泥质烃源岩系异常高压裂缝的形成条件与分布规律研究

Fluid overpressures are widely developed in muddy source rocks of rifted basins. Fractures induced by overpressure are important mechanisms for hydrocarbon accumulation and migration. However, the distribution patterns and nonhomogeneity of overpressured fractures are difficult to predict. We include this research a overpressured fractures case study of Bonan sag, in which overpressure is widely developed and the hydrocarbon is relatively rich. Integrated of petroleum geological, geophysical and experimental analysis data, based on present fluid pressure, overpressure structures were analyzed, we observe fractures and identify overpressured fractures with core analysis, log data and scanning electron microscopy technology, then describe the grades and distribution of overpressured fractures in complex structure of source rocks. Paleopressure recovery technology and rock mechanics properties are emphasized to analyze fracture opening conditions by overpressure.We identify fracture opening conditions from the analysis of multifactor composite and establish overpressured fractures development model with the combination of micro and macro analysis. Therefore, the source rock petroleum expulsion pathway and unconventional oil and gas distribution can be predicted form the model. This study has the implication of providing evidence for the complexity of hydrocarbon expulsion and the realistic significance of unconventional oil and gas exploration. Besides, the study also can promote the development of episodic expulsion theory and hydrocarbon accumulation theory in overpressured systems.

陆相断陷盆地的泥质烃源岩系往往伴生超压，超压作用形成的裂缝是烃类储存和运移的一种重要机制。作为常规油气排烃和非常规油气储集的关键，超压裂缝具有分布不均、发育规律不清、难以预测的特点。以超压发育的富油凹陷--渤南洼陷为例，综合油气地质、地球物理、实验分析等新理论和新技术，以现今烃源岩系压力场特征分析和压力结构类型划分为基础，利用岩心观察、测井识别、扫描电镜观察等方式对超压裂缝进行识别与统计，刻画复杂压力结构下超压裂缝的发育特征，重点利用流体包裹体古压力恢复与岩石力学性质相结合的方法量化超压裂缝形成的动力条件，以及多因素叠合下的超压裂缝形成的主控因素分析，通过微观与宏观相结合探讨烃源层系超压裂缝的成因模式以及分布规律，实现烃源岩排烃通道以及页岩油气分布预测的目标。该研究成果对于揭示超压系统下烃源岩排烃的复杂性以及非常规油气勘探具有现实意义，同时可促进超压幕式排烃理论以及超压成藏理论的发展。

陆相断陷盆地的烃源层系往往伴生超压，超压破裂烃源岩形成的微裂缝是常规油气排烃和非常规油气储集的关键，具有分布不均、难以预测的特点。以超压发育的富油凹陷——渤南洼陷为例，综合油气地质、地球物理、实验分析等新理论和新技术，以现今烃源层系超压特征分析为基础，利用岩心观察、扫描电镜、成像测井等技术和方法对超压裂缝进行识别和统计，刻画复杂压力系统下超压裂缝的发育特征，并建立常规测井的综合判识方法，预测了超压裂缝的分布规律及其形成条件，定量评价了超压裂缝的开启条件，明确了超压裂缝成因模式。.结果表明：渤南洼陷超压发育，超压发育层系及超压中心分别与沙三段和沙四段烃源层系及其生烃中心相对应。超压层段可识别裂缝广泛发育，其中压力过渡带为裂缝密度带，裂缝开度、长度较大，高角度裂缝发育；超压体内微裂缝为主，多水平缝，开度、长度较小。超压成因裂缝往往具有较高的GR值，AC和Rs的振荡最为明显，AC甚至出现周波跳跃，密度曲线低值的特点，据此建立了常规测井综合识别超压裂缝的方法。预测结果表明，超压裂缝往往分布于压力梯度变化急剧的岩层段；在压力系数较大且压力平稳分布的区域，超压裂缝虽发育，但数量和规模较低；当压力系数大于1.4，很少见可识别裂缝。油气主成藏期，渤南洼陷成熟烃源层系古压力幅度较大，达到超压裂缝产生和开启的动力学条件。超压裂缝的发育使得油气通过烃源岩中裂缝通道，把生成的油气以幕式运移的方式排放到邻近的有效储层中聚集成藏。另一方面由于超压裂缝的广泛发育，对烃源岩层位进行改造，使得烃源岩层本身的储油空间得到了提高，具有了一定的油气储集能力。因此，油气藏的分布与超压裂缝带相吻合，油气多在超压裂缝带内或裂缝带上下邻近的砂体部位发生聚集。该研究成果对于揭示超压系统下烃源岩排烃的复杂性以及非常规油气勘探具有现实意义，同时可促进超压成藏理论的发展。