各向异性薄煤层纵波AVAZ分析

通过建立HTI型薄煤层的传播矩阵,推导了水平界面情况下含各向异性薄煤层反射系数精确计算公式,并利用该公式对含有薄HTI型各向异性煤层进行了纵波AVAZ分析。经过研究发现,当HTI型煤层为薄层时(厚度小于地震波长的1/4时),其纵波反射系数与煤层为厚层时(厚度大于地震波长)顶板的纵波反射系数规律相似,但其值不仅与上下层介质物性参数有关,还与厚度有关,可见煤层为薄层时采用经典公式反演会带来误差;薄层厚度、Thomsen等效各向异性参数和裂缝密度对纵波反射系数有较大影响,裂缝纵横比对反射系数影响较小。入射波方位角为90°时,入射波在HTI介质各向同性面,此时各向异性参数对反射系数影响最小。     

基于方位各向异性理论的地震预测裂缝方法及应用综述

裂缝预测在碳酸盐岩储层评价中是至关重要的,预测裂缝的方法主要包括基于岩芯观察描述、测井识别裂缝、地震资料预测裂缝等。重点阐述了地震预测裂缝的4种方法,如多波多分量预测裂缝、P-S转换波预测裂缝、VSP地震预测裂缝以及纵波AVAZ预测裂缝。综合比较各种方法的原理和费用投资情况认为,纵波AVAZ预测裂缝是一种有效且价格相对合理的方法。最后介绍了纵波AVAZ预测裂缝方法在A油田的应用实例,有一定的预测效果。     

叠前AVAZ裂缝预测技术在车排子凸起的应用

近几年裂缝型油气藏越来越受到人们的重视,车排子凸起东翼石炭系发育高角度、高密度的火山岩裂缝储层。首先开展叠前P波反射系数的各向异性理论分析,然后结合工区特点进行裂缝地震响应正演模拟,并在此基础上对叠前地震资料进行方位角道集的划分,最后使用AVAZ裂缝预测技术完成裂缝空间展布特征预测。裂缝发育密度和方向预测结果与研究区成像测井资料具有良好的一致性,为该区今后的油气勘探与开发奠定了基础,也为车排子凸起其他地区的裂缝储层预测提供了技术思路。     

陆西凹陷特殊储层地震预测方法探讨

陆西凹陷为中生代凹陷,储层类型多样,除常规砂岩储层之外,钻井还揭示了薄层砂岩、凝灰质砂岩和火山岩3类特殊储层。现阶段3类特殊储层均取得较好勘探效果,已成为主要勘探对象。但是利用常规储层预测技术难以准确识别和描述,严重制约该地区的进一步勘探部署和评价研究。基于此,针对不同类型储层的特点、预测难点及对油气成藏的控制因素,采用不同的储层预测技术进行研究。采用拟声波波阻抗反演技术识别九佛堂组上段的薄层砂岩并刻画其空间展布,利用叠前弹性参数反演技术预测九佛堂组下段凝灰质砂岩的"甜点"区,通过叠前、叠后联合裂缝预测技术检测火山岩裂缝发育密度及方向。预测结果与实际钻探结果吻合良好,并指出了有利勘探区,为下步勘探部署提供重要依据。     

Fracture prediction approach for oil-bearing reservoirs based on AVAZ attributes in an orthorhombic medium

Fracture systems in nature are complicated. Normally vertical fractures develop in an isotropic background. However, the presence of horizontal fine layering or horizontal fractures in reservoirs makes the vertical fractures develop in a VTI (a transversely isotropic media with a vertical symmetry axis) background. In this case, reservoirs can be described better by using an orthorhombic medium instead of a traditional HTI (a transversely isotropic media with a horizontal symmetry axis) medium. In this paper, we focus on the fracture prediction study within an orthorhombic medium for oil-bearing reservoirs. Firstly, we simplify the reflection coefficient approximation in an orthorhombic medium. Secondly, the impact of horizontal fracturing on the reflection coefficient approximation is analyzed theoretically. Then based on that approximation, we compare and analyze the relative impact of vertical fracturing, horizontal fracturing and fluid indicative factor on traditional ellipse fitting results and the scaled B attributes. We find that scaled B attributes are more sensitive to vertical fractures, so scaled B attributes are proposed to predict vertical fractures. Finally, a test is developed to predict the fracture development intensity of an oil-bearing reservoir. The fracture development observed in cores is used to validate the study method. The findings of both theoretical analyses and practical application reveal that compared with traditional methods, this new approach has improved the prediction of fracture development intensity in oil-bearing reservoirs.