Roles of Dissolved Methane and Sulfide in Sedimentary Dolomite Formation

溶解甲烷和硫化物在石化作用中的作用研究PI：许惠芳，威斯康星州大学？美国的大多数油气藏都与沉积岩有关，沉积岩在地质记录中很丰富，但在全新世和现代海洋沉积物中很少。沉积白云岩的形成机制至今仍有争议。虽然铁白云石已被报道在硫酸盐还原菌和产甲烷地下水的培养基中，白云石和原白云石没有在室温下无机或非生物合成。水溶液中Mg ~（2+）离子的强烈水化作用是抑制白云石和无序白云石成核和结晶的主要因素。PI假设原白云石和无序白云石可以在含有溶解的硫化物和/或具有低分子偶极矩的有机物的溶液中成核和生长。 具有低分子偶极矩的溶解分子表现为催化剂，其削弱水偶极子和Mg 2+之间的键，因此降低水合Mg 2+脱水的动能势垒。 为了验证这一假设，研究人员建议进行以下几组实验：（i）系统研究温度和溶解有机物和硫化物浓度对镁掺入白云石和HMC的影响。(ii)白云石中钙镁有序化动力学研究(iii)采用密度泛函理论（DFT）对溶解甲烷对表面Mg 2+脱水的影响进行了计算机模拟，以了解中性甲烷物种在降低白云石结晶动能势垒中的作用。所有的沉淀物将仔细表征使用X射线衍射，SEM和透射电子显微镜（TEM）与相关的化学和结构分析技术。由于溶解的甲烷和其他低介电有机物作为降低脱水和白云岩结晶的动能势垒的催化剂，具有白云岩胶结的沉积泥岩和砂岩可能与烃源岩或受含烃流体影响的岩石直接相关。这一机制也为烃源岩和储层的实际问题以及碳封存地点的长期性能评价提供了新的思路。拟议的研究将有助于选择适当的碳封存地点。

Investigation on the roles of dissolved methane and sulfide in dolomitization PI: Huifang Xu, University of Wisconsin ? MadisonEAR-0958000Most hydrocarbon reservoirs in the US are related to sedimentary dolomites which are abundant in the geologic record, yet scarce in Holocene and modern marine sediments. The formation mechanism for sedimentary dolomite is still under debate. Although ankeritic dolomites have been reported in cultured media of sulfate-reducing bacteria and methanogenic groundwater, dolomite and protodolomite have not been synthesized inorganically or abiotically at room temperature. The main factor inhibiting dolomite and disordered dolomite nucleation and crystallization is the strong hydration of aqueous Mg2+ ions. PIs hypothesize that protodolomite and disordered dolomite can nucleate and grow in solutions containing dissolved sulfide and /or organics with low molecular dipole moments. The dissolved molecules with low molecular dipole moments behave as catalysts that weaken the bonds between the water dipoles and Mg2+ therefore lowering the kinetic energy barrier of dehydration of the hydrated Mg2+. In order to test the hypothesis, PIs propose to carry out the following sets of experiments: (i) a systematic investigation on the effects of temperature and concentrations of dissolved organics and sulfide on Mg incorporation into dolomite and HMC. (ii) Study on Ca-Mg ordering kinetics in dolomite. (iii) Computer modeling of the effect of dissolved methane on surface Mg2+ dehydration using Density Function Theory (DFT) in order to understand the role of neutral species of methane in lowering the kinetic energy barrier of dolomite crystallization. All of the precipitates will be carefully characterized using X-ray diffraction, SEM, and transmission electron microscope (TEM) with associated chemical and structural analysis techniques. Because dissolved methane and other low dielectric organics serve as catalysts for lowering the kinetic energy barrier of dehydration and dolomite crystallization, sedimentary dolomites and sandstones with dolomite cementation may be directly related to hydrocarbon source rocks or rocks influenced by hydrocarbon-bearing fluids. The proposed dolomitization mechanism may also shed new light into practical problems of hydrocarbon source rocks and reservoirs and long-term performance evaluation of sites for carbon sequestration. The proposed study will help choose appropriate sites for carbon sequestration.