bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of Elastic Wavefield Evolution in Heterogeneous Fractured Media Based on a Combined Displacement Discontinuity-Discrete Fracture Network Model
Authors: Wang S. F. , Zhang Z. X. , Huang X. , Lei Q. H. 
Published: August 2024

ABSTRACT:
The evolution of elastic waves in heterogenous fractured rocks is studied based on numerical simulations. We use the discrete fracture network method to represent the distribution of a natural fracture system and employ the displacement discontinuity method to compute the propagation of elastic waves across individual fractures. The variability of matrix Young's modulus is assumed to obey the Weibull distribution, which is characterized by a homogeneity index m. The rock matrix becomes more heterogeneous as m decreases. The results indicate that the dimensionless angular frequency ῶ = ωZ/κ dominates the wavefield evolution of a plane wave travelling through the heterogeneous fractured rock with less heterogeneous materials (m = 10) or high heterogeneous fractures (ῶ ≥ 1). Here, ω, Z, and κ are the angular frequency, seismic impedance, and fracture stiffness, respectively. As the heterogeneity of the rock materials increases (i.e., m ≤ 5) with small ῶ (say 0.1), both the fracture network and rock matrix jointly dominate the wavefield. An asynchronous arrival phenomenon of wave energy occurs and becomes more significant with an increased ῶ and decreased m. The breakthrough time of elastic wave energy has a positive relationship with ῶ but a negative relationship with m.

1. INTRODUCTION
Rock masses typically contain numerous natural fractures of variable lengths, locations, and orientations (Bour et al. 2002; Davy et al. 2010; Lei et al. 2017; Afshari Moein et al. 2019; Miranda et al. 2023). The heterogeneous matrix with spatially varying mechanical parameters is also commonly present (Tang et al. 2000; Molz et al. 2004; Lei and Gao 2019; Yan et al. 2023). The resultant heterogeneities arising from natural fractures and rock materials may significantly affect the seismic wave transport in the subsurface (Sato and Fehler 2009; Hamzehpour et al. 2016; Zhu et al. 2020; Ma et al. 2023; Wang et al. 2023), which has attracted considerable attention from various disciplines such as rock mechanics, geophysics, seismology, and earthquake engineering (Khoshhali and Hamzehpour 2015; Fan et al. 2018; Feng et al. 2020; Zhang et al. 2021). Thus, comprehending the evolution of waves in heterogeneous fractured rocks and quantifying the relationship between wavefield characteristics and rock mass properties are fundamentally important for characterizing crustal heterogeneities in many rock engineering applications. However, the current studies mainly focus on the onefold impact of fracture- (Shao and Pyrak-Nolte 2016; Lei and
Sornette 2021; Wang et al. 2023) or material-induced (Allaei and Sahimi 2006; Hamzehpour et al. 2016; Ba et al. 2017; Ma et al. 2023) heterogeneity on the wave transport. The competing roles of the fracture network and rock matrix heterogeneity in the wavefield evolution has not been well revealed.
Numerical Simulation of Fracture Propagation on Proactive Utilization of Stress Interference in the Yingxiongling Shale Oil Reservoir
Authors: Chen X. , Xian C. G. , Liu Y. Y. , Wan Y. Y. 
Published: August 2024

ABSTRACT:
In the development of shale oil and gas, the tridimensional development model centered around factory drilling, horizontal wells, and hydraulic fracturing has been widely adopted. This development model inevitably triggers both positive and negative hydraulic fracturing interference as well as production interference. Especially during the hydraulic fracturing process, actively controlling stress interference can effectively utilize these interferences to generate positive effects, thereby increasing the complexity of fractures and enhancing the efficiency of oil and gas extraction. This paper develops an analytical expression mathematical model of a spatial stress field, which is used to explore how the coupled design of different well spacings and fracturing layouts proactively affects the spatial stress field. Based on the geoscience & engineering integration software platform, this study combines fracture propagation simulation with finite element numerical simulation of the stress field, clarifying how to proactively utilize and control stress interference. The research indicates that strengthening well interference and implementing staggered fracturing strategies can promote the formation of complex fracture networks at distant ends, while effectively inhibiting excessive extension of the main fractures towards neighboring wells. Through the deployment of a tridimensional well network, and the coupled design of well spacing and fracture spacing, an overall optimization and utilization of the spatial stress field can be achieved.

1. INTRODUCTION
In the global oil and gas industry's exploration and development sector, there is a gradual shift from conventional oil and gas, which accounts for 20% of the total oil and gas resources, to unconventional oil and gas resources, which make up 80% (Zou et al., 2023). As the first country to achieve commercial development of shale oil globally, the United States has effectively driven cost reduction and efficiency improvements through the scaled-up development of shale oil via "super well factories" (Guo et al., 2023). China's shale oil resources are extremely abundant. According to exploration assessments, the recoverable resources are estimated to be about 5 billion tons. However, compared to the marine shale oil in North America, China's continental shale oil exhibits some unique geological characteristics, such as strong reservoir heterogeneity, thin individual layer thickness, and rapid changes in lithology and facies (Li et al., 2023). These characteristics make the use of a tridimensional development strategy particularly important for the overall mobilization of the reservoir.
Geological Feature Extraction and Data-Driven Production Prediction Based on Well Logging Data
Authors: Hsu Maoya , Ma Zhengchao , Tian Shouceng , Zhou Xiaoxia , Dai Jiacheng , Weng Jintao , Wang Tianyu 
Published: August 2024

ABSTRACT:
Data-driven fracturing production prediction relies on geological engineering parameters to forecast production indicators. These parameters are traditionally derived from manual summarization and statistical analysis of well logging curves, potentially leading to inaccuracies due to incomplete encapsulation of formation complexities. This research, however, employed objective recorded data to enhance data credibility. Leveraging a convolutional neural network model, precise production predictions were achieved through the extraction of abstract features from the logging data. The study utilized the Gram angle field method for two-dimensional transformation of sequence data, preserving overall data coherence. By incorporating engineering parameters into deep neural network models or integrated learning models, the study facilitated production prediction, validating the correlation between formation characteristics and production. The study also explicated the convolutional network's operational mechanics, resulting in the development of a novel geological parameter description scheme. Notably, substituting manual statistical data with objective well observation data significantly enhanced the model's predictive accuracy and robustness. Ultimately, this research introduces an intelligent model that integrates well logging data for data-driven production forecasting, optimizing workflow processes through the extraction of critical information from raw data.

1. INTRODUCTION
Production forecasting in oil and gas extraction is a critical task that affects operational strategies and investment decisions in the industry. Artificial intelligence methods have been widely applied to scenarios such as production forecasting due to the accumulation of oilfield data and the advancement of machine learning methods (Lolon et al., 2016). Machine learning models can overcome the limitations of traditional analytical methods in correlating high-dimensional data due to their powerful nonlinear fitting capabilities (Pankaj et al., 2018). Various machine learning models have been used by researchers, including artificial neural networks (ANN) (Clar et al., 2019), imperialist competitive algorithm (ICA) (Berneti et al., 2011), higher order neural networks (HONN) (Chakra et al., 2013), nonlinear autoregressive neural networks (NARX) (Sheremetov et al., 2014), and multivalued neuron complex neural networks (MLMVN) (Aizenberg et al., 2016). A fusion model of a multilayer perceptron (MLP) network (Shi et al. 2021) and a long-short-term memory (LSTM) network (Wang et al., 2021) was constructed to predict production using geological and fractured reservoir parameters, historical data, and other metrics (Mohd Razak et al., 2021).
Control Technology of High Prestress Excavation Compensatory Support in Tunnels Through Fault Fracture Zones
Authors: Sun Jihao , Yang Xiaojie , He Manchao 
Published: August 2024

ABSTRACT:
Taking the Tabaiyi tunnel in Yunnan Province as the research background, the tunnel has suffered from disasters such as large deformation of initial support, deformation of steel arches, and mud and water inrush under the original support conditions. According to the theory of excavation compensation and the requirements of traffic tunnel engineering on the anchorage system, this paper proposes a high prestressing anchorage system applicable to large deformation tunnels traversing fault fracture zones and capable of realizing the concept of timely support, and the application of the supporting technology is carried out in the experimental study. Based on the resin anchorage that can be prestressed after the rapid condensation of the overrun double-gradient grouting reinforcement, the rapid prestressing NPR anchorage system of "overrun grouting+resin anchorage" and its supporting active support technology system are proposed. The results of the field experiment show that: under the implementation of double gradient grouting and NPR anchor cable timely active support system, the effect of large deformation control is remarkable, and the large deformation of surrounding rock is effectively controlled within 300mm, which verifies the superiority of the deformation control technology based on rapid prestressing anchorage support in large deformation tunnels through the fault fracture zone.

1. Introduction
With the quick development of underground engineering in recent years, the construction of railway, highway, and water conservancy tunnels in China has also developed rapidly. Among them, there is no lack of some tunnels through fault fracture zones, which are prone to risky disasters such as large peripheral rock deformation, water and mud inruch during the construction process (Jiang (2023) and Chen (2023)). Taking the Jian-ge-yuan Expressway tunnel as a typical example, the Tabaiyi tunnel is one of the high-risk tunnels along the whole route. The length of the tunnel is 2.6 kilometers. The cross-section area is close to 140 m2. The construction took five years, and some sections of the tunnel still showed deformation, cracking, falling block misalignment, arch rise, and other phenomena after the second lining was poured. Therefore, the construction of the Tabaiyi highway tunnel is one of the most difficult problems in the world of tunneling.
Transient Effects of Time-Dependent Drilling Fluids on Wellbore Stability
Authors: Ma Y. , Dokhani V. , Miao H. , Geng T. , Shi Z. 
Published: August 2024

ABSTRACT:
Accurate prediction of dynamic pressures is essential for wellbore integrity analysis in deep water wells and wells with narrow operational windows. During the start-up of circulation, a higher circulating pressure is needed due to the gelation effect of drilling fluid. A coupled poro-elasto-dynamic model is developed to examine the effects of pump start-up on borehole stability. Firstly, a transient hydraulic model is developed to predict the temporal variation of pressure in flow conduits during the pump ramp-up periods. A constitutive equation is used to describe the time-dependent rheology of gelled fluid. The hydraulic model is then coupled with a wellbore stability model to study the effect of dynamic pressures on wellbore integrity. The method of characteristics is employed to solve the governing equations of the hydraulic model. Failure analysis is performed to evaluate the gelation effect of drilling fluid and pump ramp-up on borehole stability. The results of the hydraulic model are validated through comparison with field data and that of a published study. The results indicate that maximum circulating pressure is initially attained before approaching an equilibrium circulating pressure. A time-dependent failure can occur in the vicinity of the borehole depending on the magnitude of gel strength and pump ramp-up speed. The study concludes that by ignoring the time-dependent characteristics of drilling fluids the magnitude of circulating pressures in early times can be underestimated. Therefore, an integrated framework is suggested to consider the time-dependent effects of drilling fluids on circulating pressure and hence wellbore stability. The developed poro-elasto-dynamic model can be utilized to improve our understanding of the transient effects of drilling fluids on wellbore stability.

1. INTRODUCTION
Drilling hydraulics is one of the most important factors to control the safety of drilling operations. It has received special attention in the past through downhole measurement tools to improve downhole pressure monitoring. However, it is not possible to deploy such tools in sensitive and risky areas. In addition, it is required to have a reliable hydraulic model to predict downhole pressure for design purposes. Several hydraulic models have been developed to estimate the frictional pressure losses during drilling fluid circulation under steady-state conditions (Reed and Pilehvari, 1993; Merlo et al. 1995; Mitchell and Miska, 2011). The major rheological models to describe the pressure losses in pipe and annuli include the Bingham-Plastic, Power-law, and Yield Power-law (Herschel-Bulkley) model. Drilling fluids generally exhibit thixotropic behavior due to their mixture composition (Bourgoyne et al. 1990). Nevertheless, the fluid gelation and thixotropic effect are not commonly considered in the majority of the abovementioned studies.
The Sunset Solution: Closure on Leaking Proppant
Authors: Peirce A. P. , Abbas S. , Detournay E. 
Published: August 2024

ABSTRACT:
Recent analytic work (Peirce and Detournay, 2022a) has established the tip asymptotics for receding hydraulic fractures that close due to leak-off to the permeable rock. This asymptotic result enabled the development of rigorous numerical schemes to explore the recession dynamics of hydraulic fractures that develop in a state of plane strain (Peirce and Detournay, 2022b) and radially symmetrically (Peirce, 2022). These detailed studies enabled the identification (Peirce and Detournay, 2022c) of the so-called Sunset Solution, which is a similarity solution that emerges close to the ultimate collapse of the fracture. The asymptotic analysis performed in (Peirce and Detournay, 2022c) establishes that the existence of the sunset solution is due to a fundamental decoupling of the kinematics from the dynamics in the governing equations, which leads to a robust way to measure the Carter leak-off coefficient from the rate of change in the fracture aperture at the wellbore. These results were established assuming that no fluid is leaking from the closed section of the fracture. In this paper, we explore the viability of the procedure to estimate the Carter leak-off coefficient using the sunset solution when the fracture is assumed to close on proppant that is filled with fluid upon closure and which continues to leak off and exchange fluid with the open portions of the fracture.

1 INTRODUCTION
The diagnostic fracture injection test (DFIT) is used in petroleum engineering to assess the minimum in situ stress, Carter's leak-off coefficient, and other reservoir parameters. The test consists of monitoring the well pressure during injection of fluid over a time long enough to create a hydraulic fracture, as well as after shut-in of the well. Interpretation of the pressure decline that follows the end of pumping was pioneered by Nolte (1979, 1986). His original analysis relies on two main assumptions: (i) the fracture stiffness remains constant after shut-in until the fracture completely closes and (ii) Carter's leak-off coefficient CL is a constant. In Nolte's analysis, the coefficient CL is interpreted from the pressure decline following the sudden drop of pressure observed when the well is shut-in, by expressing the declining pressure as a linear function of G(Δt), which is a function of Δt - the time elapsed since shut-in divided by the shut-in time ts (Nolte, 1979, 1986).
Intact Rock Properties of the Rotondo Granite for the PRECODE Project in the BedrettoLab
Authors: Perras M. A. , Golabchi Y. , Bahrani N. , Hamdi P. , Amann F. 
Published: August 2024

ABSTRACT:
In order to estimate the depth of the Excavation Damage Zone (EDZ) using empirical or numerical approaches, the key intact properties include the Uniaxial Compressive Strength (UCS), the tensile strength, and the crack initiation threshold. In addition to these test derived values, plotting triaxial test results and determined Crack Initiation values from those tests can help to define Damage Initiation and Spalling Limit failure envelops for numerical modelling of brittle behaviour. In order to predict the extent of the EDZ in the Rotondo granite around a mine-by tunnel being excavated as part of the PRECODE project in the BedrettoLab, Switzerland, a testing program has been conducted. It was found that the static Young's modulus was 52.5 GPa, that the Poisson's ratio was 0.22, that the Direct Tensile Strength reduced from the Brazilian Tensile Strength by a factor of 0.86 was 6.0 MPa and the UCS was 180.9 MPa. In addition, triaxial tests with confinements up to 20 MPa were conducted to determine the intact Hoek-Brown failure envelop, with a mi of 36. These laboratory derived values will be used to predict the EDZ depth and compare it to the measured EDZ from the PRECODE mine-by tunnel in the future.

1. INTRODUCTION
Development of brittle damage around underground excavations in highly stressed conditions is a common phenomenon. For deep geological repositories, interest in brittle damage studies began in mid-1980's (Kelsall et al. 1984) with a focus on determining the changes in permeability due to blasting. Much research has since been conducted on various topics related to the development of Excavation Damage Zones (EDZ) for nuclear waste repositories (see Alcaino-Olivares et al. 2024 for details). However, only until more recently has the focus in rock mechanics turned back to time-dependent behaviour of brittle rocks with a related focus on the long-term behaviour of deep geological repositories. Time-dependent brittle fracturing may lead to an interconnected fracture network that could enhance and, in the framework of nuclear waste disposal, may provide preferential pathways for radionuclide migration. Therefore, a comprehensive understanding of brittle fracturing requires a spatial and temporal characterization of the EDZ. A crucial input into characterizing the EDZ are the intact rock mechanical properties, in particular the Crack Initiation (CI) value which has been shown to be a useful intact rock parameter to determine the depth of brittle failure around excavations (Diederichs 2007). This study examines preliminary rock testing results for input into the characterization of the Rotondo granite for the PRECODE project at the BedrettoLab in Switzerland.
Improve Mechanical Earth Model Calibration Using Statistical Concepts
Authors: Ray P. 
Published: August 2024

ABSTRACT:
Mechanical Earth Model (MEM) has a broad impact on drilling, completion, production, and reservoir management decisions. For example, wellbore stability calculated using a MEM can provide safe mud windows for drilling, thereby reducing wellbore instability related non-productive time and drilling costs. A MEM can also provide safe injection limits for CO2 storage, enhanced oil recovery, and wastewater injection.
The process of building and calibrating a MEM often involves collecting and analyzing offset well drilling observations, such as leak-off tests (LOT), diagnostic fracture injection test (DFIT), breakouts (BKOUT), and drilling induced tensile fractures (DITF) along with mud weights used. This process can be time-consuming and challenging because of the large number of wells available for review within a field and the difficulty of finding a single solution that provide best matches for all observations. This process requires multiple iterations and is based on minimizing the error between the model and data. The process can also be subjective due to the lack of sufficient information. This paper demonstrates how statistical tools can be leveraged to streamline and reduce subjectivity of the calibration process.

1. INTRODUCTION
The process and procedure for building a MEM are well documented (Goodman & Connolly, 2007; Plumb et al., 2003; Ray et al., 2007). One of the key components in building a one-dimensional mechanical earth model (1DMEM) is to estimate the magnitudes of horizontal stresses. The horizontal stresses for an isotropic formation are commonly calculated using the following equations:
(equation)
(equation)
Where:
σ h = minimum horizontal stress.
σ H = maximum horizontal stress. σv = vertical stress (overburden). ν = Poisson's ratio.
E = Young's modulus.
α = Biot's coefficient.
Pp = pore pressure.
εh = tectonic strain in the minimum horizontal stress direction.
εH = tectonic strain in the maximum horizontal stress direction.
To solve Eq. (1) & (2), the tectonic strains in both (minimum and maximum) horizontal directions is required, however, these parameters cannot be measured directly. Generally, tectonic strains are estimated from stress measurements, such as leak-off tests (LOT) or diagnostic fracture injection tests (DFIT), however these tests only measure the minimum horizontal stress. Consequently, there are infinite possible combinations of minimum and maximum tectonic strains that can fit the LOT and DFIT measurements. Figure 1 illustrates five MEMs with different combinations of minimum and maximum tectonic strains that all match the DFIT measurement yet produce different tectonic stress regimes. Models 1 and 2 are characterized by an extensional stress regime, Models 3 and 4 by a mix of extensional and strike-slip stress regimes, and model 5 by a strike-slip stress regime.