Xinglin Lei - Academia.edu (original) (raw)

Papers by Xinglin Lei

Earth and Planetary Science Letters

SSRN Electronic Journal, 2021

CO2 injection and storage in aquifers can cause pore pressure build up and deformation of the aqu... more CO2 injection and storage in aquifers can cause pore pressure build up and deformation of the aquifer-caprock system due to extra-fluid accumulation. Active reservoir pressure management, a concept that using brine production before or during CO2 injection to reduce reservoir pressure build up, has been suggested to avoid potential risks posed by geomechanical deformation during large-scale CO2 injection [1], [2]. Sedimentary formations usually develop heterogeneities in fluid properties and mechanical properties. When conducting CO2 injection or brine production, acquiring the in-situ information of pore pressure and fluid distribution and rock deformation would be much helpful for the project operating. In this presentation, we propose to give guidance and surveillance of the CO2 injection and brine production operations in real time using a distributed fiber optic strain sensing (DFOSS) system. We show the field and lab studies and numerical simulation results to demonstrate the feasibility and the advantages when using DFOSS for pressure management in a storage reservoir. Existing difficulties when using DFOSS are also presented.

Springer Proceedings in Physics, 2017

In order to shed light on the mechanism and characteristics of the reactivation of unfavorably or... more In order to shed light on the mechanism and characteristics of the reactivation of unfavorably oriented faults due to natural or man-made stress changes, we investigated the stick-slip behavior of precut faults having different angles to the greatest principal stress in granite rock samples using an acoustic emission (AE) technique under well-controlled laboratory conditions. The results show that the friction coefficient of a precut fault depends only on its stick-slip history, being independent of fault angle. In all cases, the fault friction drops from ~0.75 to 0.6 after a few stick-slip iterations. Many AE events preceding each stick-slip event were observed. We mapped both on-fault and off-fault microcracks in detail with their AE hypocenters. A tendency toward decreased AE activity was observed. Experimental results suggest that there are two competing mechanisms governing the evolution of the frictional properties and the damage zone characteristics of such faults. On the one hand, the fault plane is smoothed by fault slippage as a result of asperities failing on the fault plane and a fault gauge is created. On the other hand, the fault plane is roughened by new damage. As a result, both AE activity and fault friction tend to decrease, but with significant fluctuations.

Physical Modelling in Geotechnics, 2006

Journal of Geophysical Research: Solid Earth, 2021

Subtle elastic rock deformation during aquifer testing may bear hydraulic parameter (permeability... more Subtle elastic rock deformation during aquifer testing may bear hydraulic parameter (permeability and compressibility) information owing to the poroelastic hydromechanical coupling effect. Here we report that such in situ rock deformations (∼50 µε) during an aquifer pumping test are successfully measured along a vertical well by a high‐resolution fiber optic distributed strain sensing (DSS) tool with an accuracy of 0.5 µε. We investigate the feasibility of hydraulic parameter estimation at meter scale using DSS data through a coupled hydromechanical model. Both synthetic and field cases are tested with sensitivity analysis. The results indicate that the simultaneous estimation of permeability and compressibility using DSS data is possible at low noise levels. However, only non‐global near‐optimal solutions can be obtained using the applied gradient‐based inversion algorithm, because of parameter crosstalk and sensitivity problems when the data contain large noise. In particular, est...

Engineering Geology, 2021

Abstract To investigate the effect of water on the fracture mechanism and associated acoustic emi... more Abstract To investigate the effect of water on the fracture mechanism and associated acoustic emission (AE) characteristics, triaxial compression experiments were performed on dry and water-saturated tight sandstone specimens sampled from the Sichuan Basin, China. The saturated specimen was precisely controlled by different drainage conditions at the two ends. The detailed spatiotemporal distribution of AE activities and the P-wave velocities were used to examine the initiation and propagation of microcracks, as well as fault nucleation process. There are significant differences in mechanical behavior, P-wave velocity, AE activities, and fault nucleation between the dry and saturated specimens. The mechanical behavior of the saturated specimen is characterized by water weakening, with 10% and 26% reductions in peak strength and elastic modulus, respectively, in comparison with those for the dry specimen. Water enhances inelastic axial deformation and strain softening. The evolution of P-wave velocity is associated with microcracking-induced dilatancy. The decrease in P-wave velocity is suppressed in the saturated specimen, especially at the drained end. Significant attenuation of AE energy is observed in the saturated specimen, resulting into a lower event rate compared with that for the dry specimen. It is shown that the saturated specimen has an extended fault nucleation duration and lower rupture velocity. The precursory phase of dynamic failure can be clearly mapped based on strain softening, accelerating AE event rate, and decreasing b-value, as well as decreasing pore pressure (in undrained condition) or increasing injection rate (in drained condition).

$Research paper thumbnail of Study on anisotropy of Longmaxi shale using hydraulic fracturing experiment$

Science China Earth Sciences, 2021

Hydraulic fracturing reservoir reconstruction technology is crucial in the development of shale g... more Hydraulic fracturing reservoir reconstruction technology is crucial in the development of shale gas exploitation techniques. Large quantities of high-pressure fluids injected into shale reservoirs significantly alter compressional (P) and shear (S) wave velocities, rock mechanical parameters, and anisotropic characteristics. In this study, differentiated hydraulic fracturing petrophysical experiments were carried out on Longmaxi Formation shale under pseudo-triaxial stress loading conditions. The effects of stress loading methods, and water-rock physical and chemical reactions on P- and S-wave velocities and rock mechanical parameters were compared. The experimental results showed that isotropic stress loading may increase the P- and S-wave velocities and Young’s modulus of dry shale kldnsample. Furthermore, it may lead to a weakening of the corresponding anisotropy. In contrast, differential stress loading was able to improve the anisotropy of Young’s modulus and accelerate the decrease in the compressive strength of shale in the vertical bedding direction. The water-rock physical and chemical reactions prompted by hydraulic fracturing was found to “soften” shale samples and reduce Young’s modulus. The influence of this “soften” effect on the compressional and shear wave velocities of shale was negligible, whilst there was a significant decrease in the anisotropy characteristics of Thomsen parameters, Young’s modulus, and Poisson’s ratio. The negative linear relationship between the Poisson’s ratios of the shale samples was also observed to lose sensitivity to stress loading, as a result of the “soften” effect of fracturing fluid on shale. The results of this study provide a reliable reference point and data support for future research on the mechanical properties of Longmaxi shale rocks.

Journal of MMIJ, 2020

Elucidating the sealing capacity of caprock is very important because CO 2 sequestered in deep aq... more Elucidating the sealing capacity of caprock is very important because CO 2 sequestered in deep aquifers can remain there for several hundred years in the CO 2 sequestration. Threshold capillary pressure is a key property affecting sealing capacity, and therefore, the ability to measure the threshold pressure of a target rock conveniently is highly sought after. In this study, data collected during the CO 2 injection process in triaxial compression tests of mudstone supposed to be a caprock were used to measure threshold pressure via the dynamic method. These triaxial tests were conducted to study the mechanical properties of mudstone below depths of 1000 m. The threshold pressure for 23 out of 26 test samples was successfully measured. Measured values ranged from 0.54 to 1.57 MPa, which was within a reasonable range compared to the results reported by three other studies that used similar mudstone specimens. A small amount of shrinkage induced by a pore pressure decrease, which was caused by a threshold pressure, was observed in the experiment. The threshold pressure showed a positive correlation with the shrinkage, implying that this pressure might be estimated from the shrinkage. Thus, a volumetric elastic constant was calculated from the shrinkage assuming that the decrease in mean pore pressure was half of the threshold pressure. The mean volumetric elastic constant was 0.92 GPa, which was about 40% lower than that of the rocks from which the test samples were obtained. These results indicate that the shrinkage value cannot be directly used to estimate the threshold pressure, and that a correction of this shrinkage value is necessary.

Contributions to Mineralogy and Petrology, 2018

The role of aqueous fluid in fracturing in subducting slabs was investigated through a series of ... more The role of aqueous fluid in fracturing in subducting slabs was investigated through a series of deformation experiments on dunite that was undersaturated (i.e., fluid-free) or saturated with water (i.e., aqueous-fluid bearing) at pressures of 1.0-1.8 GPa and temperatures of 670-1250 K, corresponding to the conditions of the shallower regions of the double seismic zone in slabs. In situ X-ray diffraction, radiography, and acoustic emissions (AEs) monitoring demonstrated that semi-brittle flow associated with AEs was dominant and the creep/failure strength of dunite was insensitive to the dissolved water content in olivine. In contrast, aqueous fluid drastically decreased the creep/failure strength of dunite (up to ~ 1 GPa of weakening) over a wide range of temperatures in the semi-brittle regime. Weakening of the dunite by the aqueous fluid resulted in the reduction of the number of AE events (i.e., suppression of microcracking) and shortening of time to failure. The AE hypocenters were located at the margin of the deforming sample while the interior of the faulted sample was aseismic (i.e., aseismic semi-brittle flow) under water-saturated conditions. A faulting (slip rate of ~ 10 −3 to 10 −4 s −1) associated with a large drop of stress (Δσ ~ 0.5 to 1 GPa) and/or pressure (ΔP ~ 0.5 GPa) was dominant in fluid-free dunite, while a slow faulting (slip rate < 8 × 10 −5 s −1) without any stress/pressure drop was common in water-saturated dunite. Aseismic semi-brittle flow may mimic silent ductile flow under water-saturated conditions in subducting slabs.

The proceedings of the JSME annual meeting, 2008

Energy Procedia, 2014

This paper presents results of analysis of changes in stress state and fault stability related to... more This paper presents results of analysis of changes in stress state and fault stability related to a planned geological CO 2 injection at the Tomakomai offshore site, Hokkaido, Japan. Predicted slip tendency in shallow Moebetsu formations is much lower than that in deep overpressured Takinoue formations, and estimated effects of the planned injection are relatively limited in both formations. Another point is that poro-elastic stress development leads to changes in fault stability compared to that calculated based on pressure buildup alone and the initial stress state. These poro-elastic effects on fault stability are comparable to those due to pressure buildup itself.

Tectonophysics, 1999

ABSTRACT An experimental study of stick-slip is performed to examine the effect of a fault bend o... more ABSTRACT An experimental study of stick-slip is performed to examine the effect of a fault bend on the dynamic rupture propagation process. A granite sample used in the experiment has a pre-cut fault that is artificially bent by an angle of 5.6° at the center of the fault along strike, and accordingly the fault consists of two fault segments. The rupture propagation process during stick-slip instability is investigated by analyzing the records of shear strain and relative displacement measured with strain gauge sensors together with the hypocenters of AE (acoustic emission) events detected with piezoelectric transducers. The observed rupture propagation process of typical stick-slip events is as follows. (1) The dynamic rupture started on a fault segment is stopped near the fault bend. (2) The rupture propagation is restarted near the bend on the other fault segment 10.8 ms to 3.5 s after the stop of the first rupture. The delay time of the second rupture decreases with an increase in the slip amount of the first rupture or a decrease in the normal stress acting on the fault segment where the second rupture started. (3) The restarted rupture is not arrested by the presence of a fault bend, and slip occurs over the entire fault. We theoretically analyze the stress concentration near the fault bend to find that the normal stress produced by the preceding slip near the fault bend plays an important part in controlling the rupture propagation. A numerical simulation based on a rate- and state-dependent friction law is performed to interpret physically the retarded rupture in the experiment. The observed time interval of 10.8 ms to 3.5 s between the first rupture and the second is explained by the numerical simulation, suggesting that the rate- and state-dependence of rock friction is a possible mechanism for the retarded rupture on the fault.

Proceedings of Annual Conference, Japan Society of Information and Knowledge, 1999

has pubiished and dizitized many kind of geoiog 三 cal maps ， The dizitized 皿 aps are procesed on ... more has pubiished and dizitized many kind of geoiog 三 cal maps ， The dizitized 皿 aps are procesed on GIS (Geographical Informa童ion Sys童em) for the use of educa 皇ion， civil engineering ， enviromenIal problems ，皿 itiga｛ion of geological hazards so on ． We developed a simpleGISsoftware GeomapZ forviewingand analyzinggeologicai daIa． GeomapZ can read data fromDLG − formatted vector data files ， DEM − formatted elevation dala f皇les ， ras ' er image data files inBMP／TIF， and user data in text format． It is easy to create and to print high quality geological images uslng GeomapZ ． GeomapZ 重 s asuitableand easyviewer particularly for pub 正ication of geologica ｝ data in the way with CD − ROM．

Acoustic emission (AE) is an elastic wave radiated by rapid cracking in solids. As a technology o... more Acoustic emission (AE) is an elastic wave radiated by rapid cracking in solids. As a technology of nondestructive inspection, AE has a long history of development and has been applied in numerous areas including material sciences, medical sciences and engineering fields. In stressed rocks, macroscopic fracturing is preceded by a very complex pervasive evolution of some pre-failure damage. Thus, studies focusing on both fracture dynamics and pre-failure damage are a subject of interest and can be inferred from AE statistics as the number of AE events is proportional to the number of growing cracks, and the AE amplitudes are proportional to the length of crack growth increments in the rock. In Earth science, since the similarity in size distribution of earthquakes and acoustic emissions (AE) was found in the 1960s, many laboratory studies have been motivated by the need to provide tools for the prediction of mining failures and natural earthquakes. This report aims to draw an outline ...

Frontiers in Earth Science

In a recent paper [“Groundwater anomaly related to CCS-CO2 injection and the 2018 Hokkaido Easter... more In a recent paper [“Groundwater anomaly related to CCS-CO2 injection and the 2018 Hokkaido Eastern Iburi earthquake in Japan” by Sano et al. (Front. Earth Sci., 2020, 8)], the authors claimed that CO2-enriched fluid may have initially migrated through permeable channels, blocking the fluid flow from the source region, increasing pore pressure in the focal region and triggering a natural earthquake where the brittle crust was already critically stressed. The proposed model is very interesting, but the authors have not shown any quantitative evaluation supporting their conclusion. Here, through geomechanics model analysis, even under extreme conditions, which overestimate the impact of the injection, the impact of the CO2 injection on the Iburi earthquake fault, whether the deep section or shallow part of the fault, is much lower than that caused by Earth tides. In addition, no convincing mechanism exists that would allow fluid channels to heal within a short period of time and block ...

$Research paper thumbnail of Modeling of fracture-permeability of soft rocks for CCUS technologies$