徐家围子断陷深层混源天然气源岩贡献率计算方法

Contribution ratio of source rock to source-mixed gas reservoir in Xujiaweizi depression

松辽盆地徐家围子断陷大部分天然气出现碳同位素系列倒转,表现为混源的特征.利用源岩吸附气脱气装置获得深层4套源岩的吸附气,通过天然气色谱微量重烃指纹分析技术、多层神经网络误差反向传播计算方法及室内配比实验,建立徐家围子断陷混源天然气源岩贡献率计算模版.结果表明,断陷中部天然气主要来源于沙河子组和火石岭组源岩,贡献率多大于80.00%,最高可达99.09%;古中央隆起带的天然气主要来源于石炭—二叠系源岩,贡献率超过80.00%,最高可达85.25%.天然气来源与下伏源岩分布有良好的纵向对应关系,天然气主要以垂向运移为主,天然气气藏的分布受源岩区的控制,有效气源岩的分布区即是天然气的有利勘探区.

Partly deep-seated natural gases in Xujiaweizi depression is characterized by source-mixed gas which shows the hydrocarbon gas molecular isotope is reverse order or partly reversed order.In order to calculate the different source rocks distribution ratio to mixed-gas reservoir,the adsorbed gas in the source rock was used as original generated gas from this source rock,and some new techniques and methods were established and used.We developed an instrument which can be used to prepare the adsorbed gas in source rock.A chemical model was built,by means of natural gas allocation ratio test in laboratory and compounds ratio of fingerprinting of adsorbed gas and natural gas.A nonlinear mathematical model for determining the contribution of source rock to source-mixed reservoir was developed by using neural network method.The contribution ratio of four source rock in Xujiaweizi depression was calculated.The result showed that the natural gas in source-mixed gas reservoir located in the center of depression originated mostly from Shahezi and Huoshiling formation source rock,their contribution ratio can be reach 99.09%.but the natural gas which located in the border of pale-center uplift zone are mostly origin from C-P source rock,their contribution ratio is as high as 85.25%.The correlation between source rock contribution ratio and distribution of different source rock in this area suggested that the distribution of gas reservoir was controlled by the distribution of source rock.The natural gas mainly migrated vertically.The distribution area of source rock is a favorable area to find the natural gas reservoir.