F. Bacciotti K. D Amore J. Seguin

Transcription

1 The Role of 4D Seismic Interpretation and Dynamic Modelling in the Successful Drilling of a Late Stage Development Well in the West Brae Field, North Sea F. Bacciotti K. D Amore J. Seguin

2 Introduction Generalised tectonic framework for North West Europe (from Millennium Atlas) West Brae field: Started production in D seismic survey acquired in 2007 to aid the identification of potential late stage development targets Late drilling campaign in West Brae Presentation focus: Interpretation of the 4D seismic response Integration with the dynamic field behaviour for the Flugga reservoir Comparison of pre-drill models with well results 2

3 Presentation Outline Introduction West Brae Overview 4D seismic acquisition and interpretation Integrating the 4D results with dynamic modelling of the Flugga reservoir 2010 drilling campaign Conclusion 3

4 West Brae Two stacked turbiditic reservoirs: Balder sandstone Flugga sandstone Top Balder reservoir map 16/7a 3Z 3 Flugga reservoir V Z Amalgamated units of massive unconsolidated sandstones: 90% net-to-gross 30% porosity Darcys permeability Strong aquifer support 16/6a Balder reservoir 4Z 4 W4 31 W8Z W8 W1Z W1 W2Z 32 34Y W6Z W6 W7Z 2 W7 W2 Field production (2010): W3 Cumulative: 87 MMboe Recovered: 45% Water cut: 78% W5 4

5 4D Seismic Acquisition and Processing West Brae 4D seismic survey Seismic acquisition: 1993 Baseline and 2007 Monitor 3D surveys (streamers) Same geometry, parallel processing 4D seismic survey West Brae 6

6 4D Signal Interpretation N 4D seismic difference volume (pseudo-acoustic impedance) Balder gas coning S Flugga water coning Balder water coning Pressure changes have little influence in West Brae Mostly fluid response: Water replacing oil produces a hardening (e.g. water coning) Gas replacing oil generate a softening (e.g. gas coming out of solution an effect of reservoir depletion or gas coning) 7

7 4D Seismic Interpretation of the Flugga Reservoir In the Flugga reservoir, main 4D response is water rise caused by producing wells Water signal 4D seismic maximum amplitude map - Hardening + W8Z Flugga reservoir No water rise in the NW of the field Linear weak feature along the edge of the reservoir ( NW rise ) NW rise Uncertainties Detection/resolution limits (tuning of thin water layers or low water saturations sections) Existence of NW rise as it fails to stand out W8 4D water response 8

8 4D Seismic Interpretation N Cross section along W8Z on 4D seismic difference volume S W8Z 34Y Absence of 4D signal W8 Original oil-water contact Moved oil-water contact No water rise in the NW of the field whereas: W8Z well producing since 2005 Good reservoir properties in surrounding wells and along well path 9

9 Supporting Evidence of Compartmentalisation Flugga reservoir W8 pilot hole Good sand No water rise in /7a-34Y appraisal No gas above field GOC level W8 (2005) W8Z (2005) 34Y (1999) W6 (1999) W1Z (1997) 4D water response 10

10 Data Integration to the Dynamic Modelling History matching process indicated extensive barriers to fluid flow /pressure transmission were required West-east seismic full stack reflectivity section W E West Brae Graben fault system To be effective in high net-togross, high permeability reservoir Barrier types: Faults: West Brae lies over a horst and major graben fault Shale: shale drape or overbank shale of turbiditic complex Combination of both West Brae Basement 11

11 Data Integration to the Dynamic Modelling Numerous iterations of history matching Determine geometries to reproduce 4D signal shape, while honouring production/pressure data Possible elements of scenarios: Under seismic resolution rise or water saturations NW rise feature is noise W8Z toe not contributing Faults or shales creating protection from water encroachment Etc Examples of history matched models Water saturation 12

12 Base Case Model 3D view of West Brae pre-drill model W8Z W8 Isolated compartment Flugga reservoir outline Interpreted oil-water contact north 13

13 Objective of the Drilling Campaign Targets un-swept oil in the Flugga reservoir Pilot hole objectives: Determine presence of gas Determine water encroachment, test 4D data and interpretation Understand compartmentalisation (pressure data) Confirm reservoir quality Planned well trajectories Pilot hole 3 well path options depending on pilot results W8Z Gas cap Drilling plan Water cone Aquifer Pilot hole 34Y Well path options: shallow, mid, deep 15

14 Pilot Results W9 (2010) W9Z (2010) Outcome of the pilot holes Gas cap Good reservoir properties Water encroachment No significant aquifer rise Unswept compartment Upper section depleted Decision to drill the horizontal in un-swept compartment Target GOC W8Z W8Z Pressure 1 Pressure 2 Water encroachment Original OWC 16

15 Horizontal Results S W9X well N Swept section Production section Drilled through expected swept compartment and NW rise Penetrated un-swept compartment as planned Completed un-swept sections with sand screens equipped with Inflow Control Device, which strength against the flow diminishes towards the toe Wells confirmed base case scenario 17

16 Final Model S Interpretation of the well results N Vertical exaggeration m 18

17 Conclusion Wells confirmed a complex model based on 4D image Importance of integrating all subsurface disciplines tightly 4D key tool for West Brae reservoir management 4D changed how reservoir was viewed Targets would not have been identified/drilled without 4D W9 W9Z W9X 19

18 Acknowledgment We thank Marathon s management and our partners for the permission to show the data and their support throughout the project. The authors would like to thank their colleagues: Lisa Ashman, Ross Cameron, David Eickhoff, Tor Ellis, Simon Freeman, Alicia McGeer, Falene Petrik, Anna Vitali. 20