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由于地表山峦重叠、赤道丛林和巨厚喀斯特化的中新统灰岩,使得在巴布亚褶皱带进行油气勘探非常困难。对于地表或近地表的高速喀斯特化灰岩,常使得地震技术对地下成像无能为力。在这样的地区,大地电磁(MT)具有很强的地下构造成图能力。由于强烈的电性差异,能用MT作图的主要构造界面是高阻的Darai灰岩与下伏Ieru组中的低阻沉积层之间的接触面。在一些区域,用1-D模型与所观测的MT数据相拟合即可相当准确地将Darai底部成图。然而,在许多2-D和3-D效应较强的地区,1-D解释就会产生明显的错误。数字模拟和实测数据实例证明1-D误差的严重性,同时也证明用2-D反演则可提高精度。下面用在相邻背斜上的两条MT测线(两条都有井控数据和地震资料)来说明对构造模型所做的1-D和2-D反演情况。在这两种情况中,地震数据对解释不能提供什么帮助。Hides背斜上的实例表明无论是TE还是TM极化方法的1-D反演与这两种方式进行的2D反演所得的Darai底部具有相同的深度。两模型所提供的Darai底部埋深与钻井结果的误差小于10%。Angore背斜上的实例表明在复杂地质构造条件下,由于电法静校正所造成的复杂性使1-D反演不适用。TE法拟合得到80m的1-D Darai厚度,TM法得到3500m的1-D Darai厚度,有别于井中观测到的2450m厚度。最终2-D反演模型得出2250m的深度估计。因此,采用2-D反演对沿Angore背斜的4条MT测线进行了解释。在航空雷达成像上观测到的构造线与解释为Darai灰岩的高阻物质之内的低阻带间存在很强的相关性。这些低阻带被解释为断裂带。 3D模拟已经应用于在其他2-D地层中模拟3-D静校正。用这些资料来检测Groom-Bailey(GB)分解对于减少静校正和估计巴布亚新几内亚(PNG)野外资料的地电走向的可能作用。现已证明GB分解可以从3-D畸变资料中提供得到改善的区域2-D走向估计。然而,在类似PNG的条件下(区域2D走向是非常确实的并因此能定位),GB分解提供的视电阻率与只旋转到走向的视电阻率相同。
Overlapping surface mountains, equatorial jungles, and thick karstified Miocene limestone make oil and gas exploration in the Babu fold zone very difficult. High-velocity karstified limestones at or near the surface often make seismic techniques impotent to subsurface imaging. In such areas, MT (Magnetotelluric) has strong subsurface mapping capabilities. Due to the strong electrical difference, the primary structural interface that can be mapped with MT is the interface between the high-resistivity Darai limestone and the low-resisitite sediments in the underlying Ieru Formation. In some areas, the bottom of the Darai can be mapped fairly accurately by fitting the 1-D model to the observed MT data. However, in many areas where 2-D and 3-D effects are strong, 1-D interpretation can yield significant errors. Numerical simulations and experimental data show the seriousness of the 1-D error and prove that the 2-D inversion can improve the accuracy. The two MT lines on the adjacent anticlines, both with well control data and seismic data, are used to illustrate the 1-D and 2-D inversion of the tectonic model. In both cases, the seismic data can not help the interpretation. The example on the Hides anticline shows that the 1-D inversion of either the TE or the TM polarization method has the same depth as the Darai bottom obtained by the 2D inversion of the two modes. Both models provide less than 10% error in the depth of the bottom of Darai and the drilling results. The examples on the Angore anticline show that the 1-D inversion is not applicable due to the complexities caused by electrostatics in complex geological formations. The 1-D Darai thickness of 80 m was fitted by TE method, and the 1-D Darai thickness of 3500 m was obtained by TM method, which is different from the thickness of 2450 m observed in the well. The final 2-D inversion model yields a depth estimate of 2250 m. Therefore, 4 MT lines along the Angore anticline were interpreted using 2-D inversion. The tectonic lines observed on the aeronautical radar imaging are strongly correlated with the low resistivity bands interpreted as high-resistivity materials for the Darai limestone. These low-resistivity zones are interpreted as fault zones. 3D simulations have been applied to simulate 3-D statics in other 2-D formations. Use these data to examine the possible role of Groom-Bailey (GB) decomposition in reducing static correction and in estimating the geoelectric pathways in PNG field data. It has been demonstrated that GB decomposition can provide improved 2-D region estimation from 3-D distortion data. However, under similar PNG conditions (the region 2D travel is very positive and can therefore be located), the GB decomposition provides the same apparent resistivity as the rotation-only apparent.