基于岩石物理模型的转换横波分裂在碳酸盐岩裂缝储层预测中的应用

Application of seismic converted shear wave splitting to detect gas and water saturation in fractured carbonate reservoirs based on a rock-physics model

碳酸盐岩储层岩石组分与孔隙结构复杂,流体分布不均,反演难度大,常规储层预测方法难以有效判断有利区域。为此,本文基于修正后的岩石物理模型和横波分裂属性分析,建立了一种碳酸盐岩裂缝储层检测的技术方法。首先,根据塔里木盆地S地区鹰山组碳酸盐岩储层岩石物性特征,修正Chapman模型,建立考虑多种岩石基质组分的多尺度岩石物理模型。其次,利用反射率法正演模拟储层在不同裂缝密度以及饱含不同流体时的反射横波地震记录,并对地震记录进行了横波分裂属性分析。分析表明,饱含水时快慢横波之间的能量差异较小,而饱含气时两者之间能量差异较大,同时验证了快慢横波之间的延迟时间随着裂缝的发育密度增大而增大。因此利用快慢横波之间的延迟时间与振幅差异可以较好的检测裂缝型油气藏。最后,将快慢横波延迟时间与能量差异属性应用于研究区多波地震资料中,检测结果表明研究区西南部裂缝密度较大且以含气为主,与钻井及试生产结果吻合,表明了预测结果的可靠性以及预测方法的有效性。

Carbonate reservoirs can be extremely heterogeneous with complex rock composition and pore structures, and it is difficult to distinguish the fluid type by conventional reservoir description methods. In this paper, we establish a technical method for the detection of carbonate fractures by the combination of a modified rock physics model and shear wave splitting. Firstly, according to the rock physics characteristics of the Yingshan formation carbonate reservoirs in the S area of the Tarim Basin, we take the various rock matrix components into consideration and modify the Chapman model to establish a multi-scale rock physics model. Secondly, the shear wave seismogram is recorded with different fracture densities and different fluid types using a reflectivity method. Then the shear wave splitting properties are analyzed. We confirm that the amplitude difference between the fast and slow shear wave is quite small when the formation is saturated with brine while there is a large difference between them when it is saturated with gas. Also, we verified that the time delay between fast and slow shear waves increases with the development density of fractures. Thus we can well detect fractured reservoirs using these two attributes of time delay and amplitude difference between the fast and slow shear wave. Finally, this valuable attribute, amplitude difference, as well as the time delay, were both applied to the three-component seismic data of our study area. The prediction results show that fracture sets and gas reservoirs are more developed in the southwest of our study area, which agrees with drilling and trial production data. Hence it proves the reliability of our prediction results and the validity of our prediction method.