莺歌海盆地“平点”叠前AVO特征及识别

Prestack AVO characteristics and identification of flat spot in Yinggehai Basin

为了在复杂条件下依据"平点"地震反射特征识别油气,利用近年来莺歌海盆地中深层高温、高压领域钻探成果,总结"平点"的叠后地震反射特征,分析"平点"的叠前AVO特征。发现"平点"具有"法线入射时为正反射系数,随入射角的增加,反射系数呈逐渐增大"的变化规律。进一步研究发现,"平点"的AVO特征与Castagna的四类AVO分类方案不同,通过理论推导及地震正演证实了这一认识;提出了"平点"的叠前AVO识别特征;同时结合"平点"的叠后识别标志,建立了"叠后从‘平点’形态、反射能量影响因素综合分析,到叠前‘平点’AVO特点、砂体顶底面AVO类型综合分析"系统识别"平点"的方法。应用该方法提高了研究区"平点"识别准确性,为井位目标的确定提供了依据。

Combined with drilling data of high-temperature and overpressure in Yinggehai Basin,reflection characteristics of flat spots on poststack seismic data are analyzed systematically in order to identify hydrocarbon reservoirs under complex conditions.On this basis,prestack AVO features of flat spots are also analyzed.It is found that flat points have positive reflection coefficients at the normal incidence,and the reflection coefficient increases gradually with the increase of incident angle.AVO features of flat points are different from conventional four classes of Castagna AVO scheme.These phenomena are confirmed by theoretical deduction and seismic forward modeling.A new strategy of flat spot identification is proposed.For poststack data,the flat point identification is based flat point shapes and reflection energy;for prestack data,the flat point analysis should focus on AVO characteristics and AVO types of sand top& bottom.The proposed strategy is used in the study area and the flat spot identification is greatly improved.