塔河油田西北部奥陶系古水系结构特征及演化^*

Characteristics and evolution mode of the Ordovician paleodrainage system architecture in northwestern Tahe oilfield,Tarim Basin,China

摘要

塔里木盆地塔河油田西北部中下奥陶统发育深切的地表水系结构,对水系两侧岩溶缝洞的发育影响显著,因此,对水系结构的定量描述及其演化模式的研究至关重要。基于三维地震资料,通过地震属性提取技术,对古岩溶台面和古岩溶地表水系进行了识别。同时,对水系的平面和垂向形态学结构参数进行了量化表征,据此探讨了古岩溶地表水系的形成与演化模式,剖析了水系演化与古岩溶缝洞发育的关系。研究结果表明: (1)塔河油田西北部自东向西发育3个岩溶台面和一个深切曲峡型地表流域结构。该流域的主干水系南北向汇流、分支水系东西向汇流,呈不对称分布。(2)水系单河曲弯曲率均大于1.5,超过了定义蛇曲的弯曲率临界值,具有典型的蛇曲特征。东西向河曲带弯曲率为2.42,南北向河曲带弯曲率为1.78。(3)东西向水系形态以单一“V”字形为主,南北向水系具有复合“V”字形,水系下切深度可达100~200 m。自东向西3个岩溶台面中水系的下切深度逐渐加大,水系宽深比平均值分别为4.06、3.52、3.03。(4)研究区古岩溶地表水系经历了自由曲流和深切曲流2个阶段,分别反映了水系的侧向侵蚀和垂向侵蚀作用过程。其中,水系的垂向侵蚀是逐步发生的,与3个岩溶台面的逐级抬升相适应。(5)深切曲流是区域性的最低排泄基准面,控制了河流两侧大型岩溶暗河的发育。每个岩溶台面具备独立的水循环结构,岩溶台面的逐级抬升促进了水系的差异演化,进而控制了岩溶暗河的规模和类型的差异性。对研究区古水系结构及其演化的认识对于古岩溶缝洞储集空间发育特征与分布规律的研究提供了重要的参考依据。

Abstract

The deep surface water system structure developed in the Middle and Lower Ordovician in the northwest of Tahe Oilfield has a significant impact on the development of karst fractures and caves on both sides of the water system. Therefore,it is crucial to quantitatively describe the water system structure and conduct researches on its evolution mode. Based on three-dimensional seismic data,seismic attribute extraction technology was utilized to identify paleokarst platform and paleokarst surface water systems. In addition,the planar and vertical morphologic structure parameters of the surface drainage system were quantitatively characterized. Consequently,the formation and evolution patterns of paleokarst surface water systems was explored,and the relationship between surface water system evolution and paleokarst cave-fissure development was analyzed as well. The research results indicate that: (1)Three paleokarst paltform and a deep meandering gorge type surface watershed structure are developed from east to west in the northwest of Tahe Oilfield. The main water system in this basin flows in a north-south direction,while the branch water system flows in an east-west direction,exhibiting an asymmetric distribution pattern. (2)The curvature rate of a single river bend in the water system is greater than 1.5,exceeding the critical value for defining the curvature rate of a meander bend,and featuring typical meander characteristics. The curvature rate of the east-west meander belt is 2.42,and the curvature rate of the north-south meander belt is 1.78. (3)The east-west water system mainly has a single V shape,while the north-south water system has a composite V shape. The incision depth of the water system in the three paleokarst platform gradually deepens from east to west,and the average width to depth ratios of the water system are 4.06,3.52,and 3.03,respectively. (4)The paleokarst surface water system in the study area experienced two stages: free meandering and entrenched meandering, reflecting the lateral and vertical erosion processes of the water system, respectively. Among them,vertical erosion of the water system occurs gradually,adapting to the gradual uplift of the three paleokarst paltform. (5)Deep meandering is the lowest drainage reference level in a region,controlling the development of large karst underground rivers on both sides of the river. Each karst platform has an independent water circulation structure,and the gradual uplift of the karst platform promotes the differential evolution of the water system,thereby controlling the differences in the scale and type of karst underground rivers. The understanding of the paleokarst water system structure and its evolution in the research area provides important reference basis for the study of the development characteristics and distribution patterns of paleokarst fracture cave storage space.

关键词

古水系 / 自由曲流 / 深切曲流 / 缝洞型储集层 / 中下奥陶统 / 塔河油田

Key words

paleodrainage system / free meander / entrenched meander / fractured-vuggy reservoirs / Middle-Lower Ordovician / Tahe oilfield

基金资助

*中国科学院战略性先导科技专项(A类)(No. XDA14010302)和中国石化西北油田分公司科研项目(编号: P23034,KY2021-S-094)联合资助