古地貌恢复及其对三角洲前缘沉积砂体的控制作用——以鄂尔多斯盆地庆阳气田二叠系山西组13亚段为例

盆地内的微古地貌是控制沉积砂体的重要因素，决定着储集砂体的发育位置及分布规模。基于三维地震资料，结合钻井数据，运用残余厚度法与沉积学综合分析相结合的方法，通过残余厚度求取、去压实校正及古流向分析，恢复鄂尔多斯盆地庆阳气田二叠系山西组1³亚段（山1³亚段）沉积期的微古地貌，分析微古地貌对三角洲前缘砂体的控制作用，进而预测山1³亚段的有利砂体的分布规律，指导井位部署。研究表明：山1³期研究区西部和南部为地貌高地，东北部为低洼区，中部为缓坡过渡带；沉积期的古流向整体呈南西-北东向，自南部高地发育的3~4支分支河道在研究区中北部汇聚，形成叠合砂带；基于预测的山1³亚段砂体展布规律开展井位部署后，直井钻遇砂岩的平均厚度增加0.6m，水平井砂岩钻遇率提高20%，进一步证实了基于古地貌恢复预测砂体方法的可靠性。该方法对庆阳气田其他区块的天然气井位部署和类似地质条件致密气的开发具有借鉴和指导意义。

Paleogeomorphologic restoration and its controlling effect on deposition of delta-front sand bodies: A case study of Shan 13 sub-member of the Permian Shanxi Formation,Qingyang gas field,Ordos Basin

Micro-paleogeomorphology within basin, a key factor controlling the deposition of sand bodies, determines the development scale and position of reservoir sand bodies.In the study, an integration of 3D seismic and log data is applied to the restoration of micro-paleogeomorphology during the Shan 1³ sub-member deposition in the Permian Shanxi Formation in Qingyang gas field, Ordos Basin, by considering the residual stratum thickness, decompression correction and paleo-current direction.Furthermore, the study analyzes the effect of micro-paleogeomorphology on delta-front sand body deposition, which in turn serves to predict the distribution pattern of favorable sand bodies and guide well emplacement therein.The results show that during the Shan 1³ depositional period, the western and southern parts of the study area are topographical highs, the northeast is the bottom land, and the central area is a transitional slope zone; the paleo-current during the depositional period trends mainly SW-NE, and the No.3 to 4 distributary channels sourced from the southern topographical highs converge in the central and northern parts, forming a zone of superimposed sand bodies; with the emplacement of wells in line with the predicted distribution pattern of Shan 1³ sand bodies, the average sandstone thickness penetrated by vertical wells increases by 0.6 m, and the rate of sandstone encountering in drilling of horizontal wells increases by 20%, further suggesting the reliability of paleogeomorphology restoration-based sand body prediction.The method proposed in the study can be of referential and guiding significance to the emplacement of wells in other blocks of Qingyang gas field and the development of tight gas under similar geological conditions.