Method for predicting hydration damage degree of shale

Abstract

The invention discloses a method for predicting the hydration damage degree of shale. The method includes the following steps that: S1, target shale block standard rock samples are prepared, and are subjected to soaking treatment; S2, after being dried, the standard rock samples are subjected to a triaxial mechanics experiment; S3, on the basis of the results of the triaxial mechanics experiments,the Poisson's ratio-water immersion time curve and elastic modulus-water immersion time curve of the standard rock samples are obtained; S4, the internal friction angles of the standard rock samplesare determined according to the Mohr-Coulomb strength theory, and a relational expression of the internal friction angles and immersion time is obtained; S5, post-water immersion Weibull distributionparameter m is obtained through the softening constitutive model of Weibull distribution under water immersion, and the rock compressive strength F0 of the shale which has been damaged by hydration isobtained; and S6, the hydration damage degree of the shale is calculated. With the method adopted, the influence of hydration damage on shale rock mechanical parameters under different confining pressure and hydration time conditions can be quantitatively expressed, and therefore, the hydration damage degree can be quantitatively predicted.

Description

technical field [0001] The invention relates to the technical field of unconventional oil and gas exploration and development, in particular to a method for predicting the strength of hydration-damaged shale. Background technique [0002] Shale gas refers to unconventional natural gas that occurs in organic-rich shale-based reservoir rock series. It is a continuously generated biochemical gas, thermogenic gas or a mixture of the two. In cracks and pores, it exists on the surface of kerogen and clay particles in an adsorbed state, and a very small amount is stored in kerogen and asphaltene in a dissolved state. The proportion of free gas is generally 20% to 85%. [0003] Deep shale gas resources buried deeper than 3500 m in my country are abundant, accounting for more than 60% of shale gas resources, and have good development prospects. It is easy to close under closing pressure, which is an important reason for the poor fracturing effect. [0004] At present, hydraulic frac...

AI Technical Summary

Problems solved by technology

The water entering the formation will damage the mechanical strength of the shale, making the shale soft, resulting in the closure of self-supporting fractures and the embedding of proppant, which further exacerbates the problem that deep shale is difficult to support effectively

[0005] At present, there are few researches on the hydration intensity of deep shale at home and abroad. Therefore, it is urgent to establish a method to predict the hydration damage intensity of shale.

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