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为了研究碳酸盐岩储层中原油裂解产物及其同位素演化特征,采集塔里木盆地塔河油田TK772井奥陶系鹰山组产层的原油,利用半开放实验体系“地层孔隙热压生排烃模拟仪”开展仿真碳酸盐岩储层条件的原油裂解成气模拟实验,并对实验气体产物地球化学特征进行分析。实验结果表明,碳酸盐岩中原油裂解成气过程主要受温度的影响,实验中硫酸镁的加入导致了TSR(硫酸盐热化学还原反应)的发生,影响了原油裂解过程及其产物特征,导致重烃规模裂解的温度降低,消耗大量重烃的同时导致大量非烃气体生成。原油裂解烷烃气碳同位素变化主要受热演化程度控制,表现为随温度的升高逐渐变重,但有硫酸盐存在的温度条件下烷烃气碳同位素序列发生部分倒转(δ~(13)C_1<δ~(13)C_2>δ~(13)C_3)。研究表明,碳酸盐岩储层中TSR反应会改变天然气的化学组成,是高含硫气藏中普遍存在的碳同位素序列倒转的重要原因。
In order to study the evolution characteristics of crude oil pyrolysis products and their isotopes in carbonate reservoirs, the crude oil from the Yingshan Formation in the TK772 well in the Tahe Oilfield, Tarim Basin was collected. Using the semi-open experimental system Simulator "to carry out the simulation of carbonate cracking reservoirs into gas simulation experiments, and analysis of the characteristics of the experimental gas products geochemistry. Experimental results show that the cracking process of crude oil in the carbonate rock is mainly influenced by temperature. The addition of magnesium sulfate led to the occurrence of TSR (sulfate thermochemical reduction) in the experiment, which affected the cracking process of crude oil and its product characteristics. The temperature leading to the cracking of heavy hydrocarbons decreases, consuming a large amount of heavy hydrocarbons while leading to a large amount of non-hydrocarbon gas. The carbon isotope variation of crude oil cracking alkane is mainly controlled by the degree of thermal evolution, showing a gradual increase with increasing temperature, but the carbon isotope sequence of alkane gas partially reversed (δ ~ (13) C_1 <δ ~ (13) C_2> δ ~ (13) C_3). The results show that the TSR reaction in carbonate reservoirs can change the chemical composition of natural gas and is an important reason for the reversal of the carbon isotope sequence commonly found in high-sulfur gas reservoirs.