Orbital-scale depositional controls and reservoir heterogeneity in the Dengying formation in Northern Yunnan and Guizhou

Abstract

Based on preliminary seismic and drilling studies suggesting substantial thickness of the Dengying Formation in the Taiyang-Changning area along the southern margin of the Sichuan Basin's Northern Yunnan and Guizhou Depression as a platform margin, the risk exploration well TT1 was implemented to investigate sedimentary reservoir characteristics and exploration potential of the Dengying platform margin. Integrated analysis of astrochronological cycles, core tests, and log interpretations from the TT1 well enabled comprehensive 3D seismic interpretation of the Dengying Formation in the Taiyang area. Results demonstrate that Milankovitch cycles are extractable from calcium-element logging data of the TT1 well's Dengying Formation, with sedimentation controlled by a 35-kyr obliquity cycle at rates ranging from 6.24 to 13.17 cm/ka (mean: 9.81 cm/ka). Comparative analysis with the Yang-1 well at the same platform margin reveals well-developed reservoirs in the Yang-1 well's Dengying Formation, whereas the TT1 well exhibits overall poor reservoir development—only thin reservoirs occurring at the tops of the Deng-4 and Deng-2 Members—showing no correlation between reservoir presence and sedimentation rates, indicating dominant control by dissolution during the late Tongwan Movement. Integrated regional geological and seismic interpretation indicates that although the Changning-Taiyang platform margin features considerable stratigraphic thickness, the strong reservoir heterogeneity necessitates re-evaluation of reservoir formation and hydrocarbon accumulation mechanisms in the Dengying Formation..