Petroleum Res Eng

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Petroleum Reservoir Engineering ----Basic Concepts

Pennsylvania 1859

S.K.Pant

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Outline § Introduction § Reservoir Properties ú ú ú ú ú ú

§ § § §

Porosity Permeability Capillary Pressures Wettability Relative Permeability Reservoir Pressure

Basic PVT data Reservoir fluid type Drive Mechanism Numerical simulation Mar-2009

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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

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Cum Discovery, Gb

The law of Diminishing return

50 Hyperbolic Creaming Curve-North sea 45 40 35 30 25 20 15 10 Actual Hyperbolic Model 5 0 0 500 1000 1500 2000 2500 3000 3500 Cum Wildcat wells

Mar-2010

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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

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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. Mar-2010

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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.” Mar-2010

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Broad Functions

Reservoir Simulation

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

Mar-2010

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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

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The Traps

Mar-2010

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Porosity Porosity of rock is the ratio of pore volume to bulk volume and is usually expressed as percentage Vp is pore volume Vb is bulbk volume Vg is grain volume

Interconnected pores Isolated pores

Total or Absolute Porosity: It is the ratio of the volume of all the pores to the bulk ú volume of the material, Effective porosity

ú

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

Mar-2010

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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.

Mar-2010

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The role of Rock Texture… Soi=(1-Swi) high

Soi=(1-Swi) low

Mar-2010

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Pore Network-Reconstructed using thin section IMAGE Analysis

Porosity intergranular- 0.23 Porosity total0.28 Absolute Permeability- 426md

Porosity intergranular- 0.37 Porosity total0.39 Absolute Permeability- 5600md Mar-2010

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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)

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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) Mar-2010

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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

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

The carbonates

The clastics

Mar-2010

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Improved Permeability estimation Phi Group - RQI Plot

Porosity - Permeability Plot

10.000

HU 7 HU 6

1.000

RQI, micron

HU 5 HU 4 HU 3 HU 2

0.100 HU 1

0.010

Core Permeability, mD

1000.00 HU7,

y = 8081.6x 2.5518

100.00 HU6, 10.00

1.00

HU3,

0.10

0.05

y = 37.476x1.8785 y = 30.796x 2.1428 HU2, y = 18.846x 2.4585

HU1, 0.01 0.00

y = 1648.1x2.3492 y = 355.42x 2.0499 HU5, y = 245.68x 2.212 HU4,

0.10

0.15

0.20

0.25

0.30

0.001 0.010

0.100

1.000

Core Porosity

Phi Group

Mar-2010

0.35

0.40

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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 of Transition Zone

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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 Mar-2010 •Rock Typing

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Wettability § ‘The tendency of a fluid to spread or adhere to a solid surface in

presence of another immiscible fluid ‘

Mar-2010

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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 WP

Mar-2010

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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

Mar-2010

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

§ Relative Permeability

Mar-2010

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Relative Permeability-wettability Type

No

Nw

Krw

Water Wet

2-3

4-6

0.1-0.4

Mixed Wet

3-5

2-4

0.5-0.9

Oil Wet

6-8

1.5-3

0.8-1.0

Mar-2010

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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

Mar-2010

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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 Evaluation: Deliverability, Properties, Size ú Management: Refining forecast, Front movement ú Description: Faults, barriers ú

P Res K,s,C T

qo t

P Model K,s,C

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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 Mar-2010

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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

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Field Example XYZ 2222-2250.5m (B2) 3 distinct slopes K:588md, kh:17105 mdft Nearest distance to heterogeneity: 130ft

Mar-2010

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Field Example XYZ 2222-2250.5m (B2) 3 distinct slopes K:588md, kh:17105 mdft Nearest distance to heterogeneity: 130ft

Mar-2010

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More data More Refinement Fig-4

L-II RFT Pressure Data

920

1983-84 1993-94

940

1997-98 tvds s (m )

960 980 1000 1020 1040 900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000

Normalised pressures ( psi)

Mar-2010

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Differing Aquifer Support I4

MDT pressure of layer-II

P3

I5

MDT pressure of layer-IV

I4

P2 I2 I5

well P3-2/06 well P2-3/06

2150

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

2260

well P4-4/06 well I5-9/06

2160

well I2-10/06

2270 31%

well I1-06/08 Well I6-07/08

2170

D1-14-10/07

2280

wELL p5-9/08 well p6-11/08

2180

2290

well p1-12/08

Mar-2010

3560

3540

3520

3500

3480

3460

3440

3420

3400

2360 3380

2250

3360

2350

3340

2240

3320

2340

3300

2230

3280

2330

3260

2220

3240

2320

3220

2210

3200

2310

3180

2200

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

2300

3160

15%

2190

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Data - Fluid Properties § Expressing HC in place in surface conditions § Estimation of Pb,FVF,Rs,Bg, Viscosity § Laboratory or empirical relations Mar-2010

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Basic PVT Properties Mar-2010

Mar-2010

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Reservoir Fluid Types Tr18000

API°

>

Colour

Light

Mar-2010

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Drive mechanism § Depletion drive:

Expansion of gas evolved from solution ú ú ú ú ú

No free gas cap and no active water drive Rapid pressure decline Water free production Rapidly increasing GOR Low ultimate oil recovery (5-20%)

Mar-2010

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Drive mechanism § Gas Cap drive: Expansion of Gas cap gas ú Gas cap and no or small ú ú ú ú

active water drive Less rapid pressure decline Water free production Rapidly increasing GOR in structurally high wells Moderate ultimate oil recovery (25-40%) Mar-2010

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Drive mechanism § Water Drive: Production of oil by water displacing process is & usually most efficient process Very gradual pressure decline ú Little change in producing GOR ú Early water production from structurally lower wells ú High ultimate recovery ú

Mar-2010

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Drive mechanism § 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

Mar-2010

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Asphaltene –The problem

Mar-2010

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Scales for reservoir heterogeneity MICRO Thin sections MACRO Core

MEGA Well logging Well test 3D seismic GIGA Seismic Basin studies

RSIN3

Mar-2010

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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

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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

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Disciplinary contributions to reservoir modeling Seismic Interpretation

Petrophysics

Fluid Properties

Geological Model

NUMERICAL SIMULATION MODEL

Surface Facilities

Model Grid Effects

Wells Vertical Horizontal Multilateral

Economics

RSIN1

Mar-2010

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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

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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

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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

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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

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MICRO Thin sections

Scales for reservoir heterogeneity MACRO Core

Grouping of fine layers for upscaling 1

100%

2

3

4

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 100

RSIN3

GIGA Seismic Basin studies Mar-2010

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History Match-First Realization

Mar-2010

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History Match -Final Realization

Mar-2010

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Layer-9(c)

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Parallel Simulation

10 million cell

1 billion cell

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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

Mar-2010

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Thanks for patient hearing

Mar-2010