The Strike-Slip Fault Effects on the Ediacaran Carbonate Tight Reservoirs in the Central Sichuan Basin, China

Abstract

The largest Precambrian gas field in China has been found in the central Sichuan Basin. It is assumed as a mound-shoal microfacies-controlled dolomite reservoir. Recently, a large strike-slip fault system has been identified in the gas field that needs further study of its effect on the Ediacaran reservoirs for highly efficient exploitation of the gas field. For this contribution, we study the matrix reservoir and fractured reservoir along the strike-slip fault damage zones by the cores, FMI (Formation MicroScanner Image) and logging interpretation data, seismic description and production data. It has shown that the matrix reservoir is tight (porosity less than 3%, permeability less than 0.5 mD) that cannot support economical production by conventional exploitation technology in the deep subsurface. On the other hand, the porosity and permeability of the Ediacaran fractured reservoirs could be increased more than one time and 1–3 orders of magnitude. Except for a few localized fracture zones, the fracture elements and fractured reservoirs show a paw-law distribution with the distance to the fault core. Furthermore, the fault effect is more favorable for the increase in the porosity and permeability of the matrix reservoir in the intraplatform than in the platform margin. The overlapping of mound-shoal microfacies, fracturing and karstification could result in large-scale “sweet spots” of the fractured reservoirs in the fault damage zone. The “sweet spot” of fractured reservoir in the fault damage zone is a new favorable exploitation target in the deep central Sichuan Basin.