Abstract:

Tight sandstone in the Upper Triassic Xujiahe Formation, northeastern Sichuan Basin, has been one of the exploration targets for natural gas in the area. However, the stone, as a whole, is rather tight, deeply buried and highly heterogeneous, making commercial development of gas from it quite a challenge. The formation contains many fault-fracture gas reservoirs in the Tongjiang-Malubei area of the Tongnanba structural belt, where certain lithological facies in well-fractured zones may be used as clues to the whereabouts of the reservoirs. By recognition of source rock-rooted faults based on dynamic structure restoration, nonlinear inversion and prediction of lithology and physical properties, and multi-scale fusion as well as five-dimensional pre-stack fracture prediction in OVT domain, we effectively addressed the recognition of source rock-rooted faults, the prediction of relatively high-quality reservoirs and fractures as well as "sweet spots"-several issues easily encountered in dealing with this type of reservoir. These techniques were applied well to the predication of fault-fracture reservoirs in the northeast Sichuan Basin with prediction error of reservoir thickness being reduced from 16% to 8% and predication accuracy of fractures being increased from 60% to 85%. Four wells were so successfully drilled according to the predication results that controlled reserves of 367.91×10⁸ m³ were booked with a possible gas resource base of 100 billion cubic meters readily on the way.

Key words: source rock-rooted fault, reservoir prediction, tight sandstone, Xujiahe Formation, fault-fracture body, Sichuan Basin