Improved oil recovery and environmental aspects by using carbon - - PowerPoint PPT Presentation

Improved oil recovery and environmental aspects by using carbon dioxide as EOR fluid in carbonates

Eli J. Høgnesen

Outline

• Introduction

– Carbon dioxide in general

• CO2 flooding

– History – CO2 flooding in general

• Carbonates
• CO2 flooding in carbonates

– Sources – Example from the Permian Basin in Texas

• Environmental aspect
• CO2-EOR and CO2 storage

– Example from the Weyburn field in Saskatchewan – North Sea

Introduction

• CO2

– Greenhouse gas (CO2, CFC, CH4, N2O and O3) – Photosynthesis – An everyday gas (soft drinks, beers, fire extinguishers)

• Released by burning fossil fuels

– Coal, oil and natural gas – The main source of CO2 greenhouse gas from human activities

Physical properties of CO2

• MW= 44.011 g/ mole
• Sp. gravity= 1.529
• Tc= 31 oC
• Pc= 72.83 bar
• Soluble in water

– Forms carbonic acid

• Soluble in oil

Phase diagram for CO2

• Triple point
• Critical point
• Supercritical

state

CO2 flooding - A historical perspective

• Early EOR research in 1940’s and 1950’s

– Water flood leaves residual oil – Re-mobilize oil by miscible flooding

• CO2 research in 1950’s and 1960’s

– Oil and CO2 immiscible – Dynamic miscibility

• Permian Basin, West Texas, 1970’s

– Field testing and commercial CO2 flooding

• Commercially in 1980’s in US

– CO2 pipeline network – Only EOR motivated

CO2 solubility in crude oil

• CO2 more soluble in lighter oils

– C5-C12 fraction

• CO2 dissolution leads to

– Oil swelling and reduction in oil density – Reduction in oil viscosity

• Oil swelling leads to lower residual oil saturation
• The viscosity reduction leads more mobile oil

CO2 solubility in water

• CO2 soluble in water

– Waterflooding – WAG

• Solubility affected by

– Pressure (increases with increasing pressure) – Temperature (decreases with increasing temp.) – Brine salinity (decreases with increasing salinity)

• Viscosity of water increases slightly
• Carbonic acid

– Reacts with wellbore hardware and reservoir minerals

− + +

⇔ +

3 2 2

HCO H O H CO

Miscibility

• Miscibility

– CO2 not directly miscible with most crude oils – Extracts hydrocarbons from the residual oil – CO2 dissolves into the

• il

– Dynamic miscibility

Simon et al., SPEJ 18(1), 1978

Minimum Miscibility Pressure (MMP)

• MMP= f(T, P and composition of oil)
• The pressure needs to be above the MMP
• This is corresponds to about 800 m depth
• If flooding pressure is below MMP, only swelling

and viscosity reduction will occur

Determination of MMP

• Slimtube experiments

– Real fluids – Expensive and time consuming

• Mathematical models

– Phase equilibria data – Equation of State

• Thermodynamic MMP

Correlations

– MMP increases with increasing sp. grav. – MMP increases with increasing temperature MMP 90 %

Carbonates

• Sedimentary rocks composed of carbonate

minerals

• Chalk (CaCO3)

– Skeletons of planktonic algae

• Limestone (CaCO3)

– Re-crystallization of the skeletons

• Dolomite CaMg(CO3) 2

– Alternating CaCO3 and MgCO3

EOR in Carbonates

• Carbonates

– 60% of oil reserves in carbonates – Fractured reservoirs – 90% Neutral- or Oil-wet

• Wettability

– Acid Number of the oil – Potential determining ions (Ca2+ , CO3

• and SO4

2-)

– Recovery less than 30% – Big EOR potential

Rock-fluid interaction

• Dissolution of carbonate due to carbonic acid in

the carbonated water may take place:

• Carbonates

– Improve injectivity – Compaction – Precipitation of CaCO3 leads to reduced matrix permeability

− + +

+ ⇔ +

3 2 3

HCO Ca CaCO H

− + +

+ ⇔ +

3 2 3

HCO Mg MgCO H

Techniques for CO2 flooding

• Gas injection

– Continuous Gas Injection (CGI) – Water Alternating Gas (WAG)

Continuous Gas Injection

• Used for gravity drainage
• Often used in combination with WAG

– CGI until gas breakthrough – Change to WAG

Water Alternating Gas (WAG)

• Alternate injection of CO2 and water

Keewatin publicatons

CO2 flooding in carbonates

• Most important EOR process in US carbonate

reservoirs since early 1980’s

• 48 of 71 CO2 floods were in carbonates
• Majority located in Texas
• Cheaper than thermal and hydrocarbon flooding
• CO2 flooding is expected to expand

CO2 sources

Jarrel et al., 2002

Manufactured CO2

• Refineries

– CO2 separated from the natural gas

• Ammonia plant
• Fertilizer plants
• Power plants

– Coal – Gas

Naturally occurring CO2 sources

• Trapped in dome-like structures
• Lithology: sandstone and dolomite
• Natural commercial reservoirs:

– McElmo Dome (Dolomite) – Sheep Mountain Fields – Bravo Dome (Conglomeratic sandstone) – La Barge Field (Dolomite)

The Permian Basin

SPE monograph 22

Example from the Permian Basin

• Kelly-Snyder field

– Limestone

• Discovered in 1948
• Developed 1951

– Initially pressure depletion

• Water injection in 1954

– 1 billion bbl un-recovered after flooding

• CO2 flood planned in 1968

The CO2 project

• CO2 injection 1971
• CO2 from processed natural gas

– Pipeline

• CO2 followed by water
• Later WAG
• CO2 removal facilities installed

The CO2 WAG recovery

• Problems

– Needed additional CO2 extraction facilities – Re-complete injection wells – CO2 delivery inconsistent – Re-injected CO2 containing methane

• Production peaked in the mid 1970’s at 210,000

bbl/ d

• Followed by a decline of 20% per year
• In 1995 the oil production was 9000 bbl/ d
• The economic limit was 7000 bbl/ d

New work-over

• New operator in 1995

– Increased production well pressures – Water injection curtain around CO2 project areas to maintain miscibility pressure – Methane separated from the re-injected CO2

• The recovery rate leveled
• In 2002 the recovery had increased 50%
• The lifetime of the field has been extended by at

least 25 years

The recovery history

• Recovery in the different recovery stages

Kinder Morgan, 2001

The recovery turnaround

Kinder Morgan

Summary of the Kelly-Snyder project

• CO2 is a good EOR fluid

– But the process needs to be monitored and maintained

• This flooding has only been minded on EOR, not

for storing of CO2

• Environmental aspects?

Environmental Aspects of CO2

• Largest contribution of

greenhouse gases from human activities

• Global Warming

– Change in mean temperature and CO2 concentration in atmosphere

Effects of global warming

• Mean sea level rises
• Extreme weather (droughts, hurricanes, etc.)
• Increased damage on life, health and material values

What to do about global warming?

How to reduce CO2 emission

• Use energy more efficiently

– Buildings, transportation – Power generation

• Switching to low-carbon fuels

– Coal to gas in electricity generation

• Substituting fossil fuels for non-carbon renewable

sources

– Wind, solar, biomass, geothermal and tidal power

• Trapping and storing of CO2

– Geological storage

Combined CO2 EOR and storage

The Weyburn EOR project

• Saskatchewan
• Discovered in 1954
• Medium oil (850 – 930 kg/ m 3)
• Fractured carbonate reservoir, mostly limestone
• Waterflooding since 1964
• CO2 injection in 2000

– Extend life of Weyburn 25 years

Why CO2 flooding in Weyburn field?

• Continuous reservoir
• Geology promotes gravity segregation
• Crude oil

– Swells – Large viscosity reduction

• MMP can be achieved
• Successful waterflood

CO2 source

• CO2 piped from a synthetic fuel plant in USA
• This is the eighth by-product of this plant
• The CO2 pipeline is 325 km long

Recovery prediction

• 24 %

recovery

• At least 15%

extra with the CO2 (19.4 million Sm 3)

Historical production and predicted CO2 response

IEA Monitoring and Storage Project

• International Energy Agency (IEA)

– Research program

• Project objectives

– Develop expertise in CO2 EOR and storage – Prove the ability of oil reservoirs to store CO2 – Identify risks associated with geological storage – Develop CO2 mobility control methods – Develop technology to monitor CO2 movement – Develop an economic model

CO2 injection in Norway

• Only sandstone
• Sleipner West

– Gas contains 9% CO2 – Piped untreated to Sleipner East

• Sleipner East

– CO2 separated by liquid amine – CO2 free gas piped – Amine separated from the CO2 and reused – CO2 injected into the Utsira sand

• Gullfaks

– Not profitable

• Volve

– CO2 flooding planned Sintef

CO2 storage in the North Sea

• The oil and gas fields of the southern part of the

North Sea are chalk reservoirs

• In Ekofisk there has been a significant

compaction due to pressure depletion and water weakening

The impact of CO2 on chalk

Madland et al., JPSE (2006), in press.

• Laboratory work has shown that:

– Chalk exposed to carbonated water is weakened – Pure CO2 gas had minor effect on chalk compression – Preferentially oil-wet chalk cores at Sor were weakened more than completely water-wet cores

10 20 30 40 50 60 2000 4000 6000 8000 10000

Time (min) Axial strain (mS) CO2 gas Water CO2 + water

Summary of the presentation

• As long as CO2 is available it is a logical EOR choice for

Dolomite and Limestone reservoirs

• Dolomite and Limestone reservoirs can probably be used for

safe storing of CO2

• CO2 flooding in chalk reservoir may be used as an EOR

technique, but significant compaction can be expected.

– The compaction can be a drive mechanism but it can also result in production problems like pipe buckling and formation instability.

• Using a chalk reservoir for CO2 storage can be questionable,

since the rock layers above might fracture if the reservoir is compacted.

– Then the CO2 can escape through the fracture system.