Natural gas hydrates contain large quantities of methane trapped within ice crystal structures. Exploring and producing natural gas hydrates faces challenges related to their compact structure, formation factors, and location within stability zones. Initial production tests at the Mallik gas field involved depressurization and achieved flow rates up to 160 Mcf/day with minimal water production, demonstrating the potential for natural gas hydrate production but also issues like sand ingress. Replacing methane with carbon dioxide offers an alternative production method due to CO2's more favorable thermodynamic properties and easier distribution within the hydrate crystal structure.

1. Challenges in Exploration
& Production of Natural gas Hydrates
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By
K.Geetha Krishna Chowdary
P.Kavya
B.Tech (Petroleum Engg)
JNTU- Kakinada

2. 1 ft3 of NGH = 164 ft3 of Natural Gas
0.8 m3 of water
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GAS HYDRATES
The compact nature of the hydrate
structure makes for highly effective
packing of gas.
Factors influencing Gas Hydrate Formation
 P & T
Pore Water Salinity
Availability of Gas & Water
Geo Thermal Gradient in zone of Hydrate formation
Gas Chemistry
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3. Structure of Gas Hydrates
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 The hydrocarbon hydrates are non-stoichiometric substances
 Distinguished by the size of the cavities and the ratio between large and small cavities
 The size and shape of the guest molecule influences the structure formed

4. Classification of Hydrates & Hydrate Stable zone
Class 1:-
 Hydrate-bearing layer + underlying two-phase layer of mobile gas and water
 This type of hydrate is considered as the most promising reserve
Class 2:-
 Hydrate-bearing layer + Free Water
 Pressure Depletion is small comparatively
Class 3:-
 Absence of an underlying zone of mobile fluids.
 The whole hydrate-bearing layer is in P-T balance stability region.
Therefore, the gas production rate is slow during the exploitation
process
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5. Area Enclosed Between Phase boundary & Geothermal Gradient-
Hydrate Stable zone
The top of the HSZ is in most instances much shallower in the
onshore permafrost environment than in the oceanic environment.
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6. Identifying Gas Hydrates
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BSR
 Strong Acoustic Impedance Contrast, causing seismic wave to reflect upwards
 Mapped to the maximum depth of 1100 mts
 Only indicator but doesn’t quantifies the amount
Measures Physical properties of sediments adjacent to formation
Resistivity of massive CH4 hydrate is of order 150-170 Ω.mtr
 Based on Pockmarks & mud diapers which is indicated by
reliefs
 Whether Present/ only past hydrate presence is unknowable
from this data

7. Thermodynamically more stable
Spontaneous reaction
CO2 distribution in the hydrate is easier than
CH4
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Production
Depressurization
Thermal
Stimulation
CO2
Replacement
Dissociation/
Destabilizing
Replacement
Production with Underlying
•Free Gas
•Free water
•No fluid
Diffusion processes appeared to be the
dominant driving
 Endothermic nature of dissociation, more Heat is needed.
 Heat flux Area, no of Huff & Puff Cycles
 Production efficiency can be improved by prolonging the hot
water injection time (limited by the stronger pressurization effect)
 Most of the heat is lost to non-hydrate bearing strata

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9. Decomposition
Amount & The rate of
the heat injected
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10.  Landslide & Subsidence
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 Global Warming
 Mechanical Hazard-Safety Issue
Hydrate presence would inhibit normal compaction & cementing
 Drilling Hazard
 Water Disposal

11. Case Study
 1st Onshore Production test at Mallik field
 1o objective to measure and monitor the production response
(Prospect)
Winter 2007
 Production Test Winter 2008
 Experience with test wells at Mallik and elsewhere suggests that most
problems in drilling and completion of gas hydrate wells can be
foreseen and successfully dealt with at the design stage, including
using:
 Chilled drilling fluids
 Sand control methods
 Ports for injecting chemicals and provisions for near-wellbore Heating
 Monitoring devices
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13. Production Tests ( 1,093 to 1,105 m)
Winter 2007 ( 1 day test )
• Estimates of formation
permeability 0.1 to 1 Md
• Natural fractures are ubiquitous
to the gas-hydrate-bearing
interval
• A substantial inflow of sand into
the bore did occurred
• Several flow responses were
observed, with the flow rate
during the latter part of the test
exceeding 5,000 m3/day (180
Mcf/day) .
• Non-uniform formation
response was observed.
Winter 2008 (six-day test )
• An ESP pump, down hole
sensing instrumentation and
an electric borehole
• Sand screens were installed
across the production interval
• Three BHP of approximately
7.3 MPa, 5 MPa and 4 Mpa
were achieved.
• An average flow - 70 Mcf/day,
with peak rates as 160
Mcf/day
• Total water production was
less than 625 bbls (3,500 ft3).
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Consumption of Natural Gas is 100BCM/Year
1% = 18.94 TCM = 189 Years

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17. Depressurization
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500 psi
750 psi
1000 psi

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21. Methane Production is slow when the P-T conditions were
near the Methane Hydrate stability & at CO2 Pressure values
near saturation levels
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CO2 Substitution into Methane Hydrate Crystal

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