Shale gas reservoir crustal stress logging prediction method based on rock physics model

Abstract

The present invention relates to a shale gas reservoir crustal stress logging prediction method based on a rock physics model. According to the method, a shale gas reservoir rock physics model which takes kerogen particles into consideration is established, so as to predict a longitudinal and transverse wave velocity of the logging; based on the above, a maximum and minimum horizontal principal stress and a fracture pressure of the reservoir are calculated; and an accurate stress assessment of a shale gas reservoir is carried out while a transverse wave logging is not provided. The beneficial effects of the invention are that: the rock physics model in line with characteristics of the shale gas reservoir is established to improve precision of the prediction velocity; and based on the rock physical model, the maximum and minimum horizontal principal stress and the fracture pressure are obtained, so that while the measured transverse wave logging data are not provided, the underground stress can be predicted on the basis of a conventional logging curve, and the prediction result is high in accuracy.

Description

technical field [0001] The invention belongs to the field of in-situ stress logging prediction of shale gas reservoirs, in particular to a method for in-situ stress logging prediction of shale gas reservoirs based on rock physics models. Background technique [0002] For shale gas reservoirs, since fracturing directly affects gas production, the prediction of underground stress determines the quality of fracturing. There are many logging evaluation models for reservoir in-situ stress, the more mature ones include Mohr Coulomb model, Huang Rongzun model (see reference 1), uniaxial strain model and so on. These models can be used to calculate the maximum and minimum horizontal principal stress, and then calculate the fracture pressure, stress gradient, etc., to evaluate the reservoir; but the application of these models must be based on more accurate rock mechanics such as Young's modulus and Poisson's ratio. parameters are used as input parameters, and accurate rock mechanic...

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Problems solved by technology

Shale gas reservoirs have complex lithology, various microscopic pore types, and rich kerogen. For such unconventional reservoirs, conventional petrophysical models cannot calculate more accurate velocities. The classic Xu-White model (see Reference Reference 2), mixing sandstone and clay, using two-dimensional Kuster- model (see Ref. 6) for the elastic modulus of dry rock with porosity and for fluid-saturated rock using the Gassmann (ref. 10) equation, but this model only The properties are not complicated, and the pore types are relatively simple; the Xu-Payne rock physics model (see reference 7) and the DEM-Gassmann rock physics model (see reference 3) developed on this basis both use the 3D pore spectrum to calculate The bulk modulus and shear modulus of pore-type rocks get better results, but these two models are only suitable for relatively simple lithology, and neither of them considers kerogen, so they are not suitable for shale gas reservoirs

Bandyopadhyay et al. (see reference 8) used the Brown-Korriga (see reference 4) model to calculate the elastic modulus of rocks containing kerogen by means of solid replacement. However, according to core observations, kerogen is dispersed in a certain particle form In shale, this method does not simulate the real state of organic matter in the rock

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