Agood 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 velocity-independent inversion techniques.

A fully cored sequence of Hesse Clay, Port Campbell Limestone and uppermost Gellibrand Marl in the onshore Otway Basin, southeastern Australia, offers new insight into the evolution of the middle Miocene Port Campbell Limestone. The Port Campbell Limestone comprises grey unconsolidated to semi-consolidated and rarely lithified bioclastic muddy carbonate sands in a stack of thin repetitive cycles within cycles of predominantly shoaling-upward character. A glauconitic band with a distinctive mollusc–echinoderm–bryozoan fauna provides a distinctive marker interval in the sequence. In mineralogy, the Port Campbell Limestone is predominantly calcite with traces of remnant aragonite in muddier low-permeability sands, and with dolomitic zones in permeable intervals. The small non-carbonate component of the Port Campbell Limestone is between 3 and 15 wt% and comprises quartz silt with minor clay, feldspar and mica. Dissolution overprints are prominent throughout the carbonate sequence. Three distinct geochemical signatures of provenance are evident in the Port Campbell Limestone sequence, including possible volcanogenic contributions with felsic sources. Foraminifera are common and generally well preserved. Foraminiferal data suggest a depositional transition from outer shelf conditions in the Gellibrand Marl at ca 15 Ma to middle shelf environments in the lower part of the Port Campbell Limestone during the Middle Miocene Climatic Optimum (MMCO) at ca 14.24 Ma. Shallowing after 14 Ma indicates variable paleodepths of <70 m during and following the end of the Middle Miocene Climatic Transition (MMCT) at ca 13.2 Ma when the sequence was emergent for a brief but undetermined period, corresponding with sharp changes in geochemical ratios. Observed cyclicity in these mid-shelfal, cold-water carbonates is strongly correlated with orbital forcings—eccentricity and obliquity. Sedimentation rates determined from cyclostratigraphic analysis indicate 4–6 cm/kyr at the end of the MMCO, diminishing to 1.5–3 cm/kyr during the MMCT and the subsequent accumulation of the Port Campbell Limestone.

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.

The primary objective of seismic exploration in a hard rock environment is the detection of heterogeneities such as fracture zones, small-scale geobodies, intrusions, and steeply dipping structures that are often associated with mineral deposits. Prospecting in such environments using seismic-reflection methods is more challenging than in sedimentary settings due to lack of continuous reflector beds and predominance of steeply dipping hard rock formations. The heterogeneities and “fractal” aspect of hard rock geologic environment produce considerable scattering of the seismic energy in the form of diffracted waves. These scatterers can be traced back to irregular and often “sharp-shaped” mineral bodies, magmatic intrusions, faults, and complex and heterogeneous shear zones. Due to the natural lack of reflectors and abundant number of diffractors, there are only a few case studies of diffraction imaging in hard rock environments. There are almost no theoretical models or field examples of diffraction imaging in prestack domain. We have filled this gap by applying a 3D prestack diffraction imaging method to image point diffractors. We calculated the diffractivity by computing the semblance of seismic data along diffraction traveltime curves in the prestack domain. The performance of the method is evaluated on a synthetic case and a field seismic data set collected over the Kevitsa mineral deposit in northern Finland. The high-resolution results obtained by the application of prestack diffraction imaging suggest that diffractivity is a robust attribute that can be used in addition to other seismic attributes for the interpretation of seismic data in hard rock environment.

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.

In many parts of the world, exploration for mineral deposits is moving progressively but persistently to greater depths, relying on knowledge gained from previous exploration campaigns and on new exploration tools and techniques used to guide deep and costly boreholes to most suitable targets