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 • CO 2 flooding – History – CO 2 flooding in general • Carbonates • CO 2 flooding in carbonates – Sources – Example from the Permian Basin in Texas • Environmental aspect • CO 2 -EOR and CO 2 storage – Example from the Weyburn field in Saskatchewan – North Sea

Introduction • CO 2 – Greenhouse gas (CO 2 , CFC, CH 4 , N 2 O and O 3 ) – Photosynthesis – An everyday gas (soft drinks, beers, fire extinguishers) • Released by burning fossil fuels – Coal, oil and natural gas – The main source of CO 2 greenhouse gas from human activities

Physical properties of CO 2 • MW= 44.011 g/ mole • Sp. gravity= 1.529 T c = 31 o C • • P c = 72.83 bar • Soluble in water – Forms carbonic acid • Soluble in oil

Phase diagram for CO 2 • Triple point • Critical point • Supercritical state

CO 2 flooding - A historical perspective • Early EOR research in 1940’s and 1950’s – Water flood leaves residual oil – Re-mobilize oil by miscible flooding • CO 2 research in 1950’s and 1960’s – Oil and CO 2 immiscible – Dynamic miscibility • Permian Basin, West Texas, 1970’s – Field testing and commercial CO 2 flooding • Commercially in 1980’s in US – CO 2 pipeline network – Only EOR motivated

CO 2 solubility in crude oil • CO 2 more soluble in lighter oils – C 5 -C 12 fraction • CO 2 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

CO 2 solubility in water • CO 2 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 + + − + ⇔ CO H O H HCO 2 2 3 – Reacts with wellbore hardware and reservoir minerals

Miscibility • Miscibility – CO 2 not directly miscible with most crude oils – Extracts hydrocarbons from the residual oil – CO 2 dissolves into the oil – 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 90 % consuming • Mathematical models – Phase equilibria data – Equation of State • Thermodynamic MMP Correlations MMP – MMP increases with increasing sp. grav. – MMP increases with increasing temperature

Carbonates • Sedimentary rocks composed of carbonate minerals • Chalk (CaCO 3 ) – Skeletons of planktonic algae • Limestone (CaCO 3 ) – Re-crystallization of the skeletons • Dolomite CaMg(CO 3 ) 2 – Alternating CaCO 3 and MgCO 3

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 (Ca 2+ , CO 3 - and SO 4 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: + + − + ⇔ + 2 H CaCO Ca HCO 3 3 + + − + ⇔ + 2 H MgCO Mg HCO 3 3 • Carbonates – Improve injectivity – Compaction – Precipitation of CaCO 3 leads to reduced matrix permeability

Techniques for CO 2 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 CO 2 and water Keewatin publicatons

CO 2 flooding in carbonates • Most important EOR process in US carbonate reservoirs since early 1980’s • 48 of 71 CO 2 floods were in carbonates • Majority located in Texas • Cheaper than thermal and hydrocarbon flooding • CO 2 flooding is expected to expand

CO 2 sources Jarrel et al., 2002

Manufactured CO 2 • Refineries – CO 2 separated from the natural gas • Ammonia plant • Fertilizer plants • Power plants – Coal – Gas

Naturally occurring CO 2 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 • CO 2 flood planned in 1968

The CO 2 project • CO 2 injection 1971 • CO 2 from processed natural gas – Pipeline • CO 2 followed by water • Later WAG • CO 2 removal facilities installed

The CO 2 WAG recovery • Problems – Needed additional CO 2 extraction facilities – Re-complete injection wells – CO 2 delivery inconsistent – Re-injected CO 2 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 CO 2 project areas to maintain miscibility pressure – Methane separated from the re-injected CO 2 • 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 • CO 2 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 CO 2 • Environmental aspects?

Environmental Aspects of CO 2 • Largest contribution of greenhouse gases from human activities • Global Warming – Change in mean temperature and CO 2 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 CO 2 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 CO 2 – Geological storage

Combined CO 2 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 • CO 2 injection in 2000 – Extend life of Weyburn 25 years

Why CO 2 flooding in Weyburn field? • Continuous reservoir • Geology promotes gravity segregation • Crude oil – Swells – Large viscosity reduction • MMP can be achieved • Successful waterflood

CO 2 source • CO 2 piped from a synthetic fuel plant in USA • This is the eighth by-product of this plant • The CO 2 pipeline is 325 km long

Recovery prediction • 24 % recovery • At least 15% extra with the CO 2 (19.4 million Sm 3 ) Historical production and predicted CO 2 response

IEA Monitoring and Storage Project • International Energy Agency (IEA) – Research program • Project objectives – Develop expertise in CO 2 EOR and storage – Prove the ability of oil reservoirs to store CO 2 – Identify risks associated with geological storage – Develop CO 2 mobility control methods – Develop technology to monitor CO 2 movement – Develop an economic model

CO 2 injection in Norway • Only sandstone • Sleipner West – Gas contains 9% CO 2 – Piped untreated to Sleipner East • Sleipner East – CO 2 separated by liquid amine Sintef – CO 2 free gas piped – Amine separated from the CO 2 and reused – CO 2 injected into the Utsira sand • Gullfaks – Not profitable • Volve – CO 2 flooding planned

CO 2 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