In order to clarify the favorable reservoir types and their distribution characteristics of the main gas-producing layer system in Baxigai Formation, as well as their controlling effect on production capacity differences, and the differences between the two gas-producing layer systems, core detailed description, microscopic casting thin section, X-ray diffraction and other experimental analyses were carried out on multiple wells in Bozi 3 Well Area. Reservoir types were divided, and the relationship between reservoir thickness and unobstructed flow rate of gas wells was clarified. It is considered that there are differences between the Baxigai Formation and the Bashijiqike Formation in terms of sedimentary facies types, reservoir types and thickness, as well as the relationship between fracture (fracture) and matrix reservoir configuration. ① The main gas-producing layer system of Well Area Bozi 3 is characterized by fan delta front braided channel conglomerate deposits in the Baxigai Formation Member 2, and the Baxigai Formation Member 1 is mainly composed of interbedded siltstone and fine sandstone of fan delta front dam bodies and submarine distributary channels with lacustrine facies. The Bashijiqike Formation Member 3 is mainly characterized by large-area deposition of subaqueous distributary channels in the front of a braided river delta. The brown mudstone interbeds are primarily developed in Member 1 of the Baxigai Formation, moderately developed in Member 2, and not well developed in Member 3 of the Bashijiqike Formation. ② The second member of the Baxigai Formation is mainly composed of pore-type and fracture-pore-type reservoirs; the third member of the Bashijiqike Formation is mainly composed of pore-fracture-type reservoirs. The reservoir is divided into 4 categories based on the sandstone porosity value, among which Categories I, II, and III are effective reservoirs, and Category IV is a non-reservoir. The total thickness of Category II and III reservoirs in the second member of the Baxigai Formation is generally less than 15m; the total thickness of Category I, II, and III reservoirs in the third member of the Bashijiqike Formation is 10m-26m, with a relatively large effective reservoir thickness. ③ The second member of the Baxigai Formation is mainly composed of interbedded sandstone, conglomerate, and siltstone, with relatively thin reservoir thickness, lower fracture development degree than the Bashijiqike Formation, but better matrix reservoir development; the third member of the Bashijiqike Formation is mainly composed of thick conglomerate, with large reservoir thickness and well-developed fractures; ④ The size of the unobstructed flow rate of each well in the second member of Baxigai Formation is closely related to the thickness and distribution of II and III class reservoirs. The production capacity of each gas well is controlled by both the degree of fracture development and the thickness of the matrix reservoir; the production capacity of each gas well in the third member of Bashijiqike Formation is mainly controlled by the degree of fracture development, and the correlation with effective reservoir thickness is weak. This indicates that the development of fractures in the Bozi 3 well area is a key factor for high-yield gas wells, and favorable sedimentary facies and effective reservoir thickness also play a controlling role in high-yield gas wells. The above understanding provides important geological basis for increasing natural gas reserves and production in the area.
DownLoad: