岩石力学层定量划分及其对构造裂缝生长控制机理研究-以松辽盆地北部青山口组为例

Mechanical stratigraphy controls the formation and distribution of fractures, which is of great significance to guide the prediction of natural fractures in subsurface, the geometry and scale of hydraulic fractures, and the exploration and development of faulted reservoirs. However, it is still lack of the systematic research on the control mechanism of mechanical stratigraphy on fracture growth and the quantitative division method for mechanical stratigraphy. Taking the Qingshankou Formation of northern Songliao basin as a case study, this project will clarify the types, distribution characteristics and development pattern of fractures in layered rocks through the fine characterization of fractures from outcrops and cores, and establish the quantitative relationship between the fracture spacing and bed thickness. Using microscopic identification, X-ray diffraction, rock mechanics test, nano indentor, atomic force microscope, Schmidt hammer and logging data interpretation, we will present the quantitative division method for lithostratigraphy, fracture stratigraphy and mechanical stratigraphy respectively. Combined with finite element numerical simulation, the effects of the tectonic stress, lithology, mineral composition and content, rock mechanical properties, layer thickness, fracture dip angle and strain on fracture geometry, density and aperture will be discussed, and the control mechanism of mechanical stratigraphy on fracture growth will be clarified. Based on above research, the distribution law of the subsurface fractures can be predicted quantitatively. According to the actual subsurface geological conditions, a geological model will be established to predict the geometry and scale of hydraulic fractures.

岩石力学层控制了裂缝的形成与分布，对指导地下天然裂缝密度预测、压裂裂缝几何形态与规模预测以及断层油气藏勘探开发具有重要的指导意义。但是，目前岩石力学层对裂缝生长的控制机理及其定量划分方法仍然缺乏系统的研究。本项目拟通过野外露头区和岩心裂缝精细表征，阐明层状岩石中裂缝分布特征与发育模式，建立裂缝间距与岩石力学层厚度之间的定量关系。综合镜下鉴定、X衍射、岩石力学实验、纳米压痕仪、原子力显微镜等实验手段以及测井资料解释，建立岩性地层、破裂地层以及岩石力学层的定量划分方法，并明确三者之间的区别与联系。结合数值模拟，明确构造应力、岩性、矿物成分及含量、岩石力学层性质及厚度、裂缝倾角和离距以及应变等多因素对裂缝几何形态、密度、长度及开度等参数的影响，阐明岩石力学层对裂缝生长的控制机理。根据地下实际地质条件建立地质模型，进行地下天然裂缝分布规律、压裂裂缝形态和规模预测。

岩石力学层不但控制了天然裂缝分布和断裂带内部结构，也影响着压裂裂缝的规模和几何形态，对指导地下裂缝预测、断层解释和压裂裂缝预测具有重要的指导意义。但是，目前岩石力学层对裂缝生长的控制机理及其定量划分方法仍然缺乏系统的研究。本项目利用露头、岩心、薄片等资料，结合相关测试分析，开展了三大方面研究：①层状岩石中裂缝分布特征和发育模式表征；②岩性地层、破裂地层以及岩石力学层的定量划分；③岩石力学层对裂缝生长控制机理研究及数值模拟。通过野外露头区和岩心裂缝精细表征，阐明了层状岩石中裂缝分布特征与发育模式，建立了裂缝间距与岩石力学层厚度之间的定量关系。综合镜下鉴定、X衍射、岩石力学实验、纳米压痕仪、原子力显微镜等实验手段以及测井资料解释，建立了岩性地层、破裂地层以及岩石力学层的定量划分方法，并明确了三者之间的区别与联系。结合数值模拟，明确构造应力、岩性、矿物成分及含量、岩石力学层性质及厚度、裂缝倾角和离距以及应变等多因素对裂缝几何形态、密度、长度及开度等参数的影响，阐明了岩石力学层对裂缝生长的控制机理。受岩石力学层控制，裂缝在层状岩石中的发育经历层内发育、裂缝饱和及裂缝穿层三个阶段；裂缝在层状岩石中有2种扩展模式：a.层内裂缝，b.穿层裂缝，其中穿层裂缝数量占比较多。在层状岩石中，裂缝先在强能干性岩石力学层中形成，然后在相邻两条裂缝间充填新的裂缝；对于非平行层状岩石，裂缝会优先在强能干性岩石力学层的薄层处发育，然后依次充填到厚层处。岩石力学层的力学参数及岩石力学层厚度控制裂缝的发育强度及扩展模式，杨氏模量越大、裂缝所在的强能干性岩石力学层越薄，裂缝发育程度越高。层状岩石中两条相邻裂缝间的裂缝充填及扩展，受裂缝发育位置及裂缝高度影响，远离相邻裂缝中心点且高度较高的裂缝易扩展。