Scattering and intrinsic attenuation as a potential tool for study of a fractured reservoir
Scattering and intrinsic attenuation as a potential tool for study of a fractured reservoir
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散射和固有衰减作为研究裂缝性储层的潜在工具
DOI：
10.1016/j.petrol.2018.11.058
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发表时间：
2019
影响因子：
--
通讯作者：
A.A.I. Mohamed and A.A. Sultan
中科院分区：
文献类型：
--
作者：
Bouchaala;F.;M.Y. Ali;J. Matsushima;Y. Bouzidi;E.M.T. Takougang;A.A.I. Mohamed and A.A. Sultan
内禀衰减主要是由于地震波在地下孔隙中的流体与固体颗粒之间传播时引起的摩擦运动引起的。相反，散射衰减是由于地下非均匀性引起的小反射。由于孔隙度和裂缝是不均匀性和流体的重要来源，因此散射和固有衰减是用于调查多孔和裂缝地下区域（诸如油气储层）的合适地震属性。在本研究中，我们准确地估计了散射和内在衰减从零偏移距垂直地震剖面（VSP）和声波数据采集三个威尔斯井，位于阿拉伯联合酋长国阿布扎比的油田的储油层。此外，我们适当地分离散射和固有衰减。衰减剖面随深度变化较大。此外，散射是频率相关的，并且对总衰减具有显著贡献。这是由于碳酸盐岩的非均质性强，而碳酸盐岩又是储层的主要岩性。这意味着衰减的变化可以作为储层非均质性程度的一个指标。VSP和声波固有衰减在富油区表现出高异常，纵波声波衰减与横波衰减的比值在富气区表现出高异常，但在富油区则没有，因为石油的存在以类似的方式影响纵波和横波衰减。然而，气体的存在对纵波的衰减远大于横波。因此，可以用来区分油气富集带。裂缝性强的储层单元表现出VSP固有的负衰减异常和强散射，反映出强烈的干扰现象。这种现象导致下行波的振幅随深度增加，这导致负衰减。因此，伴随着强散射的强负固有衰减可以是高度破裂带的指示。这可能是由于地震波在裂缝上产生的压应力引起的缝间流体流动的喷流机制所致。这种机制使在低频下传播的波衰减较少，因为流体压力有足够的时间达到平衡，而在高频下并非如此。这就解释了为什么VSP固有衰减远小于高裂缝带的声波衰减。因此，VSP和声波固有衰减之间的较大差异也指示高度裂缝性储层。
Intrinsic attenuation is mainly caused by the frictional movement induced by seismic waves during their passage between fluids contained in subsurface pores and solid grains. In contrast, scattering attenuation is due to small reflections caused by subsurface heterogeneities. Since porosity and fractures are important sources of heterogeneity and fluids, scattering and intrinsic attenuation are suitable seismic attributes for investigating porous and fractured subsurface zones, such as oil and gas reservoirs. In the present study, we accurately estimated scattering and intrinsic attenuation from zero-offset vertical seismic profiling (VSP) and sonic data acquired from three wells that cross a reservoir zone of an oilfield located in Abu Dhabi in the United Arab Emirates. In addition, we properly separated scattering and intrinsic attenuation. The attenuation profiles show high variation with depth. Furthermore, the scattering is frequency dependent and has a significant contribution to the total attenuation. This is due to the high heterogeneous property of carbonate rocks, which dominate the lithology of the reservoir zone. This means that the variation of attenuation can be used as an indicator of the heterogeneity degree of reservoir zone. The VSP and sonic intrinsic attenuations exhibit high anomalies in oil-rich zones, and the ratio of the compressional sonic attenuation to the shear attenuation exhibits a high anomaly in gas-rich zones, but not in oil-rich zones, because the presence of oil influences the compressional and shears attenuations in a similar fashion. However, the presence of gas attenuates compressional waves much more than the shear waves. Therefore, can be used to distinguish oil- and gas-rich zones. The highly fractured reservoir units display negative VSP intrinsic attenuation anomalies and strong scattering, which reveals a strong interference phenomenon. This phenomenon leads to an increase in amplitude of the downgoing wave versus depth, which results in negative attenuation. Hence, strong negative intrinsic attenuation accompanied by strong scattering can be an indicator of a highly fractured zone. The VSP and sonic intrinsic attenuations in such zones have a large discrepancy, which might be due to the squirt flow mechanism due to the inter-crack fluid flow due to the compressional stress induced by seismic waves on the fractures. This mechanism attenuates the waves propagating at low frequencies less, because the fluid pressure has sufficient time to reach equilibrium, which is not the case at high frequencies. This explains why the VSP intrinsic attenuation is much smaller than the sonic attenuation in highly fractured zones. As such, a large discrepancy between VSP and sonic intrinsic attenuations also indicates a highly fractured reservoir.