New brittleness indexes and their application in shale/clay gas reservoir prediction

Abstract

Aiming at the disadvantages of the brittleness index commonly used in oil/gas exploration, this article proposed two new brittleness indexes (elastic brittleness and mineral brittleness) in order to predict brittle shale distribution accurately: the former index, based on elastic parameters (Young's modulus and Poisson's ratio), characterizes the original physical properties of reservoirs, the other takes the volume content of minerals in the shale and brittle factor of each kind of mineral into consideration. The two proposed brittleness indexes have theoretical advantages and can explain the brittleness of reservoir rocks from logging and prestack seismic inversion reasonably. According to the rock physics model of organic-enriched shale, a rock physics template for mineral-elastic parameter-brittle factor was established to find out the elastic parameter features of high quality brittle shale from logging data. As a result, the spatial distribution of high-quality gas-bearing brittle shale was predicted utilizing pre-stacked seismic inversion results, and the predicted results match well with the well-logging data. Key words: relative-brittleness index, mineral brittleness, elastic brittleness, rock physics template, shale gas