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

厚层非均质沉积层序中的自由对流、质量传输和成岩作用：对海湾盆地地压带的影响

• 批准号: 9316627
• 负责人: Jeffrey Nunn
• 金额: $ 11万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-04-15 至 1997-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9316627&HistoricalAwards=false
• 关键词: Free; Convection; Mass; Transport; Diagenesis

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. ***

Nunn海湾盆地北部的大部分沉积物压力过大（即孔隙压力超过静水压力）。在某些地区，孔隙压力可能超过静岩压力的80%。中新世，特别是上新世—更新世，地压发育为渗透性沉积。粘土脱水、烃成熟等热压化学反应产生的水和二氧化碳也可能是超孔隙压力形成的原因。许多研究都考察了沉积盆地中地压的形成和/或地压流体向上覆地层和上覆水压带的排出。然而，很少有人注意到高压带内部的流体流动。一些先验的考虑表明，区域尺度的热盐对流可能发生在高压带内：1)沉积物未压实，因此具有多孔性和渗透性；2)欠压实沉积物热导率低，增大了导热地温梯度；(3)在海湾盆地，地层高盐以圆顶或异质薄片的形式溶解，产生致密的盐水，进一步破坏了水柱的稳定。在海湾盆地，石油从烃源岩向储层的运移需要在几百万年里进行长达10公里的垂直运移。在一些高压沉积物中，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。本文拟开展为期两年的非均质沉积层序热盐盐确信和理论成岩作用研究：1)修改现有数值模型，模拟异质盐片下的热盐盐对流；2)研究非均质沉积层（如生长断层和连续砂/页岩层）对流体流动模式的影响；3)假设溶解度仅是温度和盐度的函数，建立并耦合热盐对流物理模型与石英和方解石成岩作用的数值模型；4)将数值模拟结果与海湾盆地的成岩作用模式（包括垂直或水平化学密封的形成）进行比较。＊＊＊