Ikon Science - ifz.rupetromodel.ifz.ru/fileadmin/user_upload/petromodel_site/...Xu/Payne Carbonate Rock Physics Model • A cross-plot of the measured Vp against porosity provides

От моделирования физики карбонатных пород к 3D прогнозированию

их типов пор и трещин в земных недрах.

From Carbonate Rock Physics Modelling to 3D Pore Type Prediction in the

Subsurface

Генри Моррис, Рауф Надиров, Саймон Пейн, Мритрунджай Кумар

Henry Morris, Rauf Nadirov, Simon Payne, Mritrunjay Kumar

Ikon Science ‘Providing the Missing-link between petrophysics and Reservoir models’

Балтийская школа-семинар «Петрофизическое моделирование осадочных пород»* г. Петергоф * 17-21 сентября, 2012

Overview

• Pore classification in Carbonates and the Xu/Payne model

– Separating out types of Porosity in the velocity environment.

– Fluid Substitutions in Carbonates

• Predictions from Seismic

– Impedance Analysis

– Inversion to Reservoir Properties (Bayesian Classification)


• Pore classification in Carbonates and the Xu/Payne model

– Separating out types of Porosity in the velocity environment.

– Fluid Substitutions in Carbonates


Xu/Payne Carbonate Rock Physics Model

• A cross-plot of the measured Vp against porosity

provides and indication of the relative contribution of

each pore component

• Xu & Payne (2009) suggested an extension to

the Xu-White model to represent carbonate rocks

as a multi-porosity system:

• Xu/Payne performs better than

Gassmann in fluid subsitution! G

assm

ann X

u/P

ayne

[Shear changes caused by squirt flow

(localized pressure gradients) and chemical

changes]

Hard pores

Soft pores


Cracks

Spheres

Ellipsoids

Primary Porosity (Connected / Moveable)

Secondary Porosity (Unconnected /Trapped)

Total Porosity = Phie + Clay bound water

Effective Porosity (Phie)

(not bound)

Porosity Classification


• Carbonates show a wide range in velocities for rocks of similar porosities.

• This is because of the different pore shapes e.g. vugs, cracks, etc. in addition to interparticle ellipsoidal porosity.

• Carbonates with interparticle porosity characterized by well connected ellipsoidal pores follows Wyllie’s time-average equation (Anselmetti & Eberli, 1993).

• Carbonates having spherical porosity show an increase in sonic velocities for a given porosity from reference trend e.g., Wyllie’s (Kumar and Han, 2005).

• Carbonates with fractures or crack like porosity show a reduction in velocity from reference trend e.g., Wyllie’s (Kumar and Han, 2005).

• The lithology effect is not as prominent as pore shape effect in carbonates (Saleh & Castagna , 1999).

• Decoupling Lithology, HC and Pore Shape Effect of carbonate sonic velocities improve carbonate rock reservoir characterization.

Spheres +

Ellipsoid

Cracks +

Ellipsoid

+

HC Effect

Ellipsoids

Spheres

Cracks

Dual Pore Systems in Carbonates: Assumptions


Pore Classification in Carbonates

Cracks Spheres Ellipsoids

• Any carbonate rock can be defined as a two pore system.

• Rocks with velocities similar to reference velocity (e.g. Wyllie)

are composed of well connected ellipsoidal pores.

• Rocks with velocities greater than reference velocities are

composed of connected ellipsoidal pores and stiff spherical

pores.

• Rocks with velocities lower than reference velocity are

composed of well connected ellipsoidal pores and cracks.

• The goal is to separate the ellipsoidal porosity (phip) from the

cracks and stiffer spherical pores. Xu & Payne 2009 Балтийская школа-семинар «Петрофизическое моделирование осадочных пород»* г. Петергоф * 17-21 сентября, 2012

Pore Classification in Carbonates

Ellipse indicated high density of fractures (L), corroborated by FMI analysis (R)

PhiT PhiT

Vp

Vp

Fracture Density from Xu/Payne Model Fracture Density –via FMI


Initial Vp, Vs, Rho (Invaded)

VCarb = Vlime+Vdol

Volume set = VCarb + VClay

Mixed Mineral Properties (K, mu etc)

Primary Porosity – Ellipsoids

Secondary Porosity – Spheres,

Cracks/fractures

Brine Vp, Vs, Rho

Initial Vp, Vs, Rho(Un-invaded)

PhiE

PhiT

Sxo

Swt

Gas Vp, Vs, Rho

Fluid Sub in

Primary

Porosity only

Inputs: Outputs:

By Products created along the way in-order to perform fluid subs

Xu/Payne Carbonate Rock Physics Model


Xu/Payne optimization

Vcl φ Vp Vs cracks/

pores Vcl φ Vp Vs

cracks/

pores Vcl φ Vp Vs

cracks/

pores

• Optimisation

performed to

model the

measured Vp log

by adjusting the

contribution of

interparticle

pores and micro-

cracks

• The dry and

saturated rock

properties (Vp, Vs

& ρ) are then

generated for the

optimised model

Measured log data =

black

Modelled data = red


Dual Pore System Results

Cracks

Spheres

Ellipsoids

GR Vol Dual Pore Por

On the right Ellipsoids are primary (connected) porosity.

Cracks and fractures are secondary (unconnected)

porosity.

Secondary porosity is assumed to contain 100% bound

water.

GR Lith

Pri

mary

Ph

i T

yp

es

Pri

mary

Ph

i &

Sat

PhiT

invaded

PhiT

fresh

Porosity

difference

PhiP

fresh

PhiE

invaded

Porosity and Saturation Corrections

This slide shows an Example well:

Tracks 3 and 4 show total porosity with reservoir and invaded

zone saturations respectively.

Track 5 shows the difference between total porosity and primary

(connected) porosity, phip.

Track 6 and 7 show primary porosity.

Track 6 has reservoir saturation corrected for bound water – note

that HC is relatively higher than track 3

Track 7 has flushed zone saturation corrected for bound water.

Fluid substitutions were performed using the flushed zone

saturation as initial conditions as this is what the Vp and Vs logs

are measuring

Vol Por/

Xo-Sat

Por/

Tot-Sat Rho Vp Vs

Well X Fluid Substitutions

Initial ‘flushed’ 100% water Corrected ‘fresh’

Black = initial logs

Red = flushed zone corrected logs

Blue = 100% Water logs

Correction for Invasion was

important

The top of the carbonate is

brighter if water bearing. However

in general amplitudes within the

carbonate are slightly brighter

when gas bearing.

Brighter at top

carbonates in water

case

In general amplitudes

are brighter when gas

bearing

Invaded 100% Brine Gas

Synthetic AVO Gathers


• Predictions from Seismic

– Impedance Analysis at the well

– Inversion to Reservoir Properties (Bayesian Classification)

‘Are inversions useful in Carbonate studies...?’

‘How far can we go with Carbonate inversions and Reservoir characterization?’


Acoustic Impedance

Gra

die

nt

Imp

ed

an

ce

Carbonate/Dolomite Rock Properties

Focus: Only the Carbonate Rock Properties

Cracks

Spheres

Ellipsoids


Carbonate Rock Properties from Impedance

Focus: Only the Carbonate Rock Properties

Cracks Spheres Ellipsoids

Acoustic Impedance

Gra

die

nt

Imp

ed

an

ce

Acoustic Impedance

Sh

ea

r Im

pe

da

nc

e

The Ellipsoids are found linked to both Cracks and Spheres. Whereas the Cracks and

Spheres start to separate apart from one another




Acoustic Impedance

Gra

die

nt

Imp

ed

an

ce

Acoustic Impedance

Sh

ea

r Im

pe

da

nc

e

If we simplify it back to a dual Porosity

system then the patterns become clearer.

If we invert to these facies (Primary and

Secondary) then we end up with

productive and unproductive Reservoir.

Dual Pore Systems in Carbonates from Impedance

Ellipsoids & Spheres Cracks & Ellipsoids




Acoustic Impedance

Gra

die

nt

Imp

ed

an

ce

Acoustic Impedance

Sh

ea

r Im

pe

da

nc

e

Dual Pore Systems in Carbonates from Impedance

Ellipsoids & Spheres Cracks & Ellipsoids


Well Ties Carbonates

Well Ties

Syn

Tra

ce

Seis Trace

Correlation

AI AI AI AI AI

Moving in to the seismic domain it is important to get good well

ties to gain confidence that we will be able to predict with

confidence away from the well.


The Initial Seismic - Carbonate setting

Seismic Data - Full Stack


3D Dual Porosity Network in Carbonates

Dual Porosity Volume (from Bayesian Classification)

Created from AVO Seismic – Inversion to AI & GI

Acoustic Impedance

Gra

die

nt

Imp

ed

an

ce

Ellipsoids & Cracks (Connected/Moveable)

Spheres & Ellipsoids (Unconnected /Trapped)


Documents

Ikon Science - ifz.rupetromodel.ifz.ru/fileadmin/user_upload/petromodel_site/...Xu/Payne Carbonate Rock Physics Model • A cross-plot of the measured Vp against porosity provides