bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Improved P-Wave Velocity-Stress Model for Rocks in Triaxial Compression Experiments
Authors: Wang X. Y. , Jin Y. , Li K. C. , Zhou J. 
Published: September 2023

ABSTRACT
The acoustic velocity-stress equation of rocks is important to underground stress or pore pressure prediction. The P-wave velocity has different dependencies on stresses in different directions. An improved model between P-wave velocity and stress was established. P-wave velocity was measured for sandstone at both hydrostatic and differential stress up to 60MPa in the laboratory. P-wave velocity increases with increasing confining pressure and differential stress, at different rates. The proposed model can fit the P-wave velocity measurement results very well. It provides an approach to model the stress dependency of P-wave velocity for rocks under differential stress.

INTRODUCTION
The stress dependency of elastic wave velocity of rocks is important for many geophysical applications such as pore pressure prediction and hydrocarbon detection. However, uncertainty still exists and the need to overcome it has become more critical. In the past few years, the relationships between elastic wave velocity and the effective stress in rocks has been studied by many researchers and several analytical models have been put forward. Generally, elastic wave velocity increases with increasing effective stress (Katsuki et al., 2014). In previous studies, most laboratorial measurements of P-wave velocity were made at hydrostatic pressure (Vinciguerra et al., 2005). Accordingly, most of the empirical models only focused on the dependency of elastic wave velocity on the mean effective stress, which assumes that the stresses in different directions have the same effect on the elastic wave velocities. The most popular empirical relationship originally has the following form (Zimmerman et al., 1986):
(Equation)
where VP is the wave velocities, Pe is the mean effective stress, A, B, C, D are empirical parameters determined from velocity-stress data set. Greenfield et al. (1996) proposed another wave velocity-stress model:
(Equation)
Both models are founded on the classical elastic velocity equation, in which the square of wave velocity is proportional to the elastic moduli, and the assumption that the matrix second order elastic moduli are linear functions of stress over the range of interest, and use an inverse exponential relationship to fit the effect of crack closure. (Greenfield et al., 1996) In the next few years, Zimmerman's model was developed by many researchers (Eberhart-Phillips et al., 1989; Freund, 1992; Jones, 1995; Prasad & Manghnani, 1997; Khaksar et al., 1999; Carcione & Tinivella, 2001; Pervukhina et al., 2010) to fit elastic wave velocities for different types of rocks over a wide range of effective stress levels.
Development of an Expert System for Unplanned Fall of Ground Assessment in Coal Mine Excavation Intersections
Authors: Adoko A. C. , Kaisa N. B. 
Published: September 2023

ABSTRACT
Unplanned roof falls in tunnel intersections are commonly associated with casualties, accidents, economical loss and therefore pose a serious threat for coal mine profitability. Despite the technological advance in ground control, fall of ground (FoG) in tunnel intersection often occur. Subjective data and information are inevitably used in the design of coal mine development excavations which contribute to unplanned ground instabilities. These aspects are not considered in conventional design tools. Hence, the aim of this paper is to propose expert systems capable of adequately quantify the relationship between the unplanned roof falls, support methods and the geology. Fuzzy inference system (FIS) which uses fuzzy logic to discern relationships between data is implemented in this study. FoG in tunnel intersection data were compiled from several coal mines. Expert knowledge approach was used to construct the FIS. The system parameters include the FoG size, geology, types of support and groundwater conditions. Overall, the results indicated quite good agreement with the field observations. The correct classification rate varied between 67 and 80%. It is concluded that FIS could be used to assess FoG in tunnel intersection in coal mines.

INTRODUCTION
Despite greater awareness of the environmental implication of the coal business, there is still a considerable demand for it globally. The industrial development in China, India, and Southeast Asia countries were recently reported to be the main drivers of the 0.7% rise in worldwide coal consumption (Zhironkin and Cehlár, 2021). Meanwhile, there are a wide ranges of safety issues associated with coal mining. One of them is fall of ground (FoG) which is a generic term used to describe loose rocks falling from excavation faces (roofs and side walls). Unplanned FoG in roadway intersections in coal mines present a serious threat to mine safety, as intersections are by far the most common area for FoG to happen (Mueller, 2010; Mark and Gauna, 2017). It can occur in many geological and operational situations; even with primary and secondary support structures. There are several reasons for it to happen which include over-spanned intersections, non-sufficient support, excess horizontal stress, and weak geology with low strength of rock intersection.
Effect of Alternate Fracturing on Rock Porosity and Permeability Near Hydraulic Fractures
Authors: Li Shuai , Zhang Guangqing , Zhang Liye , Wang Wenrui , Zhao Chunyang 
Published: September 2023

ABSTRACT
Stimulated Reservoir Volume (SRV) fracturing of horizontal wells significantly increases oil and gas production by generating a large amount of high-permeability main and branch fractures. This study attempts to explores the effect of fracturing sequences on smaller-scale fractures (micro-fractures, pore scales). We carried out multi-stage sequential and alternate hydraulic fracturing experiments, respectively. The effect of fracturing sequence on porosity and permeability characteristics was quantitatively analyzed from the microscopic perspective through Nuclear Magnetic Resonance (NMR) technology. The results show that: (1) the fracture deflection angle of alternating fracturing is about 50% of that of sequential fracturing, and alternate fracturing can reduce inter-fracture interference and effectively control crack propagation morphology; (2) alternate fracturing can reduce horizontal stress difference, which is more conducive to the formation of complex microcracks than sequential fracturing; (3) compared with sequential fracturing, the porosity and permeability near the fracture of alternate fracturing increased by 14.2% and 126.7%, respectively. In conclusion, alternate fracturing has more advantages in increasing the production performance of horizontal wells than sequential fracturing.

INTRODUCTION
The volume fracture formed by multi-stage fracturing of horizontal wells has significantly increased oil and gas production. It is one of the key technologies for the efficient development of unconventional oil and gas reservoirs (Shelley et al., 2012; Shelley et al., 2010). The stimulated reservoir volume (SRV) fracturing system is generally considered to be formed by main fractures and branch fractures. Multiple hydraulic fractures formed by multi-stage fracturing of horizontal wells will interact with each other. The hydraulic pressure in the formed hydraulic fractures will change the stress field distribution around the hydraulic fractures, thus affecting the initiation, extension, and development of new hydraulic fractures formed around them, thus affecting the recovery and fracturing efficiency of horizontal wells. This phenomenon is usually called the "stress shadow effect" (Bunger et al., 2012; Daneshy et al., 2012; El Rabaa, 1989; Nagel and Sanchez-Nagel, 2011).
Numerical Simulation on Damage Characteristics of Carbonate Rock Under Axial-Torsional Coupled Impact by PDC Cutters
Authors: Fu Xinkang , Huang Zhongwei , Sun Jinming , Shi Huaizhong , Zhang Jiawei , Ji Guodong , Song Hengyu 
Published: September 2023

ABSTRACT
Carbonate rock is an important oil and gas reservoir rock. Deep carbonate rocks are of high strength, hardness, abrasiveness and poor drillability, which will cause various problems as follows: PDC cutter collapse, serious wear and low drilling efficiency. Axial-torsional coupled percussive drilling can improve the drilling speed of deep hard rocks including carbonate rock. Therefore, a numerical model of axial-torsional coupled impact rock breakage was established for carbonate rocks. The damage characteristics of carbonate rock caused by spherical cutter and axe-shaped cutter under different impact parameters were analyzed. The simulation results reveal that the impact force of two kinds of cutters increases with the increase of impact speed. The torque of PDC cutters increases with the increase of torque amplitude. Under the same conditions, the tensile damage of carbonate rock caused by axe-shaped cutter is more obvious under the action of axial-torsional coupled impact and the tensile damage area under axe-shaped cutter tends to be connected. Additionally, the damage caused by PDC cutter to carbonate rocks is mainly tensile damage, supplemented by compressive damage. This work is instructive in revealing the effect of PDC cutter on breaking carbonate rocks under different impact parameters.

INTRODUCTION
As an important oil and gas reservoir rock, 50% of the world's proven oil and gas resources are stored in carbonate rocks (Al-Shargabi et al., 2022). Deep carbonate rocks are of high strength, hardness, abrasiveness and poor drillability. Conventional rotary bit drilling method has many problems in rock breaking, such as serious wear and low drilling efficiency (Jamali et al., 2019). Axial-torsional coupled percussive drilling has higher penetration rate in breaking hard rock, such as carbonate rock (Saai et al., 2020). And some oil companies designed some special-shaped PDC cutters (Zhu et al., 2022), such as axe-shaped cutter and spherical cutter. However, the characteristics of breaking carbonate rock by PDC cutters under the action of axial-torsional coupled impact is not clear. Therefore, it is of great significance to investigate the effect of different impact parameters on breaking carbonate rock by PDC cutters under the action of axial-torsional coupled impact.
Formation Sampling Optimization Using Borehole Images and Acoustic Data in Tight Gas Sand Reservoir
Authors: Hamadas Manel , Sokhal Abdallah , Bazine Badreddine 
Published: September 2023

ABSTRACT
In this paper, we present an integrated workflow designed to characterize the natural fracture systems and to optimize fluid sampling in a very complex and heterogeneous fractured tight sandstone reservoir. Conventional techniques are not suited for tight formations, and to overcome this challenge it is imperative to implement and enhance new technology. This advanced workflow aims to decrease uncertainties at different stages of the reservoir lifecycle through combined advanced tools. Electrical and Acoustic borehole images, Full Acoustic Waveform, and MDT Dual packer were incorporated in this study to optimize fluid sampling and increase the success rate of economic recovery.

INTRODUCTION
Almost all hydrocarbon reservoirs are affected in some way by natural fractures, but the effects of fractures are often poorly understood and largely underestimated. In tight reservoirs, natural fractures created through complex tectonic activity help create secondary porosity and promote communication between reservoir compartments (Irofti et al., 2022). However, these highly permeable channels sometimes short-circuit fluid flow in the reservoir, causing premature production of water or gas and rendering secondary recovery initiatives ineffective (Bratton et al., 2006).Since the introduction of the wireline formation testers in 1955, these tools have provided the oil and gas industry with measurements for the determination of formation pressure, fluids in-situ as well as giving formation fluid samples for identification and analysis. This conventional technique is well suited for thick and permeable clastic formations. Under low porosity and low permeability conditions, the wireline formations testers become unsuitable as they may not be able to isolate the zone, may miss a thin zone or in a formation with very low permeability, the contact area with the packer may be too small to let the fluid flow. When testing is to be conducted out employing pricey rig operations, evaluation of heterogeneous reservoirs using open hole logs and cores carries some risk (Aoun, Soto, et al., 2022; Ifrene et al., 2023) The modest success rate of sampling operations, fluid sampling presents a challenge in tight reservoirs, therefore it is imperative to adopt innovative techniques. To overcome this challenge, we proposed in this article a workflow to increase and optimize the success rate. This includes the combination of borehole image logs and acoustic waveforms, two technologies aiming to enhance formation sampling and recovery rate.
Sand Production Evaluation: Experimental Testing, Analytical Solution, Numerical Simulation and Field Implications
Authors: Asadi Sadegh , Khaksar Abbas 
Published: September 2023

ABSTRACT
Sand production prediction is essential from the early stages of field development planning for well completion design and later for production management. Unconsolidated and weakly consolidated sandstones are prone to fail at low flowing bottom hole pressures during hydrocarbon production. To predict the sand-free drawdown, a robust sand production prediction model that integrates near-wellbore and in-situ stresses, rock mechanical properties, well trajectory, reservoir pressure, production and depletion trends is required. Sanding prediction models should be calibrated with field data such as production and well tests observation. In the absence of field data, numerical techniques can provide a reliable estimate on potential onset and severity of sanding at various reservoir pressures. In this study, analytical and finite-element numerical models are independently used to predict the onset and extent of sanding in a high-rate gas well with poorly consolidated sandstone reservoir. The analytical method uses a poro-elastic model and core-calibrated log-derived rock strength profiles with an empirical effective rock strength factor (ESF). In the study, the ESF was calibrated against documented field sanding observation from a well test extended flow periods at the initial reservoir pressure at low drawdown pressure. This sanding model ESF was then verified against the sanding observation from another well test with higher drawdown pressure as well as with the sand-free production conditions from two producers that have been on line for several years.
The numerical method uses a poro-elasto-plastic model defined from triaxial core tests. The rock failure criterion in the numerical method is based on a critical strain limit (CSL) corresponding to the failure of the inner wall of thick-walled cylinder core tests that can also satisfy the existing wells sanding observations in the production well tests. To validate the onset and severity of sanding predicted by the analytical model, numerical simulations for an identical sandstone interval were developed to investigate the corresponding CSL. Results showed the numerical model is also able to predict the onset of sanding observed during well tests with plastic strains exceeding the CSL defined from TWC test simulations. This combined analytical and numerical modelling calibrated with field data provided high confidence in the sanding evaluation and their application for future well completion and sand management decisions. The analytical model was finally used for sanding assessment over field life pressure condition because of its processing simplicity, speed and flexibility in assessing various pressure and rock strength scenarios with sensitivity analysis over the whole production interval in compared with the numerical method which is more suitable for single-depth and pressure condition modelling.
Prediction of Heavy Oil Production Based on Geomechanical Analysis in Coupled Thermo-Hydro-Mechanical Process
Authors: Li Dengke , Gao Yanfang , Chen Zupeng , Li Yanchao , Shen Shijie 
Published: September 2023

ABSTRACT
The geomechanical response concerning porosity, permeability, and water saturation, will directly affect the prediction of oil production as well as the economic benefits of oil fields. In this paper, different models are established for the three stages of the SAGD (Steam Assisted Gravity Drainage) production period by using the coupled thermo-hydro-mechanical method, aiming to understand the influence of rock volumetric dilation or compression on oil yield. The relationship between the evolved flow parameters and the deformation parameter characterized by volumetric strain is proposed, then a mathematical model with the dilation volume and yield is derived. The ratio of the new model considering reservoir geomechanics and the conventional model is exhibited as a function with the bulk strain, and it is found that different volumetric strains will affect the yield ratio of the new model and the conventional model. The stages of the steam chamber ascending and expanding laterally are selected for typical case studies, and the predicted yield of the new model is about 1.24 and 1.17 times, respectively, that of the conventional model when the volume strain is 2%. This method can help oilfield engineers obtain more accurate heavy oil production, and quantitatively evaluate the significance of reservoir geomechanics in the process of SAGD.

INTRODUCTION
In recent years, with the massive exploitation of conventional oil and gas and the discovery of unconventional reservoirs, how to exploit unconventional reservoirs efficiently has become increasingly important. For example, hybrid thermal recovery processes have become a primary technique used to improve the recovery performance of post steamed heavy oil reservoirs and been used to exploit marginal heavy oil reservoirs effectively. SAGD (steam assisted gravity drainage) is an efficient technique for recovering heavy oil, as proposed by Butler et al. (1981). SAGD technology develops heavy oil through the use of steam drive and gravity flooding. By transforming the reservoir through the injection well, water and heated heavy oil flow downward under the action of gravity, so as to improve the efficiency and production of heavy oil exploitation (Butler et al., 1981).
Numerical Simulation of Hydraulic Fracturing Process of Shale in Jiyang Depression Layer
Authors: Chen Zupeng , Gao Yanfang , Li Yanchao , Shen Shijie , Li Dengke 
Published: September 2023

ABSTRACT
As an important unconventional energy source, shale oil is widely distributed and has huge reserves, which is one of the alternative energy sources in the future. In this paper, the shale reservoir of the grain-bearing layer of Well A in the Jiyang Depression in the Bohai Bay Basin was used as the research object to carry out the numerical simulation of hydraulic fracture. Firstly, the 3D geological model of shale oil reservoir is simplified, the spatial distribution of reservoir fracturing fractures and textured shale is described, and the 3D geometric model of the reservoir is established by ABAQUS. Secondly, based on the stress balance equation and fluid continuity equation, traction separation criterion and flow equation of cohesion unit, a coupled numerical model of reservoir stress-seepage flow is established. Then, using on-site production and original in-situ stress as the loading conditions, the required parameters are input into the model, and the finite element method is used to solve the model. It is found that the simulated fracture morphology is similar to the actual single hydraulic fracture morphology, the pressure accumulation is mainly concentrated in the reservoir, and the Mises stress at the water injection point reaches a maximum at the beginning of injection, and the stress gradually decreases as the fracturing progresses. The pore pressure in the reservoir is mainly distributed near textured shale reservoirs and fractures, and the pore pressure near the fractures can reach more than 10MPa. The width reaches a stable value after cracking, indicating that hydraulic fracturing can effectively control fracture spread and produce a relatively stable fracture structure.

INTRODUCTION
The Jiyang depression in the Bohai Bay Basin is rich in shale oil resources, with a resource volume of 4.1 billion tons. The shale in the Jiyang Basin is characterized by low evolution, deep burial, large shale thickness, and abnormally high temperature and high pressure. The shale structure is so dense that there are almost no cracks in the cores taken from deep underground, but there are obvious lamellar structures. Lamellar shale bedding developed a lot, the height of the development of bedding joints, bedding joints in the state of unfilled or semi-filled, with high seepage capacity. The lamellar facies has the characteristics of high porosity, large pore diameter, and good connectivity. According to the oil testing results, the shale facies with the most industrial oil flow are shale laminar argillaceous limestone and limestone argillaceous mudstone intercalated with thin sandstone or carbonate rock.
Constitutive Relation of Shale Poroplasticity Based on Prandtl-Reuss Model
Authors: Qi Jiayue , Zhang Guangqing , Wu Anan , Ma Fanxin , Zhang Yiwei 
Published: September 2023

ABSTRACT
The effective stress coefficient is important to describe the stress and deformation of rock. However, when shale is in the plastic stage, the mathematical expression of the effective stress coefficient is still unclear. Based on Prandtl-Reuss model, the incremental constitutive relation of shale in elastic-perfectly plastic condition is established. The plastic effective stress coefficient of shale in this condition is obtained. The mathematical expression of the effective stress coefficient tensor elastoplasticity is proposed by defining the correction function. The mechanical properties of shale are analyzed when the correction function is a power function by combining the specific parameters of shale. The results show that when 0 ≤ n ≤ 0.932, the effect of pore pressure on the plastic effective stress coefficient is related to the confining pressure. The plastic effective and Biot effective stress coefficients are gradually equal with the increase of pore pressure. Combining the four basic operations and composite operations of specific functions allows a correction function suitable for the plastic effective stress coefficient of shale.

INTRODUCTION
Shale is a typical rock used to develop oil and gas resources. With the decreasing reserves of conventional oil and gas resources and the increasing proven reserves of unconventional oil and gas resources such as shale oil, the study of shale is getting more and more attention. There are many natural microcracks and micropores in shale (Zhang et al., 2022), which cannot be ignored for their impact on rock mechanical properties. The free-moving fluid in micro cracks and micropores changes the mechanical behavior of porous media (Cheng, 1993; Xu 2001) and generates pore pressure in micro cracks and micropores of porous media. The difference between the effective stress and the total stress acting on the rock solid skeleton makes the mechanical properties of saturated rock with pore pressure significantly different from those of dry rock (Berryman, 1992; James G, 1992; Diansen Yang, 2010; Dong Chen, 2016; Liu, 2018; A M Gorshkov, 2020). Schrefler (1998) extended the saturated single-phase theory to the multiphase fluid. Zimmerman (2000) applied the pore elasticity theory to the fractured media. However, none of the above scholars have considered the issue of deep shale deformation entering the stage of pore plastic deformation. In the process of deep oil and gas extraction, the brittle shale will transform into elastic-plastic shale due to the high-temperature field, high-stress field, and high pore pressure field (Li et al., 2020; Crisci Eleonora, 2021).