桑托斯盆地盐下J油气田CO_2成因、烷烃气地球化学特征及成藏模式  

Carbon dioxide origin,alkane gas geochemical characteristics and pool-forming model of pre-salt J oilfield in offshore Santos basin,Brazil

作　　者：马安来[1] 黎玉战[2] 张玺科[1] 张忠民[1] 

机构地区：[1]中国石化石油勘探开发研究院,北京100083 [2]中国石化国际石油勘探开发有限公司,北京100029

出　　处：《中国海上油气》2015年第5期13-20,共8页China Offshore Oil and Gas

基　　金：中国石化科技部项目"中石化巴西区块盐下油气成藏条件及目标优选(编号:JP14008)"部分研究成果

摘　　要：巴西海上桑托斯盆地盐下J油气田油气藏气顶和油环流体组分存在明显差异,气顶流体中CO2含量为76%~78%,气油比为2 750~4 260 m3/m3,原油密度为32~36°API;而油环流体中CO2含量为56%~60%,气油比为170~211 m3/m3,原油密度为16~23°API。研究表明,该油气田天然气中CO2碳同位素值为-5.35‰^-8.11‰,为无机成因;天然气R/Ra为5.6,表明CO2为火山幔源型。天然气中甲烷碳同位素值为-32.50‰^-35.53‰,乙烷碳同位素值为-29.18‰^-32.23‰,烷烃气成熟度Ro为1.0%~1.2%。该油气田为混合油气藏,原油、烷烃气来自上Barremian—下Aptian阶湖相烃源岩,成熟度未达到凝析油气阶段;CO2主要来自深部幔源无机气。CO2后期注入形成的蒸发分馏作用改造了原始油气藏,形成了现今大气顶薄油环油气藏,NE—NNE向深大断裂为深部无机气提供了运移通道。Fluid components between reservoir gas cap and oil ring are very different in pre-salt J oilfield of offshore Santos basin, Brazil. For gas cap, CO2 content ranges from 76% to 78%, GOR from 2 750 to 4 260 m3/m3 , and oil density from 32 to 36°API. For oil ring, CO2 content ranges from 56% to 60%, GOR from 170 to 211 m3/m3 , and oil density from 16 to 23° API. It is concluded that carbon isotope of CO2 is from - 5.35‰ to - 8. 11‰, indi- cating inorganic origin, and R/Ra of the gas is 5.6, showing CO2 from volcanic mantle. Carbon isotopes of meth- ane and ethane are respectively from - 32.50‰ to - 35.55‰ and from - 29. 18‰ to - 32. 23‰, and maturity of alkane gas is from 1.0% to 1.2%. J oilfield is a mixing reservoir type in which oil and alkane gas are from Upper Barremian--Lower Aptian lacustrine source rocks, CO2 originates from inorganic gas in deep mantle, and the ma- turity does not reach the condensate stage. The present reservoir with big gas cap and thin oil ring results from the former reservoir modified by evaporative fractionation of later CO2 injection migrating from deep mantle along deep faults in NE--NNE direction.

关 键 词：桑托斯盆地 盐下 J油气田 CO2成因 烷烃气地球化学特征 成藏模式 

分 类 号：TE513.3[石油与天然气工程—油气田开发工程] P618.13[天文地球—矿床学]