FROZEN HEAT | Volume 2

Table 3.1-b: Production setting and associated environmental considerations for marine gas hydrate deposits

Reservoir type

Reservoir setting

Production maturity 1

Site survey & foundation considerations

Drilling, completion & production

Environmental response

Marine – “shallow” Sand- host sediment

Shallow – < 250 m below sea floor – > 500 m WD2 – Pore-space occurrence

– Discovered technically recoverable resources (Gulf of Mexico & Japan) – First offshore production test in 2013 (Nankai Trough) – First production may occur in Asia from c. 2020

– Conventional approach to hazard delineation and engineering design – Shallow settings may present increased risk of sea floor instability and disruption of shallow ecosystems – Unique challenges may be encountered related to geologic settings such as active tectonic continental margins where there is increased seismic activity and pervasive sediment deformation

– Conventional drilling practice & sand control/flow assurance measures – Horizontal drilling may be difficult due to shallow reservoir and weak formation-strength –Unconventionalsurfaceconductorand casing design due to weak formations – Dissociation primarily through pressure draw-down (down-hole pump) – Operational challenges owing to cold reservoir temperatures and formation mobilitywhengashydrate isdissociated – A water-disposal strategy is likely to be required –Sealintegritymaybeanissueduetolack of sediment strength and consolidation – Conventional drilling practice & sand control/flow assurance measures – Horizontal drilling may be difficult due to shallow reservoir and weak formation-strength – Dissociation primarily through pressure draw-down (down-hole pump) – A water-disposal strategy is likely to be required – A number of scientific and exploratory research wells have successfully penetrated these deposits using conventional drilling methods – It is unlikely that these deposits will be developed using conventional industry completion/production methods

– Shallow reservoir depths and weak sediment strengths

above producing interval pose unique challenges to field development – Conventional experience worldwide is limited in similar

settings, however engineering design methods are well developed

Marine – “deep” Sand-host sediment

Deep – > 250 m below sea floor – > 1000 m WD – Pore-space occurrence – Sites: AC 818, WR 313, GC 955 (GoM), Beta (Nankai Trough), UBGH2-2_2, UBGH2-6 (Ulleung Basin) Disseminated – Widespread occurrences – High volume but low resource density – Sites: Blake Ridge (USA) Fracture-fill – Widespread occurrences – High volume but low resource density – Sites: KG Basin (India): Ulleung Basin (Korea); Gulf of Mexico (USA) Sea floor: – Massive (mounds) – Sites: GoM, Baltic Sea, Black Sea, Bering Sea, Barkley Canyon (Canada) NGS/BS3 Vents: – Massive, disseminated & fracture-filling (?) – Sites: Bering Sea, NGS

As above

– Conventional approach to hazard delineation and engineering design, ease of application of existing approaches increases with increasing reservoir depth

– Conventional experience worldwide is limited in similar settings, however engineering design methods are well developed

Marine – Mud host sediment

–Conventionalpractice in industry wouldbetoavoidtheseoccurrences due to low resource density –Modeling to date shows no clear viable production mechanism – Conventional practice in industry would be to avoid these occurrences despite moderate to high gas hydrate saturations, due to geo-mechanical instability and restriction of fluid flow – Conventional practice in industry would be to avoid these occurrences due to their unusual geotechnical properties and association with unique biological communities

– Conventional experience worldwide is limited in similar settings, however engineering design methods are well established – Not considered for fracture fill

– Not Considered

Marine – Solid hydrate

– Not Considered

– Not Considered

– Non traditional extraction methods may be destructive to sea floor biological communities and cause sea floor settlement

1. Likely commerciality time-line (i.e., produceable/non-produceable in the near future) 2. Water Depth 3. NGS/BS: Norwegian Greenland Sea and Barents Sea

A GLOBAL OUTLOOK ON METHANE GAS HYDRATES 67