冀中坳陷深层碳酸盐岩储层天然裂缝发育特征与主控因素

早古生界奥陶系碳酸盐岩储层是冀中坳陷深层油气勘探的重要领域,裂缝是影响该类储层油气富集和单井产能的主要因素之一。为了指导该区的油气勘探部署,根据野外露头、岩心、薄片和成像测井等资料,对奥陶系碳酸盐岩储层天然裂缝的发育特征和裂缝发育的控制因素进行了研究,并结合生产数据资料和勘探成果,探讨了天然裂缝发育的非均质性对油气产量分布差异的影响。研究结果表明:(1)冀中坳陷深层奥陶系碳酸盐岩储层发育构造裂缝、成岩裂缝、溶蚀裂缝和风化裂缝等4种类型,其中构造裂缝是该区天然裂缝的主要类型,走向多为NNE—SSW向,以高角度和垂直裂缝为主,多未充填,开度小于30μm,裂缝线密度介于1.6～3.0条/m,主要为3期形成,不同期次之间相互切割限制;(2)天然裂缝的发育程度主要受岩性、构造和层厚等3个因素控制——白云岩比石灰岩天然裂缝更发育,泥岩裂缝发育程度较差,断层附近和断层上盘天然裂缝更发育,裂缝发育程度与岩层厚度关系密切,随着岩层厚度的增加,层控构造裂缝密度呈幂函数递减;(3)在不同凹陷、不同构造带以及同一构造带的不同构造部位,天然裂缝的非均质性极强,油气产量差异较大。结论认为,该研究成果为该区深层奥陶系碳酸盐岩储层的油气勘探开发提供了地质依据。

Development characteristics and main controlling factors of natural fractures in deep carbonate reservoirs in the Jizhong Depression

The carbonate reservoir of Early Paleozoic Ordovician is an important area for deep oil & and gas exploration in the Jizhong Depression. Fracture is one of the main factors affecting oil & gas enrichment and single well productivity in this type of reservoir. For better guiding the oil & gas exploration and deployment in the Jizhong Depression, the development characteristics and controlling factors of fractures in the Ordovician carbonate reservoirs in this area were studied based on the data of field outcrops, cores, thin sections and image logging. And combined with production data and exploration achievements, the influence of the development heterogeneity of natural fractures on the distribution of oil and gas production was discussed. And the following research results were obtained. First, four types of fractures are developed in the deep-seated Ordovician carbonate reservoirs in the Jizhong Depression, including tectonic fractures, diagenetic fractures, dissolution fractures and weathering fractures, among which tectonic fracture is the main type of natural fracture in the study area. They are mostly of NNE–SSW strike. Many of them are high-angle and vertical fractures and most of them are unfilled. Their opening is less than 30 μm, and the fracture density is 1.6–3.0 fractures/m. And they are mainly formed in three stages and fractures of different periods are cut and limited mutually. Second, the development degree of natural fractures is mainly controlled by three factors, i.e., lithology, structure and layer thickness. Natural fractures in dolomite are more developed than those in limestone and the development in mudstone is poor. Natural fractures near faults and in the upper wall are more developed. The development degree of fractures is closely related to rock thickness. As rock thickness increases, the density of layer-controlled tectonic fractures decreases as a power function. Third, in different depressions, different tectonic zones and different structural parts of the same tectonic belt, the heterogeneity of the natural fractures is quite strong, and oil and gas production varies greatly. In conclusion, these research results provide a reliable geological basis for the oil & gas exploration and development of deep-seated Ordovician carbonate reservoirs in the Jizhong Depression.