Abstract:

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.

Key words: 3D seismic data, residual stratum thickness calculation, paleogeomorphology, decompression correction, sendimentary sand body, tight gas, Qingyang gas field, Ordos Basin