渤海湾盆地莱州湾凹陷南斜坡中生界火山岩相模式和储层特征

精细岩相模式是油气藏研究的重要基础,为储层预测和评价提供合理的约束。目前火山岩还缺少微相尺度的相模式。参照的5相15亚相分类方案,在莱州湾凹陷南斜坡中生界火山地层中建立了相—亚相—微相划分方案,识别出3相4亚相10微相。具体为爆发相的热碎屑流亚相和热基浪亚相,细分为火山口- 近火山口、近源和远源微相。喷溢相熔岩流亚相,细分为简单熔岩流和碎屑堆积微相。火山- 沉积相崩塌再搬运堆积亚相,细分为再搬运块状堆积和基质堆积微相。钻井揭示研究区的亚相占比从高到低的顺序为爆发相热基浪亚相、喷溢相熔岩流亚相、爆发相热碎屑流亚相和火山- 沉积相崩塌再搬运堆积亚相。火山地层具有复杂岩相叠置关系,亚相单元横向延伸范围有限、对比难度大。储层孔渗条件由好到差的顺序为热基浪亚相、热碎屑流亚相、熔岩流亚相和崩塌再搬运堆积亚相。热基浪亚相近源微相、热碎屑流亚相近源微相、熔岩流亚相简单熔岩流微相上部、崩塌再搬运亚相块状堆积微相的储层较好;其中,热基浪亚相近源微相储层条件为最优。本研究可为火山岩储层预测和评价提供地质依据。

Mesozoic volcanic facies model and reservoir characteristics in the southern slope of Laizhou Bay depression, Bohai Bay basin

High- resolution lithofacies model is an important basis for reservoir research, providing essential constraints for reservoir prediction and evaluation. However, such models are often lacking for volcanic rock reservoirs. This study addresses this gap by a facies- subfacies- microfacies classification scheme, building upon a pre- existing scheme with 5 facies and 15 subfacies. Utilizing this approach, we identified 3 facies, 4 subfacies, and 10 microfacies within the Mesozoic volcanic strata on the southern slope of the Laizhou Bay depression. These facies encompass eruptive, effusive, and volcano- sedimentary types. Within the eruptive facies, both pyroclastic flow and base surge subfacies can be further subdivided into crater- near crater, proximal, and distal microfacies. Similarly, the lava flow subfacies of effusive facies can be subdivided into simple lava flow and debris deposition microfacies. Finally, the avalanche subfacies of volcano- sedimentary facies can be subdivided into reworked massive and reworked matrix microfacies. Based on observations from boreholes, the subfacies can be arranged in descending order as follows: base surge subfacies of eruptive facies, lava flow subfacies of effusive facies, pyroclastic flow subfacies of eruptive facies, and avalanche subfacies of volcano- sedimentary facies. Volcanic strata exhibit complex lithofacies with overlapping relationships. This complexity, coupled with the limited lateral extent of subfacies units, presents challenges for correlation. Furthermore, the descending order of reservoir quality is base surge subfacies, pyroclastic flow subfacies, lava flow subfacies, and avalanche subfacies. The reservoir quality of proximal microfacies in base surge and pyroclastic flow subfacies, the upper zone of the simple lava flow in the lava flow subfacies, and the reworked massive deposition microfacies in the avalanche subfacies is relatively better. Among them, the reservoir quality of proximal microfacies in the base surge subfacies stands out as the most favorable. Relevant research results can provide a geological basis for volcanic rock reservoir prediction and evaluation.