基于时空双变网格算法的碳酸盐岩裂缝型储层正演模拟

Forward modeling of carbonate fracture reservoir based on time-space dual variable grid algorithm

引入局部精细时间采样算法,对空间变网格算法进行改进。将裂缝视为局部非均质体,利用空间不同尺度的网格对裂缝介质进行表征。采用有限差分算法直接求解波动方程,实现对实际碳酸盐岩介质的微裂缝储层的地震波正演模拟技术,得到地震波在裂缝型储层传播中的一些直观的波动现象。结果表明:利用局部精细时间采样算法,对精细的空间网格在时间层内可以进行局部加密求解,从而解决全局采用精细时间采样带来的庞大计算量和计算耗时问题;裂缝缝间距、裂缝切伸参数对地震记录的反射振幅能量和极性影响较大,并在反射波后常会紧跟一个弱反射能量;裂缝受构造影响较大,平缓构造和起伏构造裂缝反射模式相差较大;在了解地下构造走向的情况下,可根据不同的裂缝反射特征寻找裂缝发育带。

The space variable grid method was improved by introducing local variable timestep scheme.Fractures were treated as local heterogeneous bodies,and fracture media was represented by using different size of grid samples.Wave equation was solved directly by finite difference method.Seismic forward modeling of micro-fractured reservoir of field carbonate velocity models was realized,and some detailed wave-propagation phenomena were gotten.The results show that local variable timestep scheme can realize local refinement calculation in a global timestep,which solves huge computing resource and time consuming problems caused by fine timesteps in the global models.Fracture density and fracture length have much effect on amplitude and polarity of seismic record,and a weak fracture reflection energy always follows reflection wave closely.Subsurface structure affects fracture characteristics a lot.Fracture reflection characteristics of flat strata and undulation strata are quite different.So fracture growing zones can be found according to different fracture reflection characteristics if subsurface structure is known.