Fluids in the Upper Continental Crust: Static or Dynamic?

9909277Demand地壳流体动力学知识中的一个主要不确定性领域是陆壳超压产生、维持和消散的时间和空间尺度。目前，学术界和产业界对几个基本问题都没有达成共识。几亿年来没有经历过活跃沉积的较老沉积盆地的超压原因是什么？是否存在压力密封？如果它们存在，岩石渗透率必须有多低才能形成密封？如果存在压力盖层，它们是由成岩蚀变作用形成的，还是实际上是气体毛细管盖层？俄克拉荷马州西南部的阿纳达科盆地将作为一个天然实验室，研究可能产生和控制高流体压力的条件。阿纳达科盆地是异常的，因为它包含了大片异常高的流体压力区域，但它在100 Ma以上的时间里一直处于构造静止状态。将从一个概念框架来处理这个问题，该框架假定了地壳水文地质学的两个终端成员概念。静态假说通过调用压力密封来解释地壳中高流体压力的存在，压力密封是在适当的时间尺度上基本上不透水的岩石单位。动力学假说将地壳中超压的存在解释为地质过程(例如，生烃)造成的瞬时不平衡，造成超压的速度快于低渗透率岩石的消散速度。为了区分这些可供选择的假说，或者确定它们实际上是否是连续体的端元行为，将收集测井和岩心数据，并使用它们来描述盆地的热、水文和地质性质。然后，压力产生和消散模型将被用来检验不同的假说，并区分不同的盆地流体状况。了解超压是如何在陆壳上部形成和消散的，可以更好地理解陆壳中发生的许多重要的物理、化学和力学过程(如成岩作用、压实作用、生烃和运移、地震活动)，以及了解地壳岩石的物理性质(如孔隙度、渗透率)如何在时间、空间和尺度上变化。

9909277DemingA major area of uncertainty in our knowledge of crustal hydrodynamics concems the temporal and spatial scales over which overpressures in the continental crust are generated, maintained, and dissipated. At the present time there is no consensus in either academic or industry circles to several fundamental questions. What is the cause of overpressuring in older sedimentary basins which have not undergone active sedimentation for hundreds of millions of years? Do pressure seals exist? If they exist, how low must rock-permeability be to form a seal? If pressure seals exist, are they created by diagenetic alteration, or are they in fact gas capillary seals?The Anadarko Basin in southwestem Oklahoma will be used as a natural laboratory to study the conditions under which high fluid pressures may be generated and contained. The Anadarko Basin is anomalous, because it contains extensive areas of abnormally high fluid pressures, yet it has been tectonically quiescent for more than 100 Ma. The problem will be approached from a conceptual framework which postulates two end-member conceptions of crustal hydrogeology. Static hypotheses explain the existence of high fluidpressures in the crust by invoking pressure seals, rock units that are essentially impermeable over an appropriate time scale. Dynamic hypotheses explain the existence of overpressures in the crust as a transient imbalance caused by a geologic process (e.g., hydrocarbon generation) creating overpressures faster than they may be dissipated from low-permeability rocks. To distinguish between these alternative hypotheses, or to determine if they are in fact end-member behaviors of a continuum, well log and core data will be gathered and used to characterize the thermal, hydrologic, and geologic nature of the basin. Models of pressure generation and dissipation will then be used to test different hypotheses and discriminate between contrasting visions of basinal fluid regimes.Obtaining an understanding of how overpressures form and dissipate in the upper continental crust could lead to a better understwiding of many important physical, chemical, and mechanical processes (e.g., diagenesis, compaction, hydrocarbon generation and migration, seismicity) that take place in the continental crust as well as an understanding of how the physical properties (e.g. porosity, permeability) of crustal rocks vary in time, space, and scale.