Characteristics of the Changxing Fm biohermal gas reservoir in the Yuanba Gasfield, Sichuan Basin and development countermeasures

Located in the Sichuan Basin, the Yuanba Gasfield is the deepest high-sulfur carbonate gas field among those discovered in the world. Its biohermal gas reservoir of the Upper Permian Changxing Fm is characterized by ultra depth, multi-stage small and scattered reef, thin reservoir, poor physical properties, strong heterogeneity, complex fluid distribution, and low production of vertical wells. The development of the biohermal gas reservoir is subject to many difficulties. For example, it is necessary to deepen the studies on time-space distribution laws of reef dolomite reservoirs; it is difficult to characterize small reefs precisely and predict thin reservoirs quantitatively; the deployment and optimization design of horizontal wells are influenced by multiple factors; and the difficulty for horizontal wells with long horizontal sections to run through high-quality thin reservoirs is high. In order to develop the Yuanba Gasfield efficiently, therefore, it is necessary to carry out a series of technical researches on the distribution laws and development models of biohermal reservoirs, precise characterization of small reefs, quantitative prediction of thin reservoirs, optimization design of horizontal wells in banded small reef gas reservoirs, and real-time trajectory optimization and adjustment of horizontal wells in ultra-deep thin reservoirs. These research results provide a powerful support for the development and construction of the Yuanba Gasfield. Based on these technologies, China's first ultra-deep high-sulfur large biohermal gas field was built with a mixed gas annual production capacity of 40 × 108 m3. The successful commissioning of the Yuanba Gasfield lays a basis for the leading position of China in the field of high-sulfur gas field development. In addition, it is of great significance to the long-term stable gas supply in 70 cities of six provinces and two municipalities along the “Sichuan-to-East China Gas Transmission Pipeline”, as well as to the industrial structure adjustment in central-western China and the economic development along the Yangtze River.