Dianna Shelander

Combining rock physics analysis, full waveform prestack inversion and high-resolution seismic interpretation to map lithology units in deep water: A Gulf of Mexico case study

A successful seismic-based reservoir properties estimation effort has three steps: accurate seismic inversion in 3D to obtain relevant reservoir parameters, rock physics transformation to relate reservoir parameters to the seismic parameters, and mapping these parameters in 3D. This problem is nonunique and thus any available information—specifically geologic interpretation—should be used to improve our ability to infer the reservoir properties of interest with confidence. Moreover, uncertainty associated with the different predicted values (i.e., confidence interval and estimate of misclassification probability) must be provided as well, so that proper decisions can be made. Thus, it is evident that this involves interdisciplinary effort that includes rock physics, geologic interpretation, and seismic inversion technology. However, for quantitative description of reservoir properties, one must derive a way to quantify the errors and uncertainties associated with the process.

SITE SELECTION FOR DOE/JIP GAS HYDRATE DRILLING IN THE NORTHERN GULF OF MEXICO

Studies of geologic and geophysical data from the offshore of India have revealed two geologically distinct areas with inferred gas hydrate occurrences: the passive continental margins of the Indian Peninsula and along the Andaman convergent margin. The Indian National Gas Hydrate Program (NGHP) Expedition 01 was designed to study the occurrence of gas hydrate off the Indian Peninsula and along the Andaman convergent margin with special emphasis on understanding the geologic and geochemical controls on the occurrence of gas hydrate in these two diverse settings. NGHP Expedition 01 established the presence of gas hydrates in Krishna- Godavari, Mahanadi and Andaman basins. The expedition discovered one of the richest gas hydrate accumulations yet documented (Site 10 in the Krishna-Godavari Basin), documented the thickest and deepest gas hydrate stability zone yet known (Site 17 in Andaman Sea), and established the existence of a fully-developed gas hydrate system in the Mahanadi Basin (Site 19).

Role of 3D seismic for quantitative shallow hazard assessment in deepwater sediments

Increased drilling activities in deep water since 1985, especially in the Gulf of Mexico (GOM), have revealed numerous hazards in the shallow sediments below the seabed, such as fault scarps, gas vents, unstable slopes, and reefs and shallow subsurface geologic hazards such as faults, gas-charged sediments, buried channels, abnormally pressured sands, and gas hydrates. Drilling risks associated with shallow aquifer-pressured sands or shallow water flow (SWF) sands and gas hydrates have received the most attention. These are global problems. In the GOM alone, more than US

Time-Depth Converted Interpretation of Regional Seismic Maps, Offshore Southeast Brazil

250 million has been lost due to SWF. While the industry has matured in handling these problems, it is estimated that the losses associated with SWF sands continue to be nearly

Introduction to special section: Exploration and characterization of gas hydrates

1.7 million per well in the GOM alone.

Regional Evaluation And Hydrocarbon Potential of the Deep Section of the Gulf of Mexico Offshore Louisiana Continental Shelf From Modern 3D Seismic Data

Regional seismic interpretation mapping of the pre-stack time migrated data produced seven key sequence boundary maps: Sea-floor, Intra-Oligocene, Top Cretaceous, Top Albian, Top Salt, Base Salt and Top Basement. Iso-time maps were subsequently constructed for the major tectono-stratigraphic mega sequences: syn-rift-lacustrine, transitional-transgressive and drift-open marine. Significant structural elements in each of these time maps are herein described and discussed. The depth conversion of each regional map adds considerably to the structural interpretation. Most of the regional structural features are in deep-water; hence the bathymetry correction itself affects the visualization of structures. It is well known that residual misties needs adjust the mapping of depth along non-dip lines. Hence, our depth conversion of deep-water maps was adjusted for these. Several of the dip-lines utilized were pre-stack depth migrated, but mostly with seismically derived velocities over the large deep/ultra-deep-water realm.

Seismic comparison of deepwater fields of the Gulf of Mexico and offshore Brazil

The characterization of marine gas hydrates from geophysical data has evolved significantly over the past decade. For many years, marine gas hydrate interpretation was largely limited to a determination as either “likely present” or “likely not present” based on the presence or absence of

Subsurface gas hydrates in the northern Gulf of Mexico

A regional interpretation of the central and outer Louisiana continental shelf has been undertaken, utilizing a reprocessed 3D pre-stack time migrated seismic survey. This survey forms contiguous coverage over 1050 OCS blocks across West and East Cameron, Vermilion, South Marsh Island, Eugene Island, Ship Shoal and South Timbalier. This dataset shows improved resolution of structural and stratigraphic features at depth, compared to previous datasets in the region. This is crucial for improving both regional understanding and raising the confidence of deep Miocene section prospect evaluations. The interpretation of this new seismic dataset has revealed a number of interesting structural and stratigraphic features in the relatively unexplored Middle to Lower Miocene section.

Occurrence of gas hydrate in Oligocene Frio sand: Alaminos Canyon Block 818: Northern Gulf of Mexico

1. Summary This study compares five deepwater fields, Mars and Diana in the Gulf of Mexico and Roncador, Marlim and Albacora Leste offshore Brazil. These reservoirs occur in basin floor fan, prograding wedge and slope fan systems tracts. Recently acquired 2D seismic data show them to consist of high amplitude high continuity and hummocky lower continuity reflectors. The Gulf of Mexico field examples occur in minibasins surrounded by massive allochthonous salt canopies. The Brazil examples are controlled by massive but autochthonous salt. Hydrocarbon migration into the Brazil fields is from a syn-rift source via large faults, which breach the salt where it is welded. Migration into the minibasins of the Gulf of Mexico is more complex due to the allochthonous salt but will probably be via salt-welded minibasin floors.