New Insights on Characteristics of the Near-Wellbore Fractured Zone from Simulated High-Resolution Distributed Strain Sensing Data

Summary Rayleigh frequency-shift-based distributed strain sensing (RFS-based DSS) is a fiber-optic-based diagnostic technique, which can measure the strain change along the fiber. The spatial resolution of RFS-based DSS can be as low as 0.2 m, and the measuring sensitivity is less than 1 μɛ. Jin et al. (2021) presented a set of DSS data from the Hydraulic Fracture Test Site 2 project to demonstrate its potential to characterize near-wellbore fracture properties and to evaluate perforation efficiency during production and shut-in periods. Extensional strain changes are observed at locations around perforations during a shut-in period. At each perforation cluster, the observed responses of strain changes are significantly different. However, the driving mechanisms for the various observations are not clear, which hinders accurate interpretations of DSS data for near-wellbore fracture characterization. In this study, we applied a coupled flow and geomechanics model to simulate the observed DSS signals under various fractured reservoir conditions. The objective is to improve understanding of the DSS measurements and characterize near-wellbore fracture geometry. We used our in-house coupled flow and geomechanics simulator, which is developed by a combined finite-volume and finite-element method, to simulate strain responses within and near a fracture during shut-in and reopen periods. Local grid refinement was adopted around fractures and the wellbore, so that the simulated strain data can accurately represent the DSS measurements. The plane-strain condition is assumed. Numerical models with various fracture geometries and properties were constructed with representative parameters and in-situ conditions of the Permian Basin. The simulated well was shut-in for 4 days after producing 240 days, and reopened again for 1 day, following the actual field operation as shown in Jin et al. (2021). The characters of the strain changes along the fiber were analyzed and related to near-wellbore fracture properties. A novel diagnostic plot of relative strain change vs. wellbore pressure was presented to infer near-wellbore fracture characteristics. The impacts of permeability and size of the near-wellbore-stimulated region, fracture length, and near-perforation damage zone on strain responses were investigated through sensitivity analysis. The strain responses simulated by our model capture the observed signatures of field DSS measurements. During the shut-in period, clear positive strain changes are observed around the perforation locations, forming a “hump” signature. The shape of the “hump” region and peak value of each “hump” are dependent on the size and permeability of the near-wellbore fractured zone. Once the well is reopened, the strain changes decrease as the pressure drops. However, in one cycle of shut-in and reopen, the strain-pressure diagnostic plot shows path dependency. The discrepancy between the shut-in and reopen periods is highly influenced by the properties of near-wellbore fractured zones. The differences in the strain-pressure diagnostic plots can help to identify the conductive fractures. This study provides better understandings of the DSS measurements and their relations to the near-wellbore fracture properties, which is of practical importance for near-wellbore fracture characterization and completion/stimulation optimization.

Experimental study on bending behavior of glulam beams strengthened with bamboo scrimber

PurposeIn view of the defects of glued wood beams, a new composite member – reconstituted bamboo board reinforced glued wood beams is proposed to improve the bearing capacity of glued wood beams.Design/methodology/approachThe bending test studied the ordinary glulam beams and the reinforced glulam beams with different layer numbers and different layer thicknesses by comparing with six kinds of glulam beams strengthened with bamboo scrimber and one kind of ordinary glulam beams and used the method of third-point stepwise loading on the glulam beams strengthened with bamboo scrimber.FindingsThe bamboo scrimber improved the bending behavior of the ordinary glulam beams. The 10 mm bamboo scrimber layer can meet the requirements of the maximum ultimate bending capacity and minimize the defects. So 10 mm bamboo scrimber layer was the optimal thickness. During the loading process, the strain change of the normal section of the reconstituted bamboo board reinforced glued wood beam basically conforms to the plane section assumption.Originality/valueThe bending rigidities of the glulam beams strengthened with bamboo scrimber increased up to 28.25%, 8.53% and 76.67%, and the ultimate bending capacity increased from 83.44% to 99.34% with the increase of the bamboo scrimber plate layers (the replacement rate). The ultimate bending capacities and the bending rigidities of the glulam beams strengthened with bamboo scrimber increased to 52.32%∼60.18% and 90.07%∼99.34% with the changing of the bamboo scrimber thicknesses from 7.1 mm to 25 mm.

Eradication, Strain Preservation, Strain Change — Outcomes of Helicobacter pylori Therapy

Relevance. If we reduce the treatment exclusively to the eradication of Helicobacter pylori (Hp), the question of monitoring the results of anti-Hp therapy is controversial, given the widely known data on the detection of Hp, including virulent strains of Hp, in most healthy individuals.The aim of the study: to track the dynamics of stomach colonization with various Hp strains in patients with gastric ulcer and duodenal ulcer (PUD) immediately after the use of standard three-component anti-Hp therapy (AHT) and 1.5–2 months after AHT.Methods. Genotyping of Hp strains was carried out by the VNTR method together with the determination of the cagA gene.Results. Assessment of the results of AHT in the form of «eradication of Hp — re-detection of Hp» (i. e., without taking the determination of Hp strains into account) showed less reliability in the differences than the «eradication — preservation of the strain or change of the strain» score in patients with PUD; in addition, the differences between the initial bacteriological picture and that observed immediately after AHT were on the verge of reliability, while the differences between the initial bacteriological picture and that observed after 1.5–2 months had a high degree of reliability. The number of eradications increased (eradication achieved immediately after AHT was not preserved, except for one) and the number of cagA-containing strains decreased (due to new eradication detected at late follow-up periods and due to a change in strains) in long-term follow-up in patients with PUD.Conclusion. Since all patients with PUD achieved clinical remission, which lasted for the next 1.5–2 months, the success of AHT should not be unambiguously associated with the eradication of Hp; the restoration of the organism's colonization resistance to Hp after a course of therapy is more likely.

Deformation Failure and Gas Seepage of Raw Coal in Alternate Loading and Unloading by Stages

In this paper, the cyclic loading and unloading confining pressure tests of raw coal samples were carried out by using the "Triaxial seepage test device of thermal fluid solid of coal and rock" developed by Chongqing University. The conclusions are as follows: (1) The axial strain change rate ε1´, the radial strain change rate ε3´ and the permeability change rate k´ under unit stress state are used to represent the sensitivity of axial stress and confining pressure to deformation and permeability characteristics of samples under unit stress state. (2) At the initial stage of unloading the confining pressure, the confining pressure has a greater influence on the permeability of the sample. At the initial stage of loading confining pressure, the confining pressure has a greater influence on the radial strain of the specimen. During the subsequent loading and unloading process, the confining pressure of loading and unloading has a greater influence on the permeability of the sample, and a smaller influence on the axial strain. The loading axial stress has a greater influence on the axial strain of the sample, and a smaller influence on the permeability of the sample. (3) When the axial stress is constant, the increase range of sample permeability increases with the increase of unloading confining pressure range, and the decreasing range of sample permeability increases with the increase of loading confining pressure range, and the increase range of sample permeability under unloading confining pressure is higher than that under increasing confining pressure. (4) In the process of loading axial stress and loading confining pressure, the permeability of samples decreases nonlinearly with the increase of principal stress difference, while the permeability of samples increases nonlinearly with the decrease of principal stress difference in the process of unloading confining pressure.

Tilt and strain change during the explosion at Minami-dake, Sakurajima, on November 13, 2017

We herein propose an alternative model for deformation caused by an eruption at Sakurajima, which has been previously interpreted as being due to a Mogi-type spherical point source beneath Minami-dake. On November 13, 2017, a large explosion with a plume height of 4200 m occurred at Minami-dake. During the 3 min following the onset of the explosion (November 13, 2017, 22:07–22:10 (Japan standard time (UTC + 9); the same hereinafter), phase 1, a large strain with changes up to 120 nstrain was detected at the Arimura observation tunnel (AVOT) located approximately 2.1 km southeast from the Minami-dake crater. After the peak of the explosion (November 13, 2017, 22:10–24:00), phase 2, a large deflation was detected at every monitoring station due to the continuous Strombolian eruption. Subsidence toward Minami-dake was detected at five out of six stations, whereas subsidence toward the north of Sakurajima was detected at the newly installed Komen observation tunnel (KMT), located approximately 4.0 km northeast from the Minami-dake crater. The large strain change at AVOT as well as small tilt changes at all stations and small strain changes at the Harutayama observation tunnel (HVOT) and KMT during phase 1 can be explained by a very shallow deflation source beneath Minami-dake at 0.1 km below sea level (bsl). For phase 2, a deeper deflation source beneath Minami-dake at a depth of 3.3 km bsl was found in addition to the shallow source beneath Minami-dake, which turned inflation after the deflation that occurred during phase 1. However, this model cannot explain the tilt change of KMT. Adding a spherical deflation source beneath Kita-dake at a depth of 3.2 km bsl can explain the tilt and strain change at KMT and the other stations. The Kita-dake source was also found in a previous study of long-term ground deformation. Not only the deeper Minami-dake source MD, but also the Kita-dake source deflated due to the Minami-dake explosion.

Influence of Unloading Conditions of Confining Pressure on the Compressive Strength and Permeability of Deep Mudstone

To investigate the compressive strength and permeability of deep mudstone under stress disturbance, a triaxial rheometer is used to conduct seepage experiments on mudstone specimens with different buried depths under triaxial compression and unloading conditions. The experimental results show that the compressive strength of mudstone specimen with a depth of 1000 m is much lower than that of specimen with a depth of 200 m, and the compressive strength of mudstone increases with the increase in confining pressure. Under constant axial pressure and unloading of the confining pressure, the mudstone with a depth of 200 m exhibits brittle failure, and the strain fluctuates in a pointwise manner with the increase in axial stress. In this case, the mudstone with a depth of 1000 m exhibits a transition from brittle failure to ductile failure, and the strain fluctuates linearly with the axial stress. Further, when the volumetric strain change reaches 0.01, it shows an oblique “Z” fluctuation. During the initial stage of unloading of confining pressure, the permeabilities of both the mudstone specimens (with depths of 200 and 1000 m) decrease gradually. As the confining pressure is unloaded, the permeability of mudstone with a depth of 1000 m increases. Until the specimen is completely destroyed, the permeability of mudstone increases rapidly. Overall, this study can serve as a useful reference for analyzing the engineering disasters associated with deep rock mass, tunnel ventilation, and gas storage.

Tilt and strain change during the explosion at Minami-dake, Sakurajima, on November 13, 2017

We herein propose an alternative model for deformation caused by an eruption at Sakurajima, which have been previously interpreted as being due to a Mogi-type spherical point source beneath Minami-dake. On November 13, 2017, a large explosion with a plume height of 4,200 m occurred at Minami-dake. During the three minutes following the onset of the explosion (November 13, 2017, 22:07–22:10 (Japan standard time (UTC+9); the same hereinafter), phase 1, a large strain change was detected at the Arimura observation tunnel (AVOT) located approximately 2.1 km southeast from the Minami-dake crater. After the peak of the explosion (November 13, 2017, 22:10–24:00), phase 2, a large deflation was detected at every monitoring station due to the continuous Strombolian eruption. Subsidence toward Minami-dake was detected at five out of six stations whereas subsidence toward the north of Sakurajima was detected at the newly installed Komen observation tunnel (KMT), located approximately 4.0 km northeast from the Minami-dake crater. The large strain change at AVOT as well as small tilt changes of all stations and small strain changes at HVOT and KMT during phase 1 can be explained by a very shallow deflation source beneath Minami-dake at 0.1 km below sea level (bsl). For phase 2, a deeper deflation source beneath Minami-dake at a depth of 3.3 km bsl was found in addition to the shallow source beneath Minami-dake which turned inflation after the deflation obtained during phase 1. However, this model cannot explain the tilt change of KMT. Adding a spherical deflation source beneath Kita-dake at a depth of 3.2 km bsl can explain the tilt and strain change at KMT and the other stations. The Kita-dake source was also found in a previous study of long-term ground deformation. Not only the deeper Minami-dake source MD but also the Kita-dake source deflated due to the Minami-dake explosion.

SIMULTANEOUS STRAIN AND TEMPERATURE MEASUREMENT USING COMBINED FIBER AND FIBER BRAGG GRATING SENSORS

We propose here a new technique for simultaneous strain and temperature measurement using a Fiber Bragg Grating sensors. This technique employs an interferometric detection using two Fiber Bragg Gratings. A fiber Bragg grating is used as a reference while another fiber Bragg grating and a length of a bare fiber are used as the two sensing elements. As the temperature and strain change, the length of the sensing elements, (Fiber and Fiber Bragg Grating) change. These changes result in a phase and wavelength shifts. To measure these effects we use a Folded Mach Zhender interferometer, and a detection system made out of two photodiodes and data processing system. The sensitivity and dynamic range are analyzed and presented.

Tilt and Strain Change During the Explosion at Minami-dake, Sakurajima, on November 13, 2017

We herein proposed an alternative model for deformation caused by each eruption at Sakurajima, which have been previously interpreted as being due to a Mogi-type source beneath Minami-dake. On November 13, 2017, a large explosion with a plume height of 4,200 m occurred at Minami-dake. During the three minutes following the onset of the explosion (November 13, 2017, 22:07–22:10 (Japan standard time (UTC+9); the same hereinafter), phase 1, a large strain change was detected at the Arimura observation tunnel (AVOT) located approximately 2.1 km southeast from the Minami-dake crater. After the climax of the explosion (November 13, 2017, 22:10–24:00), phase 2, a large deflation was detected at every monitoring stations due to the continuous Strombolian eruption. Subsidence toward Minami-dake was detected at five out of six stations whereas subsidence toward the north of Sakurajima was detected at the newly installed Komen observation tunnel (KMT), located approximately 4.0 km northeast from the Minami-dake crater. The large strain change at AVOT during phase 1 can be explained by a very shallow deflation source beneath Minami-dake at 0.1 km below sea level (bsl). For phase 2, a deeper source beneath Minami-dake at a depth of 3.3 km bsl deflated in addition to the shallow source beneath Minami-dake, which turned inflationary after the deflation obtained during phase 1. However, this model cannot explain the tilt change of KMT. Adding a spherical deflation source beneath Kita-dake at a depth of 3.2 km bsl can be explain the tilt and strain change at KMT and the other stations. The Kita-dake source was also found in a previous study of long-term ground deformation events. Not only the deeper Minami-dake source M D but also the Kita-dake source deflated due to the Minami-dake explosion.

The 3-dB FBG bandwidth Characteristics

In this paper, the effect of the grating parameters (i.e. gratings length (Lg) and the induced index profile (Δn)); the temperature variation (T) and the applied strain change on the fiber Bragg Grating (FBG) 3dB-bandwidth (i.e. full width-half maximum (FWHM)) have successfully investigated numerically using MATHCAD software. Results show that for Lg < 7 mm, the FBG 3dB-bandwidth (i.e. full width-half maximum (FWHM)) value shows a good reliable and visible impact. Otherwise, there are no significant effects except for increasing the FBG reflectivity. Also, results show that the FWHM value has affected by the change of the Δn value. In contrast, results show that there is no significant effect of the temperature on the FWHM value. Also, results shown that the dependence of the Bragg wavelength (λB) upon both strain and temperature variations is lies within the range of 0.462 – 0.470 fm με-1/C°