鄂尔多斯盆地宜川地区太原组致密砂体控砂机理

The sand control mechanism of Taiyuan Formation tight sand bodies in Yichuan area,Ordos Basin

鄂尔多斯盆地东南部宜川地区上古生界太原组致密砂体分布复杂,给该区致密气的勘探开发带来了风险和不确定性。分析致密砂体控砂机理,将有助于预测砂体和有利储层分布,降低勘探开发风险。文中从太原组古构造特征、物源供给、沉积体系及研究区经历的海侵/海退事件等4个方面总结了致密砂体控砂机理。研究发现:宜川地区太原组低洼古构造控制主砂体展布;物源决定砂体发育面积及沉积类型,碎屑供给物少,砂体发育面积小,沉积较分散;物源和沉积环境共同控制砂体展布形态和方向,形成以透镜状、块状和长条状为主的障壁砂,砂体呈北东—南西向展布;海侵/海退事件控制单砂体沉积厚度及连续性,砂体主要发育在石灰岩厚度小于8 m的区域,4期海侵/海退事件形成了4套单砂体。

The complex distribution of sand bodies in the Taiyuan Formation of the Upper Paleozoic in Yichuan area,southeast of Ordos Basin,brings risks and uncertainties to the exploration and development of tight gas in this area.Analyzing the sand control mechanism will help predict the distribution of sand bodies and favorable reservoirs and reduce exploration and development risks.The sand control mechanism is summarized from the four aspects such as the paleostructural characteristics of Taiyuan Formation,provenance supply,sedimentary system and transgression/regression events experienced in the study area.The study suggests that low-lying paleostructures controlled the distribution of the main sand bodies of Taiyuan Formation in Yichuan area;the provenance determined the development area and deposition types of the sand bodies,and the development area of the sand bodies was small and relatively dispersed since the supply of debris was small.The provenance and sedimentary environment jointly controlled the distribution shape and direction of the sand body,and the lenticular,blocky and strip-like barrier sandstones were formed,mainly orienting at northeast-southwest.Transgression/regression controlled the sedimentary thickness and continuity of the single sand body,and the sand bodies were mainly developed in areas with limestone thickness less than 8 m.Four sets of single sand bodies were formed during the fourth stage of transgression/regression events.