Brittleness evaluation of Wufeng and Longmaxi Formation high-quality shale reservoir in southeast of Chongqing

The brittleness of shale reservoirs is of great significance for shale gas development. The brittleness index is the most intuitive parameter reflecting reservoir brittleness. The key exploration and development strata of shale gas in Pengshui area of southeastern Chongqing are Wufeng Formation of Upper Ordovician and Longmaxi Formation of Lower Silurian, and the high-quality shale reservoir is Wufeng-Long 1 section. The results show that the high brittleness grade of shale corresponds to low Poisson's ratio and high Young's modulus, but the relative distribution index of brittle minerals also affects brittleness. Through the analysis and calculation of brittle minerals and clay minerals in reservoir, the brittle index is calculated using rock physical parameters and mineral composition, and the advantages and disadvantages of the two are compared. Then a new formula for calculating brittleness index is obtained by combining rock physical parameters and mineral composition. Finally, the brittleness of high-quality shale reservoir in southeast of Chongqing area is evaluated comprehensively. Compared with the measured brittleness, the new formula has good effect. The average brittleness index of the Wufeng-Long 1 is more than 70% in Nanchuan area, China. The lateral distribution is stable and the fracturing conditions are good.

Automated summary

This article investigates the brittleness characteristics of high-quality shale reservoirs in Pengshui area of southeastern Chongqing and their impact on development. By analyzing and comparing rock physical parameters and mineral composition, a new formula for calculating the brittleness index is proposed, and the brittleness of the area is comprehensively evaluated.