Fine study on lower gentle-distorted structures under the condition of few wells and its implications for oil and gas exploration

In the eastern area of South China Sea, most production oilfields are in low and gentle structures and affected by fault shadow, and there is usually a certain degree of pull-up or pull-down distortion. For larger distortion, it can be partially eliminated by improving seismic acquisition method, seismic processing technology, and structural mapping with good understanding. However, the small-scale distortions are difficult to identify thus often ignored due to subjective thinking of the researchers. Consequently, small-scale distortions could sometime bring considerable uncertainty to the real pictures of oilfield structure and reserves, and further affect the overall development plan of oilfields. Therefore, taking HA and HB oilfields as examples, we conducted a retrospective analysis in each stage of structural mapping, and considered that the structure with pull-up distortion at the location of exploration well may have a certain reserve potential in the lower part. At the same time, a correction method of trend surface constraint was proposed, by which the real shape of the structure can be effectively restored. The practice of oilfield development and rolling evaluation show that this method could well improve the accuracy of structural prediction, successfully guide the design and implementation of evaluation wells, and shall be worthy of promotion and application for the structural research of oil and gas fields under similar geological conditions.