3-D seismic detection of undrilled prospective areas in a mature province, South Marsh Island, Gulf of Mexico

effective approach to defining additional resources using 3-D seismic as the sole data source. Although this example is from a densely drilled province, such a seismic-based approach is often used in frontier areas with sparse well coverage, in step-out regions around known production, can be used for a “quick look” evaluation of existing properties, and for real-time interpretation of newly acquired data. This approach—integrating multiple seismic attributes and interpretation methods—refined the structural framework and detected undrilled prospective areas in a mature province in the Gulf of Mexico. Coherency technologies refined the fault interpretations. Surface mapping identified structural highs, and stratal-surface techniques were used to evaluate seismic stratigraphic facies. The study area covered approximately 350 square miles of coastal waters just south of Marsh Island, Louisiana (Figure 1). Data consisted of two merged 3-D surveys, Outer Continental Shelf (OCS) 310 and State Lands (SL) 340 that cover six productive offshore fields: Starfak, Tiger Shoal, Mound Point, Amber Complex, Lighthouse Point, and North Lighthouse Point. The area is in the OligoceneMiocene detachment province of the northern Gulf Coast continental margin—a region generally characterized by large-displacement, dominantly down-to-the-basin, listric growth faults that sole on a regional detachment zone above the Oligocene section. Regional deformation is a product of salt mobilization. The faults originate in the autochthonous Jurassic Louann Salt or in the detachment zone represented by a salt weld that formerly contained a thick, allochthonous salt body. A characteristic feature of this province is the thickness (typically exceeding three miles) of deltaic and shelf sediments above the detachment zone. This remarkable stacking of deltaic/shelf sandstone reservoirs helps make this province one of the world’s great petroleum provinces (Table 1). More than 500 wells within the seismic coverage document proven and remaining hydrocarbon reserves (Figure 2, composite log of Tiger Shoal/Starfak fields). Fault interpretation methods. Coherence time slices were used in the initial structural interpretation phase because this technology allows a mathematical assessment of the 3D seismic data volume without being biased by previous interpretation. Coherence calculations compare