鄂尔多斯盆地四大古隆起演化及其油气控藏意义的差异*

鄂尔多斯盆地在地质历史上曾存在中央古隆起、乌兰格尔古隆起、渭河古隆起及乌审旗古隆起4个主要的隆起构造。作者通过沉积地层分布及构造演化过程剖析等方法,系统分析了4大古隆起构造演化的差异性及其对油气成藏控制作用的差异,并首次提出“渭河古隆起”的概念。研究表明,4大古隆起分别形成于不同的地质时代和区域构造环境,并经历了不同的演化过程: 中央古隆起形成于早古生代拉伸构造环境,在印支期发生构造反转而转化为坳陷沉降区; 乌兰格尔古隆起则是自盆地基底形成以来就已存在的长期继承性隆起,但在白垩纪及新生代发生差异隆升—沉降而分化为现今构造的不同单元; 渭河古隆起形成于白垩纪的区域挤压构造环境,也是在新生代发生差异隆升—沉降而分化为今构造的不同单元; 乌审旗古隆起是前寒武纪即已存在的古地形高地,早古生代并无进一步的发展,因而仅是在寒武纪海侵沉积时突显、奥陶纪开始沉积后即快速消隐。古隆起的控藏差异主要表现为: (1)古生代及之前形成的古隆起对盆地油气成藏多具有控相、控储及控制源—储配置等积极作用,且后期“由隆转坳”的古隆起对油气的成藏演化极为有利; (2)白垩纪以来的较晚期隆起对油气成藏总体以破坏性作用为主,尤以对古生界天然气藏的影响最为显著。

Four main paleouplifts evolution in Ordos Basin and their differences in significance of oil and gas reservoir control

The Ordos Basin contains four main paleouplift structures in geological history, i.e., the Central,Ulager,Weihe,and Wushenqi Paleouplifts. This paper systematically analyzed the four paleouplifts with respect to stratigraphic distribution and tectonic evolution,and put forward a new concept of the Weihe Paleouplift. The four paleouplifts formed in different geological ages and regional tectonic environments,and it underwent different evolutionary processes: (1)The Central Paleouplift formed in the extensional tectonic setting of the Early Paleozoic,which was reversed and transformed into a depression subsidence area during the Indosinian period;(2)The Ulager Paleouplift is a long-term inherited uplift that has existed since the formation of the basin basement;different uplift subsidence occurred in the Cretaceous and Cenozoic and differentiated into different units of the present structure;(3)The Weihe Paleouplift formed in a regional compressive tectonic environment in the Cretaceous. It is also differentiated by differential uplift subsidence in the Cenozoic into different units of present structure;(4)The Wushenqi Paleouplift was an ancient topographic highland that existed in Precambrian,with no further development in the Early Paleozoic. Therefore,it was highlighted only in the Cambrian and disappeared rapidly after the Ordovician. The differences of reservoir control in paleouplifts are mainly as follows: (1)The paleouplift formed prior to and during the Paleozoic played a positive role in controlling facies,storage and source-storage configuration,and that the paleouplift later on from uplift to depression is beneficial to the evolution and accumulation of oil and gas,and reservoir formation;(2)The later uplift since the Cretaceous is mainly destructive to oil and gas accumulation,especially for Paleozoic natural gas reservoirs.