| In recent years, many large-scale biogenic gas reservoirs have been discovered in the world, which has be⁃
come one of the hotspots of natural gas exploration. Biogenic gas reservoirs are mainly distributed in passive continental
margin basin, foreland basin, craton basin, fore-arc basin, and accretionary wedge, etc. The conditions of biogenic gas
accumulation in accretionary wedge are complicated due to the intense tectonic activity, and there is a lack of systematic
understanding of biogenic gas enrichment rules and main controlling factors in accretionary wedge. Based on 2D seismic,
well data, we discuss the biogenic gas accumulation conditions in Barbados accretionary wedge, north of South America
and define the hydrocarbon migration and accumulation model, and furtherly reveal the law of oil and gas enrichment
and point out the favorable exploration direction. The results show that: (1) From west to east, the inner (western) depres⁃
sion, the central uplift, and the outer (eastern) thrust zone develop successively, and the inner zone develops the large
sag. (2) The thick mudstone in the large sag provides sufficient biogenic gas source. Large channel complexes, channel-le⁃
vee complexes, channel-lobe complexes, and lobes are mainly developed in western depression, which has a good rela⁃
tionship with traps. Early high relief thrust-faulted anticline is located in the convergence area of oil and gas, which is con⁃
ducive to efficient biogenic gas accumulation. (3) Since the Pliocene, under the compression of the Caribbean Plate, the
central uplift belt has widely developed mud diapirs, forming numerous mud diapir-related structural traps. The continu⁃
ous activity of these mud diapirs persists to the present day. The activity of late-stage mud diapirs has led to the destruc⁃
tion of biogenic gas reservoirs, resulting in the failure of all drilling attempts on the flanks of the mud diapirs. So late pres⁃
ervation conditions are the key factors for biogenic gas accumulation. (4) The model of Biogenic gas self-generation and
self-storage or lower-generation and upper-storage is established. The western depression has favorable conditions for
the formation of biogenic gas reservoirs and is a favorable exploration direction. |
