Jan – Dec, 2006
University of Alaska – Fairbanks
Pacific Northwest National Laboratory
British Petroleum Exploration Alaska
Injection of COInjection of CO22 for Recovery of for Recovery of
Methane from Gas Hydrate Methane from Gas Hydrate ReservoirsReservoirs
ObjectivesObjectives A better understanding of formation
kinetics and thermodynamics of CH4, CO2, and CH4-CO2 mixed gas hydrates in porous media
To study CO2 injection dynamics in gas hydrate bearing sediments
Build an analytical model in order to calculate hydrate equilibrium in porous medium
TasksTasks
Conduct the proof-of-principle experiments
Injection Dynamics of CO2 in Gas
Hydrate Bearing Sediments
Reservoir Modeling
Tasks CompletedTasks Completed Development of Pore Freezing Model to
predict hydrate saturation in porous medium Extension of Pore Freezing Model to predict
mixed hydrate saturation in porous medium Extension of UAF-HYD module to predict
hydrate equilibrium in the porous medium Simulation study to determine the role of
capillary pressure in producing methane from hydrates
Simulation study to determine the optimum CO2 concentration in CO2-H2O micro-emulsion
Tasks CompletedTasks Completed• 5 conference papers presented• 1 Poster presented at 2006 AADE
conference, Houston, Texas (April’06)• 1 journal paper submitted• 5 MS thesis defended
Reservoir ModelingReservoir Modeling
Pore freezing model
• Predicts Hydrate Saturation• Main feature- Consideration of salting
out phenomenon• Involves calculation of equilibrium
conditions for hydrates
Hydrate Saturation Prediction ResultsHydrate Saturation Prediction Results
Prediction of CH4 hydrate saturation
Methane gas hydrate saturation Vs Temperature
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
-6 -1 4 9 14
Temperature (OC)
Gas
Hyd
rate
Sat
ura
tio
n
Experimental
Pore Freezing Model
Hydrate Equilibrium PredictionHydrate Equilibrium Prediction
Hydrate Equilibrium in porous medium Far different from that in bulk hydrate
equilibrium Changes due to interaction of chemical
components with pore walls and due to energy required to maintain capillary equilibrium
Important to predict for any study involving hydrates in natural sediments
Results for CHResults for CH44 hydrate equilibrium hydrate equilibrium
in pore of radius 300 Ain pore of radius 300 Aoo
4
5
6
7
278 279 280 281 282
Temperature (K)
Pre
ssu
re (
MP
a)
Experimental Data Model Predictions Bulk Hydrate Equilibria
Effect of Capillary Pressure on Hydrate Recovery
Contradictory opinions on its role in hydrate recovery
Function of wetting phase saturation Calculated by van Genuchten principle STOMP simulator used for studying the
effect for various reservoirs with different soil characteristics sandstone, sand, loam, silt loam and clay
reservoirs considered
ResultsResults Capillary pressure profile in reservoir
Thermal Stimulation Capillary Pressure (2 Days)
0
0.01
0.02
0.03
0.04
0.05
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
x Distance, m
Cap
illar
y Pr
essu
re, M
Pa Clay
Silt Loam
Loam
Sand
Sandstone
ResultsResults CH4 recovery after thermal stimulation
Thermal Stimulation CH4 Flux Rate
0.0
2.0
4.0
6.0
8.0
10.0
12.0
0 50 100 150 200 250 300 350 400
Time, hr
CH
4 Fl
ux, k
g/hr
Clay
Silt Loam
Loam
Sand
Sandstone
Reservoir SimulationReservoir Simulation Objective
To study injection dynamics of CO2 in hydrate bearing sediments
To study effect of concentration of CO2-
microemulsion on hydrate recovery at various injection temperatures
To study the feasibility of injection of CO2-microemulsion for CH4 recovery from hydrate reservoir on Alaska North Slope (Mt. Elbert site located within Milne Point Unit )
Numerical Simulations: Numerical Simulations: 2-D Horizontal System: 10 x 10 x 1 Grid
Schematic representation of 2-D Reservoir Model•System Parameters:
Effective Porosity = 36%Permeability:
x-direction = 400 md y-direction = 200 md
•Initial Conditions: Hydrate Saturation (variable) System Temperature = 40C Pressure in the System = 6 MPa
Methane recovery as a function of Methane recovery as a function of Micro-emulsion temperature at Micro-emulsion temperature at
different concentrationsdifferent concentrationsResults for Methane Recovery
0.00
25000.00
50000.00
75000.00
100000.00
125000.00
150000.00
175000.00
5.0 10.0 15.0 20.0 25.0 30.0CO2-Microemulsion Temperature [C]
Met
han
e R
ecov
ery
[kg]
CO2 Conc = 10%
CO2 Conc = 20%
CO2 Conc = 30%
CO2 Conc = 35%
CO2 Conc = 45%
CO2 Conc = 50%
CO2 Conc = 60%
CO2 Conc = 75%
CO2 Conc = 85%
CO2 Conc = 90%
Effect of injection temperature and COEffect of injection temperature and CO22
slurry concentration on CHslurry concentration on CH44 recovery: recovery:
Surface PlotSurface Plot
6
15
22
28
0.100.20
0.300.35
0.450.50
0.600.75
0.850.90
0.00
20000.00
40000.00
60000.00
80000.00
100000.00
120000.00
140000.00
160000.00
180000.00
CH4 Produced
Mass [kg]
Temperature [C]
CO2-slurry
Concentration
Effect of Temperature & Concentration of CO2-slurry on CH4 Recovery
160000.00-180000.00
140000.00-160000.00
120000.00-140000.00
100000.00-120000.00
80000.00-100000.00
60000.00-80000.00
40000.00-60000.00
20000.00-40000.00
0.00-20000.00
Energy Efficiency CalculationsEnergy Efficiency Calculations
Analyze the effectiveness of CO2-
microemulsion injection technique vs.
Thermal Stimulation method.
Calculate the total energy requirement
Calculate the energy efficiency
Heat added to reservoir for producing 1 Heat added to reservoir for producing 1 kg of CHkg of CH44 under different production under different production
schemesschemes
0.00
1000.00
2000.00
3000.00
4000.00
5000.00
6000.00
7000.00
8000.00
Hea
t Added
/kg
of C
H4 P
roduce
d [k
J/kg]
Thermal Stimulation CO2 Injection CO2 Injection
50 C & 2.5 MPa
30%, 25 C & 2.5 MPa 50%, 28 C &
2.5 MPa
7277.07 kJ/kg
408.29 kJ/kg328.68 kJ/kg
Energy efficiency ratios for Energy efficiency ratios for different production scenariosdifferent production scenarios
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
180.00
Ener
gy R
ecov
ered
per
unit o
f Ener
gy S
upplied
[k
J/kJ]
Thermal Stimulation CO2 Injection CO2 Injection
50 C & 2.5 MPa
30%, 25 C & 2.5 MPa
50%, 28 C & 2.5 MPa
7.25
129.26
160.57
ConclusionsConclusions The hydrates are formed at higher pressure in
porous medium for a given temperature and at lower temperature for a given pressure than those in bulk medium
Capillary pressure has significant effect on methane recovery for different soils and it should be considered in hydrate recovery
The simulation study showed that a micro-emulsion with 30% CO2 concentration will be a good choice for reservoirs with hydrate saturation < 50%
ConclusionsConclusions If the initial hydrate saturation is in the range
of 55% to 75%, a 50% CO2 micro-emulsion injection may be a good choice .
CO2-microemulsion injection for methane recovery from a reservoir with high hydrate saturation may not be a good choice due to the low effective permeability.
It is found that the energy requirement for a gas hydrate reservoir by CO2 microemulsion injection is about 1/10th of that required by thermal stimulation method.
We gratefully acknowledge the financial support from AEDTL/NETL/DOE
AcknowledgementAcknowledgement
Questions …. ??? Questions …. ???