Petroleum reseng

Petroleum Reservoir Engineering----Basic Concepts

S.K.Pant

Pennsylvania 1859

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Outline

§ Introduction

§ Reservoir Propertiesú Porosity

ú Permeability

ú Capillary Pressures

ú Wettability

ú Relative Permeability

ú Reservoir Pressure

§ Basic PVT data

§ Reservoir fluid type

§ Drive Mechanism

§ Numerical simulation

Mar-2009


Is the Party over ??

“I should stress that we are not facing a re-run of the Oil Shocks of the 1970s. They were like the tremors before an earthquake. We now face the earthquake itself. This shock is very different. It is driven by resource constraints, …”

(Dr Colin. J. Campbell)

Mar-2010


The law of Diminishing return

Mar-2010

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0 500 1000 1500 2000 2500 3000 3500

Cum Wildcat wells

Cu

m D

isco

very

, G

b

Actual Hyperbolic Model

Hyperbolic Creaming Curve-North sea


The Hydrocarbon….

§ Hydrocarbons are the simplest of the organic compounds. As the name suggests, hydrocarbons are made from hydrogen and carbon. The basic building block is one carbon with two hydrogens attached, except at the ends where three hydrogens are attached.

Mar-2010


The Hydrocarbons…

§ When the chain is between 5 and 9 carbons, the hydrocarbon is gasoline.

§ About a dozen carbons and it is diesel.

§ Around 20 carbons is motor oil.

§ A chain of hundreds to thousands of carbon and hydrogens make plastic. This particular plastic is polyethylene.

Mar-2010


§ “Application of scientific principles to the drainage problems arising during the development and production of oil and gas reservoirs”

§ “The art of developing and producing oil and gas fluids in such a manner as to obtain a high economic recovery.”

Definition-Reservoir Engineering

Mar-2010


Broad Functions

Mar-2010

Reservoir Simulation

Therefore the Ultimate goal is…..•Hydrocarbon in place •Recoverable hydrocarbons reserves•Rate of exploitation


Data Type

§ Data that pertains to the reservoir rock and its extent

ú Geologic & seismic data

ú Well Log data

ú Well test data

ú Core data

§ Data that pertains to the properties of reservoir fluids

ú Composition of HC

ú PVT

Mar-2010


The Traps

Mar-2010


Porosity Porosity of rock is the ratio of pore volume to bulk

volume and is usually expressed as percentage

Vp is pore volumeVb is bulbk volumeVg is grain volume

Total or Absolute Porosity:

ú It is the ratio of the volume of all the pores to the bulk volume of the material,

Effective porosity

ú It is the ratio of the interconnected pore volume to the

bulk volume

Interconnected pores

Isolated pores

Mar-2010


A Pore

Spatial arrangement-Arrangement of pores of different sizes w.r.t each other

Connectivity of pores and throat-No of pore throat connecting to pores

Size & freq distribution-uncorrelated, correlated

Elements of Pore Throat

The texture of a rock consists of it's grain or mineral crystal size, the arrangement of the grains or crystals, and the degree of uniformity of the grains or crystals.

Mar-2010


The role of Rock Texture…

Soi=(1-Swi)high

Soi=(1-Swi)low

Mar-2010


Pore Network-Reconstructed using thin section IMAGE Analysis

Porosity intergranular- 0.23Porosity total- 0.28Absolute Permeability- 426md

Porosity intergranular- 0.37Porosity total- 0.39Absolute Permeability- 5600md

Mar-2010


Saturation

§ Saturation of a phase is the fraction of the pore volume occupied by the phase So+Sg+Sw=1

Connate water saturation (Swc)

Critical Oil Saturation (Soc)

Critical gas Saturation (Sgc)


§ Permeability is a measure of ‘ ease of flow’ or the capacity of formation to transmit fluids.

§ Its unit is Darcy named after a French scientist

Henry Darcy in 1856.

ú Absolute Permeability:When only one fluid is present in the rock. It is a property of the rock and is independent of the fluid used in the measurement. This assumes that the fluid does not interact with the rock.(K)

ú Effective Permeability:Effective permeability occurs when more than one fluid is present & is a function of the fluid saturation & the wetting characteristics of the rock. (Ko,Kw,Kg)

Permeability

Mar-2010


Permeability

The permeability is measured by flowing a fluid of known viscosity µ through a core plug of measured dimensions (A and L) and then measuring flow rate and pressure drop. Darcy equation becomes

Mar-2010


Permeability

Establishing a perfect Ø-K transform still remains a major challenge specially in ref to carbonates

Mar-2010

The clastics

The carbonates


Improved Permeability estimation

0.001

0.010

0.100

1.000

10.000

0.010 0.100 1.000

Phi Group

RQ

I, m

icro

n

Phi Group - RQI Plot

HU 1

HU 7HU 6

HU 4

HU 2HU 3

HU 5

y = 18.846x2.4585

y = 30.796x2.1428y = 37.476x1.8785

y = 245.68x2.212

y = 355.42x2.0499y = 1648.1x2.3492

y = 8081.6x2.5518

0.01

0.10

1.00

10.00

100.00

1000.00

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

Core Porosity

Core

Perm

eability,

mD

HU7,

HU6,HU5,

HU4,

HU3,HU2,

HU1,

Porosity - Permeability Plot

Mar-2010


Capillary pressure

§ Combined effect of surface and IFT of the rock and fluid, pore size and geometry & wettability of the system.

• Major effect of Cap pres is the creation ofTransition Zone


Capillary pressure

§ Drainage Process:

ú Non Wetting phase displacing Wetting phase

§ Imbibition Process:

ú Wetting phase displacing Non wetting phase

•Determination of Connate water•Establish Saturation –height relation•Rock Typing Mar-2010


Wettability

§ ‘The tendency of a fluid to spread or adhere to a solid surface in presence of another immiscible fluid ‘

Mar-2010


Relative Permeability§ When two or more phases flow simultaneously the ratio of

effective to absolute permeability is termed ‘Relative permeability’

Kro= ko/k

Kre= kw/k

Krg= kg/k

SocSwc

NwP

WP Mar-2010


Relative Permeability-Rock typing

§ The variation in Rock Texture imparts significant changes in Rel perm estimates in core plugs of same formation

Mar-2010


Relative Permeability-Core Condition

§ Comparison of Rel-perms of cores with natural reservoir wettability preserved against a plug cleaned, dried and resaturated.

§ Relative Permeability

Mar-2010


Relative Permeability-wettability

0.8-1.01.5-36-8Oil Wet

0.5-0.92-43-5Mixed Wet

0.1-0.44-62-3Water Wet

KrwNwNoType

Mar-2010


Reservoir Pressure§ Reservoir Pressure

§ The fluids confined in the pores of the reservoir rock occur under certain degree of pressure, generally called reservoir pressure

ú The maximum pressure is called the static bottom hole

pressure, the shut in pressure or static formation pressure

Mar-2010


Well testing§ The response of the reservoir to change in production/

injection rates in a well is monitored

§ The reservoir response is measured in terms of ‘pressure’response & is usually dependent on K, Skin, Well bore storage, boundaries, fractures, dual porosity et.c

ú Evaluation: Deliverability, Properties, Size

ú Management: Refining forecast, Front movement

ú Description: Faults, barriers

ResK,s,C

ModelK,s,C

qo

t

P

P

T


Mar-2010

Radial Flow in a porous media :

For a single phase fluid flow (radial) in a constant permeability and porosity for a fluid of small and constant compressibility, the eauation is :

Pws= Pi-162.6qµB/kh*log((T+∆t)/ ∆t)

K= 162.6qµBmh

S= 1.151[ P1hr-Pwf] –log (K / ФuCtrw2 )+3.23]m


Pressure Build-up analysis

§ Log-log Plot(Diagnostic plot):

Log ▲t Vs Log ▲P

§ Horner Plot or MDH Plot :

Log [(tp+ ▲t)/ ▲t] Vs Pwf

▲Pskin= 0.87mS

Jactual = q .

P*- Pwf

Jideal = q .

P*-Pwf- ▲Pskin

Flow Efficiency = Jactual/ Jideal

D(distance of fault)=

(0.00105K ▲t/ ФuCt)1/2

Where ▲t = point at the time of intersection between two

straight lines

Horner Plot


Field ExampleXYZ2222-2250.5m (B2)

3 distinct slopesK:588md, kh:17105 mdftNearest distance to heterogeneity: 130ft

Mar-2010


Field ExampleXYZ2222-2250.5m (B2)

3 distinct slopesK:588md, kh:17105 mdftNearest distance to heterogeneity: 130ft

Mar-2010


More data More Refinement

L-II RFT Pressure Data

920

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1040

900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Normalised pressures ( psi)

tvd

ss

(m

)

1983-84

1993-94

1997-98

Fig-4

Mar-2010


Differing Aquifer Support

Mar-2010

MDT pressure of layer-II

2150

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well P3-2/06

well P2-3/06

well P4-4/06

well I5-9/06

well I2-10/06

well I1-06/08

Well I6-07/08

D1-14-10/07

wELL p5-9/08

well p6-11/08

well p1-12/08

P3

I4

I5

15%

MDT pressure of layer-IV

2260

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well P3-2/06

well I5-9/06

well I2-10/06

well I1-06/08

Well I6-07/08

D1-14-10/07

Well P5-9/08

well p6 11/08

P2

I2

31%

I5

I4


Mar-2010

Data - Fluid Properties

§ Expressing HC in place in surface conditions

§ Estimation of Pb,FVF,Rs,Bg, Viscosity

§ Laboratory or empirical relations


Basic PVT Properties

Mar-2010

Mar-2010


Reservoir Fluid Types

§Wet gas

§Dry gas

§Retrograde condensate

§Near Critical Condgas

§Black oil

§Low shrinkage oil

§Volatile oil

Tr>TctTc<Tr<TctTr<Tc

Mar-2010

0.423.8014.9142.15C7+

0.120.601.381.59C6

0.080.832.971.15C5

0.521.744.121.6C4

0.342.294.741.93C3

2.674.397.522.75C2

95.8587.0764.3648.83C1

Dry gasGas. CondVolatile OilBlack OilMole Comp.


The Role of Heavy Components….

After Mccain,W.D


Phase Envelop-Black Oil

Mar-2010

Brown-D.Green

Colour

15-40API°

35-125GOR-v/v

1.2-1.3Bo v/rv

T T

API

GO

R


Phase Envelop-Low shrinkage Oil

Mar-2010

BlackColour

<35API°

35GOR-v/v

<1.2Bo v/rv


Phase Envelop-Volatile Oil

Mar-2010

Greenish-Orange

Colour

45-55API°

350-550GOR-v/v

< 2.0Bo v/rv

GOR API


Phase Envelop-Near Critical Crude

Mar-2010

Light Colour

45-55API°

> 550GOR-v/v

> 2.0Bo v/rv


Phase Envelop-Retrograde Gas Condensate

Mar-2010

LightColour

> 50API°

1400-16000GOR-v/v

GOR API


Phase Envelop-Wet Gas

Mar-2010

LightColour

60API°

11000-18000

GOR-v/v

GOR API


Phase Envelop- Dry Gas

Mar-2010

LightColour

>API°

>18000GOR-v/v


Drive mechanism

§ Depletion drive:

Expansion of gas evolved from solution

ú No free gas cap and no active water drive

ú Rapid pressure decline

ú Water free production

ú Rapidly increasing GOR

ú Low ultimate oil recovery (5-20%)

Mar-2010


Mar-2010

Drive mechanism

§ Gas Cap drive:

Expansion of Gas cap gas

ú Gas cap and no or small active water drive

ú Less rapid pressure decline

ú Water free production

ú Rapidly increasing GOR in structurally high wells

ú Moderate ultimate oil recovery (25-40%)


Drive mechanism

§ Water Drive:

Production of oil by water displacing process is & usually most efficient processú Very gradual pressure

decline

ú Little change in producing GOR

ú Early water production from structurally lower wells

ú High ultimate recovery

Mar-2010


Drive mechanism

§ Gravity Drainage:

As a result of difference in reservoir fluid densitiesú Low GOR in structurally low wells

ú Formation of Secondary GCG

ú High GOR in structurally high wells

ú Little or no water production

ú High ultimate recovery

ú Variable rate of pressure decline

Mar-2010


Asphaltene –The problem

Mar-2010


Scales for reservoir heterogeneity

RSIN3

MICROThin sections

MACROCore

MEGAWell loggingWell test3D seismic

GIGASeismicBasin studies

Mar-2010


Reservoir simulation

§ The dictionary meaning of the word ‘simulate’ is ‘to give an appearance of’

§ Forms an integral part of Reservoir Management Functions (RMF)

Mar-2010


Reservoir simulation§ Mimics the behavior of a real system through

a model (physical, analog, electrical or numerical) based on realistic assumptions

§ Simulation can be close to reality but it is never the reality ( should approach reality with time)

Mar-2010


Disciplinary contributions to reservoir modeling

NUMERICALSIMULATION

MODEL

Petrophysics FluidProperties

SeismicInterpretation

Model GridEffects

GeologicalModel

SurfaceFacilities

Economics

WellsVertical

HorizontalMultilateral

RSIN1 Mar-2010


Numerical Model§ Mathematical models System of equations describing the

physical behavior

These are complicated nonlinear partial differential equations relating pressure and saturation changes with time

Analytical solutions-generally impossible

Numerical solutions –generally the only way

Mar-2010


Numerical Models

§ Basic equations for fluid flow

ú Conservation of mass

ú Conservation of momentum

ú Conservation of energy

ú Rate Equation

ú EOS

Mar-2010


Numerical Models

§ Numerical solution produces answer at discrete points within the system

§ Use of ‘finite difference’ for transforming the continuous differential equation to discrete form-both space and time are discretized (grid, timesteps)

§ Common solution procedures• IMPES, Newton-Raphson

Mar-2010


Stochastic Modeling§ Measures statistical variation in data

points-maps similar statistical properties

§ Better describes the heterogeneity of the reservoir- (variograms-trends, direction)

§ Integrates independent measurements

§ Uncertainty in measured values-assessed

§ Algorithm-Kriging, Conditional simulation,co-kriging

Mar-2010


Scales for reservoir heterogeneity

RSIN3

MICROThin sections

MACROCore

MEGAWell loggingWell test3D seismic

GIGASeismicBasin studies

Grouping of fine layers for upscaling

0%

20%

40%

60%

80%

100%

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43

Fine layers of 'a' parasequence

<1 1 to 10 10 to 100 >100

1 432

Mar-2010


History Match-First Realization

Mar-2010


History Match -Final Realization

Mar-2010


Layer-9(c)


Parallel Simulation

10 million cell 1 billion cell


Role & Impact

ú Corporate impact-cash flow predictions

ú Insight to the various physical process

ú Sensitivity

ú Comparing different exploitation scenarios

ú Optimize project design to maximize economic recovery

ú Real Time monitoring

Mar-2010


Mar-2010

Thanks for patient hearing


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Petroleum reseng