Abstract Gas-chimney analysis is a useful tool for evaluating shallow and deep hydrocarbon prospects by showing likely migration routes for deeply sourced thermogenic hydrocarbons as well as shallower biogenic hydrocarbons. Specialized seismic processing conditions the 3D data set so that only meaningful gas chimneys are analyzed. Once the data have been so conditioned, the interpreter can differentiate between faults that show evidence of leakage and those that do not show evidence of leakage and may be sealing faults. Many of the shallower chimneys can be tied directly to active surface seeps as well as shallow gas prospects and known hydrocarbon deposits. When this type of chimney analysis is coupled with techniques such as waveform segmentation, amplitude variation with offset, and absorption attribute analysis, the result is a very powerful 3D data volume that can be used to derisk shallow and deep gas prospects.

Abstract The Florida Parishes of southeastern Louisiana (Fig. 1) are bounded on the west by the Mississippi River, on the east by the Pearl River, on the north by the Louisiana-Mississippi state line, and on the south by the Mississippi River deltaic plain. Principal cities include Baton Rouge and New Orleans.

In the 3000-square-mile area of southeastern Mississippi and northeastern Washington Parish, Louisiana, which has Tatum dome in its center, rocks of known Jurassic to Recent age are more than 20,000 feet thick. They are underlain by an unknown thickness of Louann Salt of Jurassic (?) age. The age, thickness, and nature of the sedimentary rocks between the salt and the basement, as well as the character of the basement, are unknown. The salt in the northern half of the area has moved upward to shallow depths as diapirs in overlying rocks. Outside of the area of shallow-piercement domes there are more deeply seated domes, ridges, and anticlines that may be the result of vertical movement of the salt. The Wiggins anticline in the south and, southwest of it, an area dipping more steeply to the southwest probably were not affected by salt movement. Structural maps of four horizons and isopach maps of rocks in the three intervals between them give information about the sedimentary and structural history of the region since the end of Early Cretaceous time. The horizons contoured mark either unconformities or the upper boundaries of zones of fairly uniform structural history. The top of the Lower Cretaceous rocks dips generally to the west. Upper Cretaceous rocks dip to the west-southwest and thicken to the northeast. Pre-Miocene Tertiary rocks dip to the southwest and thicken to the northwest. Miocene and later rocks dip and thicken to the south-southwest. The structure of the older formations is considerably more irregular than that of the younger ones; domes, ridges, and basins that were conspicuous in the Early Cretaceous became less pronounced as younger sediments progressively covered them. Of the eight shallow-piercement domes with which the author is familiar, three are known to have penetrated Oligocene rocks; two, middle Eocene; one, lower Eocene; one, Upper Cretaceous; and one, Lower Cretaceous. Some movement has taken place at Tatum dome since the sandy, gravelly Citronelle Formation was laid down.