Abstract: Mesozoic volcanic rocks are widely developed in the Bohai Sea area, demonstrating substantial hydrocarbon exploration potential. The southern Bohai Sea is one of the key areas for the exploration of volcanic rock reservoirs. The Mesozoic volcanic rocks exhibit diverse lithologies, significant spatial differences in reservoir physical properties and hydrocarbon enrichment levels, and unclear formation mechanism of high-quality reservoirs. These issues severely restrict the next step of volcanic reservoir exploration in this area. By comprehensively utilizing the drilling/logging data, core and rock thin section petrography, scanning electron microscopy observations, and geochemical element analysis, an in-depth study was conducted on the characteristics and controlling factors of the Mesozoic volcanic reservoirs in southern Bohai Sea. The research results indicate that the volcanic rocks in southern Bohai Sea are dominated by intermediate-basic types, followed by intermediate-acidic volcanic rocks. The main lithofacies are effusive lava and explosive pyroclastic rocks. The reservoir space is predominantly composed of secondary dissolution pores and fractures, exhibiting high porosity (averaging 14.0 %) but low permeability and complex pore throat structure. The dominant lithology-lithofacies assemblage serves as the material basis for the development of high-quality reservoirs, wherein the intermediate-acidic volcanic reservoirs exhibit superior quality to the intermediate-basic volcanic rocks, and the explosive pyroclastic rock reservoirs outperform effusive volcanic rocks in reservoir qualities. The weathering and leaching processes control the vertical zonation of reservoir properties, with enhanced reservoir characteristics observed within 160 meters of the top of the weathering crust. Diagenetic evolution governs the lateral heterogeneity in reservoirs. The pore evolution models of volcanic reservoirs in the study area are divided into three types, i.e., the early strong filling with late weak dissolution model (Type 1), the early strong filling with late strong dissolution model (Type 2), and the early weak filling with late strong dissolution model (Type 3). Type 3 exhibits the best reservoir physical properties. Fractures are a key factor determining the reservoir effectiveness. NNE-trending strike-slip faults and nearly EW-NWW-trending extensional faults jointly control the development of reservoir fractures. The optimal fracture effectiveness is observed in later-stage fractures that oriented parallel to the contemporary maximum horizontal stress, with favorable temporal coupling to hydrocarbon charging episodes. The study proposes a wellbore trajectory offset method for the rapid evaluation and prediction of reservoir geostress and effective fracture development. Comprehensive research suggests that in the areas where intermediate-acid eruptive volcanic rocks are developed along the Tan-Lu strike-slip fault zone, key areas for the development of high-quality volcanic reservoirs include the zones with medium to high porosity within 160 meters vertically below the weathering crust, and those exhibiting the horizontal combination of favorable diagenetic evolution patterns and well-developed effective fractures.

Key words: southern Bohai Sea, Mesozoic, volcanic rock, buried hill, reservoir characteristics, controlling factors

摘要： 渤海海域中生界火山岩广泛发育,油气勘探潜力巨大,其南部海域为火山岩油气藏勘探的重点地区之一。该地区中生界火山岩岩性多样,储层物性与油气富集程度在空间上存在显著差异,优质储层的形成机理尚不明确,这些问题严重制约了下一步火山岩油气勘探工作。综合利用钻井/测井、岩心、岩石薄片、扫描电镜以及地球化学元素分析等资料,对渤海海域南部中生界火山岩储层的特征及控制因素进行了深入研究。研究结果表明:渤海海域南部中生界火山岩以中性—基性火山岩为主,中酸性火山岩类次之,岩相主要为溢流相熔岩和爆发相火山碎屑岩;火山岩储层的储集空间以次生溶蚀孔和裂缝为主,储层孔隙度整体较高,平均为14.0%,但渗透率较低,孔喉结构复杂;优势岩性-岩相组合是优质储层发育的物质基础,其中,中酸性火山岩储层质量优于中性—基性火山岩,爆发相火山碎屑岩的储层品质优于溢流相火山岩;风化淋滤作用控制着储层的垂向分带性,距风化壳顶面160 m以浅的储层物性较好;成岩演化作用控制着储层的横向差异性,研究区火山岩储层的孔隙演化模式分为早期强充填-晚期弱溶蚀型、早期强充填-晚期强溶蚀型和早期弱充填-晚期强溶蚀型3类,其中,以早期弱充填-晚期强溶蚀型储层的物性最佳;裂缝是决定储层有效性的关键因素,NNE向走滑断裂与近EW—NWW向伸展断裂共同控制着储层裂缝的发育程度,其中,形成时代较晚、走向与现今最大水平地应力方向一致且与油气运移充注期匹配关系良好的裂缝,其有效性最好。研究提出可利用井眼轨迹偏移法对储层地应力及有效裂缝的发育情况进行快速评价与预测。综合分析认为,在沿郯庐走滑断裂带分布的中酸性爆发相火山岩发育区,纵向上在距风化壳顶面160 m以浅的中—高孔隙带,平面上在叠加了有利成岩演化模式且有效裂缝发育的区带,是渤海海域南部优质火山岩储层发育的有利区。

关键词: 渤海海域南部, 中生界, 火山岩, 潜山, 储层特征, 控制因素