断层转折褶皱作用的参数空间及其对应的力学机制与预测模型

We propose to develop a mechanical basis for our understanding of fault-bend fold, an important class of structures in petroleum basins around the world. Fault-bend folding theory is currently described by a series of kinematic models that relate fold and fault geometries,e.g. the change in fault dip,the initial cutoff angle,the final cutoff angle,and the inberlimb angle. While this theory has proven successful in many applications,it does not consider the mechanics of deformation. It is therefore unable to address important aspects of fault-bend folding, such as the influence of fault strength and mechanical stratigraphy on fold development. Moreover, the assumptions that are inherent in this theory - such as conservation of layer thickness - may be invalid in certain geologic conditions. Thus, we propose to develop an extensive series of mechanical models,in which the change in fault dip and the initial cutoff angle vary from 10 to 80 at interval of 5 ,based on the discrete element method (DEM)to rigorously evaluate the predictions of this theory and its parameter space.These mechanical models will be built by system testing of rock mechanics in Junggar basin. To better understand the incremental deformation leading to the behavior in the mechanical models, we have adopted a method to visualize the incremental strain occurring in the simulation.We will focus most on the second invariant of the deviatoric strain tensor (J2), which can be viewed as a measure of distortion. Our preliminary work has shown that some mechanical models closely reproduce the predictions of fault-bend folding theory. In many other cases, however, the mechanical models depart significantly from the theory's predictions. We plan to quantify the conditions under which these mechanical models and natural structures are effectively described by this existing theory, and to explore cases where they are not. This effort should help refine our understanding of the predictive power of the theory, while developing new mechanics-based fault and fold relations for a broader class of structures. Ultimately, this effort is aimed at improving the predictive power of fault-bend folding theory, which are valued through their application to petroleum trap and reservoir characterization.

断层转折褶皱的几何学和运动学定量模型是以弯滑褶皱作用为基础建立的，该模型的几何学要素和预测范围严格受其参数空间的制约，且没有涉及地层的力学结构，这些局限使其在含油气盆地复杂构造解释和解析中一直存在着多解性的问题。本项目拟通过中西部某盆地地层单元岩石力学参数的系统测试，用离散元方法建立符合地质实际的力学模型，以5 为间隔，模拟断层转折褶皱在断层转折角和初始截层角由10 变化至80 时的形成过程，并测量每一次模拟结果的褶皱翼间角和最终截层角，再将测量数据与现有的断层转折褶皱几何学和运动学模型对比，以确定不同的参数空间。同时，计算各参数空间内离散元模型有限偏应变张量的第二不变量，用以揭示模型内部的剪切应变和体应变，判断和评估不同参数空间下的褶皱变形机制。最终对各参数空间的测量数据进行最小二乘法拟合，建立经验方程，并将其应用于某盆地构造研究实例，通过反复验证和修正，达到在油气勘探中应用的目的。

经典的断层相关褶皱模型参数取值具有一定的限定范围，若超出这个范围，模型将出现无解，因而限制了它的应用。这种局限的根源在于经典模型是基于几何学方法建立的，没有涉及地层的力学结构。本项目与哈佛大学地球与行星科学系合作，寻求突破经典模型的局限，提出断层相关褶皱作用参数空间概念，运用离散元模拟方法，基于力学模型建立不同参数空间下的断层转折褶皱定量预测手段和变形机制分析方法，将断层相关褶皱模型提升到更具应用性的层次。.上述分析技术在中国中西部重要含油气盆地复杂构造建模与解析中得到成功应用。在柴达木盆地，共完成23口井岩芯样品的岩石力学参数测试和15条岩石力学结构剖面的建立，以此为约束，运用定量化手段探索古近系生烃凹陷边界效应对新近纪和第四纪构造变形的控制机理，据此建立生烃凹陷的预测模型，有效指导了油气勘探生产，得到中国石油青海油田分公司勘探开发研究院的认可。此外，在中国石油天然气股份有限公司科技管理部组织的中国三大克拉通中新元古代-寒武纪裂谷识别和分布研究中，本项目建立的构造定量预测和变形机制分析技术应用于地震处理和解释模型的建立，在盆地覆盖区古老裂谷识别与成因机制解释中发挥了重要作用，获得中国石油东方地球物理勘探有限责任公司研究院的认可，也因此获得了依托单位2017年科技进步奖励。.本项目共发表学术论文7篇，其中，国际著名期刊《American Association of Petroleum Geologists Bulletin》和《Journal of Geophysical Research: Solid Earth》论文各1篇，国内《石油学报》和《地质科学》等期刊论文5篇。