利用AVO正、反演预测深水浊积扇储层

Reservoir prediction in deep-water turbidite fans by using AVO forward modeling and inversion

针对赤几G区块深水浊积扇岩性复杂、流体识别难度大的特点,本文在精细井震标定与子波提取的基础上,首先进行了井旁道射线追踪正演模拟,含油砂岩振幅响应表现为近道弱、远道强的Ⅱ类AVO异常。基于AVO正演模型,对严重影响中深层成像与振幅保持的近道多次波进行了压制,采取的方法是在数据分解的基础上对多次波进行倾角扫描相干拟合消除,然后再对剩余有效数据进行重构。根据保幅处理后CDP道集上目的层位的AVO截距、梯度属性,合理划分了部分叠加道集的角度范围,判断了界面异常的大致分布。岩石物理分析与AVO反演结果均表明,研究区目的层段内纵、横波速度比小于2.0、纵波阻抗小于6.5×106kg.m-2.s-1的区域为含油砂岩,横向上自东向西发育两支水道,沉积上以朵叶体为主,含油砂体面积大、横向连通性好,厚度大、孔渗高,储量丰度大。

Regarding the complexity of lithology and difficulty in fluid identification in deep-water turbidite fans in Block G of Equatorial Guinea,this paper conducts an AVO ray-trace modeling from well logs firstly,which based on careful well-tie calibration and rational wavelet extracted.In oil-bearing sandstone,there is an AVO II abnormality.The amplitude of oil-bearing sandstone is weak in near-offset,and gets stranger with the distance increase.Based on this forward model,the near-trace multiples which seriously affect the middle-deep layer imaging and amplitude preserving are suppressed.The multiple suppression method first decomposes the initial gather data,then eliminates the multiples by using coherent fitting based on dip scanning,finally reconstructs the remaining signals.According to the intercept-gradient attributes of oil-bearing layer which extracted from CDP gather,this paper divides the angle range which used in forming the angular gather rationally,and judges the general distribution of interface abnormality.Both petrophysical analysis and AVO inversion show that the zones with V_P/V_S less than 2.0 and P-wave impedance less than 6.5×106(kg·m-2·s-1) are oil-bearing sandstones in target layer.In this area,there are two channels from east to west,with the branch channel advancing,lobe complex runs widely spread.With lateral connectivity,good thickness,high porosity and permeability,the reserves abundance is great.