准噶尔盆地沙湾凹陷三叠系百口泉组沉积相展布特征及沉积模式

Sedimentary facies distribution characteristics and sedimentary model of Triassic Baikouquan Formation in Shawan Sag,Junggar Basin

准噶尔盆地沙湾凹陷三叠系百口泉组主要发育扇三角洲沉积,准确识别扇三角洲各沉积相的展布特征对多类型油气藏的勘探开发具有重要意义。结合高精度三维开发地震和大量钻井、测井资料,采用沉积相研究、地震属性分析和古地貌恢复等方法,对沙湾凹陷百口泉组沉积相展布特征进行了研究。研究结果表明:①沙湾凹陷百口泉组可划分出3个四级层序和数个五级层序,且3个四级层序分别对应百口泉组的3个层段,五级层序受短期沉积旋回控制,分别对应不同的沉积微相。②均方根振幅属性对岩性变化更为敏感,能量高值区对应扇三角洲平原亚相,中值区对应扇三角洲前缘亚相,低能量区对应滨浅湖亚相。③百一段和百二段沉积时期,研究区湖盆面积小,主要发育扇三角洲平原和前缘亚相;百三段沉积时期湖盆面积增大,主要发育扇三角洲前缘和滨浅湖亚相,为典型的水进退积型扇三角洲。扇三角洲前缘亚相物性较好,被滨浅湖亚相的泥质岩所覆盖,形成良好的储盖组合。④研究区百口泉组扇体规模大、物源近,岩性以砂砾岩为主,为缓坡浅水扇三角洲沉积模式,扇三角洲前缘亚相为潜在的有利成藏区,是油气资源规模发现的重点勘探区。

The Triassic Baikouquan Formation in Shawan Sag of Junggar Basin mainly develops fan delta deposits.Accurately identifying the distribution characteristics of each sedimentary facies of the fan delta is of great signifi‐cance for the exploration and development of multi-type oil and gas reservoirs.Combined with high-precision three-dimensional development seismic and a large number of drilling and logging data,the distribution characteri-stics of sedimentary facies of Baikouquan Formation in Shawan Sag were studied by means of sedimentary facies research,seismic attribute analysis and paleotopography restoration.The results show that:(1)Baikouquan For‐mation in Shawan Sag can be divided into three fourth-order sequences and several fifth-order sequences.The three fourth-order sequences correspond to three members of Baikouquan Formation,and the fifth-order sequences are controlled by short-term sedimentary cycles,corresponding to different sedimentary microfacies.(2)The root mean square amplitude attribute is more sensitive to the lithology change of the target layer.The high energy zones are expressed as fan delta plain subfacies,the middle energy zones are expressed as fan delta front subfa‐cies,and the low energy zones are expressed as the shore shallow lake subfacies.(3)During the sedimentary period of the first and second members of Baikouquan Formation,the lake basin area of the study area is small,and the fan delta plain and front subfacies are mainly developed.During the sedimentary period of the third member of Baikouquan Formation,the lake basin area is expanded,and the fan delta front and shore-shallow lake subfacies are mainly developed,which is a typical transgressive retrograding fan delta.The fan delta front subfacies have good physical properties,and are covered by mudstone of shore-shallow lake subfacies,forming a good reservoir-cap assemblage.(4)The Baikouquan Formation in the study area has a large scale of fan bodies and close source rocks,with lithologies mainly of sandy conglomerate,which is a gentle slope shallow water fan delta sedimentary model.The front subfacies of fan delta are potential favorable reservoir accumulation areas,which are key explo‐ration areas for the discovery of oil and gas resources.