Search

Integrated mineralogical datasets for geoscience

This is the decree to implement the 1999 petroleum code.

Sophie Zurquiyah joined CGG in 2013 and was appointed CEO in 2018. The collapse in oil price,Covid-19 pandemic and energy transition have created a tough business environment during her near four-year tenure in this role, but also created opportunities. In this interview, Sophie talks about CGG’s path into the future.

We present a workflow for 3D MAZ PSDM velocity modeling with tilted orthorhombic anisotropy. We focus on two aspects of depth-velocity modeling that are extremely important for seismic data from the NW Australian shelf: (1) high resolution adaptive seismic tomography to deal with strong velocity anomalies in complex geological settings and (2) practical workflow to build a tilted orthorhombic anisotropic PSDM velocity model in regions with complex velocity anomalies and strong horizontal and vertical anisotropy. We use real data from 4060 km2 3D MAZ PSDM Fortuna project located in the NW Australian shelf to illustrate presented workflow and its results.

It is well known that imaging of complex regions can be significantly improved with increased illumination in terms of offset and azimuth sampling. In this case study we illustrate how an existing large scale acquisition can be enriched by acquiring a second complementary survey in a targeted area. The second survey was acquired perpendicular to the first with additional offsets for maximum impact. The long offsets were enabled during a single acquisition pass by utilising a source only vessel positioned ahead of the main source and receiver vessel using simultaneous shooting. The blended data was separated using an annihilation filter approach. In this paper we illustrate the advantages this second survey has brought to the area though improvements in the FWI velocity model and enhanced illumination for the deep structures.

The Northern North Sea is a very active area for oil and gas exploration with several commercial discoveries made over the last few years. These include the Dugong discovery on the Tampen Spur and multiple discoveries in the Greater Fram area on the Horda Platform. CGG’s Northern Viking Graben (NVG) multi-client survey provides more than 44,000 sq km of coverage over this area.

Absorption effects in the Earth attenuate high frequency seismic signal progressively with depth, reducing resolution and limiting the interpretability of the data. Conventional post-migration Q compensation methods often rely on artificial mechanisms to limit amplification of noise, at the expense of unintentionally restricting recovery of signal. We propose an amplitude Q compensation technique using 3D sparse inversion. Comparisons with a conventional approach on synthetic and field datasets highlight improved signal recovery and noise suppression with the proposed method.

Time-lapse seismic is now being used more frequently to assist reservoir development, prevent infrastructure damage or monitor geological storage. To better reveal true 4D signals while suppressing acquisition-related noise as a result of, for example, water velocity changes, source positioning errors etc., a new processing flow which focusses on correcting each noise-contributing factor based on its physical characteristics, has been developed to replace the conventional non-deterministic correction approach based on cross-survey matching. Our proposed flow is based on using common water bottom and the water-bottom travel time to invert each factor and correct for it, which allows for processing of each monitor survey independently and the possible acceleration of standard 4D processing timelines. We applied this workflow on two fields offshore Angola, one with strong subsidence and one without, and showed the superiority of this new approach to reveal the true 4D information. The subsidence effect, observable from the reservoir up to the water bottom, now better matches with the model of pressure changes in the new 4D results compared to legacy results. Even for field experiencing no subsidence effect, the time shift and NRMS maps obtained at the reservoir level are cleaner and easier to interpret from new flow.

Successful applications of full waveform inversion (FWI) to land datasets are far less numerous than marine applications, yet the development of dense, long-offset broadband acquisitions has presented promising opportunities. While challenges exist due to elastic effects, acoustic land FWI has been shown to provide accurate velocity models with a level of resolution traditionally seen only with marine data. The first successful land applications in Oman have been obtained on surveys with only minor variations in surface elevation, and have encouraged the development of FWI capabilities to handle more significant topography. We present a boundary-conforming free-surface topography method for FWI, cast in the curvilinear domain. In a synthetic example, we benchmark this approach against the use of an absorbing surface boundary and a replacement velocity in the air layer (the model extension method), and the method of applying statics shifts to compensate for elevation variations. Finally, we show two real data applications from North and South Oman where our free-surface topography tool illustrates imaging uplifts over FWI results obtained with an absorbing surface and legacy tomography.