鄂尔多斯盆地陇东地区延长组长7段沉积微相及沉积演化特征

利用大量的岩芯、露头剖面观察和测井资料,在总结分析重力流沉积理论的基础上,系统研究了鄂尔多斯盆地陇东地区延长组长7段重力流沉积特征及沉积模式。研究认为陇东长7段主要发育砂质碎屑流和浊流沉积,局部发育滑动、滑塌岩;受多物源、湖盆底形、湖岸线迁移等因素的影响,研究区沉积砂体并未呈现出明显的扇形,受西南陡窄斜坡控制的泾川—华池一带砂体呈条带状分布,发育水道型重力流沉积,沉积微相可分为限制型水道、非限制型水道、侧翼溢漫、水道间、前缘朵体和深湖泥6种,在湖盆底庆城—华池一带多期水道交汇叠置,形成了大面积的连片砂体;受南部物源控制的宁县—合水地区,由于斜坡坡度相对较缓、物源供给充足,形成了以滑塌为主的斜坡沉积模式,根据滑动的距离可分为近源沉积和远源沉积2个亚相,沉积微相可分不规则滑塌体、砂质碎屑流舌状体、朵叶状浊流岩和深湖泥4种,研究区南部主要以砂质碎屑流舌状体为主,在斜坡处多期舌状体纵横叠置,形成了多期薄、厚砂体互层的连片砂体。通过对陇东长7段沉积模式的建立和沉积微相的识别与划分,为研究区砂体展布的精细刻画提供了重要指导,也为该区致密油水平井规模建产提供了依据。

Sedimentary microfacies identification and inferred evolution of the Chang 7 Member of Yanchang Formation in the Longdong area, Ordos basin

The sedimentary characteristics of core, outcrops and logging data of the Chang 7 Member of Yanchang Formation in Longdong area of Ordos Basin were summarized and evaluated based on the theory of gravity flow sedimentation. The analyses show that the sandy debris flow and turbidity current deposits are mainly developed in Chang 7 Member of Longdong, but slip and slump rocks are locally developed. The sedimented sand bodies in the study area are affected by multiple sources, lake basin bottom shape and lake shoreline migration and do not show an obvious fan- shape. Sandbodies in Jingchuan- Huachi area controlled by steep and narrow slopes in southwest and form sandy strips, and channel- type gravity flow deposits are also developed. The sedimentary microfacies are divided into six types: restricted channel, unconfined channel, flank overflow, inter- channel, leading edge lobate sand and deep lake mud. At the bottom of the lake basin, the Qingcheng- Huachi waterway intersects and overlaps forming a large area of inter- connected sand bodies. In the Ningxian- Heshui area dominated by the southern provenance, due to relatively gentle slope gradient and abundant source supply, a slope sedimentation model dominated by slump structure is formed. According to the slip distance, it can be divided into two subfacies: near- source sedimentation and far- source sedimentation. The sedimentary microfacies can be divided into four types: irregular slumping, sandy debris flow tongue, lobate turbidite, and deep lake mud. In the southern part of the study area, sandy debris flow tongue is the main body which overlaps both vertically and horizontally with many stages on the slope, forming a large area of continuous sand body of thin and thick interbedded sand. The identification and division of sedimentary microfacies in the Chang 7 Member in Longdong and the establishment of its sedimentary model provides important guidelines for detailed characterization of sand body distribution in the study area and provides a basis for scaled production of tight oil horizontal wells in the area.