Shale brittleness index prediction method based on logging data

Abstract

The embodiment of the invention discloses a shale brittleness index prediction method based on logging data. The shale brittleness index prediction method comprises the steps of: collecting a rock core, extracting an initial logging curve of a collection well corresponding to the rock core, performing a triaxial compression test on the collected rock core to obtain a stress-strain curve, and calculating the brittleness index measured through the test; identifying and selecting an effective logging curve from the initial logging curve by adopting linear regression and sensitivity analysis, carrying out standardization processing on the effective logging curve, and then establishing a prediction model through adoption of principal component analysis and a back propagation neural network method; and performing prediction performance evaluation on the prediction model, and training and correcting the prediction model again based on an evaluation result. According to the method, the conventional logging data and the brittleness index measured in a laboratory are utilized, and the model is established by using the principal component analysis and the back propagation neural network to predict the brittleness index, so that the purposes of reducing the calculation amount and improving the prediction accuracy are achieved.

Description

technical field [0001] The embodiment of the present invention relates to the technical field of well logging data processing, in particular to a method for predicting shale brittleness index based on well logging data. Background technique [0002] Multi-stage hydraulic fracturing has become one of the most widely used and effective methods to increase shale gas production in the process of unconventional shale gas production. Practical production shows that not all shale gas reservoirs are suitable for hydraulic fracturing. The brittleness of shale is one of the important mechanical properties that affect the difficulty of fracturing. In the prior art, it is believed that high brittle shale is beneficial to fracturing and increasing production, mainly in three aspects: (1) high brittle shale is beneficial to the formation and preservation of natural fractures; (3) The healing time of fractures in brittle shale is longer. Therefore, the quantitative evaluation of brittle...

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Problems solved by technology

Calculation of rock brittleness index method based on energy conservation stress-strain curve can accurately analyze the relationship between rock sample absorbed energy and dissipated energy. This method has sufficient scientific rigor, but some shortcomings hinder its wide application.

First, it is difficult to experimentally determine when rock samples are unavailable or incomplete

Second, the experimental determination time and money costs are high

Third, the brittleness index obtained by this method is a discontinuous scatter point, which will cause some potential fracturing intervals to be ignored

Therefore, the brittleness index estimated based on only one or two log curves cannot fully reflect the brittleness characteristics of rocks

In addition, brittleness indices calculated using simple empirical formulas such as linear fits are not precise enough because this rough empirical relationship can lead to large deviations between predicted and true values

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