As introduced in a previous Seismic Tech-Notes article on Separated Wavefield Imaging [‘SWIM’], SWIM uses both the up-going pressure wavefield (‘P-UP’) and down-going pressure wavefield (‘P-DWN’) from the dual-sensor wavefield separation of GeoStreamer 3D data to fundamentally change the way that seismic migration can image the subsurface, the first 1 km or so below the surface in particular. Broadband and continuous seismic images all the way up to, and including, the seafloor seismic event—even in areas with very shallow water and where the 3D seismic surveys have towed a very large streamer spread to optimise survey efficiency. Every receiver from every streamer becomes a ‘virtual source’, thereby greatly extending the spatial extent of the migrated images, most famously mitigating the cross-line acquisition footprint associated with all 3D streamer surveys, notably those in shallow water, using large streamer spreads and with shallow targets of interest. A common vernacular has also been to describe SWIM as imaging ‘All orders of surface multiples’, which it does, but a better description is that ‘The complete seismic wavefield is being imaged’.
I discuss the power of SWIM to contribute to shallow velocity model building, imaging and interpretation below, building a platform to discuss seismic inversion and quantitative interpretation (QI) in a future article.
Shallow Velocity Model Building
Figure 1 compares shallow image gathers imaged from GeoStreamer data with Kirchhoff PSDM versus SWIM. Anyone familiar with seismic processing will understand that the fold on shallow arrival times/depths is always very small because of the combination of the 3D multi-streamer acquisition geometry and the outer trace mute applied in processing. In the worst case at the outer streamer locations for wide-tow geometry and/or shallow water areas there will in fact be zero fold for shallow depths and a very strong acquisition footprint will corrupt the shallow seismic data. The upper part of Figure 1 displays this well-known lack of shallow fold using Kirchhoff pre-stack depth migration (PSDM). Almost unbelievably, the lower part of Figure 1 illustrates how the introduction of P-DWN into a modified form of depth migration (SWIM) enables all offsets for all depths to contribute useful information using the same (GeoStreamer) survey data.
Whilst the events in the upper part of Figure 1 appear to be ‘flat’ and would satisfy a seismic processing expert picking velocities, anyone can see that it is very challenging trying to assess the ‘flatness’ of such short seismic events. In contrast, every event in the lower part of Figure 1 enables a very accurate assessment of the offset-dependent quality of the velocity model at all two-way time (TWT) or depth. Indeed, it is apparent in the SWIM gathers that the velocity model used is in fact slightly inaccurate at the far offsets (‘undercorrected’), and more sophisticated high-order/multi-offset/anisotropic velocity corrections can be applied, tested and refined with confidence. The use of SWIM in ‘Complete Wavefield Imaging’ (CWI) velocity model building has now become commonplace.
It is worth reminding ourselves that the ‘structural stability’ of depth imaging is rather useless without very accurate shallow velocity control. The 3D spatial integrity of the structures imaged, the juxtaposition of events across faults, the pull-up/push-down influence of near-surface velocity heterogeneities upon seismic-to-well ties, the ability to accurately quantify the volumes of prospects, and so on, all depend upon the seismic depth range where we historically have the worst understanding—the first 1 km below the surface.
Near Angle Illumination
It is worth noting that all SWIM events are naturally zero phase at all depths, and the angle coverage/illumination is substantially improved by comparison to conventional image gathers—particularly in terms of near-angle coverage. These considerations contribute to the spatial resolution of shallow features associated with SWIM depth slices. Whilst minimum angles in excess of 25° are routinely observed in the first 0.5 seconds on conventional angle gathers in shallow water depths (less than 300 m), the minimum angles observed on SWIM angle gathers are routinely less than 5°. This becomes particularly relevant for seismic inversion and AVO studies. We also observe in the lower part of Figure 1 that stable far angle information is available past 42° in this particular example—both because the velocity model used to convert offset to angle can be more accurate and because significantly larger offsets are imaged.
Velocity model building in complex geological regimes is increasingly moving towards using angle domain common image gathers (ADCIGs) as the preferred platform rather than traditional offset domain gathers. The challenges observed in Figure 2 are therefore also relevant to shallow velocity model building in addition to seismic inversion where small minimum incidence angles are critical to derive accurate AVO incidence and gradient information—the application for angle stacks discussed in a future article. As we will see, SWIM image gathers have densely sampled angle information for all angles of interest and all depths of interest.
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Headline crude prices for the week beginning 11 February 2019 – Brent: US$61/b; WTI: US$52/b
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Midstream & Downstream
Global liquid fuels
Electricity, coal, renewables, and emissions
2018 was a year that started with crude prices at US$62/b and ended at US$46/b. In between those two points, prices had gently risen up to peak of US$80/b as the oil world worried about the impact of new American sanctions on Iran in September before crashing down in the last two months on a rising tide of American production. What did that mean for the financial health of the industry over the last quarter and last year?
Nothing negative, it appears. With the last of the financial results from supermajors released, the world’s largest oil firms reported strong profits for Q418 and blockbuster profits for the full year 2018. Despite the blip in prices, the efforts of the supermajors – along with the rest of the industry – to keep costs in check after being burnt by the 2015 crash has paid off.
ExxonMobil, for example, may have missed analyst expectations for 4Q18 revenue at US$71.9 billion, but reported a better-than-expected net profit of US$6 billion. The latter was down 28% y-o-y, but the Q417 figure included a one-off benefit related to then-implemented US tax reform. Full year net profit was even better – up 5.7% to US$20.8 billion as upstream production rose to 4.01 mmboe/d – allowing ExxonMobil to come close to reclaiming its title of the world’s most profitable oil company.
But for now, that title is still held by Shell, which managed to eclipse ExxonMobil with full year net profits of US$21.4 billion. That’s the best annual results for the Anglo-Dutch firm since 2014; product of the deep and painful cost-cutting measures implemented after. Shell’s gamble in purchasing the BG Group for US$53 billion – which sparked a spat of asset sales to pare down debt – has paid off, with contributions from LNG trading named as a strong contributor to financial performance. Shell’s upstream output for 2018 came in at 3.78 mmb/d and the company is also looking to follow in the footsteps of ExxonMobil, Chevron and BP in the Permian, where it admits its footprint is currently ‘a bit small’.
Shell’s fellow British firm BP also reported its highest profits since 2014, doubling its net profits for the full year 2018 on a 65% jump in 4Q18 profits. It completes a long recovery for the firm, which has struggled since the Deepwater Horizon disaster in 2010, allowing it to focus on the future – specifically US shale through the recent US$10.5 billion purchase of BHP’s Permian assets. Chevron, too, is focusing on onshore shale, as surging Permian output drove full year net profit up by 60.8% and 4Q18 net profit up by 19.9%. Chevron is also increasingly focusing on vertical integration again – to capture the full value of surging Texas crude by expanding its refining facilities in Texas, just as ExxonMobil is doing in Beaumont. French major Total’s figures may have been less impressive in percentage terms – but that it is coming from a higher 2017 base, when it outperformed its bigger supermajor cousins.
So, despite the year ending with crude prices in the doldrums, 2018 seems to be proof of Big Oil’s ability to better weather price downturns after years of discipline. Some of the control is loosening – major upstream investments have either been sanctioned or planned since 2018 – but there is still enough restraint left over to keep the oil industry in the black when trends turn sour.
Supermajor Net Profits for 4Q18 and 2018
- 4Q18 – Net profit US$6 billion (-28%);
- 2018 – Net profit US$20.8 (+5.7%)
- 4Q18 – Net profit US$5.69 billion (+32.3%);
- 2018 – Net profit US$21.4 billion (+36%)
- 4Q18 – Net profit US$3.73 billion (+19.9%);
- 2018 – Net profit US$14.8 billion (+60.8%)
- 4Q18 – Net profit US$3.48 billion (+65%);
- 2018 - Net profit US$12.7 billion (+105%)
- 4Q18 – Net profit US$3.88 billion (+16%);
- 2018 - Net profit US$13.6 billion (+28%)