Challenges in Exploration & Production of Natural gas Hydrates

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ByK.Geetha Krishna Chowdary

P.Kavya

B.Tech (Petroleum Engg)

JNTU- Kakinada

1 ft3 of NGH = 164 ft3 of Natural Gas0.8 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 & TPore Water SalinityAvailability of Gas & WaterGeo Thermal Gradient in zone of Hydrate formationGas Chemistry

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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

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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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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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 formationResistivity 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

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Production

DepressurizationThermal

StimulationCO2

Replacement

Dissociation/Destabilizing

Replacement

Production with Underlying•Free Gas•Free water•No fluid

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

Thermodynamically more stableSpontaneous reactionCO2 distribution in the hydrate is easier than CH4

Diffusion processes appeared to be the dominant driving

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DecompositionAmount & The rate of

the heat injected

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Landslide & Subsidence

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Global Warming

Drilling Hazard

Mechanical Hazard-Safety IssueHydrate presence would inhibit normal compaction & cementing

Water Disposal

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 devices11

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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 Mpawere 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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Depressurization

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500 psi

750 psi

1000 psi

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Methane Production is slow when the P-T conditions werenear the Methane Hydrate stability & at CO2 Pressure valuesnear saturation levels

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CO2 Substitution into Methane Hydrate Crystal

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