利用数字露头模型技术对曲流河三角洲沉积储层特征的研究

数字露头模型技术（DOM）是利用三维可视化技术虚拟露头表面，建立由一系列结构多边形构成的初步模型体，进而在模型体上叠加露头剖面所有数字化地质信息，包括三维地面激光雷达数据、遥感图像、高精度灰度照片、探地雷达数据等露头地质剖面所有地质学信息数字化数据，实现多种地质特征综合解释与测量的数字露头模型技术，已在野外露头剖面上沉积体系三维储层建模、岩性分类、构造断裂精细解译等方面研究发挥作用。本文为准确刻画沉积体系砂体与储集层空间分布特征，尝试利用数字露头模型技术，对鄂尔多斯盆地延长组曲流河三角洲平原河道砂体空间分布特征精确测量与描述，实测不同位置河道砂体储集性能，并利用探地雷达数据预测露头区域地下砂体形态特征，综合建立砂体三维空间分布模型，为储层精细对比研究提供依据。数字露头模型显示:（1）潭家河剖面河道形态明显，砂体呈顶平底凸的透镜体，横向延伸192 m,最厚处约14 m,河道与围岩切割关系明显，内部为4期沉积充填，整体表现为复合正韵律；（2）曲流河三角洲平原的分支河道砂体呈孤立状，砂体侧向迁移，垂向多期叠加，砂体在探地雷达剖面上反射特征表明，地面之下曲流河三角洲平原的分支河道砂体也呈孤立状，横向迁移频繁；横向上不同期次砂体宽度分别为192.4 m、32.54 m、41.83 m以及79.97 m，厚度对应为14 m、4.52 m、3.85 m以及5.66 m，宽厚比平均为12∶1；（3）典型砂体储集物性解剖认为，三角洲平原分支河道砂体储集物性较差，储集物性空间分布特征表现为河道砂体内每期砂体下部物性优于上部，中间优于两翼，单期河道砂体最厚位置处储集性最好，孔隙度最高可达8%，渗透率为0.13×10-3 μm2。

A New Approach for Outcrop Characterization and Geostatistical Analysis of Meandering Channels Sandbodies within a Delta Plain Setting using Digital Outcrop Models: Upper Triassic Yanchang tight sandstone Formation,Yanhe outcrop,Ordos Basin

Digital outcrop modelling is a method of imaging outcrop as a series of polygons viewable with 3D visualization technology, on to which digital geological information (e.g., outcrop sections) may be stacked. The technique achieves a digital outcrop model (DOM) from which comprehensive measurements and interpretation may be undertaken. A DOM is able to incorporate 3D data from ground-based laser scanner, remote-sensing imagery, high precision grayscale photographs, ground-penetrating radar and other all geo-digital sources. The use of DOM in combination with traditional sedimentological field data helped improve the accuracy and efficiency of meandering delta plain sand body characterisation and consequently also improved the qualitative and quantitative assessment of data for the purpose of reservoir modelling.
      We used the DOM to measure and precisely describe the distribution characteristics of channel sands of the Quliu delta plain in the Ordos Basin. In order to provide the basis for a comparative reservoir model, the 3D distribution model can be quality controlled through the measurement of the characteristics of channel sand reservoir in varied sites and predicting the morphological characteristics of ground sand in the outcrop area by ground penetrating radar. The DOM shows: (1) Tanjiahe section channel forms; these sandstone bodies form elongate lenses with a flat upper surface, a width of 192 m and a maximum thickness of about 14 m of the most biggest channel body sand. The boundary between channel and surrounding rocks is clear.Four stages of deposition are identified within the sandstone bodies indicating a complex positive rhythm. (2) Branch channels to the meandering river are isolated on the delta plain. These sandstone bodies show lateral migration and vertical stacking which is accurately described in the 3D DOM. The horizontal width of the multi-period superimposed channels of the sandstone bodies are 192.4 m, 32.54 m, 41.83 m and 79.97 m, thickness are 14 m, 4.52 m, 3.85 m and 5.66 m giving a width to thickness ratio of 12:1. (3) Through analysis of typical reservoir performance of the sand bodies encountered, reservoir properties can be assigned to different parts of the DOM. The delta plain branch channel sandstones are classified as poor quality. In the main channel sands the highest quality reservoir would be found in the lower part of the channel which then decreases upward. The lowest quality reservoir is found in the two channel wings. Reservoir quality is best at the thickest part of the sandstone body in every period channel where it achieves a porosity of 8% and a permeability of 0.13 mD. Building of a DOM integrated with geo-data is an effective method to quantitatively analyse outcrop analogues including the 3D spatial characteristics of potential reservoir elements which can be acquired accurately. The DOM can also provide the basis of comparative studies on reservoirs in the exploitation of oil and gas.