辽西凸起南部斜坡带泥岩盖层展布及封烃能力演化过程

Shale Cap Features and Sealing Evolution in Ramp Region,South of Liaoxi Uplift

辽西凸起南部地层超覆在斜坡带之上,形成大型地层超覆圈闭,其上倾方向靠近物源供给区,砂体极为发育,所以泥质盖层的展布及其封烃能力演化特征成为制约该区油气成藏的关键因素。结合岩性特征和测井响应对其盖层的类型进行了划分,刻画了目的层段盖层类型的展布特征,表明了超覆地层上倾方向泥质盖层与下伏储层的空间配置关系,并基于影响封烃能力的主控因素分析建立的数学模型对泥质盖层的演化特征进行了定量计算。研究表明:(1)斜坡带目的层段泥岩盖层连续展布,能够对下伏砂体形成有效遮挡,储盖组合良好,在砂体分布的构造高部位和油气运移优势通道上盖层类型较好,封烃能力较强;(2)目的层段泥岩盖层以物性封闭为主,东营组沉积期封烃能力的演化受地层温度和压实作用双重因素的影响,自10 Ma(明化镇组沉积期)至今最终在压实作用的影响下形成有效的封闭。

The overlap strata that are developed on the slope in the south of Liaoxi uplift form a large scale stratigraphic overlap trap.It is close to the provenance in the updip direction with well developed sandbodies,and therefore,the distribution of the shale caps and their sealing evolution characteristics are the critical factors for the hydrocarbon accumulation in the area.This paper classifies the types of shale caps,and describes the distribution charcteristics of the caps in the targeted layers based on lithologic characteristics and logging responses.The result indicates three-space array relation between updip direction shale caps and underlying reservoir in the overlap strata zone.A mathematic model is developed to calculate quantatively the evolution characteristics of the shale caps on the basis of the analysis of the controlling factors that impact the sealing capabilities.The findings are listed as follows.（1）The shale caps are continuously distributed in overlap strata zone,forming an effective barrier to underlying reservoir,with good cap associations,better caps on the high structural position and oil-gas migration pathways with sandbody distribution,and strong sealing capacity of hydrocarbons.（2）The shale cap in the targeted layer is dominated by physical sealing,and the sealing evolution of Dongying Formation in deposition stage is affected by both formation temperature and compaction,forming the effective sealing under the influence of compaction since 10 Ma（Minghuazhen Formation deposition stage）.