松辽盆地北部深层天然气多层位成藏要素耦合度研究与有利区带预测

Study on coupling degree of multi-layer accumulation key factors and prediction of favorable zones of deep natural gas in northern Songliao Basin

松辽盆地北部深层断陷分布广、发育层位多,天然气勘探潜力大。亟需深入开展针对不同地区、不同层位的成藏主控因素的研究,以期尽快取得新区新层位勘探突破。依据生气强度>20×10^(8)m^(3)/km^(2)作为沙河子组有效烃源岩标准,徐家围子断陷沙河子组不同成熟度泥岩厚度与TOC关系的理论曲线表明,中等丰度泥岩(w(TOC)=1%)厚度应>400 m,高丰度泥岩(w(TOC)>5%)厚度可<100 m。在单井和平面有效烃源岩评价的基础上,通过计算徐家围子断陷不同层位不同地区有效烃源岩发育井数和获气流井数比例,统计获气流井数与正向构造带关系、获气流井与断层距离关系,得出不同地质因素与不同层位气藏的耦合度。结果表明,沙河子组源-藏耦合度高达90.5%,营城组构造-气藏耦合度82.6%,登娄库组断裂-气藏平均距离仅355 m,指出沙河子组、营城组、登娄库组这3个主要含气层的成藏主控因素分别为源岩、构造和断裂,反映出断陷盆地源控论在纵向上的一种表现形式:自下而上分别为源内气藏、近源气藏和远源气藏,据此预测了外围断陷15个有利勘探区带,可作为下步探井部署和风险井定位的重点方向。

The deep fault depressions in the northern Songliao Basin are widely distributed,where multiple horizons are developed and the natural gas exploration potential is great.The research on the main controlling factors of reservoir formation in different areas and horizons needs to be carried out in depth,in order to make a breakthrough in the exploration of new horizons and new areas as soon as possible.Based on gas generation intensity>20×10^(8)m^(3)/km^(2)as the effective source rock standard of the Shahezi Formation,the theoretical curve of the relationship between the thickness of mudstone with different maturities and TOC of Shahezi Formation in Xujiaweizi fault depression shows that the thickness of medium abundance mudstone(w(TOC)=1%)should be more than 400 m,and the thickness of high abundance mudstone(w(TOC)>5%)can be less than 100 m.Based on the evaluation of single well and plane effective source rocks,the coupling degree between different geological factors and gas reservoirs in different layers is obtained by calculating the proportion of the number of wells developed with effective source rocks and gas wells in different areas of the Xujiaweizi fault depression,counting the relationship between the number of gas wells and positive structural belt,and the relationship between gas wells and fault distance.The results show that the source-reservoir coupling degree of the Shahezi Formation is as high as 90.5%,the structure-gas reservoir coupling degree of the Yingcheng Formation is 82.6%,and the average distance between fault and gas reservoir of the Denglouku Formation is only 355 m.It is pointed out that the main reservoir forming factors of three main gas bearing layers of the Shahezi,Yingcheng and Denglouku formations are source rock,structure and fault,respectively.This reflects a vertical manifestation of source control theory of faulted basins,i.e.from bottom to top there are gas reservoir in source,gas reservoir near source and gas reservoir far away source.Meanwhile,15 favorable exploration areas in the peripheral fault depressions are predicted,which can be used as the key direction of exploration well deployment and risk well location in the next step.