| Abstrakt: |
The geofluid preservation in the complex tectonic zone of the Lower Yangtze Region has always been a challenge for hydrocarbon exploration. However, the Triassic Zhouchongcun Formation overpressure stratum firstly discovered by WWY-1 (Wanwei shale gas well drilling-1) in Wuwei Depression of Lower Yangtze Region provides a promising prospect for finding favorable preservation units of oil and gas in such complex areas. The overpressure characteristics and genesis of the Triassic gas reservoir in the region were investigated based on geological analysis and theoretical calculation. The lithology of the Zhouchongcun Formation in Wuwei Depression are dominated by dolomite and anhydrite rocks. The measured pressure coefficient of dolomite reservoir ranges from 1.8 to 1.9, with the pressure system of single well characterized with step-like structure of normal pressure-overpressure". The strong sealing property and dehydration of anhydrite rocks, high-pressure hydrocarbon fluid transfer, hydrocarbon pyrolysis and tectonic uplifting are considered as the primary contributors to the formation of strong overpressure. The overpressure formation process of gas reservoir was revealed based on the overpressure characteristics and linkages of different geneses. The evolution of fluid pressure experienced five stages, i.e., normal pressure stage, overpressure stage with anhydrite dehydration and expansion, overpressure stage with hydrocarbon generation fluid transfer, overpressure stage with hydrocarbon pyrolysis expansion, and overpressure preservation stage with tectonic uplifting. The present study on the overpressure characteristics and formation process of the Triassic gas reservoirs in the complex tectonic zone of Lower Yangtze Region provides valuable insights into hydrocarbon migration mode, enrichment degree and preservation phase in other similar areas. [ABSTRACT FROM AUTHOR] |
