12 Reservoir technolgy August 2015

2015-08-24 Classification: Internal

Reservoir Engineering

• Fluid types

• How is oil produced

• Fluid flow in porous media

• Drainage strategies

• Well solutions and IOR toolbox

Classifi

cation:

Internal

2012-

05-03

2

Reservoir Engineering

• Fluid types

• How is oil produced

• Fluid flow in porous media

• Drainage strategies

• Well solutions and IOR toolbox

Classifi

cation:

Internal

2012-

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3

HC are a complex mixture of:

• Methane CH4 C1

• Ethane C2H6 C2

• Propane C3H8 C3

• Butane C4H10 C4

• Pentane … C5

• Hexane… … C6

• Heptane … C7

• Octane … C8

• … C9

• and the heavier … C10+

• and contaminants N2, CO2, H2S

HydroCarbons or just “Oil” and “Gas”?

• Oil or Gas depends on chemistry and physics

− To answer we need phase diagrams:

“p vs. T” and “p vs. V”

Classifi

cation:

Internal

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Hydrocarbon “names” and Sales products

Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane … … …

Oil stable

Oil unstable

stable Condensate

LPG

NGL

Rich gas

Sales gas and LNG

C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 …

C10+

Classifi

cation:

Internal

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5

Hydrocarbons (oil/gas) From reservoir to surface

Classifi

cation:

Internal

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6

RESERVOIR SURFACE

GAS

OIL

+ NGL/CONDENSATE

+ DISSOLVED GAS

EXPANSION

SHRINKAGE

∆p

∆p

Reservoir Engineering

• Fluid types

• How is oil produced

• Fluid flow in porous media

• Drainage strategies

• Well solutions and IOR toolbox

Classifi

cation:

Internal

2012-

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7

How is Oil Produced?

• Drill a well and perforate

• Start producing by opening up the well head choke

• Oil flows into the well and to the surface due to “excess energy” in the reservoir

− the bottom hole pressure (pBH) is higher than the well head pressure (pWH) + the fluid column “weight” (ρgH) i.e. pBH – pWH > ρgH (+ pfriction)

− For some reservoirs artificial lift is “necessary”

• Gas lift (reduce ρgH)

• Downhole pump (increase pBH)

• When the well flows there is also a pressure drop from the reservoir and into the well (drawdown), pr – pBH > 0

Reservoir Pressure: pr

Bottom Hole pressure: pBH

Well Head Pressure: pWH

Classifi

cation:

Internal

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8

H

How is Oil Produced?

• The production rate q [Sm3/d], depends upon:

− Drawdown (pr - pBH)

− Permeability k

− Contact Area A between the wellbore and the sands.

− Viscosity of the fluid: m

Reservoir Pressure: pr

Bottom Hole pressure: pBH

Well Head Pressure: pWH

Classifi

cation:

Internal

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9

H

Reservoir Engineering

• Fluid types

• How is oil produced

• Fluid flow in porous media

• Drainage strategies

• Well solutions and IOR toolbox

Classifi

cation:

Internal

2012-

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10

Fluid properties

Viscosity (the ease by which a fluid can

flow through a porous medium)

Typical values for NCS reservoirs

(at reservoir conditions, cp):

μw = < 0.2, 0.6 >

μo = < 0.2, 2.0 >

μg = < 0.01, 0.05 >

Heavy oil: μo = < 10, millions >

Honey: μh = 10000

Viscosity depends on temperature

(and pressure)

Density (ρ = m/V)

Typical values for NCS reservoirs

(at reservoir conditions, g/cc):

ρw ≈ 1

ρo = < 0.6, 0.9 >

ρg = < 0.2, 0.4 >

ρw > ρo > ρg

hence gas is always on top,

water at bottom and oil in between

Density depends on temperature and

pressure (gas changes much more than liquids)

Classifi

cation:

Internal

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11

Single Phase Fluid Flow Permeability

• A measure of the ease by which a fluid can flow through a porous medium

Reservoir

quality

Permeability (k)

md

Excellent > 1000

Very good 250 to 1000

Good 50 to 250

Moderate 15 to 50

Poor < 15

Classifi

cation:

Internal

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12

Sources of information

1) Log

2) Plug/core

3) Well test (mini/standard/extended)

4) Cuttings

Beware of heterogeneities

Water injection into oil reservoir:

Classifi

cation:

Internal

2011-

09-05

Two Phase Fluid Flow Relative permeability

a

1 . 0

0 . 8

0 . 6

0 . 4

0 . 2

0 . 0

0 . 2 0 . 4 0 . 6 0 . 8 1.0 0 . 0

kro krw

Ko,eff = K * kro

Kw,eff = K * krw

Measured on core plugs

(or use analogue data)

Sorw: lowest possible value

of mobile oil

Typical values of Sorw :

< 0.15, 0.25 >

Water displaces oil

Recovery Factor / Sweep Efficiency

Classifi

cation:

Internal

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14

RF = Pore scale

displacement

Ability of recovery

process to displace oil

from accessed rock

Volumetric sweep x

Degree to which injected fluid

accesses all the rock

Cut-offs x

Physical & commercial

constraints affecting end of life

(i.e. water cut limit)

Sor

Mobility ratio

Heterogeneity

Connectivity

Faults/Barriers

Wells

Thickness

Dip/”gravity”

Reservoir Engineering

• Fluid types

• How is oil produced

• Fluid flow in porous media

• Drainage strategies

• Well solutions and IOR toolbox

Classifi

cation:

Internal

2012-

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15

16 Classification: Internal 2013-02-21

‘PRIMARY RECOVERY’

Pressure depletion; no injection at all.

NATURAL DRIVE

‘SECONDARY RECOVERY’

Injection of fluids for pressure maintanance.

PHYSICAL DRIVE

‘TERTIARY RECOVERY’

Injection of fluids designed to further improve recovery; “advanced recovery methods”.

DESIGN DRIVE

Natural depletion

ENHANCED OIL RECOVERY (EOR) All advanced recovery methods

IMPROVED OIL RECOVERY (IOR) All measures beyond current plans to improve expected oil/gas recovery. Can include all mechanisms.

Water injection

Gas injection

Thermal

Chemical

Miscible gas

WAG

Other

Drainage strategy

Find the best suited mechanism

for optimal resource exploitation

Drainage Strategy / Drive mechanism

mature field

OWC

Depletion Aquifer support

Initial OWC

virgin field

Oil rate

Water Cut

GOR

time

Classifi

cation:

Internal

2012-

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17

Pressure maintenance - Water injection

Water

Oil

Water

Oil

Basal water Edge water

Downflank water (denser than oil) injection

Classifi

cation:

Internal

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18

Pressure maintenance - Gas Injection

“Top” gas injection ”Edge” gas injection

Upflank gas (lighter than oil) injection

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cation:

Internal

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Gas

Water

Oil

Rules of thumb - The Big Picture

Recovery Factor Low Medium High

Oil field – by depletion and without

aquifer support. (a)

10% 15% 20%

Oil field – by efficient Water or Gas

injection or strong aquifer support. (a)

30% 50% 60%

Gas field - by depletion. (b)

60% 70% 80%

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cation:

Internal

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20

UR = STOOIP * RF

Number of wells – guidelines Different approaches

Oil Producers (OP) Water/Gas Injectors

1. Well drainage area: 1.5 to 3 km2. (choose upon compartmentalization,

heterogeneity level, NTG)

1. From experience; the ratio of number of producers to injectors

varies from (3:1) to (1:1).

Classifi

cation:

Internal

2012-

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21

3.

Reservoir Engineering

• Fluid types

• Fluid flow in porous media

• Drainage strategy

• Well solutions and IOR toolbox

Classifi

cation:

Internal

2012-

05-03

22

Well design and completion Benefit vs. Cost

• Vertical / horizontal / slanted / multilateral wells

• Commingled vs. dedicated completions

• Inflow control (ICV, ICD)

• Sand control

• Artificial lift (gas lift or ESP)

• Tubing diameter

Sensors

Zonal Isolation Packers

Classifi

cation:

Internal

2012-

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23

Water injection into oil reservoir:

Sor~0.20

Increased oil recovery

Statoil’s toolbox in the whole value chain

Platform technology • Low pressure production

• Debottlenecking

Subsea technology • Compression

• Boosting

Drilling and well • Advanced wells

• Well Interventions

• Standardised well solutions

Reservoir management • Conventional and advanced

recovery methods

• Geophysical reservoir

monitoring

• Mapping and modeling of

complex reservoir formations

Reservoir Engineering Toolbox Simulation models versus Analytical methods

• Reservoir simulation models may help identifying the number of wells required,

the optimal completion of wells, the present and future needs for artificial lift, and

the expected production of oil, water and gas.

− In Statoil there is a requirement to have a reservoir simulation model at DG2 level, but

most projects have a simulation model at DG1 or earlier.

• Analytical methods generally cannot capture all the details of the given reservoir

or process, but are fast and at times, sufficiently reliable.

− In modern reservoir engineering, they are generally used as screening or preliminary

evaluation tools.

− Analytical methods are especially suitable for potential assets evaluation when the data

are limited and the time is critical.

Classif

ication

:

Intern

al

2013-

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Classification: Internal 2013-07-12 26

Petrophysics

reservoir properties,

fluid saturations, etc.

Seismic interpretation

structure map, faults,

etc.

Well design

well design, drilling

schedule, lift curves

Economics

oil price & cost

assumptions

Facilities design

production, process

& export design

Uncertainty analysis

static & dynamic

uncertainty analysis

Reservoir engineering

simulations – grid and model effects

drainage strategy, # wells, well types, position

Geomodeling

reservoir properties,

pay, continuity, etc.

Calibration

field observations,

production data, etc.

Outcome

production profiles + uncertainty

project economics - for investment decision

- The subsurface workflow - Security

Classificati

on: Internal

- Status:

Draft

Cooperation between the

disciplines is the only way to

make the right decisions.

Communication is the key to

success!

2015-08-24 27 Classification: Internal

Presentation title

Presenters name

Presenters title

E-mail address ……@statoil.com

Tel: +4700000000 www.statoil.com

2015-08-24 28 Classification: Internal