塔里木盆地海相油藏热稳定性的物理化学条件探讨

Some hydrocarbon fluids were found still thermally stable occurred in the Tarim Basin, NW China, even over the burial depth of 8000m or the oil reservoirs experienced high temperature more than 200℃. Therefore recently more exploration studies have been targeted to the deeper strata in order to find more marine crude oils in the Tarim Basin. The thermal stability of crude oil reservoirs in the Tarim Basin may be somewhat special compared to those from Sichuan or Ordos Basins. Besides the tectonic evolution background, the mineral constituents of the reservoirs, the formation water occurrence, and the physiochemical reactions between hydrocarbon, water and rocks are the most important constrained factors to the thermally stable preservation of the crude oils. This project is aimed to probe the physiochemical features of the thermally stable crude oil reservoirs in the Tarim Basin, mainly through the simulation experiments to study the physiochemical reaction mechanisms between the hydrocarbon, water and rocks. Especially to evaluate the relative importance of the radical reaction and the carbon cation mechanisms during the chemical reactions of hydrocarbon/water/rocks, and thus the constrained factors of the thermally stable occurrence of the crude oils in the Tarim Basin will be probed by using the geological reservoir rocks, the formation water and the crude oils. The action of the elemental sulphur to the hydrocarbon fluids will be particularly investigated concerning its role to the thermal stability of the crude oils and the formation of sulphur-containing compounds in the oils from the Tazhong Uplift. Accomplishment of this project will be helpful to the further exploration studies targeted to the marine crude oil reservoirs deposited in the deeper strata in the Tarim Basin, NW China.

塔里木盆地在埋深超过8000米、油藏经历200℃以上高温仍然发现液态烃类流体稳定存在，目前勘探工作正在面向深层-超深层拓展。塔里木盆地原油热稳定性与四川盆地、鄂尔多斯盆地海相油藏比较起来具有特殊性，除开宏观地质构造演化、盆地热史差异等因素外，油藏储层的矿物组成、地层水的发育特征、烃/水/岩相互作用等微观物理化学过程也是重要的影响因素。 本项目结合宏观地质背景演化，从微观过程入手探讨塔里木盆地海相油藏热稳定性的物理化学特征，主要通过模拟实验研究原油组分与不同矿物组分之间的烃/水/岩相互作用特征，重点探讨其微观化学过程中自由基反应和离子反应机理的贡献程度；研究含硫化合物、特别是单质硫对原油稳定性的影响及其机制；利用塔里木盆地实际原油、储层和地层水样品模拟研究烃类流体的热稳定性。预期研究结果可以明晰塔里木盆地海相原油热稳定性的微观物理化学特征及其机制、有助于深化塔里木盆地深层油藏的勘探研究工作。

本项目工作针对塔里木盆地海相油藏热稳定性的物理化学特征开展了系统的研究，依照项目设计的研究内容，主要在以下几个层面开展了实验研究和结合塔里木盆地塔中深层油气藏原油稳定性开展了应用讨论：（1）实验模拟研究了不同矿物对小分子饱和烃和芳烃化合物在含水/不含水体系中的热演化特征，发现硫对烃类的稳定保存非常不利、在含水/不含水体系中均表现出较强的催化裂解作用；而黄铁矿则影响效果不明显，总体上看水的存在可以抑制烃类自由基裂解反应的进行、有利于其稳定保存；（2）利用n-C20H42和n-C5H12两个化合物分别代表原油中长链烷烃和小分子轻烃组分，选择5组岩石样品（R1、R2、R3、R4、R5）分别来自塔里木盆地和四川盆地的钻孔岩芯样品，其中R1、R2、R3分别来自塔里木盆地中深5井寒武系阿瓦塔格组（Є2a）、吾松格尔组（Є1w）和肖尔布拉克组（Є1x）储层，而R4、R5分别来自四川盆地下志留统龙马溪组（S1l）页岩样品。利用两个烃类化合物与不同岩石样品、以及加水/不加水等要素开展了不同系列配伍条件下的模拟实验研究工作。结果表明页岩中高的黏土矿物含量使得其在无水体系中对烃类裂解产生了明显的催化作用，而在含水条件下其催化作用的程度受到了抑制；而碳酸盐岩储层总体上有利于烃类的稳定保存，但在不同的温压条件、以及是否有水的参与下对烃类稳定保存影响复杂；水的存在总体上有利于烃类的稳定保存，这可能与其不利于烃类发生自由基裂解、从而抑制了烃类的裂解程度有关；（3）针对塔中深层油藏稳定性地质应用研究认为塔里木盆地塔中地区深层原油稳定保存的有利因素包括：台盆区内无大规模发生TSR反应、碳酸盐岩储层中缺乏对烃类有破坏作用的黏土矿物、地层水在横向上和纵向上的大范围分布降低了烃类裂解的反应速率、塔里木盆地从二叠纪开始长时间处于低地温梯度的环境、多期构造运动使原油在后期调整的过程中聚集到更加稳定的环境中，因此塔里木盆地塔中地区深层油气藏的勘探开发前景仍然较大。