Velocity-independent estimation of kinematic attributes in vertical transverse isotropy media using local slopes and predictive painting

© 2016 Society of Exploration Geophysicists. A good seismic velocity model is required for many routine seismic imaging techniques. Velocity model building from seismic data is often labor intensive and time consuming. The process becomes more complicated by taking nonhyperbolic traveltime estimations into account. An alternative to the conventional time-domain imaging algorithms is to use techniques based on the local event slopes, which contain sufficient information about the traveltime moveout for velocity estimation and characterization of the subsurface geologic structures. Given the local slopes, there is no need for a prior knowledge of a velocity model. That is why the term "velocity independent" is commonly used for such techniques. We improved upon and simplified the previous versions of velocity-independent nonhyperbolic approximations for horizontally layered vertical transverse isotropy (VTI) media by removing one order of differentiation with respect to offset from the imaging kinematic attributes. These kinematic attributes are derived in terms of the local event slopes and zero-offset two-way traveltime (TWTT). We proposed the use of predictive painting, which keeps all the attributes curvature independent, to estimate the zero-offset TWTT. The theoretical contents and performance of the proposed approach were evaluated on synthetic and field data examples. We also studied the accuracy of moveout attributes for shifted hyperbola, rational, three-parameter, and acceleration approximations on a synthetic example. Our results show that regardless of the approximation types, NMO velocity estimate has higher accuracy than the nonhyperbolicity attribute. Computational time and accuracy of the inversion of kinematic attributes in VTI media using our approach were compared with routine/conventional multiparameter semblance inversion and with the previous velocityindependent inversion techniques

Coherent interferometry migration for hard rock diamond drill-bit seismic

We use the direct wave interferometry migration with coherency measurement to image the diamond drill-bit. The success of such imaging can prove if the direct waves from the drill-bit can be detected. The drilling signals usually contain strong narrow band interference noises. We suggest to use interferometry by deconvolution for migration, which widens the cross spectrum, hence the weak coherent features can be better observed. Additionally, we suggest to integrate coherent measurement of semblance or Multiple Signal Classification (MUSIC) into the algorithm in order to detect weak drill-bit signal. We test both methods with a synthetic and a diamond drill-bit seismic-while-drilling (SWD) field data. MUSIC coherency shows relatively better spatial resolution in contrast to semblance method. It also demonstrates better detectability of weak signal than summation and semblance. Our field SWD data also indicates that the interferometry migration can image the diamond drill-bit with appropriate survey parameters, and the MUSIC method achieves a high spatial resolution

Wavefronts and Rays As Characteristics and Asymptotics

This textbook - incorporated with many illuminating examples and exercises - is aimed at graduate students of physical sciences and engineering. The purpose is to provide a background of physics and underlying mathematics for the concept of rays, filling the gap between mathematics and physics textbooks for a coherent treatment of all topics. The authors’ emphasis and extremely good presentation of the theory of characteristics, which defines the rays, accentuate the beauty and versatility of this theory. To this end, the rigour of the formulation - by a pure mathematician’s standards - is downplayed to highlight the physical meaning and to make the subject accessible to a wider audience. The authors describe in detail the theory of characteristics for different types of differential equations, the applications to wave propagation in different types of media, and phenomena such as caustics

Application of the velocity-less prestack time migration to the 2D marine line

Information about seismic velocities is an important and integral part of the seismic imaging process. The task of defining the velocity model is usually quite difficult, especially in regions with a complex geological structure and in new prospecting areas. One emerging way of obtaining a velocity model is to apply a “velocity-less” prestack time migration to the data. Here we describe an application of the velocity-less prestack time migration technique to the real a dataset of a marine 2D seismic line from the North West shelf of Australia and show a comparison of the results with Kirchhoff prestack time migration. The presented algorithm is based on an estimation of local event slopes (horizontal slownesses) in common-shot and common-receiver gathers. These attributes allow us to derive the complete information to be able to construct a time migrated image. The output of the algorithm is three parameters: migration velocity, vertical traveltime and horizontal position of the migrated reflection point. Herein we use the obtained migration velocities as an input velocity model for the Kirchhoff time migration. This experiment on the real dataset demonstrates the promising practical effectiveness of the presented velocity-less prestack time migration algorithm

Oriented surface passive seismic location using local slopes

A common acquisition scenario in microseismic monitoring is the deployment of large areal receiver arrays at or near the surface. This recording geometry has the advantage of providing coverage of the source's focal hemisphere as well as characterization of the arrival time moveout curve; however, the accuracy of many location techniques applied to these data sets depends on the accuracy of the depth velocity model provided prior to location. We have developed a simple oriented time-domain location technique so that full knowledge of the velocity model is not required a priori. The applicability of the technique is limited to horizontally layered models and also to models with dipping interfaces of small angles; however, this restriction is acceptable in many unconventional reservoirs. Implementation of the technique includes three steps: (1) smoothing of the observed time arrivals by fitting a hyperbolic moveout curve with a broad set of constraints, (2) updating and restricting the constraints using a local-slopes-based location workflow, and (3) estimation of the focal coordinates of passive sources using the updated constraints for the final least-squares fitting of the moveout curves. We have tested the performance of the proposed technique on several 2D examples and a 3D field data set. The results from synthetic examples suggest that, despite the assumption of the method that the arrival moveout can be modeled using a constant effective velocity, a reliable event location is achieved for layered models without considerable lateral heterogeneities. Our tests on the field data set find that the focal point coincides with a previously derived estimate of the source location. To assess the uncertainty of the proposed technique, bootstrap statistics was also used and applied to the field data set

Estimation of elastic anisotropy from three-component ultrasonic measurements using laser Doppler interferometry

Ultrasonic measurements using laser Doppler interferometry (LDI) have been reported to provide robust estimates of elastic anisotropy of rock samples. In this approach, an ultrasonic wave is emitted by a piezo-electric source and detected by the LDI, which can be configured to measure three components of the particle velocity in a very small area (~1 mm2) of the sample. Repeating these measurements for a dense array of points on the sample's surface gives a distribution of traveltimes and polarisation fields on the surface. Anisotropy is then obtained by inverting these fields using analytical expressions or numerical algorithms for computing phase and group velocities. The existing implementation of this approach involves the inversion of direct compressional (P) and shear (S) wave arrivals only. A previous study showed that this approach produces stable results if only a small range of source-receiver offsets is included in the inversion. This limitation resulted in a relatively large uncertainty of the result. This uncertainty can be reduced by inverting the entire traveltime field. To this end, we numerically simulate the wavefield in the sample. Analysis of the computed wavefield reveals the presence of P- and S-waves as well as a critically refracted converted PS-wave. Hence, the inversion of the entire traveltime field must include these three waves. We implement this inversion using global minimisation of the traveltime misfit function, coupled with numerical computation of ray velocities. Application of this algorithm to laboratory LDI measurements on a transversely isotropic phenolic sample provides stable anisotropy estimates consistent with previous studies

Estimation of seismic attenuation and prediction of VTI anisotropy parameters from VSP and log data: a case study from the Middle East

© 2016, Saudi Society for Geosciences. Quantitative interpretation of seismic data depends upon the amplitude analysis of reflected waves. However, the quality of the image obtained can be significantly affected by attenuation and anisotropy in the overburden. Therefore, the insights into the magnitude, sources and spatial distribution of these parameters may prove to be substantial for improving the quality of seismic image and reservoir characterisation. Both seismic vertical transverse isotropy (VTI) anisotropy and scattering attenuation could be caused by the layering. In order for these phenomena to play a major role, strong elastic contrasts between them are needed. In this paper, we present the case study from a typical setting in the Middle East where such a contrast between stiff carbonates and relatively soft siliciclastic sediments significantly deteriorates the quality of the seismic image. Vertical seismic profiling (VSP) and log data from one of the wells in the region are used to demonstrate this phenomenon. Apparent attenuation from VSP data is estimated using a modified centroid frequency shift method. The log data for seismic forward modelling is used in order to show that scattering could be a significant contributor to the apparent attenuation. In addition, by using both Backus averaging and synthetic walk-away VSP data analysis, we demonstrate that the same layering can be responsible for a significant TI anisotropy

Oriented prestack time migration using local slopes and predictive painting in the common-source domain for planar reflectors

Seismic imaging techniques often require an input velocity model. Velocity analysis is one of the most critical stages in seismic data processing. Standard ways to find the velocity model from seismic data in the time domain are constant velocity stack and semblance velocity analysis that may be time consuming and labor intensive. Oriented/velocity-less imaging using local event slopes is an alternative to the conventional imaging techniques. In some previous oriented techniques, seismic data must be sorted in two different domains, whereas seismic data are not always available in both domains and the use of interpolation is inevitable in such cases. Other methods are developed in terms of the higher order derivatives of traveltime with respect to offset, whereas estimation of the higher order derivatives is difficult to achieve with the required accuracy. We addressed the limitations by developing an oriented local slope based prestack time migration technique in only one domain: the common-source domain. The migration technique is developed for reflectors with small curvature. In the proposed approach, the need for the estimation of higher order derivatives is replaced by a point-to-point mapping of seismic data using the predictive painting technique. The theoretical contents of the proposed technique are tested on a simple synthetic data example and applied to a field data set

Diffraction Imaging for Exploration of Seafloor Massive Sulfide Deposits - Case Study Solwara 1 Site

Extraction of mineral resources on land is becoming increasingly difficult. Recent discoveries of seafloor massive sulfides (SMS), which host significant amount of mineral commodities, appear as a new potential offshore mining sector. The marine 3D seismic exploration survey was carried out over a seafloor massive sulfide deposit at Solwara 1 site in the Bismark Sea, west of New Ireland, Papua New Guinea. Despite the fact that all prospective sulfide mineralization zones are concentrated close to the seafloor, knowledge of internal deep geological structures of seabed volcanic ridges and their genesis is important for understanding of the formation of mineral deposits. The steered migration with diffractions was applied to 3D seismic volume to emphasize deep geological structures and to enhance the signal to noise ratio of the seismic images. The post-stack steered migration utilizes coherency attributes obtained by a diffraction imaging algorithm in 3D to weight or steer the main Kirchhoff summation. The application of the steered migration to the investigation of the modern subduction zone at the Solwara 1 mine enhanced the signal to noise ratio of the final migrated images and helped to understand the formation mechanisms of seabed deposits in the region by exploring the deep structures