Using Integrated Geoscience and the Latest PSDM Processing Techniques

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1 Using Integrated Geoscience and the Latest PSDM Processing Techniques CGG s Lodestone Survey, UK SNS Matthew Dack, Senior Geoscientist, Multi-Client & New Ventures

2 Contents Background Survey Background and Location Acquisition Parameters & Processing Sequence Regional Geology and Prospectivity Overview PSTM vs. PSDM Example Integrated Geoscience 3D Structural Interpretation Depth Migration Testing PSTM Imaging Issues Gravity Modelling Results Processing Uplift Data Examples Additional Geological Work Conclusions Top Zechstein Group Structural Map 2

3 Contents Background Survey Background and Location Acquisition Parameters & Processing Sequence Regional Geology and Prospectivity Overview PSTM vs. PSDM Example Integrated Geoscience 3D Structural Interpretation Depth Migration Testing PSTM Imaging Issues Gravity Modelling Results Processing Uplift Data Examples Additional Geological Work Conclusions Top Zechstein Group Structural Map 3

4 Survey Background and Location Lodestone 3D Survey Judd3D located within the UK Southern Gas Basin. Acquired in 3 phases between survey covers in total 3800km 2 Runestone Initially processed to PSTM the survey underwent Cornerstone reprocessing to PSDM with CGG s bandwidth extension technology Covers prospective areas of the Silverpit Basin and southern margin of the Mid-North Sea High Lodestone Numerous discoveries located primarily within the Carboniferous and Permian play fairways 4 Source: PetroView North-West Europe, April 2017

5 Acquisition Parameters & Processing Sequence Highlights Particular focus on demultiple processing to improve sub-zechstein imaging. Filters include: 2D SRME, 2D MWD, high-resolution Radon and 2D TMA Parameter Total area 3,850km 2 Streamer length 5100m Lodestone 3D Survey Broadband processing with pre-migration deghosting (GWE) PreSDM model building includes: 6 passes with 3 passes of structural interpretation updates via nonlinear multi-layer tomography (TOMO-ML) PreSDM CBM used for velocity model building steps Final Kirchhoff PreSDM: Migration aperture: 4km Bin size output: 12.5m x 12.5m Max depth output: 4km Sample rate: 4m Streamer type Sercel SEAL Sentinel solid streamers Number of streamers 8 Groups per streamer 408 Group length 12.5 Streamer depth 7m, flat tow Streamer separation 100m First offset 90m Number of sources 2 Source array depth 6m Source nominal air pressure 2000psi Source size 2950in 3 Shot-point interval 50m Fold 51 Record length 6sec 5 Sampling rate 2ms

6 Regional Tectono-stratigraphy & Petroleum Systems Mature Basin, New Opportunities? SW Top Rotliegend Depth Map NE Basin has a complex tectonic history, with multiple stages of subsidence and inversion 2280m 3820m Engie operated Cygnus Field Discovered initially in 1988 and remained undeveloped until 2000 s Initial production due in

7 Seismic data sample from PreSTM vs PreSDM SW 0.5s NE Tertiary dyke emplacement Salt diapirs 1.0s Base Zechstein salt Heavily deformed Hauptanhydrite 1.5s 2.0s Reservoir target interval 2.5s Mid-Devonian Limestones 3.0s CYGNUS Westphalian Namurian Coal Measures 3.5s 4.0s 7

8 Seismic data sample from PreSDM Cygnus Zoom Base Permian Unconformity well defined with no multiple contamination from sub-parallel Base Zechstein Thick Zechstein salt seal Rotliegend reservoir sands Carboniferous reservoir intervals and intra-formational seals 8 Well defined sub-salt faults 8

9 Contents Background Survey Background and Location Acquisition Parameters & Processing Sequence Regional Geology and Prospectivity Overview PSTM vs. PSDM Example Integrated Geoscience 3D Structural Interpretation Depth Migration Testing PSTM Imaging Issues Gravity Modelling Results Processing Uplift Data Examples Additional Geological Work Conclusions Top Zechstein Group Structural Map 9

10 3D Structural Interpretation SW NE Regional Lodestone PSDM PSTM Dip-Line 0.5s 1.0s 1.5s 2.0s 2.5s Eocene Unc. Top Chalk Speeton Clay 3.0s BCU Triton Anhyd. Bunter Sst Top Zechstein Intra Zechstein Base Zechstein BPU Devonian Lst 3.5s 4.0s 10

11 Depth Conversion Testing Various methods of depth converting the picked time horizons were tested in order to assess the impact crucial to assess was the Base Zechstein horizon 1. Average Velocity to Base Zechstein 2. Interval Velocity Layer Cake Model 3. V0K Method Average Velocity to Base Zechstein Jurassic Interval Velocity Map Interval V0 K Seabed-Eocene Eocene-Chalk Chalk-Speeton Clay Speeton Clay-Top Zechstein Top Zechstein- Top Rotliegend Average Velocity Method Where: BB. ZZZZZZZZZZZZZZZZZ ZZ = HH tttttt 2 VVVVVV aaaaaa HH tttttt = Time Horizon VVVVVV aaaaaa = Average Velocity Layer Cake Calculation Where: ZZ = HH bb HH uu 2 VVVVVV iiiiii + Zu HH bb = Basal Horizon HH uu = Upper Horizon Zu = Depth Upper Horizon V0K Calculation Where: ZZ = VVV KK eekkkk 1 VVV = Uncompacted Interval Velocity KK = Gradient T = Time Horizon 11

12 Depth Conversion Testing Base Zechstein V0K Horizons vs Final Depth Volume V0K more reliable to the north of survey area Layer cake model Average shows velocity method too good relationship simplistic to V0K in complex salt basin V0K Method less reliable where Mesozoic calculated depth horizons section thickens high variability in velocities Layer Cake. V0K Layer Cake. Average V0K Vel. 12

13 Depth Conversion Testing From comparing the structural maps of the Top Rotliegend in time and depth it is clear that the sub-salt structure can be expected to change quite drastically as a result of the depth migration Top Rotliegend Group Time Top Rotliegend Group Depth NE appears less structurally complex as salt effect removed Cygnus appears more structurally controlled Removal of artificial structures created by halokinesis Horst delineated to ridge structure 13

14 Integration of Multi-Physics Gravity in Salt Basins Integration of gravity data into geological and geophysical model building is of particular use in salt basins, where salt composition, geometry and deformation can be difficult to interpret with seismic alone Top Zechstein Structure and Isopach Bouger Gravity with Zechstein Isopach From the Bouger Gravity map and the Top Zechstein structure we can see there is a direct correlation Tertiary dykes Gravity highs associated to reduced Zechstein thickness 14

15 PSTM Salt Imaging Issues Mainly associated to a large, linear salt wall orientated N-S through the survey, the lack of illumination of the salt means accurate interpretation of salt structure is compromised. As such the sub-salt structure may not be accurate once depth processed East-West Crossline Through Salt Wall Large salt diapir truncates stratigraphy Poor imaging in and adjacent to salt body leading to ambiguity in salt interpretation Withdrawal of salt adjacent to salt wall 15

16 PSTM Salt Imaging Issues Mainly associated to a large, linear salt wall orientated N-S through the survey, the lack of illumination of the salt means accurate interpretation of salt structure is compromised. As such the sub-salt structure may not be accurate once depth processed Strike Line Through Salt Wall Identifying Complexity of Deformation 16

17 Gravity Modelling to Refine Salt Interpretation Lodestone 3D Gravity Modelling Input Data For the Lodestone gravity modelling, the 3D seismic velocity volume was converted into a density volume using the Gardner s relationship Relationship Between Sediment Density and Velocity Shown by Gardner s Equation Density volume could then be used as background model for gravity modelling Using the 3D interpreted horizons, the gravity response expected based on sediment densities is calculated Where calculated and measure gravity differ, structural interpretation or sediment density/velocity can be altered to produce a match 17

18 Gravity Modelling to Refine Salt Interpretation Starting model showing the initial structural interpretation, velocity model derived density values (Gardner s) and the resultant calculated gravity response vs. observed Bouger gravity 18 West East 18

19 Gravity Modelling to Refine Salt Interpretation Starting model showing the initial structural interpretation, velocity model derived density values (Gardner s) and the resultant calculated gravity response vs. observed Bouger gravity 19 West East 19

20 Gravity Modelling to Refine Salt Interpretation To initially refine the model the density voxet has been increased (rho=0.32v 0.25 ) for the Zechstein section. We can now see that the calculated and observed gravity curves are better aligned. This would suggest that the constant velocity used for the salt may be too low 20 West East 20

21 Gravity Modelling to Refine Salt Interpretation To further refine the model, the structural interpretation of the Zechstein salt can be altered. Here the addition of an overhang appears to fit well. However, drastically altering the Zechstein structure in areas of good seismic imaging is questionable considering the resolution of the gravity vs seismic 21 West East Addition of salt overhang 21

22 Gravity Modelling to Refine Salt Interpretation Final Initial Model 22 West East 22

23 Gravity Modelling to Refine Salt Interpretation By inserting the entire structural and velocity interpretations into the gravity modelling software, the difference between the observed and calculated gravity can be identified By inverting the Upper Zechstein densities we are able to identify distinct regions where there may be issues with the structural interpretation or velocities used Observed & Calculated Gravity Difference Inverted Upper Zechstein Densities Distinct NW-SE trending regions where gravity modelling suggests there is an issue 23

24 NW-SE Trending Anomalies From observing the inverted densities and the Top Zechstein horizon in conjunction we can see that the anomaly is confined to a deep synclinal structure created by salt withdrawal Inverted Upper Zechstein Densities Top Zechstein Time Structure Map with Zechstein Structural Contours Perfect delineation of anomaly with salt structure Feature in the south-west corresponds to Tertiary Igneous dykes 24

25 Main NW-SE Trending Anomaly In seismic section we can see clearly that the anomaly is confined to the withdrawal syncline, with increased post-salt sediment thickness Possible reasons for the anomaly could result from miscalculation of velocity/density of overburden or within the salt section. In areas of salt movement, halite is more mobile and thus leaves a higher anhydrite:halite in synclines. Strike linedip across syncline which coincides with anomaly line taken across NW-SE trending Sediment loading Large facies variation in Upper Zechstein Halite squeezed into adjacent pillows High amplitude variation between the Top Zechstein Halite squeezed into and Intra-Zechstein adjacent pillows interval Interpreted IntraZechstein interval Low anhydrite:halite zone High anhydrite:halite zone Evidence of this variation can Low anhydrite:halite zone be seen in the 44/12a-5 well Amplitude response show that facies above the Intra-Zechstein are not Thisanhydrite is evident when looking at stratigraphy Source: Millennium Atlas simple, with potentially numerous cycles and shale Another reason for anomaly could(2003) be dueoftohalite, higher anhydrite concentrations in axis of syncline 25 and wells

26 Main NW-SE Trending Anomaly In seismic section we can see clearly that the anomaly is confined to the withdrawal syncline, with increased post-salt sediment thickness Possible reasons for the anomaly could result from miscalculation of velocity/density of overburden or within the salt section. In areas of salt movement, halite is more mobile and thus leaves a higher anhydrite:halite in synclines. Strike line across syncline which coincides with anomaly Zechstein RMS Amplitude and Isopach Correlation Sediment loading Halite squeezed into adjacent pillows Low anhydrite:halite zone Halite squeezed into adjacent pillows High anhydrite:halite zone Low anhydrite:halite zone Another reason for anomaly could be due to higher anhydrite concentrations in axis of syncline Analysis suggests merit to using salt thickness formula in processing sequence 26 High velocity zones located within withdrawal synclines

27 Tertiary Dykes Associated to the Tertiary Igneous Province in NW Scotland and beyond, the Tertiary dykes observed in well penetrations and observed on the seismic data, result in high density anomalies apparent on the density inversion and needed accounting for Top Chalk Time Structure Map Section through Tertiary Dykes Thinning of chalk deposits Inverted due Upper Zechstein Densities to catastrophic loss of porewater and subsequently porosity which led to rapid compaction Seismic disturbance zones Large, 3km, collapse crater NW-SE trending linear crater chains Seismic disturbance zone Well 44/11-3 encountered dolerite dykes WNW-ESE Linear Crater Chain 27

28 Contents Background Survey Background and Location Acquisition Parameters & Processing Sequence Regional Geology and Prospectivity Overview PSTM vs. PSDM Example Integrated Geoscience 3D Structural Interpretation Depth Migration Testing PSTM Imaging Issues Gravity Modelling Results Processing Uplift Data Examples Additional Geological Work Conclusions Top Zechstein Group Structural Map 28

29 Results from Salt Modelling Salt wall velocity model and 20Hz RTM volumes before and after salt modelling The Base Zechstein is much better imaged along the salt wall with the final salt model 29

30 Results from Salt Modelling - PSDM PSDM Pre-Salt Modelling vs. PSDM Post-Salt Modelling PSDM Pre-Salt Modelling vs. PSDM Post-Salt Modelling Higher resolution from deghosting Much improved illumination of Base Zechstein event Flattening better migrated 30

31 Targeted Multiple Attenuation (TMA) Removal of specific multiple events associated with a specific multiple generator 3 Primary generators were used: - Top Speeton - Package between Top Speeton and Top Bunter - Top Zechstein (Shifted down 60ms onto the strongest event) Top Speeton generator Top Speeton Top Bunter package generator Top Zechstein generator (note: this was shifted slightly downwards for TMA in order to capture the strong generator event) 31

32 TMA - Input stack 32 Removal of low frequency multiple interfering with Palaeozoic section 32

33 Seismic data sample from PreSTM SW NE 0.5s 1.0s 1.5s Reduced seismic disturbance from Tertiary dykes Higher resolution of shallow section from deghosting 2.0s 2.5s 3.0s Better resolved Base Permian Unconformity Gravity modelling helping to resolve Base Zechstein Improved singal:noise and demultiple improves accuracy of Palaeozoic structural interpretation 3.5s 4.0s Deep imaging aided by the additional low frequencies better illumination of Devonian Well Name MBU1 Error MBU2 Error Final Error Mean Standard Deviation

34 Palaeozoic Structural Targets The Lodestone PSDM survey reveals Carboniferous structural targets created by Tertiary inversion in DEPTH Numerous inversion features and rollovers form targets for exploration 34

35 Seismic data sample from PreSDM The importance of the data in depth is visualised here, with the alteration of Pre-Zechstein structures SW Structural dip of Base Zechstein more apparent suggesting present day migration direction from south to north 0.5s 1km 1.0s 2km 1.5s 3km 2.0s 4km 2.5s 5km Structural relief less exaggerated in depth 3.0s 6km 3.5s 7km 4.0s 35 Structural reversal due to correct modelling of thinned salt NE

36 Palaeozoic Structural Assessment The quality of the PSDM data is best exemplified by some recent work assessing the structural configuration of the Palaeozoic section Palaeozoic faults are critical elements of trapping geometries of many discoveries Data quality allows for automated fault extraction Strike Azimuth for Palaeozoic Faults Extracted Dip Top for Rotliegend Palaeozoic Fault Planes Depth Faults Map Intersecting fault trends create numerous fault compartments over the wider Cygnus area In NE of the survey area towards the MNSH the Rotliegend group is heavily populated by NE-SW faults Tri-modal distribution All faults are extremely high angle 36 Dack, M. & Duval, G. (In Press) Structural Elements of the Northern Silverpit Basin - Implications for Hydrocarbon Prospectivity Petroleum Geoscience

37 Open Acreage Overview Benefits of Lodestone PSDM Fault compartments north of Cygnus Base Zechstein Depth Map Blocks 44/7-10 Base Zechstein Dip Map Subtle low relief features look similar to Cygnus closure Prospect A RMS Amplitude & Top Reservoir Map 37

38 Unsanctioned Discoveries Clark Prospect Bunter Sst Top Zechstein Base Zechstein BPU Top Reservoir Discovery Well 44/17a-5 Interpreted E-W Section Through Discovery Clark prospect (Well 44/17a-5) drilled by Conoco (UK) Ltd in 1998 Drilled to test Carboniferous Westphalian C/D in a down-faulted wedge 8ft gas bearing sand with Φ = 13.7% S w = 35.7% FWL from FMT = 3860m Proxy Top Reservoir Map FWL Fault Seal? SOURCE: Westphalian B Coal and Carbonaceous Mudstones RESERVOIR: Westphalian C/D Fluvial Sandstones SEAL: Silverpit Shale top seal and lateral fault seal TRAP: Tilted fault block and stratigraphic truncation combination 44/17a-5 38

39 Unsanctioned Discoveries Lauren Prospect Bunter Sst Top Zechstein Base Zechstein BPU Top Reservoir Discovery Well 44/17-2 Interpreted N-S Section Through Discovery Lauren prospect (Well 44/17-2) drilled by Conoco (UK) Ltd in 1991 Drilled to test Westphalian B Murdoch Sands Murdoch Sand penetrated at 12623ft Number of DST s performed with varying results best flowed 46.6MSCFD Top Murdoch Sst Map 44/17-2 Murdoch Field SOURCE: Westphalian A & B Coals and Carbonaceous Mudstones RESERVOIR: Westphalian B Fluvial Sandstones Murdoch Sst SEAL: Westphalian B Intra-formational Seal TRAP: Anticline and fault combination 39

40 Conclusions CGG has extensive 3D data coverage over most of the blocks available in the 30 th round (~75%) The Lodestone survey in particular, covering approximately 3800km 2 of Q44, provides 3D, long offset, broadband processed coverage over several of these blocks With the Lodestone 3D survey in the UK Southern North Sea, CGG has shown how with integrated geoscience and the latest processing techniques including, accurate velocity modelling (particularly for the salt) and proper depth imaging, it has maximised the value of its SNS dataset The resulting PSDM data help to illuminate the Pre-Zechstein Permo-Carboniferous stratigraphy and identify potential new targets for exploration If you have any further enquiries on CGG s UKCS Multi-Client data library please come and visit our booth! 40

41 Thank You