珠江口盆地惠西南地区古新世火山机构对有利储层的控制作用

珠江口盆地惠西南地区发育古新世厚层火山岩，与上覆始新统文昌组湖相沉积岩连续充填于惠州凹陷内，构成裂陷盆地早、中期主体岩层，没有明显沉积间断导致火山岩表生暴露、风化淋滤作用不强，因此，火山岩有利储层分布主要受火山机构的影响。基于岩矿、测井、三维地震等资料，通过岩心及薄片观察，开展惠西南地区火山机构及岩相特征研究，分析火山机构对有利储层的控制作用。研究表明，研究区存在“喷发方式控制火山机构类型、火山机构控制优相展布、优相控制有利储层分布”的递进特征:(1)受火山喷发时期与方式控制，研究区发育层状火山机构与穹隆状火山机构，火山口外形表现为内凹与穹隆两种类型；(2)火山岩优势岩相展布于火山机构内幕中心部位，火山口、近火山口的火山通道相、爆发相、喷溢相是有利岩相组合；(3)有利储层分布受岩相组合及裂陷期断层活动影响，储集空间分为原生孔缝、次生孔缝两类，岩相控制原生孔缝富集程度，后期断裂活动起到激活、改造、连通作用，形成规模孔—缝型火山岩油气储集层；(4)穹隆状火山机构最顶部侵出相由于岩浆挥发分含量低，导致原生孔缝不发育，岩石致密且难以改造，含油气性较差。 

Control of Paleocene volcanic edifice on favorable reservoirs: a case study of the southwestern Huizhou Sag,Pearl River Mouth Basin

Thickly developed Paleocene volcanic rocks in the southwestern Huizhou Sag of the Pearl River Mouth Basin are continuously filled with lacustrine sedimentary rocks of the overlying Eocene Wenchang Formation in the sag, forming the main rock formations in the early and middle stages of the rift basin. Absence of obvious sedimentary hiatus leads to poor supergene exposure as well as weathering and leaching effects of volcanic rocks. Therefore, the distribution of favorable reservoirs in volcanic rocks is mainly affected by volcanic edifices. Based on the latest drilling, logging and 3D seismic data, through the observation of cores and thin sections, the research on the volcanic edifice and lithofacies characteristics in the southwestern Huizhou Sag was carried out, and the controls of volcanic edifice on favorable reservoirs was analyzed. Results show that the study area has the progressive characteristics of "the eruption mode controls the type of volcanic edifice, the volcanic edifice controls the distribution of favorable facies, and the favorable facies controls the distribution of favorable reservoirs". (1) Controlled by the period and mode of volcanic eruption, stratovolcano and dome-like volcanic edifices developed in the study area, and the crater shape is of two types:subsidence caldera and dome. (2) The dominant lithofacies of volcanic rocks are distributed in the center of the volcanic edifice. The volcanic conduit facies, explosive facies and effusive facies in or near the crater are favorable combination of lithofacies. (3) The distribution of favorable reservoirs is affected by lithofacies assemblages and fault activities during the rifting period. The reservoir space is divided into primary and secondary pores and fractures. The lithofacies controls the enrichment degree of primary pores and fractures, while the later fault activities reform and connect the protogenetic pores and fractures, forming large-scale oil and gas reservoirs of pore-fracture type in volcanic rocks. (4) Extrusive facies, which is on the top of dome volcanic edifice, shows a poor oil-bearing property with hardly pores and fractures due to low volatiles content during the magma extruding.