Free Convection, Mass Transport and Diagenesis in Thick Heterogeneous Sediment Sequences: Implications for the Gulf Basin Geopressured Zone

9316627 nunn海湾盆地北部的大部分沉积物都是超压的(即孔压超过静水压力)。在一些地区，孔隙压力可能超过静岩压力的80%。中新世，特别是上更新世，地压发育为渗透性沉积。粘土脱水和碳氢化合物成熟等温压化学反应产生的水和二氧化碳也可能导致超孔压的形成。许多研究探讨了沉积盆地中地压的形成和/或地压流体向上覆水压带的喷发。然而，很少有人注意到地压带本身内的流体流动。一些先验的考虑使区域尺度的温盐对流可能发生在地压带内：1)沉积物压实不足，因此是多孔和渗透性的；2)压实不足的沉积物热导率低，这增加了传导地温梯度；3)在海湾盆地，以穹顶或异地片层形式存在的地层高盐分的溶解产生了致密的盐卤水，这进一步破坏了水柱的稳定。在海湾盆地，石油从源岩运移到储油层需要在几百万年内进行多达10公里的垂直迁移。在一些受地压的沉积物中，大量石英和方解石胶结物的沉淀也意味着大规模的流体流动。我们计划开展为期两年的非均质沉积序列中温盐信念和成岩作用理论方面的研究：1)修改现有的数值模型以模拟异地盐席下的温盐对流：2)考察非均质沉积物(例如生长断层和连续的砂页岩)对流体流动模式的影响；3)发展温盐对流物理模型，并将其与假设溶解度只是温度和盐度的函数的石英和方解石成岩作用的数值模型相耦合；以及4)将数值模型的结果与海湾盆地成岩作用的模式进行比较，包括垂直或水平化学盖层的形成。***

9316627 Nunn A large portion of the sediments within the northern Gulf Basin are over pressured (i.e., contain pore pressures in excess of hydrostatic). In some areas, pore pressures may be more than 80% of lithostatic pressure. Development of geopressure is permeability sediments in the miocene and particularly the Plio- Pleistocene. Water and carbon dioxide generated by thermobaric chemical reactions, such as clay dehydration and hydrocarbon maturation, may also contribute to the formation of excess pore pressure. Numerous studies have examined the formation of geopressure in sedimentary basins and/or expulsion of geopressured fluids into the overlying into the overlying hydropressured zone. However, very little attention has been given to fluid flow within the geopressured zone itself. A number of priori considerations make it likely that regional scale thermohaline convection may be occurring within geopressured zones: 1) sediments are undercompacted and therefore porous and permeable; 2) undercompacted sediments have low thermal conductivities which increases the conductive geothermal gradient; and 3( in the Gulf Basin, dissolution of stratigraphically high salt in the form of domes or allochthonous sheets produces dense saline brines which further destabilizes the water column. Movement of oils from source rocks to reservoirs in the Gulf Basin requires as much as 10 km of vertical migration in a few million years. Precipitation of large amounts of quartz and calcite cements in some geopressured sediments also implies fluid flow on a massive scale. We propose to carry out a two year study on the following aspects of thermohaline conviction and theoretical diagenesis in heterogeneous sediment sequences: 1) modify our existing numerical models to simulate thermohaline convection beneath allochthonous salt sheets: 2) examine the effects of heterogeneous sediments (e.g., growth faults and is continuous sand/shale layers) on fluid flow patterns; 3) dev elop and couple the physical models for thermohaline convection to numerical models for quartz and calcite diagenesis assuming that solubility is a function of temperature and salinity only; and 4) compare results from the numerical models to the pattern of diagenesis in the Gulf Basin including the formation of vertical or horizontal chemical seals. ***