Petroleum Reservoir Engineering ----Basic Concepts

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Pennsylvania 1859

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Outline

§ Introduction § Reservoir Properties ú Porosity ú Permeability ú Capillary Pressures ú Wettability ú Relative Permeability ú Reservoir Pressure § Basic PVT data § Reservoir fluid type § Drive Mechanism § Numerical simulation

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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 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. The law of Diminishing return

50 Hyperbolic Creaming Curve-North sea 45 40 35 30 25 20 15

Cum Discovery, Gb Discovery, Cum 10 Actual Hyperbolic Model 5 0 0 500 1000 1500 2000 2500 3000 3500 Cum Wildcat wells Mar-2010 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only.

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.

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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.

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Definition-Reservoir Engineering

§ “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.”

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Reservoir Simulation

Therefore the Ultimate goal is….. •Hydrocarbon in place •Recoverable hydrocarbons reserves •Rate of exploitation Mar-2010 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. 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

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Mar-2010 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Porosity Porosity of rock is the ratio of pore volume to bulk volume and is usually expressed as percentage

Vp is pore volume Interconnected Vb is bulbk volume pores Vg is grain volume Isolated pores

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

Mar-2010 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. A Pore Elements of Pore Throat Size & freq distribution-uncorrelated, correlated

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

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

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.

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Soi=(1-Swi) high

Soi=(1-Swi) low

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Pore Network-Reconstructed using thin section IMAGE Analysis

Porosity intergranular- 0.23 Porosity intergranular- 0.37 Porosity total- 0.28 Porosity total- 0.39 Absolute Permeability- 426md Absolute Permeability- 5600md Mar-2010 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only.

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) Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Permeability

§ 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)

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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

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

The carbonates

The clastics

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Phi Group - RQI Plot Porosity - Permeability Plot 10.000 1000.00 y = 8081.6x2.5518 HU7, HU 7 100.00 1.000 HU 6 2.3492 HU 5 HU6, y = 1648.1x y = 355.42x2.0499 HU 4 HU5, 10.00 2.212 HU 3 y = 245.68x HU 2 HU4, 0.100 1.8785 HU 1 1.00 y = 37.476x HU3, y = 30.796x2.1428 RQI, micron RQI, HU2,

Core Permeability,Core mD 0.10 0.010 y = 18.846x2.4585 HU1,

0.01 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.001 0.010 0.100 1.000 Core Porosity Phi Group

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§ 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 of Transition Zone Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. 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 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Wettability

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

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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

Swc Soc NwP

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Relative Permeability-Rock typing

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

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Relative Permeability-Core Condition

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

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Relative Permeability-wettability

Type KrwNwNo

Water 0.1-0.44-62-3 Wet

Mixed 0.5-0.92-43-5 Wet

Oil Wet 0.8-1.01.5-36-8

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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

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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

P Res K,s,C T qo P t Model K,s,C Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only.

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= 162.6qµB mh

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

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Pressure Build-up analysis

§ Log-log Plot(Diagnostic plot): Log ▲t Vs Log ▲P § Horner Plot or MDH Plot : Horner 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 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Field Example XYZ 2222-2250.5m (B2) 3 distinct slopes K:588md, kh:17105 mdft Nearest distance to heterogeneity: 130ft

Mar-2010 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Field Example XYZ 2222-2250.5m (B2) 3 distinct slopes K:588md, kh:17105 mdft Nearest distance to heterogeneity: 130ft

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Fig-4 L-II RFT Pressure Data

920 1983-84 940 1993-94 1997-98 960

980 tvdss (m) 1000

1020

1040 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 Normalised pressures ( psi)

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P3 MDT pressure of layer-II I4 I5 P2 MDT pressure of layer-IV well P3-2/06 I2 well P3-2/06 I5 well I5-9/06 2150 well P2-3/06 2260 well I2-10/06 well P4-4/06 well I1-06/08 well I5-9/06 2160 well I2-10/06 2270 Well I6-07/08 31% well I1-06/08 D1-14-10/07 Well I6-07/08 2280 Well P5-9/08 2170 D1-14-10/07 wELL p5-9/08 well p6 11/08 well p6-11/08 2180 2290 well p1-12/08

15% 2190 2300

2200 2310

2210 2320

2220 2330

2230 2340

2240 2350

2250 2360 3160 3180 3200 3220 3240 3260 3280 3300 3320 3340 3360 3380 3400 3420 3440 3460 3480 3500 3520 3540 3560 2920 2940 2960 2980 3000 3020 3040 3060 3080 3100 3120 3140 3160 3180 3200 3220 3240 3260 3280 3300 3320 3340 3360 3380 3400 3420 3440 Mar-2010 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Data - Fluid Properties

§ Expressing HC in place in surface conditions

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

§ Laboratory or empirical relations

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Mar-2010

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TrTctTc< §Black oil §Retrograde §Wet gas §Low shrinkage oil condensate §Dry gas § §Volatile oil Near Critical Cond gas

Dry gasGas. CondVolatile OilBlack OilMole Comp. OilMole OilBlack CondVolatile Dry gasGas. C1 95.8587.0764.3648.83 C2 2.674.397.522.75 C3 0.342.294.741.93 C4 0.521.744.121.6 C5 0.080.832.971.15 C6 0.120.601.381.59 C7+ 0.423.8014.9142.15

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The Role of Heavy Components….

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Phase Envelop-Black Oil

1 .2 -1 .3Bo v/rv 1.2-1.3Bo

35-125GOR-v/v

15-40API°

Colour Brown- D.Green GOR API

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Phase Envelop-Low shrinkage Oil

< 1.2Bo v/rv <1.2Bo 35GOR-v/v <35API° BlackColour

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Phase Envelop-Volatile Oil

< 2 .0Bo v/rv < 2.0Bo 350-550GOR-v/v 45-55API° Colour Greenish- Orange

GOR API Mar-2010 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only.

Phase Envelop-Near Critical Crude

> 2 .0Bo v/rv > 2.0Bo > 550GOR-v/v 45-55API° L ig h t Colour Light

Mar-2010 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Phase Envelop-Retrograde Gas Condensate

1400-16000GOR-v/v > 50API° LightColour

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Phase Envelop-Wet Gas

GOR-v/v 11000- 18000 60API°

LightColour

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Phase Envelop- Dry Gas

>18000GOR-v/v >API° LightColour

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%)

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§ 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 process ú Very gradual pressure decline ú Little change in producing GOR ú Early water production from structurally lower wells ú High ultimate recovery

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§ Gravity Drainage: As a result of difference in reservoir fluid densities ú 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

Asphaltene –The problem

Scales for reservoir heterogeneity

MICRO Thin sections MACRO Core

MEGA Well logging Well test 3D seismic

GIGA Seismic Basin studies

Reservoir simulation

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

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

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)

Disciplinary contributions to reservoir modeling

Seismic Petrophysics Fluid Interpretation Properties

NUMERICAL Geological SIMULATION Surface Model MODEL Facilities

Wells Model Grid Vertical Economics Effects Horizontal Multilateral

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

Numerical Models

§ Basic equations for fluid flow

ú Conservation of mass ú Conservation of momentum ú Conservation of energy ú Rate Equation ú EOS

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§ 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 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. 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

Scales for reservoir heterogeneity MICRO Thin sections

MACRO Core Grouping of fine layers for upscaling 1 432 100%

80%

60%

40%

20%

0% 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 MEGA Well logging

Well test RSIN3 3D seismic GIGA Seismic Basin studies

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History Match -Final Realization

Parallel Simulation

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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

Thanks for patient hearing

Mar-2010