bluuebunny/crossref_metadata_2025_split huggingface dataset:
Casing Stress Analysis Under Dynamic Change of In-Situ Stress
Authors: Lu Z. Y. , Zhang W. , Li J. , Xie S. Y. , Wang X. G. , Zhang H. , Song L. , Lian W. 
Published: September 2023

ABSTRACT
During hydraulic fracturing of shale oil wells, fracturing fluid enters the formation causing dynamic changes in in-situ stress in the near-wellbore region, which in turn affects the wellbore stress. This paper takes into account the change of in-situ stress caused by fracturing fluid pumped into the formation, derives the analytical solution of wellbore stress under non-uniform in-situ stress conditions, and analyzes the effects of surface pumping pressure, delivery rate, casing wall thickness, formation Young's modulus and Poisson's ratio on casing stress. The results show that: with the increase of pump pressure and Poisson's ratio of the formation, the Mises stress increase of the casing inner wall increases, and the non-uniformity of stress increases; with the increase of delivery rate and Young's modulus of the formation, Mises stress of the casing inner wall increases, and the non-uniformity of stress decreases sharply; With the increase of the casing wall thickness, the Mises stress in the inner wall of the casing decreases, but the non-uniformity increases slightly; When the Young's modulus and Poisson's ratio of the formation is high, the pumping pressure and displacement should be reasonably controlled and the wall thickness of the casing should be increased to reduce the risk of casing change.

INTRODUCTION
In recent years, more and more shale oil resources have been discovered with the continuous development of China's economy and the continuous updating of exploration technology (Xu et al., 2021; Wang et al., 2018; Ning et al., 2021). The typical terrestrial mixed-phase shale oil developed in the Lucaogou Formation of the Jimsar region has great exploration potential, and the first national terrestrial shale oil demonstration region was built in China (Kuang et al., 2012; Li et al., 2021; Wang et al., 2020; Li et al., 2021). The shale oil formation conditions in the Lucaogou Formation of the Jimsar region are complex, the reservoir is non-homogeneous, the field has a poor ability to sustain stable production, and the economic benefits of preliminary development are poor (Shen et al., 2021; Xie et al., 2020; Zhang et al., 2020; Wu et al., 2019).
The Hydration Expansion Effect on Wellbore Stability in Water-Sensitive Shales Subjected to Heterogeneous In-Situ Stress
Authors: Peng Cheng , Deng Jingen , Gao Jiajia 
Published: September 2023

ABSTRACT
Wellbore instability is a complex problem in water-sensitive shale formation and increases the cost of drilling. The hydration expansion effect changes the mechanical and strength properties of shale and causes the stresses to redistribute around a borehole drilling through the water-sensitive shale formations. the aforementioned changes are time-dependent and location-dependent. This paper provides a new predicting model for stresses around a wellbore subjected to a non-hydrostatic stress field in water-sensitive shales. With the convenience to solve the differential equations introduced by the new considered, one adopts the finite difference method and decomposes the boundary conditions into axisymmetric and deviatoric loadings. In addition, one further considers the influence of the water content on the elastic modulus, Poisson's ratio, cohesion, and angle of internal friction. The Mogi-Coulomb failure criterion is used to predict the collapse pressure. The main results show that the collapse pressure due to the hydration expansion effect is higher than drilling in the conventional formation. Two aspects are responsible for this phenomenon. On the one hand, the increasing water content decreases the elastic modulus and cohesion of water-sensitive shales, and thus decreasing the rock strength causes it to wellbore more easily to collapse. On the other hand, the hydration expansion effect causes the time-dependent safe mud pressure window to narrow. But, the conventional wellbore stress-predicting model tends to predict a wider and more conservative mud density required for borehole stability in the water-sensitive shale formation. The new model enables the drilling engineer to obtain a more accurate and safe mud density window to better deal with borehole instability.

INTRODUCTION
When drilling in a water-sensitive shale formation with water-based drilling fluid, the difference of hydraulic pressure and chemical potential will drive drilling fluid into the formation. Due to the water-sensitive clay minerals in shales, the rock around the well will swell. This phenomenon has come to be known as hydration expansion effect (Chenevert, 1969; Chenevert et al., 1970; Yew and Chenevert, 1990; Yew, 1993), which can cause the generation of hydration expansion stress and change the wellbore stress distribution. Moreover, the hydration expansion effect changes the mechanical and strength properties of shale. The aforementioned changes are time-dependent and location-dependent.
Work Hardening and Stress Memory for Granite Under Repetitious Triaxial Loading Cycles
Authors: Green A. , Benge M. , Lu Y. , Kelley M. , Bunger A. P. 
Published: September 2023

ABSTRACT
Granitic rock subjected to multiple load/unload/reload cycles is observed to have a much lower stiffness on the first loading step compared to subsequent cycles. This apparent work hardening has been proposed to provide unique insight into a rock's stress history, making this mechanism the basis for the core-based in-situ stress estimation method known as Deformation Rate Analysis (DRA). This paper presents cyclic triaxial testing of quarried granite (Cold Spring Charcoal Granite). The basic unit of the experiments is a load/unload/load/unload (LULU) cycle, where the sample is at a constant confining level and the maximum and minimum axial loads are predetermined. For multiple cycles, the peak axial stress for each cycle increases. The experiments show work hardening wherein the slope of the stress-strain relationship is significantly smaller on the first loading cycle (L) compared to the subsequent cycles. When a subsequent cycle is run to a higher peak, the strain difference increases with stress up to the prior value of the peak stress, after which it decreases, exhibiting an apparent memory of the prior peak stress. However, for these short loading cycles, the stress memory is temporary, mostly dissipating after brief unloading to atmospheric conditions and completely dissipating after 24 hours.

INTRODUCTION
Rock behavior depends upon the stress history of the rock, providing the conceptual foundations for essentially all core-based methods aimed at estimating the stress conditions from which the core was extracted (e.g. Yamamoto et al. 1990, Kang et al. 2000, Villaescusa et al. 2002, Wu and Jan 2010). In the context of the Kaiser effect and Anaelastic Strain Recovery testing, there have been studies showing stress memory can deteriorate with the time since the rock was extracted from the subsurface (Barr and Hunt 1999, Jin et al. 2009). These studies deal with stress memory induced over geological time which can deteriorate over periods of months to years. However, laboratory uniaxial compression testing of rocks is also known to induce changes in the rock which can include work hardening and stress (or strain) memory (e.g. Horibe and Kobayaski 1958, Yamamoto et al. 1990). The memory of an applied stress has been found to diminish slightly with time, but to nonetheless persists for 150 hours or more after a sample is unloaded (Yamamoto 2009). However, past investigations on the topic of observance and persistence of stress memory have been performed at relatively low stress levels under uniaxial conditions. Meanwhile, it has long been known history-dependent behaviors in cyclic loading of rocks depend heavily on confining stress (Zoback and Byerlee 1975). Therefore, this paper is aimed at examining the existence and persistence of stress memory associated with work hardening from laboratory triaxial loading cycles.
Geomechanical Tool for Evaluating Casing Deformation in Storage Caverns in Salt Dome
Authors: Ross T. S. A. , Chang Kyung Won , Sobolik Steven R. 
Published: September 2023

ABSTRACT
Sandia National Laboratories has conducted geomechanical analysis to evaluate the performance of the Strategic Petroleum Reserve by modeling the viscoplastic, or creep, behavior of the salt in which their oil-storage caverns reside. The operation-driven imbalance between fluid pressure within the salt cavern and in-situ stress acting on the surrounding salt can cause the salt to creep, potentially leading to a loss of the cavern volume and consequently deformation of borehole casings. Therefore, a greater understanding of salt creep's behavior on borehole casing needs to be addressed to drive cavern operations decisions. To evaluate potential casing damage mechanisms with variation in geological constraints (e.g. material characteristics of salt or caprock) or physical mechanisms of cavern leakage, we developed a generic model with a layered and domal geometry including nine caverns, rather than use a specific field-site model, to save computational costs. The geomechanical outputs, such as cavern volume changes, vertical strain along the dome and caprock above the cavern and vertical displacement at the surface or cavern top, quantifies the impact of material parameters and cavern locations as well as multiple operations in multiple caverns on an individual cavern stability.

INTRODUCTION
The US Strategic Petroleum Reserve (SPR), operated by the US Department of Energy (DOE), stores crude oil in solution-mined caverns in the salt dome formations of the Gulf Coast. There are a total of 60 storage caverns distributed across four different sites in Texas (Bryan Mound and Big Hill) and Louisiana (Bayou Choctaw and West Hackberry), along with several abandoned or decommissioned caverns. Each cavern is constructed and then operated through a nested series of wellbore steel casings, each cemented from the surface to near the top of the cavern.
Sandia National Laboratories (SNL) has served as the geotechnical advisor on the SPR to DOE since 1979. As part of that responsibility, SNL has long used computational geomechanical models to analyze the viscoplastic, or creep, behavior of the salt in which the oil storage caverns reside. Salt creep causes storage caverns to deform inward, thus losing volume. This loss of volume affects the salt above and around the caverns, puts stresses and strains on borehole casings, and creates surface subsidence which affects surface infrastructure. Therefore, accurate evaluation of salt creep behavior drives decisions about cavern operations.
Study and Application of Rock Breaking by PDC Bit in Ultra Deep In-Situ High-Temperature and High-Pressure Environment
Authors: Chen Changchang , Ji Guodong , Zhang Hongyuan , Sun Yuqi , Wu Qiang , Jiang Haichao 
Published: September 2023

ABSTRACT
The finite element model of the cutting tooth rock system based on ABAQUS is established by using the grid adaptive method. The average stress of each node of the cutting tooth is solved by using the secondary development of PYTHON language, and the rock breaking efficiency, real stress distribution and the influence laws of temperature and pressure of different cutting tooth shapes and rock samples are obtained. A super deep PDC bit with special non plane teeth is optimized and designed, which has achieved good results in the southern edge of Xinjiang. The research shows that the mechanical parameters of the rock change obviously under the high temperature and high pressure environment. The micro damage structure that is conducive to rock breaking by the bit is produced under the high temperature. The rock breaking efficiency is negatively related to the temperature due to the transformation of the rock from brittleness to plasticity under the high confining pressure. The double row structure of axe shaped teeth and cone shaped teeth has the best rock breaking effect under the ultra deep high temperature and high pressure environment. The drill bit footage is the longest. The problem of bit shoulder collapse is prominent under the ultra deep in-situ environment, The design of different rail double row teeth should be adopted, the design of bit stability should be strengthened, and the drilling parameters with large WOB, low speed and large displacement should be adopted.

INTRODUCTION
Onshore deep and extra deep layers where 39% of the remaining oil and 57% of the remaining natural gas are distributed [1-3]. The ultra deep layer in the south border region of Junggar basin is an important oil and gas reservoir and production increasing block in Xinjiang Oilfield. The reservoir in this block has deeply buried depth with high temperature and pressure, low ROP and long drilling cycle. The average well depth of the three risk exploration wells drilled in 2020 has reached 7205m, and the estimated well depth of well Matan 1 to be newly deployed in 2021 reaches even 8200m. There are extraordinary high pressure system and extremely thick salt gypsum layer in the deep well section, resulting in many complex situations, and long drilling cycle with the per-well average drilling cycle being 335d, and the average ROP of deep formation being less than 2m / h. Improving the ROP and reducing the complexity of accidents are the urgent needs and great challenges for the deep layer drilling in the south border region. Under the ultra-deep high temperature and high pressure environment in the south border region, the crustal stress increases. Affected by high temperature and high pressure, the rock crushing mechanism is extremely complex, which puts forward higher requirements for the design of bit [4].
Fracture Behavior of Jointed Rocks Subjected to Static Compressive Loads: An Overview
Authors: Li Peng , Cai Meifeng , Ren Fenhua 
Published: September 2023

ABSTRACT
Joints widely distributed in rock masses can possess a noticeable influence on, or even dominate, the mechanical response and fracture behavior of the rock mass. Consequently, considerable efforts have been made to explain the mechanisms involved. This article provides an overview of the mechanical properties, fracturing processes, and failure patterns of jointed rocks, which have been investigated through experimental and numerical tests. The results of these tests indicate that, under the action of static compressive load, the existence of flaws changes the stress distribution mode in jointed rocks, resulting in noticeable anisotropic characteristics. The crack evolution is mainly caused by the redistribution of stress due to the inclusion of joints. Furthermore, the fracturing process of jointed rocks often occurs at the tips of pre-existing microcracks and joints, which can lead to different failure modes. Additionally, the mechanical parameters, fracture process, and failure modes vary depending on the geometry and configuration (such as dip angle, length, and layout) of the joints. Finally, some prospects for studying the fracture behavior of jointed rocks are proposed. This work is expected to contribute to disaster prevention and mitigation in underground projects.

INTRODUCTION
The rock mass is the primary construction object for underground projects such as mining, nuclear waste treatment, carbon sequestration, and oil and gas reservoir development. The natural rock mass is a complex and inhomogeneous geological body existing in nature (Sagong et al., 2011). After long-term geological tectonic evolution, the crust is randomly distributed with different scales and directions of structural surfaces or discontinuities (such as faults, bedding planes, joints, splits, slits, soft interlayers, and holes), which intersect in the rock mass and form a special structure of discontinuous body (Li et al., 2021; Li and Cai, 2021). They will have a great effect on the mechanical behavior of the rock mass. Numerous studies indicated that many instabilities of jointed rocks are caused by nucleation, expansion, and coalescence of joints, resulting in a large number of deaths and huge losses of material wealth. For example, the typical wedge-shaped destruction along the fault on the steep slope of the Three Gorges Project and the step-type destruction of the rock slope at the Xiaowan Hydropower Station in China are all related to the joints in the rock mass (Huang et al., 2018). These disasters have seriously restricted the safe and stable development of rock engineering.
Integrating a Boundary Element Method Based Hydraulic Fracturing Simulator with a Compositional Reservoir Simulator for Well Lifecycle Simulations
Authors: Cao Meng , Zheng Shuang , Sharma Mukul M. 
Published: September 2023

ABSTRACT
In this paper we present an integrated DDM-based hydraulic fracturing-compositional reservoir simulator that can simulate each phase in the lifecycle of a hydraulically fractured well from hydraulic fracturing to shut-in, to flowback/production and gas huff-n-puff improved oil recovery. The new model is first bench marked against our in-house fully 3-D model of a penny-shaped propagating fracture by comparing the width distribution and fracture geometry. Then, the model is used to simulate production from complex fracture networks in 3-D. The results show that the reservoir drainage area is constrained by the geometry of the fracture network. The impact of pre-existing natural fractures is investigated by propagating a hydraulic fracture with and without natural fractures and conducting production from the propagated fracture networks using the compositional simulator. The results show that: (1) natural fractures can enhance well productivity from a more compact reservoir region closer to the production well, and (2) it is important to use realistic natural fracture geometry models for history matching well production. Finally, to illustrate the model capabilities, the model is used to investigate well drawdown strategies. Results show that aggressive drawdown strategies can be used in rocks with low clay content.

INTRODUCTION
Hydraulic fracturing and horizontal drilling have been employed to unlock oil and gas resources from unconventional reservoirs, including naturally fractured formations. To achieve the maximum oil and gas recovery from the subsurface, a model is needed to provide guidance on fracture treatment design and production for a well lifecycle. However, most current fracturing simulators and reservoir simulators are separate from each other, which results in restrictions for how they can be used to simulate different phases in the life of a well. In this paper, a novel fracturing-reservoir simulator is presented by integrating the displacement discontinuity method (DDM)-based hydraulic fracturing simulator with a compositional simulator for a naturally fractured formation.
Many techniques have indicated the existence of pre-existing natural fractures, such as fiber optic-based sensing, microseismic evaluation, pressure interference analysis, geochemistry analysis, and slant core wells (Cao and Sharma, 2022a; Ciezobka, 2021; Zhang et al., 2022). The presence of natural fractures can result in the formation of complex fracture networks, such as at Hydraulic Fracturing Test Site #1 (HFTS #1) and HFTS #2 (Bessa et al., 2021; Cao et al., 2023; Cao and Sharma, 2023a; Gale et al., 2021; Pudugramam et al., 2021; Shrivastava et al., 2018). Since these complex fractures can have a direct impact on the productivity of an unconventional reservoir, it is important to accurately capture the formation of propagated fracture networks with pre-existing natural fractures.
Combining Machine Learning and Physics Modelling to Determine the Natural Cave Property with Fracturing Curves
Authors: Qiao Jiangmei , Gao Fei , Wu Di , Tang Xuhai 
Published: September 2023

ABSTRACT
Currently, it is challenging to determine the geological parameters of natural caves in deep reservoirs accurately. By inheriting the advantages of Machine Learning (ML) method and physics modelling, a novel ML-Physics method is developed to determine the geological parameters of natural caves based on the data obtained during Hydraulic Fracturing (HF) operation. The process of ML-Physics method is divided into preparation-stage and operation-stage. The preparation-stage happens before HF operation without the limitation of computational time, during which the implicit relationship between cave property and fracturing curve is generated. The computational time of the operation-stage is limited because the geological parameters of natural caves should be determined in real time during HF operation. During the operation-stage, the physical modelling based inverse analysis method is carried out, in which the initial value is chosen based on the results of preparation-stage. Results show that, with the same target error, the iteration step required by ML-Physics method is much less than that of traditional inverse analysis method. With the same iteration steps, the error of ML-Physics method is lower than that of the traditional inverse analysis method. The ML-Physics method is potentially useful to optimize the HF design in real time.

INTRODUCTION
The exploitation of oil and gas resources is very important for maintaining world energy security and keeping economic development. It is necessary to determine the geometry and geological parameters of natural caves to optimize the hydraulic fracturing design (Ma et al., 2018; Ali et al., 2019). Currently, seismic tomography is widely used to detect the distribution of natural fractures and caves (Chalikakis et al., 2011; Xu et al., 2016). With the rapid development of Internet of Things (IoT) technology, large quantities of monitoring data can be obtained in real time (Wang et al., 2022). Therefore, it is critical to develop an available method to determine the geological parameters according to the evolution of fracturing curves.