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本勘探史例来自美国能源部资助的三个油田项目中的一个,为其正在开展的研究工作的一部分。该项研究目的在于提高有天然气裂隙的致密含气储层的钻探水平和生产率。对于P波三维地震,最初提出的目标是评价和勾绘出整个天然裂缝含气储层段的裂缝方位和相对裂缝密度。在Rulison油田,该储层段为白垩系Mesaverde层,有约2500ft(760m)的透镜状的砂岩、粉砂岩和泥岩。为了评价目标层的方位各向异性以及商业产气层与各向异性间的关系,进行了三维全方位P波数据采集。采用的方法是对两个沿方位各向异性自然主轴排列的具有有限方位的相互正交的三维数据体进行计算,主轴则从多方位叠前道集的速度分析估计得到。对含气饱和的Mesaverde层,两个方位的Dix层速度以及层振幅随炮检距变化(AVO)梯度都进行了计算,与工业气藏(由21口井组成的控制数据集)最有关连的两类地震属性是:(1)在目的层(含气饱和Mesaverde层)层速度的比值(炮-检方位N60E/N30W)其方位变化大于4％;和(2)层AVO梯度(N60E+N30W)之和。层AVO梯度之和是对有气存在敏感的一种属性,但它不能诊断振幅按方位的变化。在勘探区域绘出的两个方位的层速度的各向异性指出了最大水平应力场和张开(对流体)的裂缝系统的方位在空间的变化。
One of the three oilfield-funded projects funded by the U.S. Department of Energy is part of this exploration history as part of its ongoing research. The aim of this study is to improve the drilling performance and productivity of tight gas reservoirs with natural gas fractures. For P-wave 3D seismic, the initial goal was to evaluate and plot the fracture orientation and relative fracture density of the entire natural fractured gas-bearing reservoir segment. In the Rulison field, the reservoir section is a Cretaceous Mesaverde formation with lenticular sand, siltstone and mudstone of about 2500 ft (760 m). In order to evaluate the azimuthal anisotropy of the target layer and the relationship between commercial gas beds and anisotropy, three-dimensional omni-directional P wave data acquisition was carried out. The method used is to calculate two orthogonal 3D data bodies with finite azimuths arranged along the azimuthally anisotropic natural principal axes, which are estimated from the velocity analysis of the multi-directional prestack gathers. For gas-saturated Mesaverde layers, the Dix velocities at both orientations and the layer amplitudes with offset variation (AVO) gradients were calculated, most related to industrial gas reservoirs (control data set consisting of 21 wells) The two types of seismic attributes are: (1) the azimuthal variation of layer velocity ratio (gun-check position N60E / N30W) greater than 4% at the target layer (gas saturated Mesaverde layer); and (2) the AVO gradient of layer N60E + N30W). The sum of the layer AVO gradients is a property that is sensitive to the presence of gas, but it can not diagnose amplitude-dependent changes in azimuth. The anisotropy of layer velocities in the two directions plotted in the exploration area indicates the spatial variation of the maximum horizontal stress field and the orientation of the open (counter-fluid) fracture system.