Optimization of favorable zones for shale gas based on 3D visual geological modeling technology——Case study of Tiangongtang structure

Abstract

By comprehensively utilizing seismic, drilling, core, and logging data, and with the support of human-computer interaction and 3D visualization technologies of 3D geological modeling software, a shale gas geological modeling study was conducted for the Wufeng Formation of the Ordovician System and the first sub-member of the Longmaxi Formation of the Silurian System in the Tian’gongtang structure. A high-precision 3D geological model and a natural fracture model controlled by two sets of thrust faults (trending northwest-southeast and nearly east-west) were established. The porosity and geological reserves of shale gas were quantitatively characterized. Geological favorable areas were divided based on gas saturation and resource abundance as criteria, while engineering favorable areas were delineated using fracturing engineering parameters and natural fracture density as standards. On the basis of the dual geological-engineering factors, the comprehensive favorable areas for shale gas were optimized and depicted in 3D. The results show that: ① The elevation of the bottom of the Wufeng Formation in the study area ranges from −5,311 m to −1,842 m, with a large elevation difference and a complex structure. ② In the target main reservoir intervals of the study area, the porosity ranges from 0.9% to 8.2%, with an average of 5.24%; the gas saturation distributes between 0 and 92.5%, with an average of 67.2%; the adsorbed gas content varies from 0.03 to 3.77 cubic meters per ton, with an average of 1.76 cubic meters per ton; the geological reserves of shale gas are approximately 1,800×108 cubic meters, with an average resource abundance of 423 million cubic meters per square kilometer, belonging to a medium-abundance shale gas reservoir. ③ Areas with a Young’s modulus of 35-50, a Poisson’s ratio of 0.18-0.25, and a natural fracture density of 0.5-2.5 fractures per meter are favorable for fracturing stimulation. ④ Class I and Class II favorable areas are mainly distributed in the core and slope zones of the anticline in the Tian’gongtang structure; Class III favorable areas are primarily located in the northern part of the Tian’gongtang structure; and geological risk areas are mainly distributed in the deep part of the structure and areas with well-developed faults. In conclusion, the optimization of comprehensive favorable areas for shale gas using this technology can effectively promote the large-scale and beneficial development of shale gas, and provide a basis and technical support for shale gas well location deployment and fracturing stimulation.