致密砂岩多期裂缝形成机制及定量表征研究进展

致密砂岩油气是重要的非常规资源,裂缝作为主要渗流通道,其本身分布规律的复杂性以及多期发育和多期充填的特征,直接影响着裂缝预测的精度,目前尚缺乏一套全面解决构造裂缝定量预测的系统方法。因此,需要深入探讨多期裂缝的识别、充填过程和形成—叠加演化机制,建立合理的裂缝表征模型,以定量预测裂缝参数分布范围。在大量文献调研的基础上,本文认为致密储层裂缝研究主要涉及三个关键方向:通过野外露头和岩心观察,分析裂缝发育特征,结合构造演化和流体包裹体分析,确定裂缝发育期次;通过热液充填模拟实验和岩石力学实验,揭示裂缝充填机制,及其在多期应力作用下裂缝的萌生、扩展和叠加过程;采用实验统计方法,基于能量守恒定理和最大应变能密度理论,建立考虑裂缝差异充填的各向异性强度破裂准则,建立裂缝参数的定量表征模型。最终,本文形成和完善了致密砂岩多期裂缝演化及量化表征的理论体系,为此类油气田的勘探开发提供重要科学依据。

RESEARCH PROGRESS ON THE FORMATION MECHANISM AND QUANTITATIVE CHARACTERIZATION OF MULTIPHASE FRACTURE NETWORKS OF TIGHT SANDSTONE

Tight sandstone oil gas is an important unconventional resource.As the primary seepage channel, fracture networks commonly have the charactistics including complex distribution regularity as well as multiphase development and filling process, which directly influence fracture prediction accuracy.At present, there is no systematic method for solving the quantitative prediction of structural fissures, which is still in the exploration stage. Therefore, it is necessary to explore more about fraction networks identification, filling process and formation-superposition evolution mechanism. and set up a reasonable fracture characterization model for quantitative prediction of fracture networks parameter distribution range. On the basis of plenty of literature research, it is believed that the research of tight reservoir fracture is mainly in three key directions.Field observation and core observation were carried out to analyze the development characteristics of fracture networks.combing with tectonic evolution history and fluid-inclusion analysis, fractures development times were defined. Then, hydrothermal filling simulation experiments and rock mechanics experiments were conducted to reveal the mechanism of fractures filling and dynamic process of fractures from initiationto extension and superposition. Finally, experimental statistical methods were used to establish the anisotropic failure criterion in view of different filling rules and create quantitative characterization of fracture parameters based on the principle of conservation of energy and the theory of strain energy density factor. At last, a theoretical system of multiphase fractures development and their parameters characterization were formed and completed, which provides an important scientific basis for the exploration and exploit of tight sandstone gas field.