顺北地区四号断裂带奥陶系超深层油气地球化学特征与相态差异性成因  

Geochemical characteristics and phase behavior of the Ordovician ultra-deep reservoir fluid,No.4 fault,northern Shuntuoguole,Tarim Basin

作　　者：马安来[1] 漆立新[2] MA Anlai;QI Lixin(Petroleum Exploration and Production Research Institute,SINOPEC,Beijing 102260,China;Northwest Oilfield Company,SINOPEC,rümqi 830011,China)

机构地区：[1]中国石化石油勘探开发研究院,北京102260 [2]中国石化西北油田分公司,新疆乌鲁木齐830011

出　　处：《地学前缘》2023年第6期247-262,共16页Earth Science Frontiers

基　　金：国家自然科学基金项目(U19B6003,42272167,41772153);中国石油化工股份有限公司科技部资助项目(P21085-8,P23167)。

摘　　要：顺北地区4号断裂带奥陶系油气藏相态复杂,自NE向SW,油气藏相态的变化情况是挥发油藏—低气油比凝析气藏—高气油比凝析气藏—中等气油比凝析气藏。使用地球化学分析方法研究了顺北4号断裂带油气藏的地球化学特征,分析了相态差异性的成因。4号断裂带原油生标含量低甚至缺失,原油生源与1号断裂带原油生源相同。4号断裂带原油成熟度高于1号断裂带原油,等效反射率为1.14%~1.60%。4号断裂带天然气干燥系数由NE向SW方向渐进增大,天然气成熟度为1.30%~1.70%。天然气中H2S、CO_(2)含量由NE向SW方向呈现增加的趋势。全油色谱正构烷烃摩尔分数对数与正构烷烃碳数的关系表明,4号断裂带原油未遭受蒸发分馏作用;4号带原油金刚烷含量分布范围为27.26~523.31μg/g,原油裂解作用程度为20.5%~95.8%,裂解程度较1号断裂带原油裂解作用高;SB4、SB41X-C和SB42X井原油硫代金刚烷含量为33.76~76.92μg/g,表明这些油气藏发生了硫酸盐热化学还原(TSR)作用。顺北4号断裂带奥陶系油气藏相态变化与两个因素有关:一是4号断裂带地温梯度呈现两侧略低、中部较高的特点,这使得中部烃源岩生成的油气成熟度较高,中部油气藏原油裂解作用较强;二是中部及SW部油气藏发生了TSR作用,这导致油气藏中CO_(2)、H_(2)S和GOR(气油比)增加。The phase behavior of the Ordovician ultra-deep reservoir fluid,No.4 fault(F4),northern Shuntuoguole,is complex.From NE to SW,the fluid phase changes from volatile oil to condensate,with the solution GOR increasing from 358 m^(3)/m^(3) to 3200 m^(3)/m^(3) then decreasing to 1800 m^(3)/m^(3).Using geochemical methods the geochemical characteristics of the reservoir fluid and the cause of its phase change were investigated.It was found that while the biomarker concentrations in oil from F4 were low to non-measurable,the source rocks were similar for oils from F1 and F4;and oil from F4,with Rc of 1.14%1.60%,was of higher maturity.For natural gas from F4,its dryness coefficient showed an increasing trend from NE to SW,with Rc ranging between 1.3%1.7%,while its CO_(2) and H_(2)S contents showed the same spatial variation trend.The reservoir fluid experienced no evaporative fractionation as inferred from the relationship between the mole fraction and carbon number of n-alkanes.In F4,the concentration of diamondoids in oil ranged between 27.26523.31μg/g,indicating 20.5%95.8%thermal cracking which is higher than in F1;while the concentration of thiodiamondoids in oil from wells SB4,SB41X-C and SB42X ranged between 33.7676.92μg/g,suggesting occurrence of thermochemical sulphate reduction(TSR).Thus,two factors contributed to the phase change in F4:one is geothermal gradient,where relatively strong thermal gradient in the middle compared to either sides of the fault led to high-maturity oil and gas generation and high degree of cracking in the middle of the fault;the other is TSR,which took place in the middle and SW of the fault and further increased CO_(2),H_(2)S and GOR.

关 键 词：油气藏相态 次生改造 顺北地区 奥陶系 超深层 塔里木盆地 

分 类 号：TE122.1[石油与天然气工程—油气勘探] P618.130.1[天文地球—矿床学]