Figure 1 - uploaded by Zhijun Du
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Map showing the Towed Streamer EM BBK survey area, where the thick red lines indicate EM survey lines. The well log: 3/28A-06, is located approximately at the center of Bressay, as indicated by the large black dot.
Source publication
We introduce a method for integrating Towed Streamer EM and dual-sensor seismic data referred to as seismic guided EM inversion. The inversion workflow is initiated by adopting a sparse-layer depth model defined by dual-sensor seismic data to suggest resistivity boundaries without a rigid constraint. This makes good sense when considering the uncer...
Contexts in source publication
Context 1
... 2012 PGS conducted a challenging survey in a complex geological region over Bressay, Bentley and Kraken (BBK) heavy oil fields in the North Sea (Figure 1), with the newly developed controlled source Towed Streamer EM acquisition system. The towed system deploys a ~7.7 km receiver cable at 50 -100 m water depth, and a powerful (1,500 A) 800 m long bi-pole source at 10 m depth. ...
Context 2
... at the western edge of the Viking Graben, Bentley and Bressay are situated in UK Quadrant 9, North Sea, within a depth range of ~1,100-1,300 m, beneath a shallow water column of ~ 90 -130 m (Figure 1). Both fields are found in the Dornoch Formation of late Palaeocene age. ...
Context 3
... BBK Towed Streamer EM survey, as shown in Figure 1, consists of two parallel survey lines in the NNW to SSE directions over the Bressay, Bentley and Kraken fields. The CSEM data consist of a wide range of offsets, 743 -7,457 m, and 6 frequencies from 0.2 to 1.2 Hz with an increment of 0.2 Hz. ...
Context 4
... setup line BK006 (pink line in Figure 1) seismic guided inversion to have an isotropic 1Ωm half space background, as shown in Figure 4. The first step of the seismic guided inversion is to perform an unconstrained (blind without considering field geology) anisotropic inversion of the Towed EM data. ...
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Citations
... To jointly interpret sub-seafloor targets, it is preferable that the seismic and CSEM data will be acquired simultaneously with an inline arrays of seismic and EM sensors, in order to achieve an ideal complementary results from the two datasets that share coincident navigational information ( Du and Hosseinzadeh, 2014;Engelmark , 2014;Du and Key, 2015;Srnka and Constable, 2017). ...
Gas hydrate deposits are known to store vast amounts of methane, and occur worldwide in marine and permafrost regions. Methane emissions driven by hydrate dissociation may contribute to submarine slope failures, geohazards to deep water infrastructures, and possibly climate change. Alternatively, hydrates are perceived as a viable energy resource. These environmental and economic implications mean that gas hydrate research is of both academic and industrial interest. To determine the environmental impact or economic potential of gas hydrate accumulations in any given geologic setting with a high level of confidence, it is mandatory to acquire lithological and geophysical information for a well-constrained joint interpretation. Robust delineation and quantification of gas hydrate structures is not a trivial task, due to inherent uncertainties from the absence of information regarding the physical properties of the reservoir of interest. In this thesis, I develop a rigorous joint interpretation scheme using marine controlled-source electromagnetic (CSEM), seismic and core data coupled by effective medium modelling, for the detection, delineation, and quantification of marine gas hydrate structures.
The study area for this research is the CNE03 pockmark, situated on the Norwegian continental slope, Nyegga region, offshore Norway. The CNE03 pockmark is underlain by a pipe-like structure, where gas hydrate and free gas coexist. Marine CSEM data and sediment cores were acquired from the CNE03 pockmark, integrated and interpreted with collocated high-resolution two-dimensional seismic reflection and three-dimensional tomographic seismic data. The CNE03 pipe-like hydrate structure is detected and characterised using unconstrained and seismically constrained CSEM inversions of data obtained by ocean bottom electric field receivers (OBE). The unconstrained CSEM inversions detected the CNE03 pipe-like structure satisfactorily though with undefined and diffusive margins, which is mitigated by the seismically constrained inversions that improved the delineation of the CNE03 boundaries significantly. High-resolution resistivity imaging of the CNE03 pipe-like structure is achieved by a combined CSEM inversion of both the OBE and 3-axis towed electric field receiver (Vulcan) data. Robust quantification of hydrate content within the CNE03 structure is derived by comparison between CSEM and seismic datasets with joint elastic-electrical effective medium modelling scheme.
The work I present in this thesis provides an integrated approach to elucidate both structural and fluid properties of sub-seafloor gas hydrate and free gas deposits. The joint interpretation framework applied here could also be utilised to map and monitor seafloor mineralisation, freshwater reservoirs, carbon capture and storage sites, and near-surface geothermal systems.<br/
... We have introduced a method to make the inversion-based EM and seismic integration process more data and informationdriven and less a priori model driven (Du and Hosseinzadeh, 2014). The workflow is based on the cooperative approach, however, it uses the seismic image to guide the EM inversion rather than constrain it. ...
... The seismic guided inversion (Du and Hosseinzadeh, 2014) is aiming to facilitate an optimal procedure to combine the complementary information from dual-sensor seismic data and the Towed Streamer EM, with the seismic data best at constraining structure, and the EM data best at constraining the reservoir strength. In some detail, the inversions are guided by the seismic to find the stratigraphic boundaries, whereas the resistivity variations within the overburden layers are set by plausible lower and upper boundaries suggested by the previous step of unconstrained inversions. ...
... In some detail, the inversions are guided by the seismic to find the stratigraphic boundaries, whereas the resistivity variations within the overburden layers are set by plausible lower and upper boundaries suggested by the previous step of unconstrained inversions. Further technical details of the seismic guided inversion are given in Du and Hosseinzadeh (2014). Here we apply the workflow and demonstrate how it incorporates the geological information constrained by seismic data into an inversion of EM, showing how it helps substantially to raise the resolution of the EM inversions. ...
SUMMARY Integrated analysis of geophysical data can provide valuable information on reservoir properties, on the basis of which exploration, appraisal, and development decisions can be made. Hence, we have introduced a quantitative interpretation workflow that integrates dualsensor seismic and Towed Streamer controlled-source electromagnetic (CSEM) data. The workflow was designed to facilitate a reliable extraction of the complementary information from the two datasets. The seismic contribution starts with a depth-converted sparse horizon model to initialize the EM inversion, but it is not placed rigidly. This makes good sense when taking into account the uncertainties in seismic data, in the time to depth conversion, and more importantly, the fact that a reservoir can be hydrocarbon-charged to an unknown degree corresponding to the spill-point or less. We show how this approach enables a robust and reliable workflow for integrating EM and 3D seismic data with data examples acquired in an area with the complex geology of the Bressay, Bentley and Kraken (BBK) fields in the North Sea. The three heavy oil reservoirs are injectites, located in close proximity to other high resistivity settings, such as the shallow gas in the overburden, regional Balder Tuff and granite intrusions, resulting in challenging imaging issues.
