强烈气洗作用导致原油成分变化的定量计算:以库车坳陷天然气藏为例  

Quantitative evaluation of crude oil composition changes caused by strong gas washing:A case study of natural gas pool in Kuqa Depression

作　　者：张斌[1,2] 黄凌[2] 吴英[3] 王辉[4] 崔洁[5] 

机构地区：[1]中国地质大学(北京)能源学院,北京100083 [2]中国石油勘探开发研究院,北京100083 [3]中海油田服务股份有限公司,北京101149 [4]中国石油天然气股份有限公司新疆油田分公司,新疆克拉玛依834000 [5]大庆石油学院,黑龙江大庆163318

出　　处：《地学前缘》2010年第4期270-279,共10页Earth Science Frontiers

基　　金：国家重点基础研究发展计划"973"项目(2006CB202307)

摘　　要：库车坳陷以产天然气为主,同时产出少量原油和凝析油,油气充注不同步,普遍具有"油早气晚"的特点,晚期大量天然气的侵入,必然对早期聚集的油藏发生改造作用。对气藏中原油成分变化的定量计算和讨论,可为天然气的注入强度定量评价提供直接证据。未遭受气洗的原油,正构烷烃摩尔浓度的对数与相应的碳数呈线性关系,而气洗作用可使轻组分的正构烷烃最先溶解于干气中,并随着天然气继续向前运移,原始油藏中的轻组分正构烷烃大大减少。以此为理论基础,建立了正构烷烃损失的定量计算模型。结果表明克拉2构造原油正构烷烃损失程度最高,平均可达70%左右,大北构造带原油正构烷烃损失程度差异较大,与该地区断块发育有关。气洗作用导致原油正构烷烃减少,而金刚烷、多环芳烃等在天然气中溶解度较低的化合物得以浓缩富集,相对含量大大增加。轻芳烃含量也会随之而增加,原油芳香度增加,石蜡度降低。在模拟实验基础上对气洗程度进行了定量评价,初步估算表明,克拉2构造原油遭受的气洗作用最强,是其他构造带的2～5倍。The natural gas is the main product in Kuqa Depression,while there is a small amount of crude oil. Gas charged into reservoir later than oil,and the oil pools formed in early stage tended to be transformed by natural gas injected in later stage. In order to evaluate gas injection intensity quantitatively,it is very important that the crude oil composition changes are calculated,which can provide direct evidence. For crude oils undergo no gas-washing,the logarithm of molar concentration of n-alkanes have a linear relationship with the corresponding carbon number,while gas-washing can make oil components changed. During this process,some hydrocarbon components dissolve in dry gas,and migrate forward with the natural gas. The light n-alkanes are prone to dissolve in gas,thus the light fraction of n-alkanes reduces significantly in original reservoirs. Based on this theoretical foundation,the quantitative calculation model of n-alkanes loss was established. The results showed that the crude oil in Kela-2 Structural Belt had the highest level of n-alkanes loss,with an average of 70%. The crude oil in Dabei Structural Belt had different degrees of n-alkanes loss,resulted from the fault blocks in this region. Gas-washing made n-alkanes reduced in crude oil,while other compounds dissolved little in natural gas,such as diamondoids and polycyclic aromatic hydrocarbons,and could be concentrated and enriched,leading to their relative contents increased greatly in original reservoirs. The content of light aromatic hydrocarbons would also increase,resulting in aromaticity increasing and paraffinity reducing. Based on the simulation experiment,we preliminarily estimated the degree of gas washing,and it was showed that the crude oil in Kela-2 Structural Belt underwent the strongest gas-washing,2-5 times stronger than in other belts.

关 键 词：气洗作用 原油成分 金刚烷 克拉2天然气藏 蒸发分馏 

分 类 号：TE133.1[石油与天然气工程—油气勘探]