EAPSI:Reservoir Quality and Distribution of Low-Permeability Sandstones in the Triassic Yanchang Formation and Implications for Hydrocarbon Exploration

由于水力压裂，低渗透砂岩或致密砂岩可能成为非常规油气藏。鄂尔多斯盆地晚三叠世(2.28亿~2.08亿年前)延长组是中国盆地已发现的最大致密砂岩储层。这项研究将应用沉积学和层序地层学的原理来解释地下数据集，以建立延长组的古地理重建和储集层特征。该地质格架将提高盆地砂岩油气藏分布的可预测性。延长组的继续评价对了解鄂尔多斯盆地的地质历史和油气勘探具有重要意义。这项工作将与北京中国地质大学著名的鄂尔多斯盆地沉积学和地层学专家于炳松博士合作进行。延长组记录了鄂尔多斯盆地多种陆地沉积环境和构造演化。盆地中南部发育广泛的半深湖和深湖相沉积，形成泥岩沉积。北部河口砂坝砂岩由细粒(125~250µm砂粒)、低渗透(3~5 mm)、砂岩(富长石砂岩)组成。这些砂坝油气藏分布在湖相烃源岩附近。上覆的泥岩形成了一个区域性的大范围封闭，将碳氢化合物困在低渗透砂岩中。基于地震反射和测井数据的建模将产生一个层序地层格架，该格架将识别时间关联面、砂体分布和储层的连通性。该NSF EAPSI奖是与中国科技部合作资助的。

Low-permeability sandstones, or tight sandstones, can become unconventional hydrocarbon reservoirs due to hydraulic fracturing. The Late Triassic (228-208 million years ago) Yanchang Formation in the Ordos Basin is the largest discovered tight sandstone reservoir in China. This research will apply principles of sedimentology and sequence stratigraphy to interpret a subsurface data set to create a paleogeographic reconstruction and reservoir characterization of the Yanchang Formation. This geologic framework will improve the predictability of the distribution of sandstone reservoirs in the basin. The continued evaluation of the Yanchang Formation has great significance for understanding the geologic history of the Ordos Basin and hydrocarbon exploration. This work will be conducted in collaboration with Dr. Bingsong Yu, a noted expert on the sedimentology and stratigraphy of the Ordos Basin, at China University of Geosciences, Beijing.The Yanchang Formation records a variety of terrestrial depositional environments and the tectonic evolution of the Ordos Basin. Extensive semi-deep and deep lacustrine (lake) sediments developed in the central and southern parts of the basin, resulting in mudstone deposition. The sandstones of river mouth sandbars in the north are composed of fine-grained (125-250 µm sand grains), low-permeability (3-5 millidarcy), arkosic (feldspar-rich) sandstones. These sandbar hydrocarbon reservoirs are located close in proximity to lacustrine source rocks. The overlying mudstones formed a regionally extensive seal that trapped hydrocarbons in the low-permeability sandstones. Modeling based on seismic reflection and well log data will result in a sequence stratigraphic framework which will identify time correlative surfaces, the distribution of sand bodies and the interconnectivity of reservoirs. This NSF EAPSI award is funded in collaboration with the Chinese Ministry of Science and Technology.