Abstract: The paleo-subterranean river system represents one of the three principal genetic types of paleokarst reservoir in the Ordovician strata of Tahe oilfield. Drilling data reveal that these systems exhibit complex morphologies and architectures, characterized by the co-occurrence of collapse structures and infillings, strong reservoir heterogeneity, significant variations in well productivity, and substantial challenges for efficient development. To address these issues, this study integrates multidisciplinary datasets, including outcrop observations, drilling data, seismic interpretations, and production data, applying theoretical methods from karst geology, structural geology, geophysics, and geostatistics. The work aims to define the types, architectural elements, filling types, and filling sequences of paleokarst conduit systems, and further elucidates their main controlling factors, development models, distribution features, and favorable combination patterns, thereby establishing a systematic characterization framework for the morphology, architecture, and infillings of the systems. The results indicate that:(1) The paleo-subterranean river systems are mainly classified into single- or multi-layered reticulated conduits, single conduits, structural corridors, discontinuous conduits, and suspended conduits. The architectural elements comprise trunk channels, branch channels, hall caves, and inlet/outlet ports. Three principal types of infilling are identified, composed mainly of sandy-muddy deposits, collapse breccias, and chemical precipitates. (2) Three paleokarst conduit systems with distinct features are developed in study area. The paleokarst geomorphology governs the overall flow direction and spatial distribution of subsurface conduits, while paleo-water table fluctuations dictate the tiered development levels and the dimensional scale of the conduit systems. Fault assemblage patterns control the morphology and structural architecture of subsurface conduits. Specifically, the western S81-S85-S74 system, controlled by slope geomorphology and networked fault systems, is dominated by reticulated conduits with frequent collapse breccia infillings. The central TK672-S65-S67-T615 system, controlled by a graben-like geomorphology and bowed fault systems, mainly develops single conduits, with locally developed multistorey channel systems, and is predominantly filled with sandy-muddy mixtures or interbedded deposits. The eastern TK422-S64-S46 system, controlled by peak-cluster geomorphology and λ-shaped faults, is dominated by discontinuous tectonic corridor-type karst channels, frequently filled with sand-mud mixtures and hybrid deposits . (3) Seismic attributes such as spectral decomposition energy, frequency-partitioned inversion, and coherence gradients can effectively predict the geometry and infilling characteristics of subsurface conduits. Multiple-point geostatistical modeling constrained by geological patterns and seismic attributes enables fine-scale characterization of the complex architectural features of the paleokarst conduit system. Application of this method to multiple key units in Tahe oilfield demonstrates the prediction accuracy exceeding 80 % for conduit geometry, architecture, and fill characteristics, providing a robust geological basis for efficient reservoir development.

Key words: architecture types, infilling characteristics, controlling factors, distribution features, quantitative characterization, paleokarst conduit system, Tahe oilfield

摘要： 古暗河系统是塔河 油田奥陶系储层的3大古岩溶储集体类型之一,实钻揭示古暗河系统形态组构复杂、垮塌与充填并存,非均质性极强,油井产能差异大,高效开发面临挑战。针对以上问题,基于露头、钻井、地震、生产动态等多学科数据,应用岩溶地质学、构造地质学、地球物理学及地质统计学等理论方法,明确暗河类型、组构要素、充填类型及充填结构,揭示暗河分布主控因素、发育模式、展布规律及有利组合类型,建立古暗河系统形态、组构及充填表征方法。研究结果表明:①古暗河类型主要有单层或多层的网状管道型、单支管道型、构造廊道型、断续型和悬挂型,组构要素包括主干河道、分支河道、厅堂洞及出、入水口等,主要存在砂泥、角砾和化学沉积充填物组成的3种充填结构。②研究区共发育3大不同特征的古暗河系统,岩溶古地貌影响了暗河总体流向和展布,潜水面变化决定了暗河发育层数和规模,断裂组合样式控制了暗河形态和组构。其中,西部S81—S85—S74古暗河系统受斜坡和网状断裂控制,多发育网状河道,且多存在垮塌角砾充填;中部TK672—S65—S67—T615古暗河系统受箕状地貌和"弓"字形断裂控制,发育单支管道暗河,局部发育多层管道暗河,以砂泥和交互充填为主;东部TK422—S64—S46古暗河系统受峰丛地貌和"入"字形断 裂控制,主要发育不连续的构造廊道型暗河,多存在砂泥和混合充填。③分频能量、分频反演、相干能量梯度等地震属性可以较好预测暗河轮廓及充填特征,基于地质模式与地震属性的多点地质统计建模方法,能够精细表征暗河系统复杂组构特征,方法应用于塔河油田主体区多个典型单元,暗河形态、组构及充填特征预测符合率均达80%以上,为此类油藏高效开发奠定可靠地质基础。

关键词: 组构类型, 充填特征, 主控因素, 分布规律, 定量表征, 古岩溶暗河系统, 塔河油田