潜山内幕火山岩储层特征及控制因素——以渤海海域秦皇岛30A地区白垩系为例

Characteristics and Controlling Factors of Buried-hill Inner Volcanic Reservoir: An example from the Cretaceous in Qinhuangdao 30A Area,Offshore Bohai Sea,China

针对潜山内幕火山岩储层特征和控制因素复杂的难题,以渤海海域秦皇岛30A地区白垩系为例,通过岩芯观察、薄片鉴定和扫描电镜分析等,对潜山内幕火山岩储层储集空间类型、孔缝充填期次、成岩演化及控制因素进行研究。研究区火山岩储层以爆发相安山质火山角砾岩为主,储集空间分为原生孔隙、次生孔隙和裂缝3类。作为主要原生孔隙类型,储层中原生气孔先后经历早期充填和晚期充填两个充填阶段,导致原生孔隙大量减少。根据裂缝相互切割关系和充填矿物组合,将储层中裂缝分为四期,晚期裂缝充填程度低于早期裂缝。火山岩储层成岩演化经历同生成岩阶段、表生成岩阶段和埋藏成岩阶段3个阶段。同生成岩阶段火山热液作用对储层破坏作用最为明显,后期表生成岩阶段风化淋滤作用和埋藏成岩阶段溶蚀作用对储层物性进行了一定改善,但作用有限。未充填有效裂缝发育程度是控制潜山内幕火山岩储层物性和油气产能差异的关键因素。靠近大断裂和火山通道的构造高部位储层裂缝更为发育,但易受火山热液作用影响而被热液矿物充填,有效裂缝较少,储层渗透性和产能远低于距火山通道较远的斜坡带。构造部位、裂缝形成期次及宽度大小三个因素共同控制了有效裂缝发育。裂缝集中分布于靠近大断裂一定范围内,距火山通道较远、裂缝形成期次较晚且与油气成熟期和运聚期有效匹配、裂缝宽度较小的地区裂缝充填作用较弱,是有效裂缝和优质储层发育的有利地区,可作为下一步潜山内幕火山岩油气勘探的重点。

Focusing on the complex characteristics and controlling factors of buried-hill inner volcanic reservoir,this paper takes the Cretaceous volcanic rocks in Qinhuangdao 30 A area of Bohai Sea for example. The space type,filling stage,diagenetic evolution and controlling factors of buried-hill inner volcanic reservoirs were studied based on core observation,thin section identification and scanning electron microscope analysis. The lithology of volcanic reservoirs in the study area is mainly explosive facies andesitic volcanic breccia. The reservoir space can being classified as primary pore,secondary pore and fissure. As main primary pores,the gas pores experienced early filling stage and late filling stage,leading to primary pores being sharply reduced. According to the filling minerals and interaction cutting relation,the fractures are categorized as four periods while the late fractures were more weakly filled than early ones.The reservoirs experienced three diagenetic stages： syndiagenetic stage,epidiagenetic stage and burial diagenetic stage. The volcanic hydrothermal activity during syndiagenetic stage influenced the reservoirs most and is the primary cause for the reservoir physical properties becoming worse,while the weathering and leaching in epidiagenestc stage and the dissolution in burial diagenestic stage improved the reservoir physical properties to a limited extent. The development of unfilled effective fractures in reservoir is the main controlling factor,resulting in the differences of volcanic reservoir physical properties and oil-gas production capacity in the study area. The structurally high part close to volcanic conduit contains more fractures than slope zone,but the fractures were more affected by hydrothermal activity and filled by minerals,leading to less effective fractures,poorer reservoir permeability and much lower oil-gas production capacity than that in slope zone. Structure position,formation period and size of fractures controlled the development of effective fractures. The fractures are mostly distributed within a certain range nearby major faults and those developed in area far away from volcanic conduit and formed late with small width were less filled and are effective fractures. The area with those fractures developed is the favorable region of high-quality reservoirs and target for oil-gas exploration.