In the vast expanse of the East China Sea Shelf Basin, a team of researchers from the Exploration and Development Research Institute of Sinopec Shanghai Offshore Oil & Gas Company has uncovered critical insights into the sedimentary evolution of the Pinghu Formation, a significant oil and gas-bearing system. Led by WANG Jianwei, the team’s study, published in the journal *Petroleum Geology and Exploration*, sheds light on the intricate dance between sediment supply, sea level fluctuations, and paleogeomorphology that has shaped the region’s subsurface landscape over millions of years.
The lower member of the Pinghu Formation, dubbed the lower Pinghu member, is a complex interplay of deltaic and tidal flat deposits, primarily influenced by tidal processes. The researchers identified four distinct sand groups (P12~P9) within this member, each telling a unique story of sedimentary evolution. “The P12 sand group, deposited during a lowstand system tract with relatively low sea level, was primarily composed of deltaic deposits, overlain by tidal deposits,” explains WANG Jianwei. This pattern of deposition, controlled by the ebb and flow of sediment supply and sea level changes, has profound implications for the distribution of reservoirs within the formation.
The study revealed that the relative intensity of deltaic and tidal processes was largely controlled by changes in relative sea level and sediment supply. During periods of sufficient sediment supply and lower sea levels, such as those corresponding to the P12 and P9 sand groups, delta development flourished, leading to the formation of distributary channel and mouth bar sand bodies. Conversely, during marine transgression stages, like those of the P11-P10 sand groups, weakened sediment supply and rising sea levels curtailed deltaic propagation, paving the way for tidal flats, channels, and sand bars to dominate the sedimentary landscape.
One of the most intriguing findings of the study was the role of paleogeomorphology in shaping the sedimentary evolution of the region. The presence of a nose-shaped paleo-uplift in the central part of the study area during the deposition of the P12 sand group limited the eastward progradation of the western delta, resulting in distinct differences in sedimentary facies types between the east and west sides of the uplift. “This understanding of the spatial distribution of sedimentation is crucial for guiding future exploration and development efforts,” says WANG Jianwei.
The implications of this research for the energy sector are significant. By clarifying the spatiotemporal distribution characteristics of favorable reservoirs, the study offers a roadmap for targeted exploration and development within the study area and adjacent zones. In the western fault trough zone of the P12 sand group and in the P9 sand group, deltaic sand bodies such as channels, mouth bars, and sheet sands are the primary targets, with exploration and development efforts guided by the deltaic depositional model. Meanwhile, in the eastern fault step zone of the P12 sand group and in the P11-P10 sand groups, tidal sand bars or tidal channels extending seaward and parallel to the shoreline take center stage, with exploration and development efforts following the tidal depositional model.
As the energy sector continues to grapple with the challenges of meeting global demand while transitioning to a lower-carbon future, studies like this one are more important than ever. By deepening our understanding of the complex processes that shape the subsurface landscape, researchers like WANG Jianwei and his team are paving the way for more efficient, targeted, and sustainable exploration and development efforts. In the ever-evolving energy landscape, such insights are invaluable, offering a glimpse into the future of energy exploration and production.