塔河油田火山岩的层位归属、火山岩岩石学与岩相学特征

火山岩顶、底地层中的微古化石组合研究表明:塔河油田火山岩的形成时代为二叠纪。岩石学、岩相学、地球物理测井与地震学综合研究结果显示,火山岩主要为英安岩和玄武岩。存在两次火山喷发旋回,形成下部玄武岩、上部英安岩或单一英安岩的垂向火山喷发序列。玄武岩呈带状分布于研究区西部和南部古地貌低洼区,以上平下凸的透镜状河谷充填式地震反射为特点;英安岩分布于北部及东北部地区,以下平上凸的丘形反射形态为特征。可划分出火山爆发相、火山溢流相和火山沉积相3个岩相带。火山爆发相位于火山喷发中心地带,研究区以火山熔岩溢流相为主,火山沉积相布范围局限,位于岩体边缘。火山活动具有喷发频率低、间隔时间短、以宁静的溢流式喷发为主间或伴随较强烈的爆发式喷发为特点。火山活动喷发中心可能是由西南逐渐向东北方向迁移的。

HORIZON, PETROLOGY AND LITHOFACIES OF THE VOLCANIC ROCKS IN THE TAHE OILFIELD, NORTHERN TARIM BASIN

It is important both theoretically and practically in exploration and development for volcanic reservoirs to investigate rock types, associations of lithoficies, volcanic activities and spatial distributions for volcano-related rocks. The micro-fossils in the Triassic overlying the volcanic rocks directly and in the Lower Carboniferous under the volcanic rocks implied that the volcanic rocks might erupt during Permian, which was further confirmed by the isotopic dating. A study on petrology and petrochemisry indicated the main rock type being lava,with part of volcaniclastics, minor sedimentary volcaniclastics, volcaniclastic lava and volcaniclastic sedimentary rocks. The basalt and dacite were dominated among the lava. There existed two volcanic eruption cycles, which resulted in vertical volcanic eruption successions of basalt in the lower and dacite in the upper, or a simple dacite eruption cycle. The basalt's distribution was controlled by topographic relief: in the zonal depressions in western and southern part, which was characterized by upper-flat and lower convex lens-shaped valley filling seismic reflection. By contrast, the dacite was featured by up-convex and lower flat with mound seismic reflection distributed in the northern and northeastern part of the area. Three volcanic lithofacies, namely, the explosive, effusive and volcanic sedimentary facies could be recognized. The former was located only around the volcanic eruption center, the latter distributed along the margin of lava with restricted dimension, and the effusive facies distributed broadly. The volcanic activities might be of lower eruption frequency, short interval between volcanic eruption cycles, and relatively quiet eruption, occasionally accompanied by intensive explosive eruption. The eruptional centers migrated northeastwards.