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 …. ???