Theoretical Investigation of Geochemical Processes

该项目未来5年的目标包括：1)对嗜热气压微生物代谢、石油生成和成熟、可逆和不可逆成岩反应以及沉积盆地间质流体的有机化学相互依赖性进行化学和热力学评估；2)综合计算化学亲和和吉布斯自由能最小值，以量化控制油气藏中发生的生化和有机-无机反应的化学参数；3)测定嗜热生物分子在高温高压下的热力学行为，以便更好地表征反应途径和微生物在成岩过程中的作用。所采用的方法包括热力学计算和借助状态方程进行的计算机实验，利用文献中报道的成分和热力学数据来表征成岩过程中微生物活动的原因和后果。本研究的意义在于提高我们对烃类和矿物学底物对微生物代谢的影响的认识，以及在成岩过程中嗜热微生物在催化矿物与有机和无机水系及生物分子之间不可逆反应中的生物地球化学作用。近年来，了解沉积盆地中有机-无机界面的生物地球化学特征以及嗜热微生物在催化成岩反应中的作用，对于准确描述和解释沉积盆地的相关系至关重要。在成岩过程中，生物分子与其他有机含水物质、矿物与无机含水物质、碳氢化合物固体、液体和气体之间发生了无数可逆和不可逆的反应，这些反应原则上都可以用热力学分析来解释。该方法可用于评估反应途径以及嗜热菌介导成岩反应所使用的能量、碳和营养来源。它还可以用来量化在高温下维持生命所需的细胞外酶和其他生物分子的相对稳定性。文献报道的实验数据表明，随着温度的升高，生物分子对其所处的化学环境变得越来越敏感。然而，如果H2（以及O2）、H2O、CO2、NH3和H2S的化学势有利，生物分子可能在高温下持续的时间远远超过嗜热微生物再生分子所需的时间。计算沉积盆地间质流体中生物分子的相对稳定性作为这些气体逸度的函数，可以借助该实验室在国家科学基金会的事先支持下开发的群可加性状态方程来进行。将这些方程与热力学数据和状态参数方程相结合，可以研究生物分子和各种矿物、气体、碳氢化合物液体以及高温高压下有机和无机水之间反应的化学和热力学后果。这些反应包括为微生物代谢提供能量来源的不可逆反应，以及代表局部和部分亚稳态或稳定平衡状态的可逆反应，如Shock（1987、1988、1989、1990a）、Helgeson等人（1993、1995）、Helgeson和Amend（1994）、Seewald（1994、1996）和Schulte和Shock（1996）所描述的反应。为了研究和量化微生物在成岩过程中生物地球化学作用的热力学约束，本提案的目的是为本研究的继续提供长期支持。

9613753 Helgeson The objectives of this project over the next five years include 1) chemical and thermodynamic assessment of the interdependence of thermobarophilic microbial metabolism, petroleum generation and maturation, reversible and irreversible diagenetic reactions, and the organic chemistry of interstitial fluids in sedimentary basins, 2) comprehensive calculation of chemical affinities and Gibbs free energy minima to quantify the chemical parameters that control the biochemical and organic-inorganic reactions that take place in hydrocarbon reservoirs, and 3) determination of the thermodynamic behavior of thermophilic biomolecules at elevated temperatures and pressures in order to better characterize reaction pathways and the role of microbes in diagenetic processes. The methods to be employed consist of thermodynamic calculations and computer experiments carried out with the aid of equations of state using compositional and thermodynamic data reported in the literature to characterize the causes and consequences of microbial activity in diagenetic processes. The significance of the proposed research to the advancement of knowledge is to improve our understanding of the effect of hydrocarbons and mineralogic substrates on microbial metabolism and the biogeochemical role of thermophilic microbes in catalyzing irreversible reactions among minerals and organic and inorganic aqueous species and biomolecules in diagenetic processes. It has become increasingly apparent in recent years that understanding the biogeochemistry of the organic-inorganic interface and the role of thermophilic microbes in catalyzing diagenetic reactions in sedimentary basins is critical to accurate description and interpretation of phase relations in these basins. A myriad of reversible and irreversible reactions occur among biomolecules and other organic aqueous species, minerals and inorganic aqueous species, and hydrocarbon solids, liquids, and gases in diagenetic processes, all of which are in prin ciple amenable to thermodynamic analysis. This approach can be used to assess reaction pathways and the energy, carbon, and nutrient sources used by thermophiles in mediating diagenetic reactions. It can also be used to quantify the relative stabilities of extracellular enzymes and other biomolecules required to support life at high temperatures. Experimental data reported in the literature indicate that biomolecules become increasingly sensitive to their chemical environment with increasing temperature. However, if the chemical potentials of H2 (and therefore O2), H2O, CO2, NH3, and H2S are favorable, biomolecules may persist at high temperatures for periods of time well in excess of those required for regeneration of the molecules by thermophilic microbes. Calculation of the relative stabilities of biomolecules in the interstitial fluids of sedimentary basins as a function of the fugacities of these gases can be carried out with the aid of group additivity equations of state developed in this laboratory with prior NSF support. Combining these equations with thermodynamic data and equations of state parameters permits investigation of the chemical and thermodynamic consequences of reactions among biomolecules and a wide variety of minerals, gases, hydrocarbon liquids, and both organic and inorganic aqueous species at elevated temperatures and pressures. These include irreversible reactions which provide an energy source for microbial metabolism, as well as reversible reactions representing local and partial metastable or stable equilibrium states such as those described by Shock (1987, 1988, 1989, 1990a), Helgeson et al. (1993, 1995), Helgeson and Amend (1994), Seewald (1994, 1996), and Schulte and Shock (1996). The purpose of this proposal is to request long-range support for continuation of this research in order to investigate and quantify thermodynamic constraints on the biogeochemical role of microbes in diagenetic processes.