A Review and Perspective of Bioturbated Hydrocarbon and Water Reservoirs
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Abstract: Bioturbation changes the petrophysical properties of host rocks by changing the primary sedimentary fabric, decreasing or increasing the porosity and permeability of the primary formation, which in turn affects the reservoir properties and fluid flow characteristics. This paper reviews the reservoir space types, pore structure characteristics, reservoir media nature, fluid transport characteristics, reservoir types and their property characteristics of bioturbated hydrocarbon and water reservoirs. The reservoir space types of bioturbated reservoirs include: primary intergranular pores, intra-grain dissolved pores, inter-grain dissolved pores and intergranular pores. According to the relationship between the permeability of burrows and the host sediments, the bioturbated reservoir can be divided into dual-porosity biogenic reservoir media and dual-permeability biogenic reservoir media, and the two types of reservoir media have significant difference in burrow types, migration dynamics, fluid transport characteristics, and depositional environment; according to the burrow characteristics of bioturbated reservoir, fluid transport characteristics in reservoir media and reservoir petrophysical characteristics, bioturbated reservoirs can be divided into five types: (1) Surface-constrained bioturbated reservoirs, (2) Non-surface-constrained bioturbated reservoirs, (3) Weakly defined bioturbated reservoirs, (4) Cryptic bioturbated reservoirs, and (5) Diagenetic bioturbated reservoirs. The main controlling factors affecting the petroproperties of bioturbated reservoirs are analyzed in detail, including the permeability ratio of burrow-fills and hosting matrix, bioturbation intensity and connectivity, burrow-surface area, and burrow architecture. At present, the geophysical identification, reservoir description and reservoir modeling of bioturbated reservoirs are still at the pilot investigation stage, but it is foreseeable that strengthening the study of bioturbated hydrocarbon and water reservoirs is of great significance and important implications for enriching the theory of reservoir geology, increasing oil and gas storage, enhancing production and recovery.