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

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