特殊岩性体的速度—深度建模方法

The velocity-depth modeling method of special lithologic bodies

在有特殊岩性体(如火成岩、膏岩、砾岩等)分布的区域速度变化剧烈,地震波场复杂,特殊岩性体的速度建模和成像极为困难。常规层控速度建模方法很难适应特殊地质体的剧烈横向速度变化及内部速度变化,造成特殊地质体下伏构造不能准确成像。为此,以L探区的火成岩岩性体建模及成像为例,提出针对特殊岩性体的速度—深度建模方法。首先在特殊岩性体特征及正演模拟分析的基础上,利用解释层位进行形态控制和提取VSP速度相结合的方法,得到空间速度分布合理的初始速度模型;然后利用三维网格层析方法优化初始速度模型,提高特殊地质体内部的速度精度。该速度建模方案的应用不仅使L探区中深层火成岩下伏构造得到准确恢复,消除了断裂假象,也使超深层碳酸盐岩缝洞储层成像更准确,同时为类似特殊地质体的速度—深度建模及成像提供了借鉴。

An accurate seismic velocity model is important for accurate seismic imaging.However,in some complex areas with special lithology,such as igneous rock,gypsum salt rock,conglomerate rock and so on,sharp changes in the composition of the special lithology cause sharp changes in seismic velocity,then complex seismic wave field,and consequently extremely difficult to get accurate modeling and imaging of the special lithology.A conventional layer-controlling velocity modeling method can’t accurately deal with the violent lateral and internal velocity changes of the special geological body,so the underlying structure of the special geological body is unable to accurately image.Taking the special igneous rock in the L exploration area as a case,we use interpreted horizons to control the structure shape and extract VSP velocity to the special lithology and forward simulation to obtain an initial velocity model with reasonable spatial velocity distribution;then optimize the initial velocity model through three-dimensional grid tomography to improve the internal velocity accuracy.The velocity modeling method can not only restore the underlying structure of igneous rock in the middle and deep layers of the L exploration area and eliminate the underlying false faults,but also provide the more accurate image of the ultra-deep fracture-cave carbonate reservoir.The method is a reference to velocity-depth modeling and imaging of similar special geological bodies.