盆缘稠油油藏与浅层气藏联合勘探方法及实践——以渤海湾盆地济阳坳陷三合村地区为例

Combined exploration method and application of viscous oil and shallow gas in basin margin:A case study of Sanhecun area in Jiyang depression,Bohai Bay Basin

以济阳坳陷三合村地区为研究对象,对盆缘稠油与浅层气联合勘探方法进行研究.综合原油物理性质测试、饱和烃气相色谱-质谱分析、天然气样品组分及碳同位素分析,厘清了稠油油藏与浅层气藏成因相关性并提出联合勘探方法,认为三合村地区新近系稠油具有明显微生物降解成因特征,浅层气藏为混源气藏,且主要为微生物降解气.利用已发现的浅层气藏,沿着稠油-浅层气输导体系溯源逆推,并通过圈闭刻画和稠油地震识别,可以实现稠油油藏的精准勘探.研究结果表明:新近系稠油油藏与浅层气藏具有成因关系.新近系稠油正构烷烃缺失严重,甾烷部分降解,为典型微生物降解成因.新近系浅层天然气以微生物降解成因气为主,甲烷体积分数超过95%,干燥系数达到0.99;甲烷碳同位素值偏轻,为-50.03‰~-42.78‰,而甲烷氢同位素比值随着甲烷碳同位素比值减小而增大;CO_(2)碳同位素比值为17.69‰,表现为异常偏重等特征.断裂是浅层气垂向运移的重要通道,砂体发育构成油气横向运移的主要毯层,高频衰减梯度剖面可以有效刻画K119井1321.7~1326 m、K116井1323.8~1329.3 m稠油油藏.通过稠油-浅层气输导体系刻画和稠油地震识别,可以落实稠油油藏勘探方向和目标.浅层气藏主要分布在Ng^(1+2)段累计泥岩厚度大于70 m的范围内的稠油油藏上方或者上倾方向.开展地震振幅异常区、低频谐振异常区描述,共描述Ⅰ类"亮点"气藏砂体31个,预测天然气资源量5.2×10^(8)m^(3).

Taking the Sanhecun area of Jiyang depression as a research example,the combined exploration method of viscous oil and shallow gas reservoirs in the basin margin was studied.The genetic correlation between the viscous oil reservoir and shallow gas reservoir was clarified based on the analyses and tests including the property test of crude oil,gas chromatography-mass spectrometry of saturated hydrocarbons,composition and carbon isotope of natural gas.Then,a combined exploration method was proposed.The Neogene heavy oil in the Sanhecun area has obvious genetic characteristics of microbial degradation.The shallow gas reservoir is a mixed-source gas reservoir dominated by microbial degradation gas.According to the established shallow gas reservoirs,tracing back along the transport system of viscous oil and shallow gas by the means of the trap characterization and heavy oil seismic identification,the accurate exploration of viscous oil reservoirs can be realized.The results indicate that there is a genetic relationship between Neogene heavy oil reservoir and shallow gas reservoir.The n-alkanes in the Neogene viscous oil are seriously absent and the steranes are partially degraded,which is a typical characteristic of microbial degradation.The Neogene shallow gas is mainly formed by microbial degradation,in which the volume fraction of methane exceeds 95%and the drying coefficient reaches 0.99.The carbon isotope value of methane is relatively light,-50.03‰—-42.78‰,and the hydrogen isotope ratio of methane increases with the decrease of carbon isotope ratio of methane.The carbon isotope ratio of CO_(2) is 17.69‰,which is characterized by abnormal bias.Faults are important channels for vertical migration of shallow gas,and sand bodies constitute the main blanket for lateral migration of oil and gas.High frequency attenuation gradient profiles can effectively depict the viscous oil reservoirs of 1321.7—1326 m in well K119 and 1323.8—1329.3 m in well K116.Through the characterization of the viscous oil-shallow gas transport system and viscous oil seismic identification,the exploration targets of viscous oil reservoirs can be realized.The shallow gas reservoirs are mainly distributed in the upper or updip direction of the Ng^(1+2) viscous oil reservoirs with a cumulative mudstone thickness of more than 70 m.At the same time,there are 31"bright spot"gas reservoirs that are clearly described by seismic amplitude abnormity and low frequency resonance abnormity,and the volume of predicted natural gas resources are as large as 5.2×10^(8)m^(3).