Comparison of strength-based rock brittleness indices with the brittleness index measured via Yagiz’s approaches

Despite the vast usage of machine learning techniques to solve engineering problems, a very limited number of studies on the rock brittleness index (BI) have used these techniques to analyze issues in this field. The present study developed five well-known machine learning techniques and compared their performance to predict the brittleness index of the rock samples. The comparison of the models’ performance was conducted through a ranking system. These techniques included Chi-square automatic interaction detector (CHAID), random forest (RF), support vector machine (SVM), K-nearest neighbors (KNN), and artificial neural network (ANN). This study used a dataset from a water transfer tunneling project in Malaysia. Results of simple rock index tests i.e., Schmidt hammer, p-wave velocity, point load, and density were considered as model inputs. The results of this study indicated that while the RF model had the best performance for training (ranking = 25), the ANN outperformed other models for testing (ranking = 22). However, the KNN model achieved the highest cumulative ranking, which was 37. The KNN model showed desirable stability for both training and testing. However, the results of validation stage indicated that RF model with coefficient of determination (R2) of 0.971 provides higher performance capacity for prediction of the rock BI compared to KNN model with R2 of 0.807 and ANN model with R2 of 0.860. The results of this study suggest a practical use of the machine learning models in solving problems related to rock mechanics specially rock brittleness index.

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A Convenient Technology to Calculate Geomechanical Properties From Drilling Data

Volume 11: Petroleum Technology ◽

10.1115/omae2020-18923 ◽

2020 ◽

Author(s):

Mazeda Tahmeen ◽

Geir Hareland ◽

John P. Hayes

Keyword(s):

Young’S Modulus ◽

Poisson’S Ratio ◽

Young's Modulus ◽

Poisson's Ratio ◽

Brittleness Index ◽

Eagle Ford ◽

Horizontal Drilling ◽

Geomechanical Properties ◽

Drilling Data ◽

Rock Brittleness

Abstract The multistage hydraulic fracturing is the best practice to stimulate unconventional hydrocarbon reservoirs for optimal production. Recent studies suggested that selective stimulation design could significantly increase production rates at a reduced cost rather than using non-selective geometric stages. An optimal design needs detailed logging and core information to selectively perforate and optimize the stimulation treatment. In most cases, the non-selective evenly spaced geometric stimulation design is used, primarily due to the time consuming and expensive conventional logging tools and techniques. In this article, a 3D wellbore friction model is used to estimate the effective downhole weight on bit (DWOB) from the drilling data, directional survey data and drill string information. The estimated DWOB is used as an input to the inverted rate of penetration (ROP) model along with other drilling data, drill bit specifications and reservoir specific formation constants, to calculate rock mechanical and reservoir properties including, compressive strength, Young’s modulus, porosity, permeability and Poisson’s ratio without the use of expensive downhole logging tools. The rock brittleness index is calculated from the relationship between Young’s modulus and Poisson’s ratio based on the definitions of rock brittleness used in recent years. The field data from horizontal drilling of three sample wells were used to investigate the geomechanical properties in the Montney shale formation and the lower Eagle Ford formation in North America. The calculated geomechanical properties were compared to the corresponding test analysis on cores. The authors investigated the rock brittleness index from the sample well data drilled horizontally in the lower Eagle Ford formation. This novel technology could help geologists and reservoir engineers better exploit unconventional reservoirs leading to optimal selective stimulations and greater net present value (NPV).

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Quantitative seismic interpretation of rock brittleness based on statistical rock physics

Geophysics ◽

10.1190/geo2018-0094.1 ◽

2019 ◽

Vol 84 (4) ◽

pp. IM63-IM75 ◽

Cited By ~ 1

Author(s):

Lin Wang ◽

Feng Zhang ◽

Xiang-Yang Li ◽

Bang-Rang Di ◽

Lian-Bo Zeng

Keyword(s):

Random Field ◽

Markov Random Field ◽

Rock Physics ◽

Seismic Interpretation ◽

Brittleness Index ◽

Simple Relationship ◽

Elastic Parameters ◽

Markov Random ◽

Rock Brittleness ◽

Statistical Rock Physics

Rock brittleness is one of the important properties for fracability evaluation, and it can be represented by different physical properties. The mineralogy-based brittleness index (BIM) builds a simple relationship between mineralogy and brittleness, but it may be ambiguous for rocks with a complex microstructure; whereas the elastic moduli-based brittleness index (BIE) is applicable in the field, but BIE interpretation needs to be constrained by lithofacies information. We have developed a new workflow for quantitative seismic interpretation of rock brittleness: Lithofacies are defined by a criterion combining BIM and BIE for comprehensive brittleness evaluation; statistical rock-physics methods are applied for quantitative interpretation by using inverted elastic parameters; acoustic impedance and elastic impedance are selected as the optimized pair of attributes for lithofacies classification. To improve the continuity and accuracy of the interpreted results, a Markov random field is applied in the Bayesian rule as the spatial constraint. A 2D synthetic test demonstrates the feasibility of the Bayesian classification with a Markov random field. This new interpretation framework is also applied to a shale reservoir formation from China. Comparison analysis indicates that brittle shale sections can be efficiently discriminated from ductile shale sections and tight sand sections by using the inverted elastic parameters.

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An Evaluation Method of Rock Brittleness Based on the Prepeak Crack Initiation and Postpeak Stress Drop Characteristics

Mathematical Problems in Engineering ◽

10.1155/2021/5639649 ◽

2021 ◽

Vol 2021 ◽

pp. 1-9

Author(s):

Meiben Gao ◽

Tianbin Li ◽

Lubo Meng

Keyword(s):

Crack Initiation ◽

Stress Drop ◽

Evaluation Method ◽

Triaxial Compression ◽

Experimental Tests ◽

Confining Pressure ◽

Brittleness Index ◽

Comparison Results ◽

Confining Pressures ◽

Rock Brittleness

Recent research shows that the brittleness of rock is closely related to the initiation and propagation of internal microcracks, but there are few brittleness evaluation indices considering the characteristics of rock initiation. Based on the theoretical analysis of brittleness and the characteristics of rock initiation, this study proposes an evaluation method of rock brittleness based on the prepeak crack initiation and postpeak stress drop characteristics. First, based on the description and definition of brittleness by George Tarasov and Potvin et al., the feasibility of an evaluation method based on the prepeak crack initiation and postpeak stress drop is theoretically analyzed. Second, the component Bi representing the prepeak brittleness of rock and component Bii representing the prepeak brittleness of rock are constructed, and the product of the two is the brittleness index BI, representing the prepeak crack initiation and postpeak stress drop. Finally, experimental tests of granite and marble were conducted to evaluate the new index, and the brittleness indices of different methods are calculated and compared. The results show that, like other brittleness indices (B1∼B5), the brittleness index BI can effectively reflect the effects of different confining pressures and loading modes on rock brittleness. The brittleness of marble decreases with increasing confining pressure from 5 MPa to 35 MPa. At a confining pressure of 5 MPa, the brittleness of granite during a triaxial unloading test is greater than that during a triaxial compression test. The calculated results are consistent with the experimental results. By tests and comparison results, the reliability of this evaluation method was verified, which provides a way to evaluate rock brittleness from the perspective of crack initiation and is helpful to enrich the analysis and evaluation of rock brittleness in the laboratory.

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A New Rock Brittleness Index Based On Energy Dissipation in the Process of Uniaxial or Triaxial Compression Test

80th EAGE Conference and Exhibition 2018 ◽

10.3997/2214-4609.201800676 ◽

2018 ◽

Author(s):

Y. Ren ◽

Z. Yang ◽

M. Lu ◽

X. Yan ◽

X. Li

Keyword(s):

Energy Dissipation ◽

Compression Test ◽

Triaxial Compression ◽

Triaxial Compression Test ◽

Brittleness Index ◽

Rock Brittleness

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Effect of Bedding Angle and Confining Pressure on the Brittleness of Geomaterials: A Case Study on Slate

Advances in Materials Science and Engineering ◽

10.1155/2019/1650170 ◽

2019 ◽

Vol 2019 ◽

pp. 1-17

Author(s):

Xianjie Hao ◽

Quansheng Xu ◽

Dequan Yang ◽

Shaohua Wang ◽

Yingnan Wei

Keyword(s):

Energy Release ◽

Triaxial Compression ◽

Great Influence ◽

Confining Pressure ◽

Brittleness Index ◽

Compression Tests ◽

External Energy ◽

Whole Process ◽

Bedding Angle ◽

Rock Brittleness

Brittleness is one of the most significant properties of geomaterials. However, very few studies have been conducted on factors influencing the rock brittleness indices. In this paper, conventional triaxial compression tests were carried out to investigate the effects of confining pressure and bedding angle on the brittleness of slate. From the perspective of energy, brittleness is an index that could reflect the release rate of energy that accumulated in the slate under the effect of external energy after reaching peak strength. Therefore, a new brittleness index of slate based on postpeak energy release is proposed herein. The applicability of this index is illustrated by comparing with other five existing brittleness indices. The following results can be obtained. (1) The confining pressure exerts a great influence on the brittleness of slate. With the increase of confining pressure, the brittleness of slate decreases significantly. The dispersion of brittleness values of slate declines with increasing confining pressure. (2) There is a parabolic relationship between slate brittleness and bedding angle. As bedding angle increases, the brittleness is intensified and reaches its maximum at a bedding angle of about 45° and then decreases gradually. (3) In contrast to the previous indices, the brittleness index proposed in this paper can describe the whole process of the postpeak stage through an index of the energy release, which makes this measure more suitable for rock that has the characteristics of step-drop or bench-drop at the postpeak stage.

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A Review of Brittleness Index Correlations for Unconventional Tight and Ultra-Tight Reservoirs

Geosciences ◽

10.3390/geosciences9070319 ◽

2019 ◽

Vol 9 (7) ◽

pp. 319 ◽

Cited By ~ 5

Author(s):

Mews ◽

Alhubail ◽

Barati

Keyword(s):

Clay Content ◽

Detailed Comparison ◽

Unconventional Reservoirs ◽

Brittleness Index ◽

Tight Reservoirs ◽

Correlation Parameters ◽

Rock Brittleness ◽

Universal Correlation ◽

The U.S

Rock brittleness is pivotal in the development of the unconventional reservoirs. However, the existence of various methods of calculating the brittleness index (BI) such as the mineral-based brittleness index (MBI), the log-based brittleness index (LBI), and the elastic-based brittleness index (EBI) lead to inconclusive estimations of the brittleness index. Hence, in this work, the existing correlations are applied on prolific unconventional plays in the U.S. such as the Marcellus, Bakken, Niobrara, and Chattanooga Formation to examine the various BI methods. A detailed comparison between the MBI, LBI, and EBI has also been conducted. The results show that a universal correlation cannot be derived in order to define brittleness since it is a function of lithology. Correlation parameters vary significantly from one shale play to another. Nevertheless, an overall trend shows that abundant quartz and carbonates content yield high brittleness values, while the high clay content and porosity lower the rock brittleness.

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A New Rock Brittleness Evaluation Method Based on the Complete Stress-Strain Curve

Lithosphere ◽

10.2113/2021/4029886 ◽

2021 ◽

Vol 2021 (Special 4) ◽

Author(s):

Chenyang Liu ◽

Lizhi Du ◽

Xiaopei Zhang ◽

Yong Wang ◽

Xinmin Hu ◽

...

Keyword(s):

Stress Drop ◽

Evaluation Method ◽

Triaxial Compression ◽

Strain Curve ◽

Confining Pressure ◽

Brittleness Index ◽

Peak Strain ◽

Stress Strain ◽

Rock Brittleness ◽

Drop Rate

Abstract Brittleness is a crucial parameter of rock mass and the key indicator in rock engineerings, such as rockburst prediction, tunnelling machine borehole drilling, and hydraulic fracturing. To solve the problem of using present brittleness indexes, the existing rock brittleness indexes were firstly summarised in this paper. Then, a brittleness index (BL), which considers the ratio of stress drop rate and stress increase rate and the peak stress, was proposed. This new index has the advantage of simplifying the acquisition of key parameters and avoiding dimensional problems, as well as taking the complete stress-strain curves into account. While applying the BL, the peak strain is used to describe the difficulty of brittle failure before the peak point, and the ratio of stress drop to strain increase can reflect the stress drop rate without dimension problem. In order to verify the applicability of BL, through the PFC2D, the microparameters and confining pressure were changed to model different types of rock numerical specimens and different stress condition. The results show that the BL can well reflect and classify the brittleness characteristics of different rock types and characterise the constraint of confining pressure on rock brittleness. Moreover, the influence of microparameter on macroparameter was studied. In order to further verify the reliability of the brittleness index (BL), this study conducted uniaxial and triaxial compression tests (30 MPa) on marble, sandstone, limestone, and granite under different confining pressure.

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Investigation on the Anisotropy of Mechanical Properties and Brittleness Characteristics of Deep Laminated Sandstones

10.21203/rs.3.rs-660247/v1 ◽

2021 ◽

Author(s):

Mingyang Zhai ◽

Zenglin Wang ◽

Liaoyuan Zhang ◽

Aishan Li ◽

Zilin Zhang ◽

...

Keyword(s):

Mechanical Properties ◽

Triaxial Compression ◽

Confining Pressure ◽

Brittleness Index ◽

Energy Transformation ◽

Compression Tests ◽

Shape Variation ◽

Inherent Anisotropy ◽

Rock Brittleness ◽

Anisotropy Of Mechanical Properties

Abstract Rock brittleness is a crucial mechanical property and essential for fracability evaluation and fracturing scheme design in unconventional reservoirs. However, the influence of inherent anisotropy on deep laminated sandstone’s mechanical properties and brittleness characteristics is rarely investigated. The energy transformation and damage evolution reflected by complete stress-strain curves are analyzed during the entire process of rock rupture under compressions. A new brittleness index is established based on energy evolution during sandstone failure. Its advantages involve comprehensively considering the energy transformation characteristics at both pre-peak and post-peak stages and the capability to characterize the effect of confining pressure and bedding plane (BP) geometry on sandstone brittleness. The triaxial compression tests on sandstones are conducted to validate the reliability and accuracy of the new brittleness index. Numerical simulations are then performed to further investigate the manner in which BP angle, BP density, and confining pressure control the brittleness anisotropy of deep laminated sandstones based on the finite element method. Then the acoustic emission (AE) characteristics of anisotropic sandstone and correlations between AE mode and brittleness index are discussed. The results indicated that the anisotropy of mechanical properties and brittleness of deep laminated sandstones were significantly affected by BP angle, BP density, and confining pressure. With the increase of BP angle, the brittleness index of deep laminated sandstone decreases first and then increases, showing a U-shape variation law, whose maximum and minimum values are obtained at φ =0° and φ =45°, respectively. The AE characteristics were closely related to rock brittleness, which was jointly controlled by BP geometry and confining pressure. The results provide a basis for the brittleness and fracability evaluation and optimum hydraulic fracturing design in deep laminated sandstones.

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