Modeling and analysis of seismic AVAz in shale reservoir based on anisotropic rock physics model: A case study from Southwest China

This paper presents a predictive rock-physics model for unconventional shale reservoirs based on an extended Maxwell scheme. This model accounts for intrinsic anisotropy of rock matrix and heterogeneities and shape-induced anisotropy arising because the dimensions of kerogen inclusions and pores are larger parallel to the bedding plane than perpendicular to this plane. The model relates the results of seismic amplitude variation with offset inversion, such as P- and S-impedance, to the composition of the rock and enables identification of rock classes such as calcareous, argillaceous, siliceous, and mixed shales. This allows the choice of locations with the best potential for economic production of hydrocarbons. While this can be done using well data, prestack inversion of seismic P-wave data allows identification of the best locations before the wells are drilled. The results clearly show the ambiguity in rock classification obtained using poststack inversion of P-wave seismic data and demonstrate the need for prestack seismic inversion. The model provides estimates of formation anisotropy, as required for accurate determination of P- and S-impedance, and shows that anisotropy is a function not only of clay content but also other components of the rock as well as the aspect ratio of kerogen and pores. Estimates of minimum horizontal stress based on the model demonstrate the need to identify rock class and estimate anisotropy to determine the location of any stress barriers that may inhibit hydraulic fracture growth.

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Anisotropic Rock Physics Model Based Statistical Inversion

Petroleum & Petrochemical Engineering Journal ◽

10.23880/ppej-16000113 ◽

2017 ◽

Vol 1 (2) ◽

Author(s):

Xiaoyang Wu

Keyword(s):

Rock Physics ◽

Anisotropic Rock ◽

Model Based ◽

Physics Model ◽

Rock Physics Model

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Construction of a novel brittleness index equation and analysis of anisotropic brittleness characteristics for unconventional shale formations

Petroleum Science ◽

10.1007/s12182-019-00372-6 ◽

2019 ◽

Vol 17 (1) ◽

pp. 70-85

Author(s):

Ke-Ran Qian ◽

Tao Liu ◽

Jun-Zhou Liu ◽

Xi-Wu Liu ◽

Zhi-Liang He ◽

...

Keyword(s):

Random Distribution ◽

Rock Physics ◽

Brittleness Index ◽

Anisotropic Rock ◽

Shale Formations ◽

Shale Formation ◽

Dip Angle ◽

Physics Model ◽

Rock Physics Model ◽

Two Parameters

Abstract The brittleness prediction of shale formations is of interest to researchers nowadays. Conventional methods of brittleness prediction are usually based on isotropic models while shale is anisotropic. In order to obtain a better prediction of shale brittleness, our study firstly proposed a novel brittleness index equation based on the Voigt–Reuss–Hill average, which combines two classical isotropic methods. The proposed method introduces upper and lower brittleness bounds, which take the uncertainty of brittleness prediction into consideration. In addition, this method can give us acceptable predictions by using limited input values. Secondly, an anisotropic rock physics model was constructed. Two parameters were introduced into our model, which can be used to simulate the lamination of clay minerals and the dip angle of formation. In addition, rock physics templates have been built to analyze the sensitivity of brittleness parameters. Finally, the effects of kerogen, pore structure, clay lamination and shale formation dip have been investigated in terms of anisotropy. The prediction shows that the vertical/horizontal Young’s modulus is always below one while the vertical/horizontal Poisson’s ratio (PR) can be either greater or less than 1. Our study finds different degrees of shale lamination may be the explanation for the random distribution of Vani (the ratio of vertical PR to horizontal PR).

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