准噶尔盆地玛湖凹陷百口泉组沉积古环境分析——以玛18井为例

Sedimentary environment of Lower Triassic Baikouquan Formation in Mahu Sag, Junggar Basin: A case study from Ma 18 well

碎屑岩的古沉积环境直接控制沉积相的类型、分布和演化,从而影响优质储层和油气有利区的分布。利用元素地球化学特征对碎屑岩储层沉积环境进行分析,并以准噶尔盆地西北缘玛湖凹陷玛18井为重点研究对象,应用便携式X射线荧光光谱分析测试仪(XRF),系统测试了下三叠统百口泉组(T_1b)415组样品的40多种元素含量。通过测试数据分析了其元素地球化学特征和沉积环境的古气候、古盐度和氧化还原状态等的变化趋势及与含油气性的关系。结果表明,尽管百口泉组自下而上元素丰度和比值有一定波动,但总体表现为温暖潮湿、淡水—微咸水、水体分层不强的弱氧化环境,从T_1b_1到T_1b_3温度、湿度和盐度均有增加的趋势,另外,Si/Al值与含油饱和度具有一定的正相关性。

The ancient sedimentary environment of clastic rock directly controls the type, distribution and evolution of sedimentary facies, which affects the distribution of high quality reservoir and favorable oil and gas area. The geochemical characteristics of element were used to analyze the sedimentary environment of elastic rock reservoir, and portable X-ray fluorescence （XRF） tester was applied to systematically test the contents of more than 40 elements from 415 groups of samples of Lower Triassic Baikouquan Formation in Ma 18 well in Mahu Sag in the northwestern margin of Junggar Basin. The geochemical characteristics of elements and the changing trend of paleoclimate, paleosalinity and oxidation-reduction states of the sedimentary environment were analyzed. The results show that element content and ratio have certain fluctuations from bottom to top, while in overall, it was formed in the warm and humid, freshwater, brackish water, weak layering and oxidizing environment. In addition, from Tlbl to T1 b3, the water temperature, humidity and salinity all have a tendency to increase, and the Si/A1 ratio has a certain positive correlation with oil saturation.