关键词: 全油气系统, 常规油气, 非常规油气, 有序富集, 成藏模式, 北部湾盆地

Abstract: Beibuwan Basin is one of the six major offshore petroliferous basins in China and is characterized by the development of diverse types of hydrocarbon reservoirs. However, the formation conditions of conventional and unconventional hydrocarbons, as well as their ordered coexisting patterns, and sequential accumulation mechanisms remain poorly understood, thereby limiting further exploration progress. To elucidate the enrichment patterns of hydrocarbons across all reservoir types and identify potential directions for exploration breakthroughs in the basin, a systematic analysis of the Whole Petroleum System of Beibuwan Basin was conducted based on an integrated dataset comprising drilling, mud logging, well logging, seismic, and laboratory data. The results indicate the following. (1) The Eocene Liushagang Formation developed multiple sets of high-quality, widely distributed carbon-rich and algae-rich source rocks in Beibuwan Basin. Marked differences in thermal evolution are observed among different structural zones, forming a concentric zonation pattern characterized by low mature to mature oil generation in the peripheral areas, and high- to over-mature condensate and dry gas generation in the inner central zones. The whole-process hydrocarbon generation of source rocks provides abundant hydrocarbon supply for the accumulation of both conventional and unconventional hydrocarbon reservoirs. (2) From the basin margin toward the center, prolonged sediment transport distance, weakened provenance supply, and intensified compaction result in a systematic transition from sand-rich to mud-rich lithology, accompanied by a progressive fining of grain size and increasing reservoir densification. This sequential evolutionary pattern gives rise to full-scale reservoir spaces, thereby providing different accumulation settings for conventional and unconventional hydrocarbon reservoirs. (3) Distinct differences exist in hydrocarbon migration dynamics across structural zones. In near- and intra-sag areas, hydrocarbon migration is primarily governed by restricted or confined fluid dynamic systems, in which residual pressure serves as the primary driving force for hydrocarbon accumulation, resulting predominantly in the formation of tight hydrocarbon reservoirs through vertical backflow or shale hydrocarbon reservoirs via self-generation and self-storage. In contrast, far-sag areas are characterized by free fluid dynamics systems, where buoyancy represents the principal accumulation driving force, leading mainly to the formation of conventional hydrocarbon reservoirs through stepwise long-distance migration and accumulation. (4) The differential thermal evolution of source rocks, ordered densification of reservoirs, and dynamic evolution of fluid fields collectively control the vertical composite stacking and planar zonal distribution of source-reservoir-separated conventional reservoirs, source-reservoir-integrated shale reservoirs, and source-reservoir-adjacent tight reservoirs in Beibuwan Basin. As a result, an orderly accumulation model of full-series conventional and unconventional oil and gas resources has been established. These results further enrich and advance the fundamental theory of the whole petroleum system, propose new strategies for comprehensive hydrocarbon prospecting across all reservoir types and stratigraphic sequences in offshore continental rift lacustrine basins, and provide useful references and guidance for hydrocarbon exploration in similar basins both in China and abroad.

Key words: Whole Petroleum System, conventional oil and gas, unconventional oil and gas, orderly enrichment, accumulation model, Beibuwan Basin