P-Cable UHR3D Seismic What is it, and when is it better? Presented by: Brian Brookshire, NCS SubSea By Invitation of: SUT Houston's Offshore Site

Transcription

1 P-Cable UHR3D Seismic What is it, and when is it better? Presented by: Brian Brookshire, NCS SubSea By Invitation of: SUT Houston's Offshore Site Investigation and Geotechnics Committee

2 Contents What is it? P-Cable Acquisition Methodology Production Statistics Processing Flows (basic outline) When is it better? (data examples from GoM unless otherwise noted) Faults Shallow Exploration MTCs Seeps 4D Study Lessons learned Moving forward Conclusions

3 What is it?

4 P-Cable UHR3D Methodology Receiver Array 18 x 100 m long streamers 6.25 m group interval (16 groups per streamer, 12 phones per group) 12.5 m cross-line streamer spacing Source 210 in 3 GI Gun in Harmonic Mode (G = 105 in 3, I = 105 in 3 ) ~ 6 bar-m peak to peak Survey Parameters ~4 kts survey speed 12.5 m shotpoint spacing m x 6.25 m bins 4 fold 100 m sail line spacing (2cmp lines of overlap) Recording Parameters 0.25 ms sampling interval (8 times conventional rate) 18 db pre-amp gain SAFE-BAND P-Cable Final Configuration v2 - Detailed-Model.pdf Brookshire, Jr. BN, Landers FP and Stein JA. (2015). Applicability of ultra-highresolution 3D seismic data for geohazard identification at mid-slope depths in the Gulf of Mexico: Initial results. Underwater Technology. 32:

5 1.8m 4.8m

6

7

8 Relatively rapid deployment from vessels of opportunity

9

10

11

12 courtesy Fugro/Geometrics

13 Production km^2 Activity Breakdown Less Mob 13.5% Production Stats Repeatability Prime Infill Reshoot Production vs Turn Crew Change Chargeable Standby Technical Downtime Operational Recording time (hrs) Acquisition Total % Line change time (hrs) Average Daily km^2 Production Job Total Best Consecutive Month Other Recent P-Cable Job 12.7% Why is job total production lower than anticipated? -Slow speed over ground in one direction due to issues with Loop Current (as little as 1.5 kts!!). -Growing pains with system. Repeatability Prime Infill Reshoot

14 Different Iterations of the SAFE-BAND Data Fast Track 3D Volume Current 3D Volume Brand New, Deghosted 2D Examples 20 Hz low cut filter Temporal resample to 0.5 ms Basic wavelet processing Noise elimination Static corrections 3D stack Post-stack time migration Basic post migration processing 20 Hz low cut filter Temporal resample to 0.5 ms Statics corrections 2D SRME on common channel/shots Zero phase operator Noise attenuation Regularization Pre-Stack time migration 3D stack Amplitude balancing 2 to 4 Hz high pass filter Noise attenuation DUGBroad (deghosting) 2D SRME Pre-stack time migration 2D stack Frequency enhancement

15 Survey Area

16 When is it better?

17 Complex Areas (or otherwise) Where Resolution Really Counts ~ 40 km

18 Comparison Reprocessed Short Offset Conventional 3D P-Cable Modified from: Hill A., et al. (2015). Slicing and dicing HR seismic acquisition: Varied approaches to delivery of high-resolution 3D seismic data volumes for drilling hazards. TLE 34:

19 Faults

20 Small Faults Base of visible gas anomaly ~ 15 m wide inline Displaced blocks ~38 m wide inline, beds as narrow as ~ 1.5 m to 3.0 m (empirically). Brookshire, Jr. BN, Landers FP and Stein JA. (2015). Applicability of ultra-highresolution 3D seismic data for geohazard identification at mid-slope depths in the Gulf of Mexico: Initial results. Underwater Technology. 32:

21 Regional Faults ~ 12.5 km

22 For the freely available 3D volumes visit: Tectonically Active Faults San Luis Obispo Bay Slip Rates ~7km Modified from: Green HG and Graham SA. (2014). Central California Coast Seismic Imaging Project Chapter 3: Offshore Low Energy Seismic Reflection Studies in Estero Bay, San Luis Bay, and Point Sal Areas. PG&E.

23 For the freely available 3D volumes visit: Tectonically Active Faults San Luis Obispo Bay Slip Rates Modified from: Green HG and Graham SA. (2014). Central California Coast Seismic Imaging Project Chapter 3: Offshore Low Energy Seismic Reflection Studies in Estero Bay, San Luis Bay, and Point Sal Areas. PG&E.

24 Shallow Exploration

25 Traps ~3 sec ~7km

26 Barents Sea Shallow Exploration Targets ~0.5 sec

27 Barents Sea Shallow Exploration Targets ~0.5 sec

28 MTCs

29 MTCs sea floor pick (first zero crossing) ~ 40 km Depth range = 700 m to 1000 m Brookshire, Jr. BN (2015). Mass transport complex imaging with P-Cable ultrahigh-resolution 3- dimensional seismic SEG Near Surface Asia Pacific Conference, Extended Abstract.

30 Subsurface Mass Transport Complex (MTC) Imaging Oblique cut similarity attribute volume Top of MTC-I time horizon Corresponding top of MTC-I amp. extraction Oblique cut dip of maximum similarity attribute volume Brookshire, Jr. BN (2015). Mass transport complex imaging with P-Cable ultrahigh-resolution 3- dimensional seismic SEG Near Surface Asia Pacific Conference, Extended Abstract.

31 MTC I zoom profile zero phase, American polarity ~50 mbsf Most Positive Amp. Most Negative Amp. ~ 2 km Brookshire, Jr. BN (2015). Mass transport complex imaging with P-Cable ultrahigh-resolution 3- dimensional seismic SEG Near Surface Asia Pacific Conference, Extended Abstract.

32 MTC I zoom profile zero phase, American polarity ~50 mbsf Most Positive Amp. A B C Most Negative Amp. ~ 2 km Brookshire, Jr. BN (2015). Mass transport complex imaging with P-Cable ultrahigh-resolution 3- dimensional seismic SEG Near Surface Asia Pacific Conference, Extended Abstract.

33 MTC I zoom top (A) amplitudes Most Positive Amp. Most Negative Amp. ~ 2.75 km Brookshire, Jr. BN (2015). Mass transport complex imaging with P-Cable ultrahigh-resolution 3- dimensional seismic SEG Near Surface Asia Pacific Conference, Extended Abstract.

34 MTC I zoom bottom (B) flattened Hz sub-band ~35 m wide Most Positive Amp. Most Negative Amp. ~ 2.75 km Brookshire, Jr. BN (2015). Mass transport complex imaging with P-Cable ultrahigh-resolution 3- dimensional seismic SEG Near Surface Asia Pacific Conference, Extended Abstract.

35 MTC I zoom profile zero phase, American polarity ~50 mbsf Most Positive Amp. A B C Most Negative Amp. ~ 2 km Brookshire, Jr. BN (2015). Mass transport complex imaging with P-Cable ultrahigh-resolution 3- dimensional seismic SEG Near Surface Asia Pacific Conference, Extended Abstract.

36 MTC I zoom bottom ( sec, ~17.5 m below) (C) flattened similarity ~25 m peak to peak Dissimilar Similar ~ 2.75 km Brookshire, Jr. BN (2015). Mass transport complex imaging with P-Cable ultrahigh-resolution 3- dimensional seismic SEG Near Surface Asia Pacific Conference, Extended Abstract.

37 Subsurface Mass Transport Complex (MTC) Related to Seafloor Expression 3D volume with top of MTC superimposed Top of MTC with Seafloor transparency overlain. MTC is ~ 40 ms (30 m) below the seafloor. Brookshire, Jr. BN (2015). Mass transport complex imaging with P-Cable ultrahigh-resolution 3- dimensional seismic SEG Near Surface Asia Pacific Conference, Extended Abstract.

38 Seeps

39 Multiple Surface and Subsurface Expressions Brookshire, Jr. BN, Scott L (2015). Reducing risk in offshore planning and development. GEOExPro. 12 (2):

40 Gas Anomaly Amp. (flipped) Amplitudes Subsurface Through Water Column Seafloor Amp. RMS Amp. Water Column sec to sec above seafloor ~ 1.9 km

41 4D Study

42 Repeatability Lines Same racetrack shot twice with approximately 6 hours between successive passes on same line Assess repeatability with minimal environmental variance

43 Largest difference is receiver (real world) Y coordinate Likely due to changes in feather Navigation Repeatability - How successful were we in putting the source and receivers in the same place?

44 NRMS NRMS = 200 * RMS (Base Monitor) / (RMS Base + RMS Monitor) Gives the ratio of the RMS of the difference to the RMS of the inputs (does not preserve sign/polarity) 1000 ms window beginning 50 ms below water bottom. For conventional streamer seismic (lower frequency) <20 % NRMS is considered excellent. Final 4D Processing Steps Presented 4D post stack matching 21 pt (pt = 0.5 ms) least squares filter 150 Hz high cut filter

45 inline (base) inline - 4D matching (monitor)

46 Line Inline - 4D Matching Difference/NRMS NRMS = %

47 inline (base) inline - 4D matching (monitor)

48 inline with 150 Hz high cut (base) inline - 4D matching with 150 Hz high cut (monitor)

49 Line Inline - 4D Matching Difference/NRMS with 150 Hz High Cut NRMS = %

50 Lessons Learned

51 Lessons Learned Environmental Conditions Watch out for the loop current (and associated mesoscale eddies). Observed current velocities of over 3 kts dramatically impacted vessel (and array) speed over ground and speed through water. This led to lower production rates, variable streamer depths, etc Earth Scan Laboratory, LSU URL:

52 Hmmm trouble may be a brewin. Sargassum (seaweed) mat

53 Oooh, can we go around that?

54 Nope!

55 I don t get paid enough for this s#it.

56 Lessons Learned Better Depth Control / Determination Variable receiver depth, especially problematic during low speed through water scenarios, led to data distortion / acquisition footprint.

57 Frequency Hz Lessons Learned Better Depth Control / Determination Near Channel Cable 1 Frequency Spectra for Entire Line Far Channel FSP LSP FSP LSP

58 Lessons Learned Deghosting is Necessary Cable 1 Near Channel

59 Lessons Learned Deghosting is Necessary Cable 1 Far Channel

60 Moving Forward Can t change the environment (e.g. - currents, seaweed), but better to have a backup area/acquisition strategy during the summer in the GoM. It is essential that we have better streamer depth control, so we will be using single birds at the ends of the streamers. It will also be essential to more precisely derive individual receiver depths using the receiver ghost notch. Empirical results confirm that deghosting is a must. When it is within our sphere of influence, we will require that deghosting be performed on all data sets.

61 Deghosting and Frequency Enhancement

62 Current 3D ms, no deghost

63 2D Test Line ms, deghosted

64 Current 3D ms, no deghost

65 2D Test Line ms, deghosted

66 Conclusions What is it? A small-scale 3D seismic system characterized by high spatial and temporal sampling resolution and precise, accurate positioning. When is it better? It s better when resolution is critical, and understanding the subtle character of the stratigraphic sequences is necessary. Limitations Short Offsets no velocities; good at seeing gas, but not below it. ~ 3 seconds below seafloor is more or less the P-Cable zone.

67 Acknowledgements SAFE-BAND Partners NCS SubSea, Geotrace Technologies and Spec Partners 4D Study Shell, Geotrace Technologies (UK) Deghosted Data DownUnder Geosolutions