Use of Seismic Attributes and Modeling in Gas Hydrate Reservoir Interpretation, North Slope, Alaska

Abstract Gas clathrates, commonly known as methane or gas hydrates, are an ice-like crystalline solid composed of water and natural gas, primarily methane. Gas hydrates occur in the shallow subsurface where both water and gas are present within low-temperature and moderate-pressure regimes. The shallow subsurface geology of the North Slope of Alaska is structurally dominated by a broad antiform, known as the Barrow Arch, and is riddled with a myriad of high angle normal faults trending roughly north south and east-west. In addition to the complex structure, the hydrate-bearing units are predominantly fluvial and northward prograding deltaic strata. The complexity of the local geology, coupled with the lack of a consistent amplitude anomaly associated with hydrate occurrences, make simple horizon interpretation of hydrates difficult. In order to gain a better understanding of the hydrate distribution as well as a clearer picture of the structural geology, seismic attributes are used in conjuncti on with traditional horizon-to-well-tie interpretation techniques. Several of the attributes, based on the Hilbert Transform, can yield information about the physical properties of the hydrate-bearing units. For example hydrate layers may have an anomalous frequency response based on their relatively high acoustic velocity. Delineation of high-angle faults and possible channel deposits are aided by the use of calculated event similarity prediction (ESP) volumes. ESP volumes are essentially a measure of trace-totrace similarity, so discontinuities in the seismic data are brought into better focus. The use of these attributes, as well as others, yields a clearer picture of hydrate distribution as well as a more accurate structural model.