Abstract:

Shale oil tight reservoirs are developed in the middle and lower part of Permian in southeastern margin of Junggar basin. Brittleness prediction and evaluation are of great significance to its exploration and development. In this paper, the brittleness index of Permian tight reservoir in southeastern margin of Junggar basin is calculated by using petrophysical experiments, well logging data and prestack seismic data, and the Rickman classical formula method, the method of ratio of Young’s modulus and Poisson’s ratio, the Lamé coefficient method and the shear modulus method are compared, analyzed and evaluated. The results show that: 1) Compared with Poisson’s ratio, Young’s modulus has a better discrimination of lithology, and the mudstone distribution resolution represented by Lamé coefficient is higher；2) The method of calculating brittleness index based on logging multi-parameters obtained in the literature has a poor application effect, but the brittleness index calculated on the basis of converting shear wave velocity by Castagna’s formula has a good application effect；3) The change rates of elastic parameters inverted by YPD (Young’s modulus-Poisson’s ratio-density) formula and LMR (Lamé coefficient-density) formula can also indicate favorable reservoir, especially the density change rate is the best, and the characteristics of upper fan delta front and distributary channel can be well demonstrated by this attribute； 4) Petrophysical experiments and actual data applications show that ρE/σ is the best characterization formula of brittleness in the study area, and the effect is better than Rickman’s classic formula and other methods.

Key words: Junggar basin,  , tight reservoir, shale oil, petrophysical experiment,  , shear wave velocity, Young’s modulus, Poisson’s ratio, brittleness index