively few assumptions, render accurate pictures of the interior of the earth. Interestingly, the earth and the subjects we want to image inside it are varied enough that, so far, no single migration technique has dominated practical application. All techniques continually improve and borrow from each other, so one technique may never dominate. Despite the progress in structural imaging, we have not reached the point where seismic images provide quantitatively accurate descriptions of rocks and fluids. Nor have we attained the goal of using migration as part of a purely computational process to determine subsurface velocity. In areas where images have the highest quality, we might be nearing those goals, collectively called inversion. Where data are more challenging, the goals seem elusive. We describe the progress made in depth migration to the present and the most significant barriers to attaining its inversion goals in the future. We also conjecture on progress likely to be made in the years ahead and on challenges that migration might not be able to meet.

This paper presents an overview and a detailed description of the key logic steps and mathematical-physics framework behind the development of practical algorithms for seismic exploration derived from the inverse scattering series.

Abstract Constant angle projections of seismic sections can be designed to provide maximum discrimination between fluids or lithologies. The optimum projection for a noise-free, isotropic environment can be obtained using an extension to the elastic impedance concept, which itself is an extension of acoustic impedance (AI) to nonzero angles of incidence. To achieve this, we modify the definition of elastic impedance (EI) beyond the range of physically meaningful angles by substituting tanχ for sin2θ in the two-term reflectivity equation. The primary variable now becomes χ rather than θ. We allow it to vary between −90° and +90°, which gives an extension of EI for any combination of intercept and gradient. We refer to this form of elastic impedance as extended elastic impedance (EEI). In this paper we demonstrate that EEI can be tuned using different χ values to be approximately proportional to a number of elastic parameters, and we give EEI expressions for shear impedance (SI), bulk modulus, shear modulus, Lamé's parameter, and Vp/Vs. This leads to the identification of different areas of EEI space that tend to be optimum for fluid and lithology imaging. Having identified an appropriate χ value, the equivalent seismic section can be obtained from combinations of intercept and gradient stacks from routine AVO processing.

Abstract Historically, seismic migration has been the practice (science, technology, and craft) of collapsing diffraction events on unmigrated records to points, thereby moving (“migrating”) reflection events to their proper locations, creating a true image of structures within the earth. Over the years, the scope of migration has broadened. What began as a structural imaging tool is evolving into a tool for velocity estimation and attribute analysis, making detailed use of the amplitude and phase information in the migrated image. With its expanded scope, migration has moved from the final step of the seismic acquisition and processing flow to a more central one, with links to both the processes preceding and following it. In this paper, we describe the mechanics of migration (the algorithms) as well as some of the problems related to it, such as algorithmic accuracy and efficiency, and velocity estimation. We also describe its relationship with other processes, such as seismic modeling. Our approach is tutorial; we avoid presenting the finest details of either the migration algorithms themselves or the problems to which migration is applied. Rather, we focus on presenting the problems themselves, in the hope that most geophysicists will be able to gain an appreciation of where this imaging method fits in the larger problem of searching for hydrocarbons.

Abstract The structure of the Pannonian basin is the result of distinct modes of Mid-Late Miocene extension exerting a profound effect on the lithospheric configuration, which continues even today. As the first manifestation of extensional collapse, large magnitude, metamorphic core complex style extension took place at the beginning of the Mid-Miocene in certain parts of the basin. Extrapolation of the present-day high heat flow in the basin, corrected for the blanketing effect of the basin fill, indicates a hot and thin lithosphere at the onset of extension. This initial condition, combined with the relatively thick crust inherited from earlier Alpine compressional episodes, appears to be responsible for the core complex type extension at the beginning of the syn-rift period. This type of extension is well documented in the northwestern Pannonian basin. Newly obtained deep reflection seismic and fission-track data integrated with well data from the southeastern part of the basin suggests that it developed in a similar fashion. Shortly after the initial period, the style of syn-rift extension changed to a wide-rift style, covering an area of much larger geographic extent. The associated normal faults revealed by industry reflection seismic data tend to dominate within the upper crust, obscuring pre-existing structures. However, several deep seismic profiles, constrained by gravity and geothermal modeling, image the entire lithosphere beneath the basin. It is the Mid-Miocene synrift extension which is still reflected in the structure of the Pannonian lithosphere, on the scale of the whole basin system. The gradually diminishing extension during the Late Miocene/Pliocene could not advance to the localization of extension into narrow rift zones in the Pannonian region, except some deep subbasins such as the Makó/Békés and Danube basins. These basins are underlain coincidently by anomalously thin crust (22–25 km) and lithosphere (45–60 km). Significant departures (up to 130 mW m −2 ) from the average present-day surface heat flow ( c. 90 mW m −2 ) and intensive Pliocene alkaline magmatism are also regarded as evidence for the initiation of two newly defined narrow rift zones (Tisza and Duna) in the Pannonian basin system. However, both of these narrow rifts failed since the final docking of the Eastern Carpathians onto the European foreland excluded any further extension of the back-arc region.

Abstract During the past decade, the size of 3D seismic data volumes and the number of seismic attributes have increased to the extent that it is difficult, if not impossible, for interpreters to examine every seismic line and time slice. To address this problem, several seismic facies classification algorithms including k-means, self-organizing maps, generative topographic mapping, support vector machines, Gaussian mixture models, and artificial neural networks have been successfully used to extract features of geologic interest from multiple volumes. Although well documented in the literature, the terminology and complexity of these algorithms may bewilder the average seismic interpreter, and few papers have applied these competing methods to the same data volume. We have reviewed six commonly used algorithms and applied them to a single 3D seismic data volume acquired over the Canterbury Basin, offshore New Zealand, where one of the main objectives was to differentiate the architectural elements of a turbidite system. Not surprisingly, the most important parameter in this analysis was the choice of the correct input attributes, which in turn depended on careful pattern recognition by the interpreter. We found that supervised learning methods provided accurate estimates of the desired seismic facies, whereas unsupervised learning methods also highlighted features that might otherwise be overlooked.

Abstract It is a generally recognized fact that there is a certain similarity between structural contours and gravity contours. This is particularly true in the case of flat, shallow structures. In fact, in the limit, in the case of a surface distribution of matter, the gravity picture very near this surface becomes identical with the surface density distribution aside from a constant factor.

Abstract Converted-wave processing is more critically dependent on physical assumptions concerning rock velocities than is pure-mode processing, because not only move-out but also the offset of the imaged point itself depend upon the physical parameters of the medium. Hence, unrealistic assumptions of homogeneity and isotropy are more critical than for pure-mode propagation, where the image-point offset is determined geometrically rather than physically. In layered anisotropic media, an effective velocity ratio gamma eff identical with gamma 22 /gamma 0 (where gamma 0 identical with V p /V s is the ratio of average vertical velocities and gamma 2 is the corresponding ratio of short-spread moveout velocities) governs most of the behavior of the conversion-point offset. These ratios can be constructed from P-wave and converted-wave data if an approximate correlation is established between corresponding reflection events. Acquisition designs based naively on gamma 0 instead of gamma eff can result in suboptimal data collection. Computer programs that implement algorithms for isotropic homogeneous media can be forced to treat layered anisotropic media, sometimes with good precision, with the simple provision of gamma eff as input for a velocity ratio function. However, simple closed-form expressions permit hyperbolic and posthyperbolic moveout removal and computation of conversion-point offset without these restrictive assumptions. In these equations, vertical traveltime is preferred (over depth) as an independent variable, since the determination of the depth is imprecise in the presence of polar anisotropy and may be postponed until later in the flow. If the subsurface has lateral variability and/or azimuthal anisotropy, then the converted-wave data are not invariant under the exchange of source and receiver positions; hence, a split-spread gather may have asymmetric moveout. Particularly in 3-D surveys, ignoring this diodic feature of the converted-wave velocity field may lead to imaging errors.

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2000Extended elastic impedance for fluid and lithology predictionAuthors: David N. WhitcombePatrick A. ConnollyRoger L. ReaganTerry C. RedshawDavid N. WhitcombeBP Amoco, Aberdeen, Patrick A. ConnollyBP Amoco, Sunbury, Roger L. ReaganBP Amoco, Houston, and Terry C. RedshawBP Amoco, Sunburyhttps://doi.org/10.1190/1.1815660 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Permalink: https://doi.org/10.1190/1.1815660FiguresReferencesRelatedDetailsCited byPressure and saturation changes estimated from extended elastic impedance properties using time-lapse seismic data: Enfield Field, NW AustraliaSergey Shevchenko and Wayne D. Pennington1 November 2022 | The Leading Edge, Vol. 41, No. 11Genesis and regularity of bright spots in Guantao Formation and its significance for oil and gas indicationJinhui Zhang, Zhijun Zhang, Hongtao Shen, and Hongbo Ding15 August 2022References19 January 2018Rock Physics Templates in AI-GI and Extended Elastic Impedance DomainsJuan-Mauricio Florez* and Stanislav Kuzmin19 August 2015Study of prestack elastic parameter consistency inversion methods29 December 2011 | Applied Geophysics, Vol. 8, No. 4Analysis on Factors of Elastic Impedance Based on Connolly FormulaGoing quantitative with 4D seismic analysisGeophysical Prospecting, Vol. 54, No. 3 SEG Technical Program Expanded Abstracts 2000ISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2000 Pages: 2484 publication data© 2000 Copyright © 2000 Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished Online: 04 Jan 2005 CITATION INFORMATION David N. Whitcombe, Patrick A. Connolly, Roger L. Reagan, and Terry C. Redshaw, (2000), "Extended elastic impedance for fluid and lithology prediction," SEG Technical Program Expanded Abstracts : 138-141. https://doi.org/10.1190/1.1815660 Plain-Language Summary PDF DownloadLoading ...

Anaerobic digestion (AD) involves a consortium of microorganisms that convert substrates into biogas containing methane for renewable energy. The technology has suffered from the perception of being periodically unstable due to limited understanding of the relationship between microbial community structure and function. The emphasis of this review is to describe microbial communities in digesters and quantitative and qualitative relationships between community structure and digester function. Progress has been made in the past few decades to identify key microorganisms influencing AD. Yet, more work is required to realize robust, quantitative relationships between microbial community structure and functions such as methane production rate and resilience after perturbations. Other promising areas of research for improved AD may include methods to increase/control (1) hydrolysis rate, (2) direct interspecies electron transfer to methanogens, (3) community structure-function relationships of methanogens, (4) methanogenesis via acetate oxidation, and (5) bioaugmentation to study community-activity relationships or improve engineered bioprocesses.

Abstract We interpret and document Late Cretaceous and Cenozoic reactivation of older structures on the obliquely rifted margin of southeastern Brazil, attributing them to the combined effects of far-field stresses and hot-spot activity. Our conclusions are based on current seismicity, digital topography, fission-track ages, gravity data, regional reflection seismic profiles, and well data. Our results have important implications for risk factors associated with deep-water exploration plays, especially the prolific Early Cretaceous lacustrine petroleum system of the Campos and Santos basins. Onshore, widespread crustal seismicity indicates a current transpressional stress regime. The Moho is 37-42 km deep, and neotectonic fault-block tilting has resulted in mountain ranges up to 2700 m high and extensive river capture. Based on fission-track data, the mountains were exhumed in the Cretaceous and Eocene. A series of Tertiary continental pull-apart basins, developed during Paleogene right-lateral transtension, became inverted during Neogene right-lateral transpression. Late Cretaceous-Paleogene alkaline intrusions, attributable to the Trindade hot spot, were emplaced along reactivated Neocomian strike-slip faults and transfer zones. Offshore, current seismicity is widespread across the continental margin. The locus of clastic fan deposition shifted during the Late Cretaceous and Tertiary because of onshore block faulting and drainage reorganization. Cretaceous sedimentary rocks were folded, tilted, eroded, and unconformably onlapped above an inferred Neocomian Moho uplift to produce an accentuated nearshore hinge line. Neocomian transfer zones were reactivated during ongoing sedimentation, accompanied by abundant volcanism and deep-seated folds attributed to lithospheric buckling. In the Campos area, a coastal salient was uplifted and turbidites were redeposited. In general, regional tilting resulted in thin-skinned deformation above Aptian salt.

A large proportion of rainfall in dryland ecosystems is intercepted by plant foliage and is generally assumed to evaporate to the atmosphere or drip onto the soil surface without being absorbed. We demonstrate foliar absorption of intercepted rainfall in a widely distributed, continental dryland, woody-plant genus: Juniperus. We observed substantial improvement in plant water status, exceeding 1.0 MPa water potential for drought-stressed plants, following precipitation on an experimental plot that excluded soil water infiltration. Experiments that wetted shoots with unlabeled and with isotopically labeled water confirmed that water potential responded substantially to foliar wetting, that these responses were not attributable to re-equilibration with other portions of the xylem, and that magnitude of response increased with water stress. Foliar absorption is not included in most ecological, hydrological, and atmospheric models; has implications for interpreting plant isotopic signatures; and not only supplements water acquisition associated with increases in soil moisture that follow large or repeated precipitation events, but also enables plants to bypass soil water uptake and benefit from the majority of precipitation events, which wet foliage but do not increase soil moisture substantially. Foliar absorption of intercepted water could be more important than previously appreciated, especially during drought when water stress is greatest.

“All rock masses are seismically anisotropic, but we generally ignore this in seismic acquisition, processing, and interpretation. The anisotropy nonetheless does affect data, in ways that limit the effectiveness with which we can use it, as long as we ignore it. This book, produced for use with the 2002 SEG/EAGE Distinguished Instructor Short Course, helps us to understand why this inconsistency between reality and practice has been so successful in the past and why it will be less successful in the future as we acquire better seismic data (especially including vector seismic data) and correspondingly higher expectations of it. This book helps us to understand how we can modify our practice to more fully realize the potential inherent in data through algorithms which recognize the fact of seismic anisotropy. Sections include 1: Physical Principles, 2: P-waves (Subsurface Imaging), 3: P-waves (Subsurface Physical Characterization), 4: S-waves, and 5: C-waves. (DISC on DVD, 751A, is also available.)”

Abstract Structures in the Cenozoic section of the U.S. Gulf of Mexico margin are thin-skinned, gravity-driven, and powered by the deposition of sediment on the shelf and upper slope. Deformation driven by sedimentation takes the form of salt displacement (including diapirism, salt withdrawal, and salt canopy formation), plus seaward gravity spreading and sliding. Lateral flow of salt gives rise to the emplacement of large-scale salt canopies of different ages. Lateral tectonic movement of both sediment and salt results in linked systems on a wide range of scales. We identify four structural provinces that contain distinct groups of structural elements believed to be genetically related: (1) far-eastern Gulf, in which no major Cenozoic deformation is seen; (2) eastern Gulf, defined mainly by a middle-late Miocene linked system of extension and contraction; (3) central Gulf, in which Oligocene updip extension was absorbed within a preexisting giant salt canopy; and (4) western Gulf, defined by several Paleogene-middle Miocene linked systems of extension and contraction. The ages and extents of each linked system match the major foci of sediment input to the shelf.

We simultaneously estimate fault probabilities, strikes, and dips directly from a seismic image by using a single convolutional neural network (CNN). In this method, we assume a local 3-D fault is a plane defined by a single combination of strike and dip angles. We assume the fault strikes and dips, respectively, are in the ranges of [0°, 360°] and [64°, 85°], which are divided into 577 classes corresponding to the situation of no fault and 576 different combinations of strikes and dips. We construct a 7-layer CNN to classify the fault strike and dip in a local seismic cube and obtain the classification probability at the same time. With the fault probability, strike and dip estimated at some seismic pixel, we further compute a fault cube (centered at the pixel) with fault features elongated along the fault plane. By sliding the classification window within a full seismic image, we are able to obtain a lot of overlapping fault cubes which are stacked to compute three full images of enhanced and continuous fault probabilities, strikes, and dips. To train the CNN model, we propose an effective and efficient workflow to automatically create 900 000 synthetic seismic cubes and the corresponding fault class labels. Although trained with only synthetic data sets, our CNN model can be applied to accurately estimate fault probabilities, strikes, and dips within field seismic images that are acquired at totally different surveys. With the estimated three fault images, we further construct fault cells that are represented as small 3-D squares, each square is colored by fault probability and oriented by fault strike and dip. We recursively link the fault cells by following the fault strikes and dips to finally construct fault skins, which are simple linked data structures to represent fault surfaces.