西昌盆地上三叠统白果湾组层序格架下沉积演化及油气勘探意义

西昌盆地上三叠统白果湾组具有较好的油气勘探潜力，但目前在沉积方面的基础地质研究尚缺乏系统认识，很大程度制约了该地区的油气勘探进程。以白果湾组一、二段为研究对象，根据露头、钻井岩心、测井和元素地球化学资料综合分析，理清了沉积相划分标志与特征，搭建了全区可对比的高精度层序地层格架，恢复了沉积体系时空展布与演化规律，建立了构造—气候响应下的沉积演化模式。结果表明：西昌盆地白果湾组一、二段可划分为一个三级层序，包含低位体系域、湖扩体系域和高位体系域3个体系域，主要发育辫状河流、辫状河三角洲和湖泊3种沉积相。低位体系域时期盆地以辫状河流和三角洲连片沉积为主，湖泊面积较小；湖扩体系域时期以湖泊沉积为主，辫状河流和三角洲向盆地边缘大面积萎缩；高位体系域时期短轴强物源向湖心进积，湖泊面积再次减小。层序沉积演化是构造作用和古气候条件的叠加效应，其中区域构造运动作为主控因素决定了盆地地貌格局、沉降速率和湖平面变化，古气候旋回通过影响湖平面升降对沉积充填产生控制。白果湾组一、二段成藏配置关系良好，低位体系域有利储集体可作为该区下一勘探阶段重点关注的方向。该成果可为川西南地区陆相油气勘探新领域突破开拓思路。

Sedimentary evolution under the sequence framework of the Upper Triassic Baiguowan Formation in Xichang Basin and its significance for oil and gas exploration

The Upper Triassic Baiguowan Formation in Xichang Basin has a good potential for oil and gas exploration. However， there is still a lack of systematic understanding on the basic sedimentary geology， which restricts the speed of the oil and gas exploration in this area. Based on integrated outcrops， cores， well-logs and elemental geochemical analyses， this study clarified the marks and characteristics of sedimentary facies and established the high-resolution sequence stratigraphic framework of the 1^st and 2^nd members of Baiguowan Formation in the whole area. What is more， the temporal and spatial distribution and evolution of sedimentary system were restored and the model of sedimentary evolution was proposed. It is found that the 1st and 2nd members of Baiguowan Formation in Xichang Basin consisting braided fluvial， braided-river delta and lacustrine deposits can be divided into one third-order sequence which includes lowstand， transgressive， and highstand systems tracts. Lowstand systems tracts （LST） include braided river and delta facies spread widely with small lacustrine deposits. Transgressive systems tracts （TST） is dominated by lacustrine deposits with braided river and delta deposits shrinks toward the basin margin. Highstand systems tracts （HST） include expanded areas of braided river and delta deposits with lacustrine deposits shrinks again. Sequence sedimentary evolution is the superposition effect of tectonics and palaeoclimate. The regional tectonic movement as the main controlling factor determines the morphology pattern of basin， subsidence rate and lake-level， and the palaeoclimate cycle controls the sedimentary filling by affecting the rise and fall of lake level. The 1^st and 2^nd members of Baiguowan Formation have perfect accumulation configuration， and the favorable reservoirs in the Lowstand systems tracts can be regarded as the key direction of the next exploration stage in this area. This work can be a breakthrough in the new field of continental oil and gas exploration in southwest Sichuan Basin.