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San Juan盆地Cedar Hill油气田的裂隙型储煤层中盛产甲烷气,由于煤层中基岩无渗透性,因此裂隙和局部应力控制了甲烷气的产量。为弄清储层内流体的流动情况,我们必须了解裂隙的方向、裂隙大小、储层压力以及储层分区。为了加强对煤层甲烷气储层的特征描述,我们开展了多分量3D地震测量。通过分析多分量数据并结合岩石物理和油藏工程研究,我们对储煤层的非均匀性(包括孤立的压力单元、裂隙密度加大带以及裂隙方向的变化等)进行了解释。通过对3D P波地震资料作构造解释识别了分隔储层的走滑断层。这些断层形成的压力单元边界可由P波反射振幅异常来识别。 通过分析横波地震数据的反射振幅、旅行时及偏振识别了具不同裂隙方向和裂隙密度的区域。由构造解释推断的应力与由横波偏振所指示的应力之间具有很好的一致性。通过岩芯采样获得的岩石物理数据按地震速度和储层压力对地震振幅进行了标定。 我们已开发了一些新方法用于实现叠前和叠后横波偏振的统计分析,并精确地确定了旅行时各向异性。叠前偏振分析法可以快速有效地确定主偏振方向。 利用旅行时和薄层反射响应定量确定了储层区的横波各向异性,两种方法间具有较好的一致性。由各向异性计算的裂隙密度指示了两个高裂隙密度区域,一个区域对应封闭的超压单元,
Methane gas is abundant in fractured coal seams in the Cedar Hill field in the San Juan Basin. Because of bedrock permeability in the coal seam, fractures and local stresses control the production of methane gas. To understand the fluid flow in a reservoir, we must understand the direction of the fracture, the size of the fracture, the pressure of the reservoir and the division of the reservoir. To enhance the characterization of coalbed methane gas reservoirs, we conducted multi-component 3D seismic surveys. By analyzing multi-component data in combination with petrophysical and reservoir engineering studies, we explain the heterogeneity of the coal seams (including isolated pressure units, the increase of fracture density and the change of fracture direction, etc.). The strike-slip faults of separate reservoirs are identified by tectonic interpretation of 3D P-wave seismic data. The pressure cell boundaries formed by these faults can be identified by the P-wave reflected amplitude anomalies. By analyzing the reflection amplitude of shear wave seismic data, the regions with different fracture directions and fracture densities were identified when traveling and polarized. There is good agreement between the stress inferred from tectonic interpretation and the stress indicated by shear wave polarization. The rock physics data obtained through core sampling are used to calibrate the seismic amplitude according to seismic velocity and reservoir pressure. We have developed several new methods for statistical analysis of Polarization Prestack and Poststack S-waves and accurately determine travel-time anisotropy. Pre-stack polarization analysis can quickly and efficiently determine the main polarization direction. The shear wave anisotropy in the reservoir area is quantitatively determined by travel time and thin-layer reflection response, and the two methods have good agreement. The crack density calculated from the anisotropy indicates two high crack density zones, one corresponding to the closed overpressure unit,