Petrophysics of Thin Beds - lps.org.uk · Thin Beds –Conventional Petrophysics struggles to quantify due to resolution Tailwind Energy Ltd. Ltd. 15 2 ft In previous work, these

Tailwind Energy Ltd. 1

Petrophysics of Thin Beds

Paul Hoddinott7th March 2019

Geological Outcrop examples of Thin Beds

2Tailwind Energy Ltd. Ltd.

Deepwater Thin Beds, Carboniferous Ross Fm, Ireland Triassic Blomidon Fm, Bay of Fundy, Nova Scotia

E. Jurassic, Bridport Sands, West

Bay, Dorset, UK

Quiz - Scale of Wireline Logs sampling volume


Question 1/

The Bulk Density wireline tool samples a volume of rock

similar to the volume of what household item ?

A B C



Question 1/ The Bulk Density wireline tool samples a volume of rock similar to the

volume of what household item ?

Answer/

A



Question 2/

The Induction Resistivity wireline tool samples a volume of rock similar to the volume of what household item ?

A B C



Question 2/

The Induction Resistivity wireline tool samples a volume of rock similar to the volume of what household item ?

Answer/

C

Scale of Wireline Logs sampling volume


Based on Rider, 1997

Thick Beds are well quantified byPetrophysics 1)


5 ft 5 ft

Core Oil

Stain Flag

Net

Reservoir &

Net Pay

Flags

Core

Porosity

Core

Permeability

Water

Saturation

curve

(shaded to

show

hydrocarbons

Thick Beds are well quantified by Petrophysics 2)


2 ft

Tight or shaley

interval

indicating no

fluorescence

in UV light i.e.

No oil stain.

Computed

Shale Volume,

VSH, log curve

Oil-leg N.B. Thick sands

showing UV

fluorescence

i.e. oil stain)

Core photos can even detect Oil-Water contacts in Thick beds


5 ft

Tight or shaley

interval

indicating no

fluorescence

in UV light i.e.

No oil stain.

Water-leg N.B. Lack of UV

fluorescence

(i.e. oil stain)

Gap in core

Oil-leg N.B. Thick sands

showing UV

fluorescence

i.e. oil stain)

Thin Beds – Conventional Petrophysicsstruggles to quantify due to resolution


1

2

50 ft

Wireline logs struggle to resolve and quantify Thin Beds e.g. < 2 feet thick.

Thick Beds are well quantified byPetrophysics – although still resolution issues 1)

12Tailwind Energy Ltd. Ltd.Generally Net Reservoir & Net Pay shows good agreement to Oil Staining in core over Thick beds. However,

Petrophysics not flagging some Net Pay (Oil Stain) due to log vertical resolution issues.

Core Oil Stain

Flag

Petrophysics

Net Flags

2 ft

Thin Beds – Conventional Petrophysicsstruggles to quantify due to resolution 2)

13Tailwind Energy Ltd. Ltd.However, over Thin beds Petrophysics can underestimate Net Reservoir & Net Pay (in this example by 3.5 feet)

compared to Oil Staining as indicated by core photos.

Core Oil Stain

Flag over Thin

Beds

Petrophysics

Net Flags

2 ft



Core Oil Stain

Flag over Thin

Beds

2 ft

Here, for computed Net Pay to match core oil stain footage a strict VSH cut-off of <=0.40 is required



2 ft

In previous work, these oil-stained Thin Beds were totally underestimated by Petrophysics.

A more relaxed VSH cut-off of <0.65 is required to match core oil stain footage

Special Case: Glauconitic interval & Thin Beds


Interval looks shaly but is due to Glauconitic sand (mica). ALWAYS CHECK COMPOSITE LOG (Cuttings)

& CORE DESCRIPTIONS. Also, useful to generate a Density/Neutron Separation log to detect thin sandy beds

1) Section appears to be

entirely shaley. However, the

interval was tested and gave

good rates. Presumably he

interval was tested based on

core/cuttings indicating sands.

Also Deep Res > Shallow Res

indicating moveable

hydrocarbons.

1) Core indicates sand units with

oil stain, totaling 23 feet of oil

stained sands. These sands

contain Glauconite – giving the

shaley appearance on logs.

Density/Neutron separation

closing up indicates sandy units.

To match core and well test

result petrophysics requires

increased RHOsh parameter.

10 ft

Thin Beds – Petrophysical Findings


• Standard Wireline & LWD logs may not be able to detect / quantify ThinBeds e.g. less than 2 ft (60 cm) thick.

• It is always good practice to refer to lithology cuttings and coredescriptions / core photographs for evidence of thin beds and unusualmineralogy. e.g. Micas such as Glauconite.

• Modern day technology can help detect and quantify Thin Beds e.g.Image logs, NMR, Multi-array Resistivity, Forward modelling.

• Core oil stain footage can be replicated by Petrophysical evaluations bycomparing/contrasting to Petrophysical cut-offs when computing NetPay footages.

• Petrophysical Cut-offs may need to meet more relaxed or stricter criteria,depending on the nature of the geological setting.

Acknowledgements


• Rich Hiney & Dave Freeman (Tailwind Energy)

& for kind permission to release slides

• Mike Millar (Independent)

Documents

Petrophysics of Thin Beds - lps.org.uk · Thin Beds –Conventional Petrophysics struggles to quantify due to resolution Tailwind Energy Ltd. Ltd. 15 2 ft In previous work, these