www.petrelrob.com Worldwide Petroleum Consulting

Seismic Analysis For

Unconventional ReservoirsPresented by Kathleen Dorey

For the CSUR Technical Webinar

Calgary, Canada

September 30th, 2020

Source: Financial Post, March 2019

Offshore Natural Gas Production

Natural Gas Bills Across Canada

Average Gas Bill January 2018 – 7.37 Gj of Consumption

Source: NEB

Study Area and Pipeline Proximity

Source: Keppie, 2017

Sable Island

Cumberland Onshore Basin

Source: Classification of Nova Scotia Sub-Basins

(NSDNR, 2010)

Natural Gas Potential

Source: Keppie, 2017

Unconventional Resources

Source: Keppie, 2017

9

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.

Basin Setting

W-E Cross Section

N-S Cross Section

Note Horton

thickness:

Can be 3000

m+ in area,

most gas

potential in

this formation

Basin Stratigraphy

• 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.

14

Seismic Analysis Method

Seismic and Well Control

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.

16

Well Log Considerations

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.

17

Attribute Analysis

18

High Porosity / Tight Sand Facies

Shale Facies

Non–Reservoir Facies

Boss Point / Mabou Classification

Horton Classification

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.…

23

Seismic Inversion

Seismic Facies Classification

Boss Pt.

Mabou.

Horton

• 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.

25

Mapping Methods

Boss Point High Porosity Facies Count Map

Boss Point Medium-Low Porosity Facies Map

27

Note the lower ‘count’ (cooler colours) of shale for the Boss Point

28

Boss Point Shale Facies Map

Mabou High Porosity Facies Count Map

29

Lower Mabou Facies Slice Map

30

Pervasive Tight Sand Facies (grey)

Horton High Porosity Facies Count Map

31

Horton Shale Facies Count Map

32

Horton Non-Reservoir Count Map

33

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.

34

Environment of DepositionBoss Point

Boss Pt.

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.

35

Mabou – Marine Influence

Mabou.

Evidence of turbidite sand bodies if the marine interpretation is correct.

36

Mabou - Turbidites

High quality sand intervals appear continuous in other areas and show an angular relationship with the overlying strata.

37

Mabou – Continuous Sands

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.

38

Environment of DepositionHorton

• 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.

39

Conclusions

Acknowledgements

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www.petrelrob.com Worldwide Petroleum Consulting

Seismic Analysis For

Unconventional Reservoirs

Presented by Kathleen Dorey

kdorey@petrelrob.com