Structural Characteristics And Oil And Gas Prospects Of The Yuxing Formation In The Northeastern Sichuan Basin

The reef gas reservoirs in Changxing Formation of the northeast Sichuan Basin are playing an important role in the "Gas Transmission in Sichuan to Eastern part of China " project which is a significant part of the development of the Natural Gas Industry in Sichuan Basin and the national energy structure adjustment. This area experienced a polyphase and complex structural superimpositions and transformations, resulting in the present tectonic framework. Based on the knowledge of'structure influencing accumulation'and the studies of'structural characteristics', this article aims to analyze the structural evolution in Changxing formation and its controlling on oil and gas generation, and further speculate and evaluate the favorable exploration area.The results are:(1) Changxing Formation is considered to be a trough (basin) with carbonate platform environment. It is thick and the distribution is stable. The platform margin reef is the optimal reservoir facies zone, and the deep water trough-slope is the optimal source rock phase, followed by the open platform.(2) Changxing Formation is the middle structural layer, mainly develops NW and NE structural systems, and faults are well developed in this area. Depending on the size and its impact on migration and accumulation of oil and gas, the third-level faults are the best hydrocarbon migration channels. In the compressive stress fields, a variety of complex tectonic styles are well developed, such as strong-deformed imbricate thrusts, duplex structures, recoil block structures, and triangular structure belts.(3) The northeast Sichuan Basin experienced multistage tectonization including the Indosinian, late Yanshanian-early Himalayan and Himalayan tectonic stresses. The north-east structure formed in the Indosinian, and finalized in the early Himalayan, which was good for the early formation and preservation of reservoirs. The north-west structure formed in the late Yanshan and finalized in late Himalayan. The complex tectonic stress field, fault systems and stacking patterns had significant controls on the oil and gas accumulation and migration.(4) The gas accumulation pattern of Northeast Sichuan Changxing formation was established. The early-middle Indosinian was the formation stage of the reservoirs and traps in Changxing Formation. Silurian source rocks entered the peak period of oil generation and filled slowly into the Changxing Formation in the late Indosinian-early Yanshan. In middle Yanshan, source rocks began to crack into gas and and filled into Changxing Formation. The late Yanshan-Himalayan was the adjustment stage of gas reservoirs, and Permian hydrocarbon source rocks continued to fill into Changxing Formation.(5) The Luojiazhai-Dukouhe-Tieshanpo tectonic belt is the optimum exploration zones in the northeast Sichuan Basin, and the Wubaochang tectonic belt is second favorable exploration zones.