川北元坝地区茅口组生屑滩岩溶储层识别及预测

川北元坝地区二叠系茅口组顶部生屑滩岩溶储层受古地貌、生屑滩发育程度及岩溶作用等控制,储层薄、非均质性强,精细刻画优质生屑滩岩溶储层分布对该区茅口组油气勘探具有重要意义。在井震标定基础上,根据实际沉积微相相序组合,建立了生屑滩、生屑滩叠加岩溶缝洞2种储层正演模型并模拟总结其地震响应特征的变化规律,建立生屑滩岩溶储层地震识别模式;在单井岩性、测井相和地震波形分析的基础上,利用地震相和古地貌确定生屑滩发育优势相带;利用波形分解与重构技术去除茅口组顶部强反射界面影响,突出生屑滩储层信息;利用相控高分辨率波阻抗反演确定生屑滩储层厚度;结合分频数据体裂缝预测结果圈定优质生屑滩岩溶储层分布范围。预测结果表明:茅口组顶部生屑滩岩溶储层具有“低频、强振幅、宽波峰”反射特征,3个生屑滩平面上呈北西向分布于工区西南部缓坡坡折带,滩体边界清楚,位于古地貌高部位,储层厚度大,网状微裂缝发育,预测结果与钻井结果相吻合,为下一步油气勘探提供了可靠依据。

A breakthrough has been achieved in the karst reservoir of the upper Permian Maokou Formation in the Yuanba area of the northern Sichuan Basin.Owing to the formation landscape,featuring a bioclastic beach affected by karstification,a thin and heterogeneous reservoir was formed.Identifying the distribution of high-quality bioclastic beach karst reservoirs is of great significance to oil and gas exploration in Maokou Formation.Based on a well-seismic calibration,two types of forward models for beach facies in karst reservoirs were established,and the characteristics of their seismic response were simulated according to the actual sequence of the sedimentary microfacies.Based on a comprehensive analysis of lithology,facies,and seismic waveform in a single well,the zone in which the target facies was dominant was estimated.Moreover,waveform decomposition and reconstruction techniques were used to remove the influence of the strongly reflecting interface at the top of the Maokou Formation and highlight information regarding the bioclastic beach reservoir formation.Facies-controlled high-resolution wave impedance inversion was used to determine the thickness of the bioclastic beach reservoir.The distribution pattern of the high-quality bioclastic beach karst reservoir was estimated from the results of fracture prediction using a frequency divider.The prediction results showed that the reservoir at the top of the Maokou Formation was characterized by low frequency,large amplitude,and a wide-wave peak.Three bioclastic beaches were distributed in the gentle slope break zone in the southwest of the working area in northwest direction.The boundary of the beach body was clear,and the results were consistent with the drilling data.

中国石化油田事业部勘探先导项目“四川盆地西南探区重点区带评价与勘探目标优选”(YTBXD-01-XN06-2019)和中国石化科技部项目“西南探区天然气富集规律与目标评价”(P20059-3)共同资助。