塔河油田西部古暗河缝洞结构特征及控制因素

Analysis on fracture-cave structure characteristics and its controlling factor of palaeo-subterranean rivers in the western Tahe Oilfield

由于古暗河非均质性强、空间结构复杂,难以明确塔河油田西部古暗河缝洞结构特征及控制因素。为此,利用井震标定技术和频谱分解技术对塔河油田西部古暗河进行系统刻画与识别,研究表明:塔河油田西部奥陶系碳酸盐岩发育1—4号共4条古暗河,平面上呈较为复杂的网状或树枝状结构特征,平面上的缝洞结构可分为连续发育的条带状和不连续发育的团块状2大类;纵向上自上而下可分为未充填、砂泥质充填和角砾充填3种缝洞充填类型,其中有利缝洞主要发育在中—上奥陶统顶面反射轴之下的第1个波谷和波峰上,以"串珠状"反射特征为主。古构造形态、断裂系统和开放性入口对古暗河形态及缝洞结构特征起控制作用。其中断裂系统对油气充注具有建设性作用,古暗河与断裂匹配性好的区域为油气富集的有利目标区。

The palaeo-subterranean river has strong heterogeneity and complex spatial structure,which bring difficulties in understanding on facture-cave structure characteristics of palaeo-subterranean river in the western Tahe Oilfield and its controlling factors. To solve these problems,the well-seismic calibration technique and the spectral decomposition tech？ nique were utilized to identify and characterize the palaeo-subterranean rivers systemically in the western Tahe Oilfield.Results show that there are four major palaeo-subterranean rivers in the Ordovician carbonate rocks in the western Tahe Oilfield,presenting as complex reticular or dendrimer structure in the plane. From the dynamic and static data of drilling wells and well-seismic calibration,there are two types of horizontal distribution pattern for the karst caves of the palaeosubterranean rivers,which are the ribbon-like cave with continuous distribution and the block-like cave with scattered dis？tribution. In the vertical,it can be divided into three types from top to bottom：unfilled cave,sand and mud filled cave and breccia filled cave. The seismic reflection of favorable fracture-cave reservoirs in the seismic section is characterized by the first trough and peak under the reflection of middle-upper Ordovician top surface in“string”. The Palaeostructural form,fracture system and open entrances control the morphology of palaeo-subterranean rivers and the structural features of fracture-cave reservoirs. As the fault system plays a constructive role in the hydrocarbon charge,the development areas of the palaeo-subterranean river matching well with faults are favorable targets for hydrocarbon enrichment.