基于地震数值模拟的溶洞型储层地震特征分析

Seismic Characteristics Analysis of Karst Cavity Reservoirs Based on Seismic Numerical Simulation

为了解不同溶洞的“串珠”响应特征,以实际地震资料解释为基础,建立了塔里木盆地塔河南地区全层系的碳酸盐岩缝洞体与走滑断裂三维模型,包括流体类型、溶洞大小、强反射轴干涉距离、纵向分辨距离、横向分辨距离、充填类型和孔隙度7种单因素变量控制模式。对所建模型进行地震数值模拟实验并对模拟结果进行逆时偏移成像。分别从分辨率、振幅能量与控制因素方面对7种单因素控制模式在偏移剖面中的“串珠”响应特征进行了详细比较分析,发现溶洞内的流体类型变化无法在叠后剖面的“串珠”响应形态上进行区分,其影响主要表现为振幅能量随等效弹性参数变化;溶洞大小的影响与“串珠”响应振幅能量呈正相关,溶洞越大“串珠”响应越强;剖面中的强轴与溶洞间的干涉距离会影响“串珠”响应振幅能量;溶洞间纵向距离不会影响单个溶洞的“串珠”响应形式,其主要影响表现为相连部分的振幅能量;而溶洞间横向距离过小,会使两个溶洞的“串珠”响应合并,形成大溶洞的“串珠”假象。溶洞内的泥质充填程度与孔隙度均会影响“串珠”响应振幅能量。通过总结不同因素变量控制模式下地震响应特征的变化规律,为缝洞型储层的有效预测提供参考依据。

The“string of beads”response is a common feature on seismic section of carbonate karst reservoir in Tarim Basin.In order to understand the beaded response characteristics of different karst caves,a three dimensional model constituted of carbonate fracture-cavern bodies and strike-slip faults has been built based on the interpretation from real seismic data.Seven single-factor controlled modes of karst cavity body combinations are imbedded in the model.According to fluid type,cave size,distance to strong reflection interface,vertical resolution distance,lateral resolution distance,filling type and porosity.The numerical seismic simulation is performed over the model and the reverse time migration is done to the simulated data.For the“beads”response characteristics of the seven single-factor controlled modes on the migration section,a detailed comparison and analysis is made in respect of the relationship between the resolution,amplitude energy and controlling factors.The corresponding changing patterns on seismic section to the variation of controlling factor are concluded,and the following conclusions are obtained.The“beads”response of the different fluid type in karst cave are hardly distinguished on the migrated section.And its influence is mainly reflected in the variation of relative amplitude energy with effective elastic parameters.The energy amplitude of“beads”response has a positive relationship with the cave size.The distance of cave apart from the strong axis will affect the energy amplitude of the response.The vertical distance between caverns does not affect the beading response form of a single caverns,but affects the amplitude energy on the connection part.If the horizontal distance between caverns is too small,the“beads”response of two caverns will merge and form the“beads”illusion of a large cavern.The degree of mud filling and porosity in the cave will affect the amplitude energy of the“beads”response.By summarizing the variation rules of seismic response characteristics under the control modes of different factors and variables,the pattern recognition can provide a reference for effective prediction of fracture-cavity reservoirs.