Subsurface Imaging with Reverse Vertical Seismic Pro les

A novel imaging process, referred to as vector image isochron (VII) migration, is specifically designed to reduce artifacts caused by arrays with limited apertures. By examining the assumptions behind generalized Radon transform (GRT) migration, a new approach is found which identities and suppresses array artifacts, based on the array geometry and the migration earth model. The new method works in four steps: 1) The conventional image is broken down according to the orientation of imaged planes within the image space, forming a vector image of the earth; 2) the earth model and the geometry of the arrays are used to derive vector image isochrons, which define the shape of reflection events in the vector image space; 3) the vector image is transformed by summing along the isochrons so that it depends on subsurface location and reflector orientation, rather than imaged plane orientation. This process is referred to as vector image isochron (VII) transformation; and 4) the transformed vector image is collapsed to a scalar image by summing over reflector orientations. The VII imaging method is derived in both 2D and 3D with the assumption that at least one of the arrays, source or receiver, is oriented horizontally. The surface array can have any distribution along the surface. The other array can have any orientation, although in this paper it will be assumed to be either another surface array or a vertically oriented downhole array. Downhole surveys in deviated wells, or in multiple wells, can be imaged with VII migration, at the likely cost of more computation time. The VII imaging method is tested on field data acquired in 1998 by MIT and several industry partners. The dataset is a 3D reverse vertical seismic profile (RVSP) over a hydrocarbon-bearing pinnacle reef in the northern Michigan reef trend. The survey exhibited two features of note: 1) A new, strong, downhole vertical vibrator, and 2) a random distribution of surface receiver locations. Due to adverse conditions, a large portion of the surface spread had to be abandoned. The reduced spatial coverage presents a challenge to the new migration method, but also limits the extent of the migrated image, precluding an evaluation of the reflectiveness of the random receiver spread. The limited nature of the receiver array also causes artifacts in the image which resemble migration "smiles". These are partially suppressed by limiting the dip aperture of the migration, but this also limits the reflector dips that can be imaged. The new VII imaging scheme, on the other hand, removes the artifacts without diminishing dipping reflectors. The VII images show more continuity along reflectors than images made with the conventional method

Finite Difference Modeling of Attenuation and Anisotropy

A nite difference scheme which includes the effects of attenuation and anisotropy is tested for seismic reflection and borehole acoustic models. The validity of the scheme is established using a 3D homogenous isotropic model to compare results to the discrete wavenumber method. Three models are then investigated. First, reflections from a 3D at layered model are analyzed for o set and azimuthal dependence of attenuation. Second, discrete fractures are included in a 2D at layered model to examine their effect on reservoir top and bottom reflections. Third, a 3D borehole in both hard and soft formations is modeled to test the effect of attenuation on guided waves.Massachusetts Institute of Technology. Earth Resources LaboratoryUnited States. Dept. of Energy (Grant DE-FC26-02NT15346)Eni S.p.A. (Firm

Sensitivity Analysis Of Amplitude Variation With Offset (Avo) In Fractured Media

The variation in seismic P to P reflection amplitude with offset (AVO) caused by a system of fractures embedded in an isotropic background is investigated. Additionally. a sensitivity analysis of AVO parameters with respect to the fracture system parameters is made. The fracture system is assumed to be aligned vertically or horizontally and can be gas filled or fluid filled. Elastic constants are calculated by using formulations of Schoenberg (1988). From the elastic constants, the reflection amplitude as a function of angle is calculated using equations from Ruger (1997). Theoretical results for a single interface between fractured and unfractured media, both with and without lithology change, show opportunities for extraction of crack density information from seismic P-wave data collected in fractured geothermal or hydrocarbon reservoirs. For vertically oriented fractures, wide angle data (> 30°) is crucial for the estimation of fracture parameters.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation Consortiu

Frequency Dependence Of Seismic Data From Nigeria: Preliminary Results

Seismic data from the Niger Delta is used to test processing sequences involved in prestack and poststack amplitude and frequency analysis of marine seismic data. Water bottom reverberations are found to present a formidable challenge in poststack frequency and amplitude analysis. However, reflectors with anomalously high amplitudes show low frequency content both in deconvolved poststack data and in the near offsets of prestack data with no deconvolution, which agrees with results in the literature. Lack of detailed knowledge of the lithology prevents investigation of the physical nature of the amplitude and frequency variations.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation Consortiu

3-D Finite Di erence Modeling for Borehole and Reservoir Applications

ERL's in-house nite difference code (Krasovec et al., 2003) has undergone several upgrades in the past year. Most notably, a stretched grid can now be used to greatly reduce the amount of RAM memory needed by certain types of models. Improvements have been made in the GUI front end, allowing more freedom and ease in building the model, source or source array, and receiver array. The finite difference code has contributed to several different research projects at ERL in the past year. A few of these projects, including borehole seismics, reservoir delineation, and source mechanics, are shown in this report.Massachusetts Institute of Technology. Earth Resources LaboratoryMassachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu

Fracture Detection using Amplitude versus Offset and Azimuth Analysis of a 3D P-wave Seismic Dataset and Synthetic Examples

Amplitude versus offset (AVO) analysis of seismic reflection data has been a successful tool in describing changes in rock properties along a reflector. This method is extended to azimuthal AVO (AVOA) in order to characterize vertically aligned fractures within a reservoir, which can be important fluid migration pathways. AVOA analysis is performed on synthetic data using a least squares inversion method to investigate the effects of varying acquisition geometry, amount of noise, and fracture properties. These tests show that it is possible to detect the fractured layer and determine the fracture strike orientation under typical acquisition conditions. This method is also applied to field data collected during an Ocean Bottom Cable (OBC) survey. These data include a broad offset-azimuth range, which is important for the AVOA analysis. The fracture location and strike orientation recovered from the field data analysis are well correlated with borehole information from this area. Based on an understanding of AVOA behavior under synthetic conditions, this technique provides an effective methodology for describing the spatial variability of a fractured reservoir using 3D seismic data.Eni S.p.A. (Firm)United States. Dept. of Energy (Grant number DE-FC26-02NT15346)Massachusetts Institute of Technology. Earth Resources Laborator

Crustal and uppermost mantle structure of Caucasus and surrounding regions

A 3-D P-wave velocity model is developed for the crust and uppermost mantle of Caucasus and the surrounding area by applying the tomographic method of Zhao et al. using 300 000 high-quality P-wave first arrivals from 43 000 events between 1964 and 2005. This tomographic method can accommodate velocity discontinuities such as the Moho in addition to smooth velocity variations. The spatial resolution is 1°×1° in the horizontal direction and 10 km in depth. The velocity images of the upper crust correspond well with the surface geology. Beneath the southern Caucasus high velocity anomalies are found in the middle crust and low velocity anomalies are found in the uppermost mantle. Relatively low Pn velocities are located under the Lesser Caucasus, eastern Turkey, and northern Iran. Higher Pn velocities occur under the eastern portion of the Black Sea and the southern Caspian Sea, and also extend into the eastern edge of Azerbaijan. Tomographic model significantly reduces the travel-time residuals.United States. Defense Threat Reduction Agency (Contracts DE-AC-52-04NA25612, NNSA-03-2S2 and W-7405-ENG-483)Chinese Academy of Sciences (Fund KJCX2-EW-121

Features of the opportunistic behaviour of the marine bacterium marinobacter algicola in the microalga ostreococcus tauri phycosphere

Although interactions between microalgae and bacteria are observed in both natural environment and the laboratory, the modalities of coexistence of bacteria inside microalgae phycospheres in laboratory cultures are mostly unknown. Here, we focused on well-controlled cultures of the model green picoalga Ostreococcus tauri and the most abundant member of its phycosphere, Marinobacter algicola. The prevalence of M. algicola in O. tauri cultures raises questions about how this bacterium maintains itself under laboratory conditions in the microalga culture. The results showed that M. algicola did not promote O. tauri growth in the absence of vitamin B12 while M. algicola depended on O. tauri to grow in synthetic medium, most likely to obtain organic carbon sources provided by the microalgae. M. algicola grew on a range of lipids, including triacylglycerols that are known to be produced by O. tauri in culture during abiotic stress. Genomic screening revealed the absence of genes of two particular modes of quorum-sensing in Marinobacter genomes which refutes the idea that these bacterial communication systems operate in this genus. To date, the ‘opportunistic’ behaviour of M. algicola in the laboratory is limited to several phytoplanktonic species including Chlorophyta such as O. tauri. This would indicate a preferential occurrence of M. algicola in association with these specific microalgae under optimum laboratory conditions

A Deep Learning based Pipeline for Efficient Oral Cancer Screening on Whole Slide Images

Oral cancer incidence is rapidly increasing worldwide. The most important determinant factor in cancer survival is early diagnosis. To facilitate large scale screening, we propose a fully automated pipeline for oral cancer detection on whole slide cytology images. The pipeline consists of fully convolutional regression-based nucleus detection, followed by per-cell focus selection, and CNN based classification. Our novel focus selection step provides fast per-cell focus decisions at human-level accuracy. We demonstrate that the pipeline provides efficient cancer classification of whole slide cytology images, improving over previous results both in terms of accuracy and feasibility. The complete source code is available at https://github.com/MIDA-group/OralScreen.Comment: Accepted to ICIAR 202