关键词: 抱球虫, 浊流, 底流, 深水, 超深水, 碳酸盐岩, 珠江口盆地

Abstract: A major exploration breakthrough has been achieved in the ultra-deepwater Liwan area of Baiyun sag of Pearl River Mouth Basin, where a unique globigerina mixed reservoir was drilled in the Member 5 of Lower Miocene Zhujiang Formation. In 2024, production testing of Well L4 in the Liwan4-1 structure yielded a high-capacity natural gas flow of 43×10⁴m³/d, marking a significant milestone in this novel exploration domain. This reservoir exhibits mixed carbonate and silt-argillaceous clast characteristics. It is predominantly developed across palaeogeomorphic highs surrounding the Yunli low-uplift with a semi-deep-sea environment, where the intraparticle chambers of globigerina provided the basis for the formation of the high-porosity reservoir. By integrating palaeogeomorphic and paleo-oceanographic frameworks with datasets from cores, thin sections, grain sizes, whole rock major elements, and foraminifer-ichnofossil assemblages, this study elucidates the sedimentary dynamics, spatial distribution, and reservoir-forming mechanisms of the globigerina mixed reservoir under the control of dual interactions between turbidity currents and bottom currents, and between bottom currents and paleo-highs. The research results indicate as follows. (1) The interaction between distal turbidity currents far from the provenance and bottom currents delivered silt- to sand-grade clastic sediments to the Yunli low-uplift. (2) The interaction between bottom currents and paleo-highs dictated the developmental scale and spatial heterogeneity of the globigerina mixed rocks. (3) Reservoir petrophysical properties are co-controlled by hydrodynamic sorting and burial diagenesis. Strong hydrodynamic energy effectively winnowed fine-grained matrix and enhanced reservoir porosity, while high terrigenous clay content potentially inhibited cement precipitation, favoring the preservation of primary intraparticle pores. (4) Intensive cementation significantly reduced porosity. Focusing on high-porosity and low-permeability reservoirs, a technical framework integrating depositional-reservoir theoretical innovation, precise geophysical prediction, and engineering-technology-integrated stimulation was established. By developing a novel multi-dentate coordination chelating acid system and implementing stimulation via long horizontal well acidification, matrix permeability and drainage area were enhanced, enabling the large-scale release of oil and gas reservoir production capacity. The sedimentary model of globigerina mixed rocks, which is controlled by dual interactions between turbidity currents and bottom currents, and between bottom currents and paleo-highs, challenges the traditional consensus that deep-water reservoir development relies heavily on terrigenous clasts, points to a new frontier for natural gas exploration in the ultra-deepwater areas of the Pearl River Mouth Basin, and offers practical insights for deep-water and ultra-deep-water oil and gas exploration in China.

Key words: globigerina, turbidity current, bottom current, deepwater, ultra-deepwater, carbonate rocks, Pearl River Mouth Basin