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Wenchang Field in the South China Sea contains a well-developed fault system, resulting in complex subsurface geology. Imaging the complex fault system plays an important role in hydrocarbon exploration in this area since the fault system forms a link between the source rocks and reservoirs. However, it is difficult to obtain a high-quality depth image of the fault system due to the effects of complex velocity and seismic absorption. Inaccurate depth velocities lead to fault shadows and structure distortions at the target zone. Absorption effects further deteriorate seismic imaging as they cause amplitude attenuation, phase distortion, and resolution reduction. We demonstrate how a combination of high-resolution depth velocity modeling and Q imaging work together to resolve these challenges. This workflow provides a step change in image quality of the complex fault system and targeted source rocks at Wenchang Field, significantly enhancing structure interpretation and reservoir delineation. A couple of commercial discoveries have been made, and several other potential hydrocarbon reservoirs have been identified based on the reprocessed data, which reveal new hydrocarbon potential in this region.

A new broadband wide-azimuth towed-streamer (WATS) survey was acquired to better resolve reservoir compartments in a shallow-water region of the East China Sea. To offset the shortcomings of narrow-azimuth acquisition along the strike direction, two vessels were added side-by-side as additional source vessels to form the WATS acquisition geometry for this survey. This WATS acquisition was much sparser than typical WATS surveys used in deepwater environments due to its one-sided configuration. The combination of sparse acquisition, shallow water, and deep targets set the challenge of how to optimally reveal the potential of side-gun data to improve the final image. Three-dimensional effects and severe aliasing in the crossline direction pose significant challenges for side-gun data processing. We present a comprehensive workflow to resolve these challenges consisting of 3D deghosting, 3D model-based water-layer demultiple, 3D surface-related multiple elimination, and 4D regularization for sparse and shallow-water wide-azimuth data. A tilted orthorhombic velocity model is built with better constraints from the wide-azimuth data, leading to improved fault positioning and imaging. Side-gun data clearly enhance the final target reservoir image and tie better with well data due to improved illumination. A new channel is discovered based on interpretation from the inverted VP/VS, explaining the previous incorrect prediction for one failed well that was drilled into a thinner and shallower channel unconnected to the main reservoir. An analysis of the impact of side-gun data from different offsets and azimuths shows that better azimuthal distribution within middle offset ranges had a more significant impact than far offsets in the final image of this survey. This information provides valuable reference in similar geologic conditions for future acquisition designs.

In this paper, we present a reprocessing case study that applied the latest processing technologies to improve the seismic imaging inside the granite basement reservoir. The highlight of this effort is the application of the latest Controlled Beam Migration (CBM) technology, and a stack sweep method for updating velocity inside the basement.

Summary In this paper, we present the first variable-depth streamer seismic survey offshore China. The objective of the broadband survey is to obtain high resolution and high fidelity seismic data in order to better assess the exploration potential in the region. The acquisition and imaging were done on two separated blocks. The initial result is encouraging, and shows the benefit of broadband data to interpretation.

In this paper we present a case history of multi-azimuth 3D PSDM processing. The datasets show strong HTI as well as VTI anisotropy. We show the processing workflow with emphasis on the construction of an imaging velocity model that correctly represents the orthorhombic anisotropy and short-wavelength velocity variations. The PSDM image is improved over earlier processings.

Abstract In early 2008, Chevron Thailand and partners contracted CGGVeritas to reprocess forty of their key 3D seismic surveys in the Pattani Basin, Gulf of Thailand, with a combined area of more than 15,000 sq.km. The 40 surveys had been acquired over a period of 26 years (1979 to 2005) with variable acquisition parameters, geometries and azimuths, which resulted in variable amplitude and frequency content and variable fold or sampling density. The benefit of the reprocessing is enormous, but the technical challenges are just as great. In this paper we present some of the technical challenges and solutions in the data processing work. A) Detecting and correcting navigation errors in vintage data. Old surveys tend to have navigation errors. Some errors are not obvious until merging with adjacent surveys. We show how we detect the errors and correct them. B) Data regularization. The data of the 40 surveys were loaded into common grid and offset slots for imaging. A challenge is to bridge any acquisition gaps caused by existing platforms at the time of acquisition. Using advanced interpolation technology, we filled in gaps as wide as 350m. C) Offset-dependent matching of frequency bandwidth, amplitude, time and phase between surveys. We present a workflow that was tested and implemented successfully. D) Fault imaging. We show how fault imaging was improved by incorporating anisotropy in migration. Introduction The Gulf of Thailand Super Cube project in the Pattani Basin was initiated and financed by Chevron Thailand, and carried out by CGGVeritas over a period of 3 years. The project area is shown in Figure 1. The 40 3D seismic surveys cover approximately 15,000 sq. km. Prior to the current project, the data had been processed individually or in small groups for use in interpreting individual field areas. The primary objective of the reprocessing was to produce superior seismic imaging by making use of more advanced processing technology, and by making use of neighbouring surveys as migration aperture input. Specifically, the reprocessing aimed to accurately define the principal faults, and to broaden bandwith for high resolution definition of the reservoirs and near water bottom reflectors for the assessment of drilling hazards. The reprocessing also brought about other benefits, which include: regional consistency with DHI or AVO assessment; continuous regional interpretation and data management; fewer seismic volumes to manage; reducing the number of (redundant) faults and horizons in the database; and conveniently working in multiple field areas without the need to switch seismic workstation projects during an interpretation session. The 40 surveys were acquired over a time span of 26 years (1979 to 2005) with variable acquisition parameters, geometries and azimuths, which resulted in variable amplitude and frequency content and variable fold or sampling density. To merge them seamlessly requires great effort in spectral conditioning, time/phase matching, and AVO characteristics preservation. In addition, for some vintage surveys, essential information such as source signature, accurate navigation and well preserved trace data could be missing or incomplete. The essential information had to be cross-examined and reconstructed to facilitate the reprocessing.

Abstract This paper gives an overview of the latest developments of advanced finite element analysis (FEA) tools that are used for the design of subsea pipelines. It focuses on the deepwater and high pressure / high temperature conditions. The paper demonstrates through the use of FEA, that designs can be undertaken for complex scenarios that were not previously possible. This paper includes three main sections. The first section looks at the ‘global’ analysis of pipelines using a set of highly non-linear finite element programs based on ABAQUS. These programs have been widely utilized for over ten years in oil and gas industry and for hundreds of field developments around the world, in various design stages, from pre-FEED, FEED, to final detail design. The programs are used to undertake the complex design cases, such as lateral buckling, upheaval buckling, pipeline walking; pipe-in-pipe (PIP); thermal buckle management; and pipeline span identification, as well as span stress and collapse screening. The programs have been calibrated against the observed pipeline structural responses in the field. The simulation process covers from installation to operation and can be expanded to pipeline span analysis, route curve stability, and pressure-thermal load fatigue assessment. The second section demonstrates how FEA can be used to undertake ‘local’ modeling of pipelines to address local issues and provide verification and support for a reliable global pipeline design. Pipeline end structure behavior, thermal mitigation buoyancy and soil interaction, thermal mitigation sleeper embedment and installation tolerance, PIP inner pipe lock-in load, field joint stress/strain localization, and free span VIV analysis, are some typical applications. These works can be in component level or represent some local pipeline section. Such detail analyses ultimately relies on the ‘global’ FEA to provide trustworthy loading and boundary conditions. This paper also presents the analysis strategies based on the project experiences, the lessons learned, and future improvement. The presentations include, the route selection versus thermal expansion and global buckling, the FEA modeling process (1-D, 2-D versus 3-D), the pipeline-soil interaction, the selection of mitigation for lateral buckling, and related design issues. The combination of these analysis advancements and extensive project experiences will provide the strong supports on solving the most complex engineering problems presently faced in the offshore industry, and in some cases have allowed significant cost savings to be achieved in the engineering.