Physical property characteristics of gas hydrate-bearing reservoir and associated seal sediments collected during NGHP-02 in the Krishna-Godavari Basin, in the offshore of India

Junbong Jang; William F. Waite; Laura A. Stern; Timothy S. Collett; Pushpendra Kumar

doi:10.1016/j.marpetgeo.2018.09.027

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Physical property characteristics of gas hydrate-bearing reservoir and associated seal sediments collected during NGHP-02 in the Krishna-Godavari Basin, in the offshore of India

Junbong Jang·William F. Waite·Laura A. Stern·Timothy S. Collett·Pushpendra Kumar

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Abstract

India’s National Gas Hydrate Program Expedition 02 (NGHP-02), was conducted to better understand geologic controls on gas hydrate occurrence and morphology, targeting potentially coarse-grained sediments near the base of the continental slope offshore eastern India. This study combines seismic, logging-while-drilling data, and a petroleum systems approach to provide a regional geologic context for the core- and grain-scale analyses. This multi-scale approach provides insight on the gas hydrate distribution, morphology and anticipated system response to depressurization-induced methane extraction. The study area, NGHP-02 Area B in the Krishna-Godavari Basin, contains a buried anticline/syncline structure that hosts fracture-filling gas hydrate in fine-grained sediment overlying coarser sediments with pore-occupying gas hydrate. Core- and grain-scale measurements show fine-grained sediment exerts a primary control on the distribution and morphology of gas hydrate in Area B. Diatoms in the fine-grained overburden cause porosity to increase with depth, reaching ~70% at the underlying reservoir contact. High porosity, combined with near-vertical faults, suggests the overlying sediment is an imperfect seal. This allows methane to escape the gas hydrate reservoir sediments and form primarily grain-displacing gas hydrate veins in the fine-grained overburden. Within the reservoir, fine-grained layers are interbedded with coarser-grained gas hydrate reservoir sands. Even in the reservoir sands, however, a soil classification study shows the fines content is high enough to control hydraulic and mechanical properties, such as permeability, compressibility and shear strength. Fluid motion during methane extraction from gas hydrates can mobilize those fines, which can then clog pore throats, limiting production rates. Pore-water freshening during gas hydrate dissociation can increase fines mobilization, particularly given the smectite identified in the fine-grained interbeds. Accounting for fines content and specific fines mineralogy throughout the gas hydrate petroleum system is important for predicting production efficiency from gas hydrate occurrences along the crest of the anticline in NGHP-02 Area B.

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Source-reported bounding extent: 7.96553° to 35.49401° latitude; 68.17665° to 97.40256° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Junbong Jang, William F. Waite, Laura A. Stern, Timothy S. Collett, Pushpendra Kumar. 2019. Physical property characteristics of gas hydrate-bearing reservoir and associated seal sediments collected during NGHP-02 in the Krishna-Godavari Basin, in the offshore of India. https://doi.org/10.1016/j.marpetgeo.2018.09.027

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