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Collaborating Authors
Li, Y.
ABSTRACT The brittle to ductile transition phenomenon in deep shale gas formations is a challenge for hydraulic fracturing and is of interest from both a geological and an engineering perspective. A series of uniaxial and triaxial compressive experiments at increasing confining pressures was conducted on Longmaxi shale core plug samples from a deep gas reservoir (>3500m). The stress-strain curves at confining pressure <45MPa show the shale samples experience linear elastic response and brittle failure. The peak strength increases greatly as confining pressure increases. At 100MPa confining pressure, approximately the in-situ horizontal stress of the shale samples, the test demonstrates the existence of an elastic-plastic response and high residual strength after peak failure, indicating ductile property. The brittleness index was calculated from elastic properties and strength properties, respectively, and the correlation model was established with respect to the confining pressure. The correlation model is used to modify the log-based brittleness index from elastic response. This model reflects the ductile property of a deep shale gas formation subjected to brittle-ductile transition. This method can be applied to the nearby wells that have no drilling cores and improve the accuracy of the brittleness index evaluation. INTRODUCTION Deep shale reservoirs will be a source of oil and gas resources in the upcoming decades as shallow reservoirs are steadily depleted (Ma et al., 2021). On the other hand, developing and utilizing natural gas is an important step towards the carbon-neutral goal as the world is transferring from conventional oil to clean energy (Wang et al., 2022). Fuling Area is the one of the most commercialized shale gas fields in China and the Longmaxi shale formation has been studied extensively in the past decade (Nie et al., 2020). Yet, studying geological features in deep formation (deeper than 3500 meters depths) bring up more challenges in tectonics, sedimentology, and diagenesis. Particularly, stimulation by hydraulic fracturing didn't provide detail to the level of expectation which impacted gas production (Zhao et al., 2022). The critical problem lies in the geomechanical properties and brittleness evaluation.
- Research Report > New Finding (0.47)
- Research Report > Experimental Study (0.47)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Asia > China > Sichuan > Sichuan Basin > Fuling Field (0.99)
- Asia > China > Hubei > Jianghan Basin > Jianghan Field (0.99)
- North America > United States > Louisiana > China Field (0.97)
Cement Placement Modeling—A Review
Bois, A.-P. (CURISTEC (Corresponding author)) | Zhao, H. (China Oilfield Services Limited) | Wen, D. (China Oilfield Services Limited) | Luo, Y. (China Oilfield Services Limited) | Li, Y. (China Oilfield Services Limited) | Badalamenti, A. M. (CURISTEC) | Song, M. (China Oilfield Services Limited) | Calvo, C. (CURISIT) | Reñe, J. (CURISIT) | Liang, H. (CURISTEC)
Summary Ensuring cement sheath placement is of paramount importance for the success of a primary cementing operation. Poor mud displacement and fluid contamination can lead to cement isolation failure, loss of production, and even well abandonment. Over time, many cement placement computerized models have been developed, leading to a significant number of theoretical and case history papers. However, using these to design a cement job is difficult because their physical and mathematical assumptions are most of the time unclear, and because their application requires balancing precision with computation time. Models that are too precise may lead to very long runs, while oversimplified models could result in nonpredictive simulations. To the authors' knowledge, nothing has been published to explain how to perform efficient predictions with a cement placement computerized model. Such is the object of this paper. It presents an extensive analysis of all the available cement placement computerized models, highlighting their advantages and disadvantages and listing their assumptions. This analysis indicates that (1) the actual methods used to estimate the equivalent circulating density window are not rigorous enough; (2) there still exist a lot of uncertainties when predicting the tubular standoff; (3) modeling fluid contamination, especially when the fluids are not compatible, remains very cumbersome, if not impossible, because the true interfaces' physics is not completely considered; (4) a local contamination observed at an intermediate time can disappear at the end of the simulation due to numerical diffusion, meaning that just looking at the concentration maps at the end of placement is not sufficient to judge the efficiency of a displacement scenario; and (5) changes in geometries along the cement sheath are not considered with precision. This work allows establishing guidelines to help understanding how to manage simulation inputs and analyzing and communicating the produced results. Introduction Ensuring a good cement sheath placement is of paramount importance for the success of a primary cementing operation. Poor mud displacement and fluid contamination can lead to cement barrier isolation failure, loss of production, and even well abandonment. Over time, many cement placement computerized models have been developed, which has resulted in many papers being published, either on the underlying theories or on their use. However, nothing has been published to explain how to use them to make efficient predictions. Such is the objective of this paper.
- Europe (1.00)
- Asia (0.67)
- North America > United States > Louisiana (0.46)
- (2 more...)
- North America > United States > Mississippi > Improve Field (0.99)
- North America > United States > Louisiana > China Field (0.99)
Summary In-situ combustion (ISC) is a promising thermal enhanced oil recovery method with benefits for deep reservoirs, potentially lesser energy requirements as compared to steam injection, and low opportunity cost. Although successful ISC projects have been developed all over the world, challenges still exist including difficulties in monitoring combustion-front progress in the field, describing multiscale physical processes, characterizing crude oil kinetics fully, and simulating ISC at field scale. This work predicts combustion front propagation and the effect of thermally induced stress at the scale of an ISC pilot project. Reservoir deformation was characterized by a geomechanical model to investigate the correlation of combustion front progress with reservoir and surface deformation. We upscaled the reaction kinetics directly from combustion tube experiments and calibrated the laboratory-scale model compared with experimental measurements. We then upscaled numerical simulation to a 3D geometry incorporating a geomechanical model. The change in scale is significant as the combustion tube is 6.56 ft (2 m) in length, whereas the dimensions of the 3D model are 1,440 ft by 1,440 ft (439 m) by 1,400 ft (427 m). The elastic properties were defined by Young’s modulus and Poisson’s ratio, whereas the plastic properties were defined by a Mohr-Coulomb model. A sensitivity study examined the reliability of the model, showing the reaction progress and geomechanical responses were not significantly impacted by gridblock dimensions and reservoir heterogeneity. Finally, a field-scale model was developed covering an area of 5,960 ft (1817 m) by 4,200 ft (1280 m). We observed successful ISC simulation including ignition as air injection started. The temperature increased immediately to more than 800°C (1,400°F) based on the chemical kinetics implemented. The temperature history indicated that the combustion front propagated from the injection well into the reservoir with an average velocity of 0.16 ft/D (0.049 m/d). A surface deformation map correlated with the progress of ISC in the subsurface. Land surface uplift because of ISC ranges from 0.1 ft (0.03 m) to several feet, depending on the rock properties and subsurface events. This proof-of-concept model indicated strong potential to detect the surface movement using interferometric synthetic aperture radar (InSAR) and/or tiltmeters to monitor dynamically combustion front positions in subsurface.
- Europe (1.00)
- North America > United States > California (0.46)
- North America > United States > Oklahoma (0.28)
- (2 more...)
- South America > Colombia > Meta Department > Llanos Basin > Chichimene Field (0.99)
- North America > United States > Louisiana > Sabine Uplift > Bellevue Field (0.99)
- Asia > India > Gujarat > Cambay Basin > Balol Field (0.99)
Summary In-situ combustion (ISC) is a promising thermal enhanced oil recovery method with benefits for deep reservoirs, potentially lesser energy requirements as compared to steam injection, and low opportunity cost. Although successful ISC projects have been developed all over the world, challenges still exist including difficulties in monitoring combustion-front progress in the field, describing multiscale physical processes, characterizing crude oil kinetics fully, and simulating ISC at field scale. This work predicts combustion front propagation and the effect of thermally induced stress at the scale of an ISC pilot project. Reservoir deformation was characterized by a geomechanical model to investigate the correlation of combustion front progress with reservoir and surface deformation. We upscaled the reaction kinetics directly from combustion tube experiments and calibrated the laboratory-scale model compared with experimental measurements. We then upscaled numerical simulation to a 3D geometry incorporating a geomechanical model. The change in scale is significant as the combustion tube is 6.56 ft (2 m) in length, whereas the dimensions of the 3D model are 1,440 ft by 1,440 ft (439 m) by 1,400 ft (427 m). The elastic properties were defined by Young’s modulus and Poisson’s ratio, whereas the plastic properties were defined by a Mohr-Coulomb model. A sensitivity study examined the reliability of the model, showing the reaction progress and geomechanical responses were not significantly impacted by gridblock dimensions and reservoir heterogeneity. Finally, a field-scale model was developed covering an area of 5,960 ft (1817 m) by 4,200 ft (1280 m). We observed successful ISC simulation including ignition as air injection started. The temperature increased immediately to more than 800°C (1,400°F) based on the chemical kinetics implemented. The temperature history indicated that the combustion front propagated from the injection well into the reservoir with an average velocity of 0.16 ft/D (0.049 m/d). A surface deformation map correlated with the progress of ISC in the subsurface. Land surface uplift because of ISC ranges from 0.1 ft (0.03 m) to several feet, depending on the rock properties and subsurface events. This proof-of-concept model indicated strong potential to detect the surface movement using interferometric synthetic aperture radar (InSAR) and/or tiltmeters to monitor dynamically combustion front positions in subsurface.
- Europe (1.00)
- North America > United States > California (0.46)
- North America > United States > Oklahoma (0.28)
- (2 more...)
- South America > Colombia > Meta Department > Llanos Basin > Chichimene Field (0.99)
- North America > United States > Louisiana > Sabine Uplift > Bellevue Field (0.99)
- Asia > India > Gujarat > Cambay Basin > Balol Field (0.99)
Study on the Wellbore Shrinkage During Drilling Operation in Frozen Soil
Li, Y. (China University of Petroleum (East China)) | Cheng, Y. F. (China University of Petroleum (East China)) | Yan, C. L. (China University of Petroleum (East China)) | Yang, H. L. (China University of Petroleum (East China)) | Gao, Q. (School of Engineering, The University of Western Australia) | Han, S. C. (Chengdu University of Technology)
ABSTRACT: During drilling operations in cold regions, the frozen soil obtains strong creep characteristics, which will result in wellbore shrinkage. An unreasonable drilling fluid density may cause engineering accidents, such as blocking and stuck drills. To solve this problem, a drilling fluid density calculation model based on the power law model of frozen soil creep was established in this paper for controlling the wellbore shrinkage in frozen soil. The factors affecting the wellbore shrinkage rate in frozen soil were analyzed. A map of the wellbore shrinkage and drilling fluid density was also established. The results show that the wellbore shrinkage rate is affected not only by the physical properties of the frozen soil but also factors such as the temperature, formation depth, drilling fluid density, wellbore size, and well opening time. The density of the drilling fluid required for safe drilling in frozen soil increases as the formation depth increases, and the magnitude gradually decreases. As the temperature decreases, the drilling fluid density at the same depth gradually decreases, and the magnitude also gradually decreases. The results provide an important basis for determining the drilling fluid density and the selection of drilling methods in cold regions. 1. INTRODUCTION As the oil and gas energy situation becomes increasingly severe, unconventional oil and gas is gradually becoming the focus in the petroleum industry. In 2008, the US Bureau of Geodetic Survey conducted exploration in the Arctic and confirmed that the Arctic region is rich in oil and gas resources (Bird et al., 2008). The petroleum industry began to pay attention to the polar regions (Li et al., 2019; Vernikovsky et al., 2013; Sekretov, 2001). Compared with the conventional stratum, there are ice particles in the pores of the frozen soil. The change of temperature and pressure will cause the ice to melt, seepage and secondary solidification, which greatly changes the structure and mechanical properties of the frozen soil and makes the frozen soil own strong creep property. The unique mechanical properties of frozen soil, especially its creep characteristic, would bring a significant impact on drilling operations (Yu et al., 2013; Yang et al., 2010), such as wellbore shrinkage, stuck drilling, and casing could be crushed after cementing. These seriously hinder the exploration and development of oil and gas resources. Therefore, research on the wellbore shrinkage of frozen soil is of great significance for the development of petroleum in cold regions.
- North America > United States (1.00)
- Asia > China (1.00)
- Research Report > New Finding (0.66)
- Research Report > Experimental Study (0.66)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Yian Formation (0.99)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Mingshui Formation (0.99)
Abstract Instability of faults and weak joints of rock mass is affected by underground three-dimensional loading conditions as well as hydrostatical fluid pressure within pores and cracks. This paper presents a direct shear testing method to characterize the shear behavior of Kimachi sandstones under various pore pressures and joint roughnesses. The direct shear test was conducted under three mutually perpendicular loads and with various levels of pore pressure through effective utilization of a true triaxial loading system. An overview of the experimental method, its advantages, and results showing the usefulness of the experiment were presented. Sample permeability in the direction parallel to the joint was measured during the shear test. Introduction Instability of faults and weak joints of rock mass is affected by underground three-dimensional loading conditions as well as hydrostatical fluid pressure within pores and cracks. For example, the intermediate principal stress modifies the shear strength of rock mass, and elevated pore pressure can promote opening or sliding of the existing faults. Effects of these conditions on shear strength of rock joint are important for predicting and mitigating geohazards related to fault and rock joint instability. Direct shear test under high pore pressure using the conventional triaxial loading machine has been conducted to investigate the shear behavior of geomaterials. Carey et al. (2015) conducted a direct shear test with a cylindrical specimen using the conventional triaxial testing machine to study the effect of the anisotropy of shale on the shear behavior [1]. Zhang et al. (2019) also conducted a direct shear test to study the effect of supercritical carbon dioxide injection on the shear behavior of sandstone under high pore pressure and temperature [2]. Welch et al (2020) conducted experiments on the relationship between shear behavior and permeability of shear surfaces in cementitious materials [3]. The flow rate at the boundary between the cementitious and steel materials was measured during the direct shear test to understand the hydraulic characteristics before and after the shear slip.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.47)
Numerical Modeling of Heat Extraction in Hot Fractured Vuggy Reservoir With Thermal Hydraulic Mechanical Coupling Method Based on Discrete Fracture-Vug Model
Zhang, X. (Research Centre of Multiphase Flow in Porous Media, China University of Petroleum (East China)) | Huang, Z. (Research Centre of Multiphase Flow in Porous Media, China University of Petroleum (East China)) | Yao, J. (Research Centre of Multiphase Flow in Porous Media, China University of Petroleum (East China)) | Bi, Y. (Research Centre of Multiphase Flow in Porous Media, China University of Petroleum (East China)) | Li, Y. (Research Centre of Multiphase Flow in Porous Media, China University of Petroleum (East China)) | Lei, Q. (ETH Zurich)
ABSTRACT We develop a coupled thermo-hydro-mechanical (THM) model to study the fluid flow and heat extraction processes in hot fractured vuggy reservoirs consisting of natural fracture network and vug. Fluid flow along fractures and vugs are determined according to the cubic law and Navier-Stokes equation, and an extended Beavers-Joseph-Saffman boundary condition is adopted to couple the porous media-vug interface. Heat exchange between the interface of fracture, vug and matrix are calculated based on local thermal nonequiuilibrium. We implement a fracture constitutive model to capture the variation of fracture apertures due to normal compression-induced closure and shear dislocation-induced dilation. We conduct a series of numerical experiments to systematically analyze how hydraulic properties and heat extraction parameters are affected by the combined effects of geometrical distribution and geomechanical deformation of fracture vug networks. The results show geometrical connectivity of fracture vug networks plays a critical role in dominating the thermo-hydro-mechanical processes of fractured vuggy rocks and the geomechanical deformation of fractured vuggy reservoir exerts a secondary-order influence on the response of hydraulic and thermal performance. 1. INTRODUCTION Hot fractured vuggy reservoir consisting of rock matrix, fractures and vugs are naturally existed in the fracture/karst dominated carbonate rock, classified as one of the resource types of geothermal play [1]. Well-developed Fractures (distributed with disconnected or connected form) and vugs (isolated or connected with fractures, varied in size from centimeter to meters in diameter) are existed due to the tectonic movement and paleokarst dissolution effects [2]. Long-term circulation of cold fluid into a fractured vuggy reservoir tends to disturb the hydraulic, thermal and mechanical equilibrium of the reservoir, leading to spatial and temporal variations of fracture transmissivity, due to compression-induced closure and shear-induced dilatancy of rough fractures [3–6]. Meantime, the fractures play a vital role in enhancing the conductivity of low permeable rock mass and increase the efficiency of heat extraction. Therefore, the understanding of fluid flow and heat transport in the context of combined effects of geometrical distribution and geomechanical deformation of fracture vug networks in fractured vuggy geothermal reservoirs is of great importance for optimizing the long-term heat extraction [7, 8]. However, due to the complex geometry of fracture and vug and distinct flow patterns of different reservoir space, it is challenge to conduct numerical simulation of fluid flow and heat transfer in fractured vuggy reservoir with the consideration of geomechanical process.
- Europe (0.93)
- North America > United States (0.47)
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.48)
- North America > United States > West Virginia > Appalachian Basin (0.99)
- North America > United States > Virginia > Appalachian Basin (0.99)
- North America > United States > Tennessee > Appalachian Basin (0.99)
- (7 more...)
ABSTRACT A two-dimensional grain-based model (GBM) is developed using the finite element program RS2 to reproduce the laboratory behavior of intact and granulated Wombeyan marble subjected to unconfined compression. The term "granulated" refers to a heat-treated marble of which the grains have been separated at their boundaries due to the anisotropy of the thermal expansion of calcite grains. Medium regular Voronoi cells are employed in RS2-GBM to mimic the microstructure of Wombeyan marble. RS2-GBM is first calibrated to the Unconfined Compressive Strength (UCS) and the Young's modulus (E) of intact and granulated marble. The simulation results of elastic GBMs demonstrate that the orientation of grain boundaries has a significant impact on the generation of tensile stresses within the specimen. Next, calibrated plastic models are used to better understand the fracturing processes of intact and granulated marble under unconfined compression. The granulated marble has been suggested to serve as an analogue for a highly interlocked jointed rock mass. In this regard, a highly interlocked joined pillar with a width-to-height ratio of 1 is simulated using the calibrated model of granulated marble. The simulation results of the jointed pillar suggest a higher strength and elastic modulus than those of the calibrated model of granulated marble under unconfined compression. The failure of the pillar model is initiated by the yielding of sub-vertical joints near the walls of the pillar during the early stages of pillar loading. This condition is similar to "spalling" and "slabbing" observed in the field. With further increase of the load on the pillar, block yielding initiates from the pillar walls and then propagates towards the core. The overall failure mode of the pillar model resembles the "crushed" pillars observed in hard rock mines. 1. INTRODUCTION Heterogeneity is observed in all rock types at different scales. At the rock mass scale, heterogeneity is represented by discontinuities of various lengths, orientations, and levels of persistence as well as rock blocks of different sizes and shapes. At the rock block scale, heterogeneity is in the form of veins and cemented joints. At the laboratory scale specimen, heterogeneity is governed by the complex microstructure, various mineral grains, and small veins and fractures. All these types of heterogeneities affect the strength and deformation properties of the rock mass and therefore the design of surface and underground excavations. According to Laubscher and Jakubec (2000), depending on the scale, the strengths that need to be determined for rock engineering design include the Intact Rock Strength (IRS), the Rock Block Strength (RBS) and the Rock Mass Strength (RMS). The weakening defects (i.e., heterogeneities) that may influence these individual strength categories are shown in Fig. 1.
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Abstract The purpose of this study is to investigate the relationship between groundwater level changes and the physical characteristics of rock mass during an earthquake. We conducted laboratory experiments to study the effect of pore pressure oscillation on the permeability of fractured sandstones and granite. The rocks used were Shirahama sandstone, which has relatively high permeability, and Kimachi sandstone, which has low permeability. Inada granite was also evaluated. The effect of the amplitude difference of pore pressure on the rock permeability was investigated. Two different drainage conditions (drained and undrained) in the downstream side were tested. For both cases, we measured the permeability through the flow pump test. The results show that the permeability of the rocks tended to increase as a result of the oscillation of pore pressure. The permeability of the fractured rock was higher in Shirahama sandstone than in Kimachi sandstone and the difference was clearly confirmed. The increases in permeability were greater with the larger amplitude of pore pressure oscillation. The permeability of the fractured rocks was influenced by the crack width and roughness of the macroscopic cracks. The results show that the rock type influences the flowability of the macroscopic cracks. 1 Introduction Fluctuations in groundwater levels during an earthquake are closely related to the mechanical and hydraulic characteristics of the underground rock mass and thus critical indicators for understanding changes in underground rock mass behaviour associated with earthquakes. Changes in the hydraulic properties of underground rock mass including that of aquifers resulting from earthquakes affect various geological changes in regional groundwater flow paths, effects on fault reactivation, and changes in resource productivity in oil and gas (Manga et.al 2012). The groundwater levels during an earthquake can be classified into two types: fluctuations with shortperiod oscillation and long-term sustained fluctuations. Groundwater level changes with short-period vibrations are believed to be caused by the passage of seismic waves through the pore water of the aquifer. The most observed period of short-period oscillatory groundwater level changes is 15 to 30 s. However, sustained changes in ground water levels gradually increase or decrease over several weeks following an earthquake, and they gradually recover in some cases. According to Wang and Manga (2014), these fluctuations in groundwater levels are related to the elastic strain of porous media, undrained compaction characteristics, increase in permeability resulting from earthquakes, and their interactions. However, few examples exist in which the spatial and temporal effects of changes in hydraulic and mechanical properties of rocks during earthquakes on groundwater level fluctuations have been examined in detail. In addition, difficulties remain in observing the changes in conditions of aquifer rock mass with the passage of seismic waves. Therefore, relating the continuous groundwater level fluctuations to the physical properties of the rock mass is difficult.
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Rock Type (1.00)
Summary Here we study the feasibility of using 3D DAS-VSP data acquired inside salt to delineate the salt-sediment boundary. We analyze DAS-VSP waveform data and perform ray tracing modelling to understand the features of the direct wavefield. We calculate sediment proximity with direct arrival times and model-based arrival angles and compare the results with the salt shape in the model. Sediment proximity imaging tests of salt boundary with Kirchhoff migration using synthetic DAS data are encouraging. Both migration imaging results of the salt boundary and the salt entry points derived from model-based sediment proximity confirm the “fish mouth” of the salt bag. Migration imaging tests using real DAS data with both Kirchhoff migration and reverse time migration (RTM) are underway.
- North America > United States (0.42)
- North America > Mexico (0.42)