Seismic geomorphology analysis and petroleum geology significance of presalt Jurassic carbonate in the right bank of Amu Darya River

Abstract

Paleogeomorphological pattern has a great influence on the formation of carbonate reef-shoal complexes and the evolution of carbonate reservoirs. Accurate paleogeomorphology restoration is one of the significant tasks while exploring oil and gas stored in carbonate rocks. However, the previous paleogeomorphology restoration methods mostly rely on high-density drilling data or high-quality seismic data. The applicability of these methods to areas with low-quality seismic data of presalt reservoirs and less drilling control is often low, and they cannot accurately restore paleogeomorphology. This will seriously affect the success rate of oil and gas exploration in presalt reservoirs. Hence, this study aims to address the problem associated with paleogeomorphology restoration under the conditions of highly flexible salt-gypsum rock and low-quality seismic data. By comparing the paleogeomorphology restoration principles of the impression and residual thickness methods and considering multiple factors such as sediment filling and tectonic evolution settings, an innovative model representing the relationship between geomorphology and seismic attributes was established and the paleogeomorphology in the period of deposition of the Middle Jurassic Callovian strata in the eastern part of the right bank of Amu Darya River was restored based on seismic geomorphology, 3D seismic data, drilling data, well log data, core data, and thin-section data. Based on the analysis of the reconstructed paleogeomorphology, it is observed that the high paleogeomorphology shoals in the western part of the study area obstruct the growth of the eastern shoals, affecting the development thickness. However, the quality of thin-layered shoal reservoirs in the eastern part is superior to those in the western part. The distribution of well-developed thick shoals and high-quality reservoirs in this area exhibits obvious spatial differentiation on the plane. Under the unique paleogeomorphology pattern of alternate uplifts and depressions in this area, the quality of reservoirs in the western part is poor, the development quality of reef-shoal reservoirs in the central and eastern region is superior, and the reservoirs in the paleogeomorphologic lowlands are poorly developed.