In-situ stress measurement method based on indentation technology and machine learning

An in-situ stress measurement method based on indentation technology and machine learning, comprising:

• step 1:
• drilling and taking a rock core, recording an original temperature of the rock core, and moisture-preserving and storing the rock core;
• step 2:
• processing the rock core into a rock core sample;
• step 3:
• calculating a pressure of an overlying rock layer of the rock core sample;
• step 4:
• heating the rock core sample to the original temperature of the rock core, conducting a shallow indentation test on the rock core sample using a conical indenter to obtain an indentation load-depth curve, and deriving an equivalent elastic model of rock core;
• step 5:
• heating the rock core sample to the original temperature of the rock core, setting minimum horizontal principal stresses and maximum horizontal principal stresses, conducting a deep indentation test on the rock core sample using the conical indenter to obtain test data, and using the test data as an actual training sample for machine learning;
• step 6:
• constructing a training set of a neural network based on the test data, and inputting the training set into the neural network for network training to obtain an inverse problem model of in-situ stress;
• step 7:
• performing an in-situ indentation test on the rock core sample to obtain an in-situ indentation load-depth curve, calculating a curvature of loading curve, a slope at a maximum indentation depth of unloading curve, and a ratio of residual work to total work of the in-situ indentation load-depth curve;
• inputting the curvature of loading curve, the slope at the maximum indentation depth of unloading curve, and the ratio of residual work to total work into the neural network after being trained to obtain output values being a dimensionless value of maximum horizontal principal stress and a dimensionless value of minimum horizontal principal stress, and then calculating a minimum horizontal principal stress and a maximum horizontal principal stress based on the equivalent elastic model of rock core derived in the step 4;
• and
• step 8:
• measuring, by an imaging logging tool, a direction of main crack of an indentation at a bottom of a borehole as a direction of the maximum horizontal principal stress;
• wherein the step 5 comprises:
• obtaining a series of indentation load-depth curves through the deep indentation test;
• calculating a curvature of loading curve, a slope at a maximum indentation depth of unloading curve, and a ratio of residual work to total work of each of the series of indentation load-depth curves, and taking the curvature of loading curve, the slope;
• wherein the curvature of loading curve C, the slope
• dP
• u
• dh
• ❘
• "\[RightBracketingBar]"
• h
• =
• h
• max
• of at the maximum indentation depth of unloading curve, and the ratio
• W
• T
• -
• W
• E
• W
• T
• of residual work to total work of each of the series of indentation load-depth curves of the rock core sample are related to mechanical parameters of rock core expressed by formulas (7)-(9) as follows:
• C
• =
• P
• h
• 2
• =
• E
• *
• ⁢
• ∏
• 1
• (
• σ
• Y
• E
• *
• ,
• n
• ,
• c
• 0
• E
• *
• ,
• φ
• 0
• ,
• σ
• H
• σ
• h
• ,
• σ
• h
• E
• *
• ,
• T
• T
• 0
• )
• (
• 7
• )
• dP
• u
• dh
• ❘
• "\[RightBracketingBar]"
• h
• =
• h
• max
• =
• E
• *
• ⁢
• h
• max
• ⁢
• ∏
• 2
• (
• σ
• Y
• E
• *
• ,
• n
• ,
• c
• 0
• E
• *
• ,
• φ
• 0
• ,
• σ
• H
• σ
• h
• ,
• σ
• h
• E
• *
• ,
• T
• T
• 0
• )
• (
• 8
• )
• W
• T
• -
• W
• E
• W
• T
• =
• E
• *
• ⁢
• h
• max
• ⁢
• ∏
• 3
• (
• σ
• Y
• E
• *
• ,
• n
• ,
• c
• 0
• E
• *
• ,
• φ
• 0
• ,
• σ
• H
• σ
• h
• ,
• σ
• h
• E
• *
• ,
• T
• T
• 0
• )
• (
• 9
• )
• where E* represents an equivalent Young's modulus.