We discuss the problem of creating low frequency models for inversion and suggest a simple facies trend-based method which reduces reliance on prior laterally-varying assumptions about the heterogeneity of native reservoir properties. In our example, we were able to identify key hydrocarbon-bearing facies from inversions and tie them accurately to the corresponding petrophysical facies derived from logs
The oil-bearing fractured granite basement rocks are a very important and complicated hydrocarbon reservoir in offshore Vietnam. In this paper, we present a case study of improving the fracture imaging in the Cuu Long Basin offshore Vietnam through Broadband technology, which not only provide great uplift in the low frequency penetration but also make it possible to incorporate TTI/HTI anisotropy inside granite basement. We will review the issues with conventional data and present the new approach, the result and its importance as to the interpretation for drilling.
Model-based water-layer demultiple (MWD) is an effective method for attenuating water-layer-related multiples (WLRMs), especially in shallow water environments. Regular 3D MWD use regularized common-offset cubes for both shot- and receiver-side multiples. We propose a selective-input adaptation of the regular 3D MWD workflow that uses both regularized shot gathers and regularized cubes as input and prioritizing the data selected for model prediction; data is first selected from regularized shot gathers and then regularized cubes. We demonstrate with field data that this selective-input MWD works better than regular MWD, especially for high-order multiple reverberations.
Blended acquisition of ocean bottom node (OBN) surveys may provide important time savings when the survey duration is tightly constrained. We present a method that focuses on the deblending of OBN data recording two simultaneous sources in the Gulf of Mexico. By knowing the respective shot time interval and shot location of two or more sources in the continuous recording data, we can extract the common receiver gathers of each source and deblend them using an iterative coherency-enhancement and subtraction method. In this method, the initial energy model is estimated in the Tau-P domain, and the noise model is estimated adaptively in the curvelet domain. Results show little signal leakage after three iterations of separation.
The scope of this paper is to illustrate how surface-consistent deconvolution operators can help to image the shallow subsurface on land data. Two case studies from modern, dense, wide-azimuth surveys recently acquired in Oman are presented. The predictive deconvolution operators were computed from an advanced simultaneous inversion of surface consistent scalars and autocorrelations. Source and receiver operator volumes were compared to the migrated stack of primary reflections. A significant improvement in the imaging of the shallow layers was achieved. Some structures that were almost invisible on the migrated stack were revealed and the shallow reflectivity was recovered in undershoot areas. These high resolution reflectivity volumes can be used as a guide for velocity model building of the shallow subsurface or as an input to internal or surface multiple modelling.
Anisotropic parameter estimation is very challenging for new exploration areas where there are no wells. In an offshore survey of over 3000 km2 in the west of Africa, we used surface seismic data in a non-linear tomographic inversion to simultaneously estimate migration velocity and anellipticity. Although a blank model of anisotropic parameters was used as input model, the joint tomography created an anellipticity model which followed the geological structures. It was one of the first projects where the non-linear tomography achieved to build an anisotropic model which was geologically consistent and minimized residual moveout.
Reverse Time Migration of Multiples (RTMM) adapted for OBN data with examples from deepwater Gulf of Mexico.
Standard joint AVO inversion of PP and PS seismic data rely on a registration process beforehand to align PP and PS data in a common time domain. This is a difficult step prone to error that may deteriorate the inversion results. We present a new method to jointly invert PP and PS data without prior registration by integrating the travel times as well as the amplitudes in a model-based inversion. Including the travel times brings extra constraints on the VP/VS ratio and therefore helps the inversion converge. This new method is demonstrated on a shale gas data example and shows better results than PP inversion and standard joint inversion.
The high costs associated with hydrocarbon exploration in deepwater have led to an increased business demand for acquisition and processing of high-resolution broadband seismic data. In this paper, we review our experience of working on the Shell Sandman 3D survey, which was acquired using variable-depth streamers and synchronized multi-level sources. We focus on the key factors that influence the surface seismic temporal resolution and the technologies that provide solutions to these challenges: (1) source deghosting using source designature with near-field hydrophone data; (2) receiver deghosting using the 3D deghosting algorithm; and (3) compensation for the Earth absorption using centroid frequency shift Q tomography (FS-QTOMO) and QPSDM. The extra-wide bandwidth obtained from these processes provides a final image with detailed resolution that enhances quantitative characterization, not only for shallow geo-hazards but also for resolving relatively thin reservoirs in the deep section. Therefore, we can conclude that broadband seismic methodologies coupled with advanced seismic processing techniques, provide an effective solution for generating high-resolution seismic images, especially in challenging areas.