综合有机地球化学和测井信息的烃源岩地震评价--以辽中凹陷沙三段为例

Source rock evaluation based on seismic data combined with organic geochemistry and logging information:a case study on the Es_3 in Liaozhong Sag,Bohai Bay Basin

海域和勘探前沿地区钻井和取心资料少,仅利用常规地球化学和测井资料评价烃源岩的方法难以满足高精度资源量计算的要求。为此,利用辽中凹陷覆盖全区的三维地震资料,通过建立综合有机地球化学和测井信息的烃源岩地震评价方法预测深层烃源岩发育相带。利用研究区热模拟TOC(有机碳含量)值与测井参数AC及RT标准化值进行拟合,分别建立了辽中凹陷沙三中及沙三下TOC测井预测模型;通过烃源岩地震相识别和地震波阻抗反演查明了烃源岩的分布范围和厚度;通过优选平均光滑反射强度、均方根振幅、平均瞬时频率和平均瞬时相位等4种地震属性参数,拟合出烃源岩归一化TOC经验公式,预测了烃源岩有机质丰度。对比所提方法得到的烃源岩TOC和厚度值与钻井实测值,发现两者的相对误差的平均值分别为9.56%和10.06%,说明方法具有较高可靠性和实用性。利用所提方法预测了辽中凹陷3个洼陷的烃源岩厚度和TOC平面分布,认为厚度较大的烃源岩分布在辽中北洼和辽中中洼,为该区主力烃源灶,沙三中亚段烃源岩TOC、厚度以及分布范围均优于沙三下亚段。

In this paper we propose a source rock evaluation based on seismic data combined with organic geochemistry and logging information.3D seismic surveys covered almost the entire area of Liaozhong Sag,Bohai Bay Basin.First we achieve the fitting of the total organic carbon content(TOC)values obtained from the thermal simulation and the log parameters AC and RT normalized values,and establish respectively TOC log prediction models for the middle Es_3 and the lower Es_3.Then we identify the distribution and thickness of source rocks with seismic phase identification and seismic wave impedance inversion.After that,with the fitting of the average fiattened reflection strength,RMS amplitude,mean instantaneous frequency,and average instantaneous phase,we establish a TOC empirical formula of source rocks.Finally we predict the organic matter abundance of source rocks with this formula.The average relative error for TOC is only 9.56% between our prediction and the measured value of source rocks from logging data,and the average relative error for source rock thickness is only 10.06%,which proves the high reliability and practicality of the proposed approach.Based on our prediction in Liaozhong Sag,thicker source rocks are distributed in Liaozhongbei and Liaozhongzhong sub-sags,and source rock TOC and thickness in the middle Es_3 is better than in the lower Es_3.