High-Resolution Sequence Stratigraphy and Subtle Reservoir Characterization Analysis: A Case Study from the Qingshankou Formation in Southern Songliao Basin

Abstract

The Honggang–Sifangtuozi area in southern Songliao Basin spans two tectonic units: the western slope area and the central depression area. The Qingshankou formation is located in the steep slope zone and the intersection of the southwest Tongyu and the western Baicheng rivers, which has the basic geological conditions for the subtle oil and gas reservoir exploration. Based on the large quantities of cores analysis, drilling, well logging, and 3D seismic data with theory of high-resolution sequence stratigraphy, the sequence stratigraphic frame of the Qingshankou formation in the western slope area was constructed, which was composed of three long-term base-level cycles and six middle-term base-level cycles. At the same time, to the middle-term base-level cycles as a unit, we solved the non-uniform stratigraphic correlation problem between north and south. Based on the high-resolution sequence stratigraphic framework with the combination of the well and seismic data in the western front zone, we carried out the study of the sedimentary facies in the sequence stratigraphic framework and identified the main sedimentary facies: the braided river delta, slump turbidite fan, shallow lake, and semi-deep lake facies. And then, we analyzed the strata characteristics in the sequence framework and pointed out that the sedimentation center migrated from south to north with the bottom-up. On the basis of the analysis of the distribution and accumulation of oil and gas and reservoir factors, it is also concluded that the main controlled factors of the subtle traps in the study area which the sequence framework is controlling the strata, the paleogeomorphology is controlling sand bodies and the sedimentary facies belt is controlling the traps. In comprehensive analysis of the conditions of subtle traps, we provided the three areas of the subtle traps in the study area and predicted five subtle traps in the target areas. This research also plays an important role in the further study on subtle oil and gas reservoir in the Songliao Basin.