bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Theoretical Study of the Dilation Factor of Sandstone Analogues and Pre-Salt Reservoir Carbonates
Authors: Garcia P. F. V. , Rossi D. F. , Ferreira F. H. , Justen J. C. R. , Vasquez G. F. , Lonardelli J. N.
Published: September 2023

In 4D Seismics, the dilation factor has become a very interesting rock property in recent years due to its simplicity in linearly relating rock deformation with acoustic velocity variation or time-lapse time shift. Its lab-scale characterization through coupled acoustic-mechanical tests has been demanded for uncertainty reduction of multiphysics simulations of oil field models necessary for long-term reservoirs monitoring and rock properties predictions. However, the linear nature of rock dilation factor has been found to be limited under certain stress ranges and deformation regimes to different lithologies. The authors present new results of dilation factors obtained experimentally for five lithotypes of sandstone anologues and three lithotypes of pre-salt reservoir carbonates found in Santos Basin, Brazil. The samples were subjected to drained load-unload hydrostatic, oedometer and triaxial tests with simultaneous ultrasonic data acquisition. In general, the dilation factor presented itself very large (order 101-102) for low to mid-level stresses (up to 50 MPa) and very small (order 100-101) for higher level of stresses due to the highly asymptotic behavior of longitudinal wave velocities. At the end of the work, the authors also propose mathematical relations for dilation factor variation due to infinitesimal pulse frequency variation and stress reference changes under specific hypothesis.

INTRODUCTION

In order to monitor the fluids and rocks properties variation on large extensions of rock layers on oil exploitation fields and carbon storage fields, 4D Seismics has showed to be a reliable method throughout Geophysics literature (Kasahara & Hasada, 2017). For this purpose, it is imperative that acoustic, petrophysical and geomechanical properties of different rock layers of an oil field should be well correlated among themselves. An important advance on seismic-geomechanical correlation was made by Landro & Stammeijer (2004), when they proposed a very useful correlation between first order differentiates of time shift Δt, rock layer thickness L and the longitudinal velocity of the layer Vp, simply derived from differentiation of V = L/t:

(Equation)
Analysis of Factors Influencing the Deflection Capacity of the Internal Push Point-The-Bit Rotary Steering Tool
Authors: Chen T. , Liu G. H. , He X. , Li J.
Published: September 2023

The internal push point-the-bit rotary steering tool is a new type of dynamic point-the-bit rotary steerable system. Deflection capacity is an important index to measure the performance of rotary steering tools. To study the influencing factors of deflection capacity, it is necessary to clarify the variation law of build-up rate with each influencing factor, which can provide a basis for tool design optimization and drilling process design. Based on the calculation model of the build-up rate of the internal push point-the-bit rotary steering tool, this paper analyzes the influence of BHA design, well trajectory, WOB, bit-cutting anisotropy, and formation characteristics on the deflection capacity of the internal push point-the-bit rotary steering tool. The research shows that the change in the structure size of BHA has little effect on the build-up rate. The main means to improve the deflection capacity of the tool is to select the bit with strong lateral cutting ability. With the increase of WOB, the build-up rate of the internal push point-the-bit rotary steering tool decreases. Formation characteristics significantly influence the deflection capacity of the internal push point-the-bit rotary steering tool, so formation structure research and formation anisotropy logging evaluation are very important.

INTRODUCTION

Rotary steerable drilling technology overcomes the defects of traditional steerable drilling and has the advantages of low friction, high drilling efficiency, good hole quality and, strong formation adaptability. It has become a new direction of drilling technology development. Point-the-bit rotary steering tools are more widely used than push-the-bit rotary steering tools because they have better formation adaptability and buildup ability (Xiao et al.,2006; Wang et al.,2018).

Liu et al. (2021a); (2021b) developed the internal push point-the-bit rotary steering tool (IPPRST) that is currently in the stage of making a mechanism prototype to check if the design works in principle. As a new type of dynamic point-the-bit rotary steerable system (RSS), IPPRST is very different from the existing rotary steering tools in its steering actuation structure and control method. To further optimize the tool design and realize the precise control of the wellbore trajectory, it is necessary to analyze the factors influencing the deflection capacity of IPPRST.
EDFM-AI for Calibration of Hydraulic and Natural Fracture Geometry
Authors: Liu Chuxi , Xie Hongbing , Mao Zhenyu , Yu Wei , Li Ning , Gong Yiwen , Leines Joseph , Miao Jijun , Sepehrnoori Kamy
Published: September 2023

Due to highly uncertain nature of unconventional reservoirs and difficult monitoring of the engineering effectiveness, a reliable, accurate, and efficient reservoir model calibration workflow is essential to help operators understand/plan their assets. In this paper, a collection of the non-intrusive EDFM (Embedded Discrete Fracture Model), AI (artificial intelligence), and an unconventional-targeting in-house reservoir simulator URSim is built to perform automatic history matching and uncertainty calibration of hydraulic and natural fractures (abbreviated as EDFM-AI). By implementing the proposed workflow, highly uncertain parameters, such as hydraulic fracture half-length, height, conductivity, closure coefficient, etc. are easily characterized. To validate the robustness of the proposed workflow, especially on the level of simultaneous multi-well calibration, a field-scale shale gas reservoir model is prepared with 3 horizontal wells and 200 hydraulic fractures for each well. Known set of hydraulic fracture parameters are inputted, constant gas flow rates are the well constraints, and the simulation outputs are defined as benchmark data. The history matching results showed high accuracy matches. More importantly, the maximum error between calibrated P50 and true value is only 6.8%. This novel EDFM-AI workflow sheds light on post-frac evaluation and completion optimization in unconventional resources.

INTRODUCTION

Current unconventional reservoir developments are characterized as fast-paced, real-time, and multi-well (pad-wise drilling). Many operators can drill and completion more than 100 unconventional horizontal wells per year. Under this scenario, it is crucial for operators to understand the effectiveness of hydraulic fracturing. Multitude methodologies/studies have been dedicated to study the man-made hydraulic fractures. These include fracturing simulation models (Wan et al., 2020; Weijermars et al., 2020; Leem et al., 2022), experimental methods (Magsipoc et al., 2020; Wei et al., 2021), and diagnostic technologies (Gutierrez et al., 2010; Ugueto et al., 2021; Wang et al., 2022). However, uncertainties associated with fracture geometries still remain as the most challenging problem in the unconventional oil/gas industry.
Finite Element Modeling of TBM Tunneling in Mixed-Face Ground Conditions
Authors: Witasse R. , Kashfi S. M. , Iman K. P.
Published: September 2023

This article aims at demonstrating how the use of advanced numerical methods such as the Finite Element Method can provide a reliable prediction of the different ground formation behavior and development of structural forces during tunnel construction. It will particularly illustrate how the challenges associated with TBM excavation in mixed faced conditions could be efficiently dealt with using the finite element analysis. More specially detailed numerical analysis techniques for dealing with the construction of closed twin tunnels in mixed face conditions will be provided using the FEA software PLAXIS 2D.

INTRODUCTION

With the ongoing advancement of Tunnel Boring Machine (TBM) capabilities, the ability to tunnel through mixed face conditions has been improved dramatically and the risks have been reduced significantly. Still, mixed-face ground encountered in TBM tunneling presents great design and construction challenges for the tunnel engineers. From a geological viewpoint, the mixed-face condition is defined as the simultaneous occurrence of two or more geological formations with remarkably different properties in rock/soil mechanics, engineering geology as well as hydrogeology, or the same geological formation with different weathering grades. This paper aims at demonstrating how the use of advanced numerical methods such as the Finite Element Method can provide a reliable prediction of the different ground formation behavior along with development of structural forces and remarkably help geotechnical engineers to reach cost-effective and reliable tunnel design and construction.

One of the first challenges is the consideration of the specific in-situ stress conditions with a large variation of initial orthotropic stresses from one geological formation to the neighboring one with possible significant initial locked stress in certain rocky layers that must be accounted for. The soft soil at the top of the face and the hard rock at the bottom makes it difficult to maintain a proper face-support pressure and face stability, and increases the risk of excessive cutter wear, face collapse, sinkholes, or damage to surrounding structures. This is another challenge that should also be properly addressed. To avoid undesirable ground surface settlement as well as provide appropriate safety measures and limit impact on existing assets, tunnel engineers must also be able to reliably predict the amount of settlement under all given ground conditions. The ground movement around the excavated ground mass will lead to stress changes (arching) the extend of which will define the effective load on the tunnel lining and will greatly condition its design. The mixed-face ground conditions will also induce uneven loading on the segmental lining that must be accurately assessed with the proper consideration of segment-to-segment non-linear contact interaction.
Fully Coupled Near-Wellbore Multiphase Poromechanics Simulation for CO2 Storage
Authors: Huang J. , Hamon F. , Gazzola T. , Gross H. , Cusini M. , Settgast R. R. , White J. A.
Published: September 2023

In geological CO2 storage operations, wellbore deformations and leakage pathways formations can occur around injection and abandoned wells subjected to high rates and long-term CO2 injection. To guide engineering design and prevent CO2 leakage risks, a full understanding of the underlying physics and robust numerical models are necessary to evaluate the response of underground formations in the near wellbore region and in the reservoir. In this study, a multi-scale and multi-physics open-source simulator (GEOS) is used to simulate multiphase flow and poromechanical deformations over time in three dimensions. The governing equations for mechanical deformations of the rock body and multiphase compositional fluid flow within the rock matrix are solved with a fully coupled finite element and finite volume approach. Simulation results are validated against multiple analytical solutions for multiphase flow and wellbore problems, thus demonstrating the accuracy of this advanced simulator. This work focuses on short-term processes in the vicinity of injection wells where stress evolutions, rock deformations and multiphase compositional flow and transport are simulated jointly to ensure wellbore stability and prevent damage. This fully coupled geomechanical model can simulate multiphase flow and any associated poromechanical effects within the CO2 storage site and in the surrounding formations. Such a large-scale, long-term, multi-physics simulation model is useful in many ways: it can guide operational decisions for CO2 injection, assess the containment potential and risks of a site, and analyze the wellbore stability and integrity during and after CO2 injection.

INTRODUCTION

Geological carbon sequestration (GCS) is a method to reduce atmospheric carbon concentration by storing vast amounts of CO2 in underground formations. The mechanical deformation of underground formations around CO2 injectors can lead to operational and geological hazards. If subjected to high rates and long-term CO2 injections, leakage pathways might be formed around abandoned wells and mega-faults (Nogues et al., 2011; Gan et al., 2021). Therefore, during and after CO2 storage operations, wellbore and caprock stability and integrity should not be compromised to mitigate the risk of CO2 leakage (Bachu and Bennion, 2009; Vilarrasa, 2014; Torsæter et al., 2017; Onishi et al., 2019).
Numerical Modeling of Seismic Wave Propagation in Mimicked Underground Mine Models
Authors: Mukhamedyarova Z. , Suzuki Morales K. , Suorineni F. , Madenova Y.
Published: September 2023

Underground mines are going deeper worldwide with increasing production of mineral resources and decreasing ore grade, and this fact is creating challenging conditions. This fact makes the research into mine seismicity problem paramount. This manuscript focuses on the study of seismic wave propagation in a single material medium imitating the conditions found in underground mines. Understanding how waves propagate in a medium is fundamental to better interpret real-time information for accurate rockburst prediction. For this purpose, a numerical model is developed to represent results from laboratory experiments in which a signal of AE is transmitted through the material to measure the arrival time at different sensors located in the sample. The objective of the model is to better understand the physics of wave propagation and attenuation in the medium, which cannot be directly observed in a laboratory experiment. The model will be further used for other materials and geometries to study seismic wave propagation. The study considers two configurations: the first is a solid granite cube and the second is a solid granite cube with an empty hole in the middle. These configurations are modeled in FLAC3D. The main assumptions are that materials are elastic, and the signal's waveform is sinusoidal. The study results showed wave propagation within a sample and quantified differences between modeled configurations. The model will be further used for other materials and geometries to study seismic wave propagation.

INTRODUCTION

With increasing production and depletion of mineral resources, underground mines are going deeper worldwide (Feng et al., 2019). Moreover, there are geotechnical engineering projects such as tunnels and underground laboratories located in very deep areas with complicated geology and ground conditions (Jiang, Feng, Xiang, & Su, 2010; Zhang, Feng, Zhou, Qiu, & Wu, 2012). Factors controlling seismic activity in the mine are not equivalent to those controlling the volume of the damage caused by seismicity. High stress is not the only factor causing seismicity; in fact, not all highly stressed areas are amenable to seismicity. There is a strong correlation between areas with a considerable decline in the volume of stored energy and seismically active regions. A threefold analysis is needed for the assessment of potential energy release that responds to mining works and major components of the analysis are stress, energy and loading system. Some of the conditions to be satisfied with seismic energy release from the rockmass are that (a) applied stresses have to exceed the strength of the rockmass, (b) a considerable volume of energy needs to be stored and released, and (c) energy release must be in a short period to initiate the dynamic, non-linear response of the rockmass (Kaiser, McCreath, & Tannant, 1996).
Numerical Simulation of the Effects of Casing Eccentricity on Inclined Wellbore Integrity in Salt-Gypsum Formation
Authors: Liao Jianhua , Liu Nanxiang , Chen Xuyue , Yin Siyuan , Yang Qiqi , Wang Gan
Published: September 2023

Protecting the integrity of the wellbore is a major challenge for the sustainable development of hydrocarbon resources in nitrate formation. In this paper, A numerical model for investigating the effects of casing eccentricity on inclined wellbore integrity in salt-gypsum formation is developed. The effects of creep time, eccentricity distance, cement sheath modulus of elasticity and internal casing pressure on wellbore stress were investigated using the finite element method. The results show that for a given eccentricity, the stress on the wellbore increases with creep time, affecting the integrity of the wellbore. At eccentric distances above 0.25R(the outer diameter of the cement sheath), the stress on the inner and outer walls of the cement sheath are higher than the ultimate strength of the cement sheath and damage occurs to the cement sheath. The increase in the modulus of elasticity of the cement sheath is effective at low eccentricity distances and destroys the cement sheath at high eccentricity distances. The increase in casing pressure is beneficial in protecting the integrity of the wellbore.

INTRODUCTION

The Salt Paste Formation is one of the most extensive formations covering hydrocarbon resources in the world. The typical creep nature of the salt formation leads to casing necking and deformation during production and development, which affects the development of oil and gas fields. The main directions of research on casing damage in salt formation are: (1) Proposing block-specific creep models for salt formation through triaxial creep experiments and parameter fitting (Duan et al. 2013). (2) Using numerical simulation methods to study the effects of formation creep and other factors on casing stress (Yang et al. 2021).

Taheri et al. (2020) carried out triaxial creep experiments on rock samples from the Gachsaran Formation and obtained creep parameters that differed significantly from those of salt rocks from other areas. Ge et al. (2013) combined creep experiments on salt rocks to determine creep parameters and study the effect of casing wear on casing equivalent stress under creep conditions. Zhao et al. (2020) simulated the loading and unloading processes of the injection and pumping phase cycles to investigate the effect of loading waveforms on the creep-fatigue properties of rock salt.
Preliminary Laboratory Results of Irregularly Shaped Specimens Modeled After Irregularly Shaped Stone Pillars
Authors: Wedding Z. , Agioutantis Z. , Calnan J.
Published: September 2023

Underground stone or hard rock mines typically employ the room-and-pillar mining method. Room-and-pillar mines are designed in traditional patterns with square or rectangular shaped pillars. This method is favorable because the symmetric pattern aids in optimizing mining operations. In active mines, deviations from the mine plan often result in irregularly shaped pillars. In older mines, which were designed when pillar design methodology was less developed, irregularly shaped pillars are more common than in current operations. The performance of hard rock pillars is primarily based on the pillar's stability factor and the width to height ratio, where the width is the smallest dimension of the rectangular base. The estimation of pillar strength in room-and-pillar stone mines has been studied by researchers and empirical relationships between traditional geometry (square and rectangular), and strength have been developed. Determining the strength of irregularly shaped pillars is integral to determining the pillar and regional stability. This paper presents preliminary laboratory results for specimens with irregular geometry that correspond to odd-shaped pillars and contrast to the strength of traditional specimens. Although a statistically significant difference between the UCS values measured for different specimen geometries was not established, preliminary results indicate that the intact core areas are of different dimensions.

INTRODUCTION

Underground stone or hard rock mines typically employ the room-and-pillar mining method. Room-and-pillar mines are designed in traditional patterns with square or rectangularly shaped pillars. This method is favorable because the symmetric pattern aids in optimizing mining operations. In active mines, deviations from the mine plan often result in irregularly shaped pillars.

The performance of stone or hard rock pillars is primarily based on the pillar's stability factor, which is a function of rock mass strength and the width-to-height ratio of the pillar. Width typically refers to the smallest dimension of the rectangular base. The estimation of pillar strength in room-and-pillar stone mines has been studied by researchers, and empirical relationships between traditional geometry (square and rectangular) and strength have been developed (Esterhuizen 2006; Esterhuizen et al., 2011; Lunder & Pakalnis, 1997; Martin & Maybee, 2000). Determining the strength of irregularly shaped pillars is integral to determining the pillar and regional stability, as the effective design of an underground pillar will maintain the local and global stability.
Crack Classification During Tunneling in Scale Model Testing Using Acoustic Emission
Authors: Gautam Pradeep K. , Gutierrez Marte , Wibisono Doandy Y. , Majumder Dipaloke
Published: September 2023

Detecting the damaged precursor of deep tunnel excavations using crack classification is essential for ensuring structural safety and durability since the cracking mode of a crack (tensile or shear) is connected to a rockburst. Acoustic emission (AE) is related to the mechanisms of spalling (or slabbing) and rockburst phenomena. Acoustic emission is a passive nondestructive technique that allows for classifying cracking modes by analyzing AE signals using mostly empirical relationships between rise time of amplitude (RA) and average frequency (AF). Using AF-RA plots for different rocks, transition lines could be set up to show the difference between tensile and shear cracks. The main objective of this study is to investigate the impact of excavation on tunnel spalling observed in a scale model test on a brittle synthetic. The scale model test used a cubical specimen 300 mm × 300 mm × 300 mm in size with a 51-mm diameter tunnel drilled through one of the specimen faces. The tunnel length is approximately 150 mm or half of the specimen length. Six AE WSα sensors were employed during the excavation to record the accompanying AE signals during and after tunnel excavation. The locations of micro-or mesoscale fracturing were identified, and a comprehensive analysis of the intensity, temporal-spatial distribution, and quantitative investigation of the crack classification mechanisms was conducted. A frequency–amplitude relationship of AE signals in an excavation at each stage was proposed. The lower (60-120 kHz) and the higher (120-290 kHz) frequency ranges were revealed by the fast Fourier transformation (FFT) analysis of the AE signals. The AE signals have a high frequency and low amplitude when the specimens are under relatively low loading. But, as the load increases, the AE signals shift more towards a signature of high amplitude. It is observed that there are much higher amplitude and lower frequency events close to the specimen spalling failure. Hence, it directly reflects the lower frequency range of the shear cracks, and the higher frequency range is the tensile cracks that occurred. It was found that more than 74% of the AE signals were found below the transition line, and shear cracks dominated the surface during excavation.
Numerical Investigation of Hydraulic Fracture Propagation and Proppant Transport in Multi-Well Fracturing Stimulation
Authors: Yang P. , Zhang S. C. , Zou Y. S. , Ma X. F. , Li J. M. , Tian G. , Wang M. X. , Wang J. C.
Published: September 2023

Multi-well fracturing techniques are beneficial to enhance stimulated reservoir volume and completion efficiency in unconventional oil and gas development. However, severe inter-well stress interference aggravates the uncertainty of fracture propagation and proppant transport, which poses challenges to the efficient development of reservoirs and the optimization of completing parameters. In this study, a fully coupled multi-well fracturing model considering both 3D propagating fracture and proppant transport is established based on the displacement discontinuity method and Eulerian-Eulerian approach, and the integrated model accounts for hydraulic fractures interaction (i.e., stress-shadow effects), gravitational proppant settling, proppant bridging, and the transition of fracturing fluids from Poiseuille to Darcy flow. The numerical results indicate that fracture propagation geometry under the multi-well fracturing completion is jointly affected by a variety of stress interference mechanisms, such as asymmetric fracture propagations due to the intense inter-well stress interference and the heel bias resulting from inter-stage stress interference. Because proppant transport capacity is mainly controlled by fracture geometry and width, proppant accumulation and bridging are easy to occur at smaller fracture widths, resulting in a limited proppant placement range on the whole. Through several scenarios designed to investigate the influence of key parameters, it is found that increasing well spacing and cluster spacing can reduce the inter-fracture stress interference, and promote the fracture lateral propagation and proppant distribution uniformly in each fracture. Increasing proppant concentration and reducing proppant size are effective methods to improve the propped fracture area. The obtained conclusions can be helpful to provide a better insight into fracture propagation and proppant transport in multi-well fracturing stimulation.

INTRODUCTION

In response to the demand for unconventional oil and gas development, well pads with hydraulic fracturing technology are widely used due to high efficiency and cost saving. Compared to single-well fracturing, the stress interference mechanism in multi-well fracturing is more complex, increasing the uncertainty of fracture propagation and proppant distribution. It further causes fracture-hit and premature tip screen-out, which seriously affects the stimulated volume and completion efficiency of well pads. Therefore, the research of fracture propagation geometry and proppant distribution in multi-well fracturing can contribute to the formation of hydraulic fractures with appropriate size, orientation, and propped area, which is indispensable for the economic development of unconventional reservoirs.
Comparative Study of Proppant Transport in the Vertical Fracture for High Viscosity Friction Reducers and Slickwater Fracturing with High-TDS Marcellus Shale Formation Water
Authors: Ge Xiaojing , Imqam Abdulmohsin , Bai Baojun
Published: September 2023

High viscosity friction reducers (HVFRs) have been gaining more attention and increasing in use as proppant carriers. Reusing of produced water has also been driven by both environmental and economic benefits. However, high total dissolved solids (TDS) of produced water and high reservoir temperature significantly decrease the viscoelastic properties of HVFRs even for the cationic ones, which further reduce their proppant transport capabilities. Increasing loadings of HVFRs also has very limited effects on improving their proppant transport performances under high-TDS and high-Temperature conditions. The ultimate objective of this experimental study is to investigate the injection rate effects on the proppant transport performance of HVFRs, especially under high-TDS conditions. 1 gallon per thousand gallons (GPT) slickwater and 4 GPT HVFRs were comparatively analyzed by conducting rheology measurements and dynamic proppant transport experiments with both deionized (DI) water and 30,000 mg/L TDS Marcellus formation water at 60°C. The 1 GPT slickwater was injected at a rate of 1.5 gal/min, whereas the 4 GPT HVFR was injected at a lower rate of 0.75 gal/min. The results showed that HVFRs with low injection rates were preferred when using fresh water. In contrast, slickwater with high pumping rates was preferred during produced water fracturing.

INTRODUCTION

Over the past few years, the use of HVFRs in hydraulic fracturing has been increasing as they offer operational and economic benefits compared to traditional fracturing fluids such as slickwater and guar (Hu et al. 2018; Johnson et al. 2018; Biheri and Imqam 2021a). HVFRs have been found to lower operational costs, require less equipment, exhibit better conductivity in fractured formations, and lead to production improvements (Johnson et al. 2018; Ba Geri et al. 2019; Biheri and Imqam 2021b, 2022). However, hydraulic fracturing fluids are usually prepared using fresh water, which can be costly and present challenges when freshwater resources are scarce. As a result, the industry has been exploring the use of produced or formation water, which typically has high levels of salinity and hardness. Currently, most high TDS applications are focused on the Marcellus shale formation. The Marcellus shale is a Middle Devonian source rock and reservoir that spans over multiple states in the Appalachian Basin, including Kentucky, West Virginia, Ohio, Pennsylvania, and New York. This formation has an average temperature of around 140°F (60°C) and can reach bottom hole pressures up to 6000 psi. The produced and flowback water in this area has high levels of TDS, with a typical concentration range of 30,000 ppm to 50,000 ppm. (Williams et al. 2011; Johnson et al. 2018).
Study on Evolution Law of Pore Pressure Around Well Under Different Fracturing Technology Conditions of Platform Wells
Authors: Zhao Y. F. , Wang F. W. , Huang J. B. , Zhang X. J. , Li J. , Lian W. , Liu G. H. , Huang H. L.
Published: September 2023

In recent years, some platform Wells in the Fengnan 4 well area of Xinjiang Oilfield have adopted the zipper fracturing technology in the production process, which causes the change of pore pressure near the wellbore, and then leads to the complex distribution of ground stress around the well, and increases the risk of casing deformation. Therefore, this paper considers different fracturing technology of platform wells, such as sequential fracturing of platform wells and alternating fracturing, and zipper fracturing, establish corresponding numerical models, analyzes the evolution law of pore pressure around the well, and compares and analyzes the influence of different fracturing processes on pore pressure around the middle well of the platform. The results show that the pore pressure is circularly distributed with the fracturing stage as the center during the fracturing process, and the pore pressure decreases as the distance from the center increases. During the fracturing process of the platform wells, the pore pressure diffusion regions of adjacent wells will gradually connect and influence each other. All fracturing technologies have a cumulative increase effect on pore pressure around intermediate well, and the effect of alternating fracturing in platform Wells is the most significant. The results of this study lay a foundation for the study of the variation of in-suit stress around the well during the fracturing process of the platform wells.

INRTUDUCTION

Multi-stage fracturing of horizontal Wells is a key technology for the economic exploitation of shale oil and gas. By "breaking" the reservoir as much as possible, a large and complex fracture network is formed to maximize the production of a single well (Jiang, 2014; Chen, 2016; Jiang, 2017; Li, 2013). With the spread of the "well factory" model, simultaneous fracturing techniques using alternating fracturing of two or even three wells, zipper fracturing, and cross-zipper fracturing techniques optimize the sequence and location of fracturing have been developed to further improve fracture complexity and reservoir reconstruction volume (Rafiee M, 2012; Waters G, 2009).
Sanding in Sliding-Sleeve Completed Wells in Moderately Competent Reservoir Formations – A Field Case
Authors: Xiao Yuxing , Agrawal Madhusuden , Vaziri Hans , Anthony Rosemary
Published: September 2023

A sliding-sleeve sandface completion consists of a series of blank pipe segments, isolation packers, and short sleeves in-between serving as flow ports. That geometrical configuration renders a unique sanding mechanism. Due to a large opening in the annulus rock starts to disaggregate at a lower depletion than in a cased and perforated completion, but rock aggregates tend to be mainly in blocks and chunks, which are favorable in lowering sanding risk as bigger aggregates have a higher apparent strength and require a higher fluid velocity to mobilize and transport toward the flow ports. Also, fluid flow in the annulus accumulates from the packer and converges toward the sleeve. The annular fluid velocity thus is zero at the packer and the highest at the sleeve. Therefore, an effective practical measure to mitigate and lower sanding risk is to optimize the number and locations of packers and sleeves in relation to the reservoir formation strength and sandface flow contributions.

The above sanding mechanism and practical ramifications are illustrated through historical sanding responses in 11 horizontal wells in an oil field in the UK North Sea. The reservoir formation is moderately competent and its UCS is 1000-3000 psi. The well flow rate ranges from a few thousand barrels per day (mbd) to 25mbd and most of wells have experienced watercut. Despite weak formation intervals that are expected to disaggregate from the get-go, high well rate and watercut, sanding to date is below the design tolerance. A method, including CFD modeling, was developed to estimate the annular fluid velocity and rock aggregate's pickup velocity – the minimum velocity required to mobilize rock aggregates. Through cross-referencing historical sanding responses empirical relationships between sand mass per meter length and annular fluid velocity were established for sand-prone formation intervals with and without watercut respectively. The method and empirical relationships can be used in optimizing sandface completion design in future wells and production and interventions in existing wells.
The Effect of Moisture Content on the Acoustic Properties of Regolith Analogs
Authors: Lisabeth H. P. , Schmerr N. , Lekic V. , Zhu W. , Siegler M. , Ghent R.
Published: September 2023

Successful location of icy deposits on the moon and other planets requires detailed knowledge of the physical properties of both icy and ice-free potential reservoir materials in order to design geophysical equipment, implement surveys, and interpret data. In support of this goal, we have conducted acoustic characterization experiments to measure the physical properties of dry and icy regolith simulant using synchrotron x-ray transmission microtomography and ultrasonic acoustic sensing as a function of temperature. Measurements were performed on a porphyritic basaltic glass from a cinder cone. Synchrotron x-ray microtomography was performed at beamline 8.3.2 at the Advanced Light Source (ALS). Ultrasonic measurements were made on an ultrasonic pulse-transmission system consisting of an upright cylindrical acrylic column outfitted with ultrasonic and temperature sensors. Samples were cooled to −35°C and allowed to equilibrate. Ultrasonic measurements were then taken as the samples were slowly warmed. Waveforms from experiments were then analyzed to calculate changes in acoustic velocity and attenuation as a function of temperature. Oven dried samples show only slight variations in velocity with temperature, while slightly wet samples show significant variations, suggesting water on grain surfaces plays a significant role in the physical behavior of the samples. Further work is needed to address the temperature dependence of truly dry materials versus those with adsorbed volatiles; however, these initial results suggest that temperature-dependent acoustic measurements may be useful in the location of volatiles in regolith.

INTRODUCTION

There has been evidence for trace amounts of water trapped in lunar minerals for at least a decade (Saal et al., 2008), but more recent studies have identified signs that there may be free water stored as ice within the regolith (Schultz et al., 2010). Evidence for water in the lunar regolith from remote sensing shows that the lunar south pole in particular has a significant water resource (Sanin et al., 2017). Recent spectroscopic data suggest that there is between 100 and 400 mg/g of water in the regolith, much more than ever assumed (Honniball et al., 2020). The challenge will be to locate exactly where it sits in the regolith. Planetary science has always been driven by remote sensing, but as the US, other countries and private corporations ramp up robotic and manned missions to the moon in the next decade, direct, experimental measurement of the properties of icy regolith are needed.
Study on the Influence of Injection Rate on Hydraulic Fractures Crossing Natural Fractures
Authors: Chen Houze , Zhang Guangqing , Cao Lutong , Zhang Lu
Published: September 2023

The interaction between hydraulic fractures and natural fractures will directly affect the complexity of fractures, which is an important content that needs to be paid attention to in the fracturing process. To study the interaction between hydraulic fractures and natural fractures at different injection rates, a large-scale true triaxial hydraulic fracturing simulation system was used to conduct fracturing experiments on artificial specimens with prefabricated natural fractures. Results show that increasing the injection rate can generate more complex hydraulic fractures in formations with natural fractures. Hydraulic fractures can cross natural fractures and maintain the original direction of expansion easier by increasing the injection rate. When the injection rate increases from 4ml/min to 6ml/min, the time for the blunt hydraulic fracture to reach the opposite natural fracture is reduced by 29%, and the pressure rise in the fracture increases by 0.6MPa. The cementation at the end of natural fractures is weaker. When the natural fractures are fully activated, generating new fractures at the ends of natural fractures is easier by increasing the injection rate.

INTRODUCTION

Hydraulic fracturing is an important production stimulation method in reservoir exploitation. The generated hydraulic fractures provide migration channels for oil and gas, and the complexity of hydraulic fractures also directly affects the effect of fracturing. Early studies generally believed that the hydraulic fracture is a double-wing symmetrical shape. Faults, veins, and joints in rocks are collectively called natural fractures. (Gale, J. F., Laubach, S. E., Olson, J. E., Eichhubl, P., & Fall, A. 2014) Due to the presence of natural fractures, the actual fracture shape is more complicated. The impact of natural fractures is multifaceted: increased fracturing fluid loss, premature screen-out, fracture stop propagation, formation of multiple fractures, fracture offset, and high net pressure.

There have been many experimental studies on the interaction between hydraulic and natural fractures. Lamont and Jessen (1963) found that when the approach angle between hydraulic and natural fractures ranges from 30° to 60°, hydraulic fractures can cross natural fractures and propagate along the direction orthogonal to natural fractures. Blanton (1982) and Warpinski (1987) showed that hydraulic fractures penetrate existing fractures at large stress differentials and large approach angles. At lower approach angles and stress differentials, natural fractures open, diverting fracturing fluid and preventing passage of induced fractures, at least temporarily. Daneshy (1974) studied the effect of natural fracture size and found that the crystal and matrix boundaries of granite blocks, small fractures (0.5 inches), have little or no influence on the direction of propagation of hydraulic fractures. In contrast, in a few cases, hydraulic fractures cannot penetrate large natural fractures.
Experimental Development and Investigation of Grouting Reinforced Rock for High Geo-Temperature Environment
Authors: Fan L. D. , Su Z. H. , Sun L. , Yu Y. Q. , Wang X. D.
Published: September 2023

With the increase of long and deep-buried tunnels, the disaster caused by high geo-temperature was more and more prominent. Grouting reinforcement was an important tunnel support measurement. Therefore, this study was aimed at an investigation of grouting reinforced rock under the high geo-temperature. Firstly, a new experimental device for grouting reinforced rock was designed, which could be used for laboratory tests under simulate different geo-temperature. Then, an experiment of grouting reinforced rock under different temperatures (20, 30, 40, 50, and 60°C) was carried. Finally, the results indicated that the newly developed device was applicable for the physical and mechanical properties investigation of grouting reinforced for broken rock under different temperatures, which also had the advantage of small size and flexible installation. The strength, ultrasonic velocity, and permeability resistance of grouting reinforced rock first increased and then decreased with temperature, which had an optimal value at the temperature 30°C. In addition, the positive correlation among the strength, ultrasonic velocity, and permeability resistance under different geo-temperature was also demonstrated in this paper. It was expected to make a reference for the tunnel grouting reinforcement design under the high geo-temperature environment.

INTRODUCTION

With the advancement of tunnel design and construction technology, the number of deep-buried long tunnels crossing geologically active areas increases. The high geo-temperature phenomenon (temperature exceeding 28°C during construction operations) is presented in deeply-buried long tunnels, which is due to hydrothermal activity, active fractures, and magmatic activity (Sun et al., 2021). For example, the length of high geo-temperature region accounts about 1/3 of the Gaoligong Mountain Tunnel in China, and the highest geo-temperature is about 50°C (Du et al., 2021). There are more than 10 high geo-temperature tunnels along Sichuan-Tibet Railway. The high geo-temperature not only deteriorats the construction environment but also seriously damages the performance of support materials and surrounding rock stability (Chen et al., 2022; Sun et al., 2022). Therefore, the investigation of support materials under different geo-temperature is imperative.
The Conceptual Subsurface Carbon Storage Development Planning for a Seashore Carbon Storage Site in Taiwan
Authors: Fan C.-H. (Chenners) , Wu W.-J. , Shiao T.-W. , Yang C. C. , Tseng Y.-C. , Bouchet F. , Qiu K. , Zhang H. , Zhao G. , Wang F.
Published: September 2023

As a feedback to the plan to achieve net-zero carbon emissions by 2050 unveiled by the Taiwanese government, this study, the conceptual subsurface carbon storage development plan, was conducted for a selected seashore carbon storage site to blueprint the project and make an initial feasibility assessment. The development plan includes the placement of injection and monitoring wells, conceptual design of injection wells and monitoring wells, and conceptual risk management plan and monitoring planning. In this paper, we describe the conceptual design process, summarizes the key considerations and findings from the work, and provides good references for those CCS projects at the inception stage.

INTRODUCTION

In 2022, The government of Taiwan announced the goal of "2050 Net-Zero Emissions" to combat climate change, and carbon capture and storage (CCS) is considered a critical part of the overall solution to achieve this goal. Under the mandate of the government, CPC Corporation, Taiwan has set up an ambitious plan to commence commercial carbon capture and storage (CCS) operations in 2030. The goal is to inject 5 million metric tons/yr (MTPA) and gradually build up to 14 MTPA CO2 into the selected seashore site and offshore sites.

Unlike other large-scale oil and gas field development projects, CCS projects face unique challenges because of the lack of regulations in many places around the world, the long CO2 flow chain from capture, transportation and storage, and relatively high geological and geomechanical risks for long-term containment in the data-scarce saline aquifers. To mitigate these risks, an extensive literature review of the international CCS guidelines and standards and the previous CCS projects were conducted, the relevant guidelines and standards were identified, and lessons learned and best practices from the previous CCS projects were captured. A conceptual subsurface CCS field development plan was conducted by leveraging the enriched knowledge of worldwide CCS regulations and standards, the best practices and lessons learned. The development plan mapped out the timeline, requirements and cost of the key components of the CCS projects, which paves the foundation for the successful execution of the project.
Experimental Study on Improving the Fracture Conductivity of Acid Etched Fracture for Ultra-Deep and High Stress Carbonate Reservoirs
Authors: Zhou Jun , Zhang Xudong , Zhou Linbo
Published: September 2023

With the development of carbonate reservoirs moves to the ultra-deep layer, the etched fracture would be closes quickly in the high stress. In this paper, high channel sanding method with acid fracturing technology are combined, the strength and spread ways of the different type proppant are optimized, and the fracture conductivity of continuous sanding and channel sanding are tested. The experiment result shows that high strength ceramic proppant can improve the conductivity of acid erosion fractures under high pressure. In the stress of 50MPa, fracture conductivity by high channel sanding with 86MPa ceramic could be increased by more than 51% than that of conventional acid etched fracture. The flow conductivity increase amplitude reaches more than 700% in the condition of 90MPa. By changing the sanding mode, the quantity of proppant can be saved, the pump risk can be reduced, and the stable and solid support channel can also be formed to improve the conductivity of acid etched fractures in ultra-deep carbonate reservoirs.

INTRODUCTION

With the gradual development of the Carbonate reservoir to the ultra-deep layer, the depth of the reservoir has reached 8,800 meters, and the temperature has been raised from 120°C to 180°C. The increase of reservoir depth and temperature brings many new challenges to reservoir stimulation. When the effective closure stress of the reservoir increases from 10 MPa to 55 MPa, the conventional acid etched fracture conductivity decreases by 95% (Yao et al., 2015). With the increase of closure stress, the insufficient support strength is the main reason for the rapid decrease of the fracture conductivity. In order to increase the fracture validity period after acid fracturing, the main objective is to improve the long-term etched fracture conductivity.

The existing acid fracturing is to dissolve calcareous minerals on the fracture surface, leaving the unreacted rock skeleton as the supporting point. Due to the uneven distribution of each point and its low compressive resistance, it will be crushed gradually under high closure stress. Many scholars (Yi et al., 2006, 2008, 2010, Gao et al., 2015, Wang et al., 2012,2016, He et al., 2014) tried to improve the fracture conductivity by using cross-linked acid carrying sand or compound acid fracturing, and achieved certain effect in the oilfield application. However, with the increase of reservoir depth, it becomes more and more difficult to add sand into the carbonate reservoirs. In the meantime, proppant concentration cannot be effectively increased, making it difficult to achieve the effect of high concentration proppant placement (Zhuang et al., 2014). In recent years, many researchers try to use high channel pulse sand-adding method in low permeability reservoir (Zhong et al., 2012, Wu et al., 2014, Liu, 2015, Fu et al., 2016).