Seismic Analysis For Unconventional Reservoirs
Transcript of Seismic Analysis For Unconventional Reservoirs
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www.petrelrob.com Worldwide Petroleum Consulting
Seismic Analysis For
Unconventional ReservoirsPresented by Kathleen Dorey
For the CSUR Technical Webinar
Calgary, Canada
September 30th, 2020
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Source: Financial Post, March 2019
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Offshore Natural Gas Production
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Natural Gas Bills Across Canada
Average Gas Bill January 2018 – 7.37 Gj of Consumption
Source: NEB
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Study Area and Pipeline Proximity
Source: Keppie, 2017
Sable Island
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Cumberland Onshore Basin
Source: Classification of Nova Scotia Sub-Basins
(NSDNR, 2010)
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Natural Gas Potential
Source: Keppie, 2017
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Unconventional Resources
Source: Keppie, 2017
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Project Objective
• To de-risk the presence of reservoir in the basin.
• Gain information about reservoir EOD’s.
• Reservoir can be sands or shales in a unconventional basin.
• Basin relatively unexplored with 19 wells, most shallower than the Horton.
• Ideal opportunity to use seismic to identify reservoir trends.
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Basin Setting
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W-E Cross Section
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N-S Cross Section
Note Horton
thickness:
Can be 3000
m+ in area,
most gas
potential in
this formation
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Basin Stratigraphy
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• Cross plotting of attributes such as porosity, density, impedance, shale content to define facies types.
• Post-stack seismic inversion to generate the impedance seismic sections.
• Facies types plotted on the inverted seismic sections.
• Generation of maps for the facies in the basin.
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Seismic Analysis Method
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Seismic and Well Control
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Used caliper cut-offs to remove hole washouts –giving erroneous values for sonic and densities in the formations of interest.
There was no full Horton section penetrated in the basin, so one of the nearby wells from Windsor basin had to be combined with one of the shallower logs.
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Well Log Considerations
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The well control was analysed for porosity, density, and impedance trends. As a result, the facies were split into six different types:
• Non-Reservoir (Basement)
• Tight Sands
• Low Porosity Sands
• Medium Porosity Sands
• High Porosity Sands
• Shale Facies.
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Attribute Analysis
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High Porosity / Tight Sand Facies
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Shale Facies
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Non–Reservoir Facies
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Boss Point / Mabou Classification
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Horton Classification
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Process to remove the wavelet and have impedance values remaining.
Tie these impedance values to the facies classifications that were defined.
Very challenging inverting 2D seismic in complicated structural areas, making sure inversion follows the correct packages across faults, salt flows etc.…
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Seismic Inversion
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Seismic Facies Classification
Boss Pt.
Mabou.
Horton
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• Facies count maps
• For any given isopach, for example, you can add up the amount of a particular facies across that thickness of the formation. This was the predominant method used for analysis. The formation was divided into upper and lower isopachs, for ease of mapping.
• Facies slice maps
• Slices through the seismic impedance volumes showing the distribution of the 6 facies types across the map area. Advantages for certain trends.
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Mapping Methods
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Boss Point High Porosity Facies Count Map
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Boss Point Medium-Low Porosity Facies Map
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Note the lower ‘count’ (cooler colours) of shale for the Boss Point
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Boss Point Shale Facies Map
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Mabou High Porosity Facies Count Map
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Lower Mabou Facies Slice Map
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Pervasive Tight Sand Facies (grey)
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Horton High Porosity Facies Count Map
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Horton Shale Facies Count Map
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Horton Non-Reservoir Count Map
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Much of the coarse-grained continental facies that make up the Boss Point succession might be tightly cemented, and show up generally as low to moderate porosity facies on the seismic.
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Environment of DepositionBoss Point
Boss Pt.
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On seismic there appears to be an overall coarsening- and sandier-upward succession in this formation.
This suggests a marine transgression at the base followed by regional regression culminating in nearshore sandstones at the top.
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Mabou – Marine Influence
Mabou.
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Evidence of turbidite sand bodies if the marine interpretation is correct.
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Mabou - Turbidites
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High quality sand intervals appear continuous in other areas and show an angular relationship with the overlying strata.
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Mabou – Continuous Sands
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Little evidence of orderly stratigraphy
Better quality facies to the north with low-quality facies to the south – direction of regional shale-out in the basin
Some localized area of high porosity deposition in the Upper Horton, in red circle.
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Environment of DepositionHorton
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• Verifies the presence of significant reservoir using seismic control.
• Map the distribution of the sand and shale reservoirs.
• Insight into the EOD’s.
• Basis future exploration and development of a local natural gas source.
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Conclusions
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Acknowledgements
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www.petrelrob.com Worldwide Petroleum Consulting
Seismic Analysis For
Unconventional Reservoirs
Presented by Kathleen Dorey