A fully coupled thermo-poroelastoplasticity analysis of wellbore stability

Zhu, Xiaohua,Liu, Weiji,Zheng, Hualin Techno-Press 2016 Geomechanics & engineering Vol.10 No.4

Wellbore instability problem is one of the main problems that met frequently during drilling, particularly in high temperature, high pressure (HPHT) formations. There are large amount of researches about wellbore stability in HPHT formations, which based on the thermo-poroelastic theory and some achievements were obtained; however, few studies have investigated on the fully coupled thermo-poroelastoplasticity analysis of wellbore stability, especially the analysis of wellbore stability while the filter cake formed. Therefore, it is very necessary to do some work. In this paper, the three-dimensional wellbore stability model which overall considering the effects of fully coupled thermo-poroelastoplasticity and filter cake is established based on the finite element method and Drucker-Prager failure criterion. The distribution of pore pressure, wellbore stress and plastic deformation under the conditions of different mud pressures, times and temperatures have been discussed. The results obtained in this paper can offer a great help on understanding the distribution of pore pressure and wellbore stress of wellbore in the HPHT formation for drilling engineers.

The rock fragmentation mechanism and plastic energy dissipation analysis of rock indentation

Zhu, Xiaohua,Liu, Weiji Techno-Press 2018 Geomechanics & engineering Vol.16 No.2

Based on theories of rock mechanics, rock fragmentation, mechanics of elasto-plasticity, and energy dissipation etc., a method is presented for evaluating the rock fragmentation efficiency by using plastic energy dissipation ratio as an index. Using the presented method, the fragmentation efficiency of rocks with different strengths (corresponding to soft, intermediately hard and hard ones) under indentation is analyzed and compared. The theoretical and numerical simulation analyses are then combined with experimental results to systematically reveal the fragmentation mechanism of rocks under indentation of indenter. The results indicate that the fragmentation efficiency of rocks is higher when the plastic energy dissipation ratio is lower, and hence the drilling efficiency is higher. For the rocks with higher hardness and brittleness, the plastic energy dissipation ratio of the rocks at crush is lower. For rocks with lower hardness and brittleness (such as sandstone), most of the work done by the indenter to the rocks is transferred to the elastic and plastic energy of the rocks. However, most of such work is transferred to the elastic energy when the hardness and the brittleness of the rocks are higher. The plastic deformation is small and little energy is dissipated for brittle crush, and the elastic energy is mainly transferred to the kinetic energy of the rock fragment. The plastic energy ratio is proved to produce more accurate assessment on the fragmentation efficiency of rocks, and the presented method can provide a theoretical basis for the optimization of drill bit and selection of well drilling as well as for the selection of the rock fragmentation ways.

Mechanical plugging—solid expandable tubular refracturing technology

Xiaohua Zhu,Feilong Cheng,Changshuai Shi,Kailin Chen 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.6

To solve the three major problems of low production, low efficiency and low permeability of oil fields, it is necessary to develop new tight oil layers or shale oil outside the original perforated section in the well that has been perforated. The key to the success of repeated fracturing operations is the ability to block the original perforation of the well. At present, with tubing fracturing construction, volume fracturing of the target reservoir cannot be achieved due to limited displacement, and the effect of reservoir transformation is not obvious, affecting the productivity of the old well. Based on the above problems, this paper proposes a new blocking method suitable for fracturing wells - solid expansdable tubular (SET) plugging. In this paper, it established SET-expansion cone-casing-rubber ring 2D dynamic model which considers the friction, and contact, to analyze the effect of compression and length of rubber ring and the constraint condition of SET on sealing performance; laboratory experiments were carried out and data on driving force, sealing capacity and suspension force were obtained. The results show that optimizing the parameters of expansion cone structure can effectively reduce the residual stress of SET and driving force after expansion; the construction method of SET and the parameters of rubber ring are the main factors that affect the suspension sealing ability, and paper proposes an effective solution; in addition, experiment results show that the SET meets the requirements of fracturing construction with internal pressure greater than 60 MPa and suspension force greater than 600 kN after expansion, and can be used to seal the well body structure of refracturing wells with fewer perforations and shorter distances, and the diameter can be guaranteed to reach 112 mm. The research results provide new ideas and solutions for repeated pressure wells and high-pressure plugging.

Design and analysis of sealed suspension module based on solid expandable tubular repair technology

Xiaohua Zhu,Feilong Cheng,Changshuai Shi,Jia’nan Li,Kailin Chen 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.2

The ability of sealing suspension of solid expandable tubular (SET) is one of the important factors that determine whether pipe can expand normally and serve. To solve the problem that the SET deviates from the original position (causing for the failure to repair of leakage well) due to the insufficient suspension force after expansion, this paper establishes the two-dimensional coupling model of SET-rubber ring-expansion cone-casing based on laboratory experiment parameters, designs the parameters of the sealed suspension rubber ring and conducts simulation. The results show that when the compression amount of the rubber ring is designed to be 47 %-58 % of the rubber thickness, the SET has excellent sealing ability after expansion and can meet the requirements of suspension force; too much compression will affect the service life of the rubber ring. When the length of the rubber ring is 50 mm-110 mm, the driving force and contact pressure during expansion are suitable; the rubber ring spacing is designed to be 110 mm, which avoids interference after rubber compression and saves material. In addition, the vulcanizing bonding strength of the rubber ring should be greater than 120 kN to avoid peeling off due to the failure of the rubber ring and SET bonding. The research results of this paper provide a theoretical basis for the design of sealing suspension module of SET repair technology.

The investigation of rock cutting simulation based on discrete element method

Zhu, Xiaohua,Liu, Weiji,Lv, Yanxin Techno-Press 2017 Geomechanics & engineering Vol.13 No.6

It is well accepted that rock failure mechanism influence the cutting efficiency and determination of optimum cutting parameters. In this paper, an attempt was made to research the factors that affect the failure mechanism based on discrete element method (DEM). The influences of cutting depth, hydrostatic pressure, cutting velocity, back rake angle and joint set on failure mechanism in rock-cutting are researched by PFC2D. The results show that: the ductile failure occurs at shallow cutting depths, the brittle failure occurs as the depth of cut increases beyond a threshold value. The mean cutting forces have a linear related to the cutting depth if the cutting action is dominated by the ductile mode, however, the mean cutting forces are deviate from the linear relationship while the cutting action is dominated by the brittle mode. The failure mechanism changes from brittle mode with larger chips under atmospheric conditions, to ductile mode with crushed chips under hydrostatic conditions. As the cutting velocity increases, a grow number of micro-cracks are initiated around the cutter and the volume of the chipped fragmentation is decreasing correspondingly. The crack initiates and propagates parallel to the free surface with a smaller rake angle, but with the rake angle increases, the direction of crack initiation and propagation is changed to towards the intact rock. The existence of joint set have significant influence on crack initiation and propagation, it makes the crack prone to propagate along the joint.

The Investigation of Rock Indentation Simulation Based on Discrete Element Method

Xiaohua Zhu,Weiji Liu,Xianqun He 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.4

Rock indentation is widely encountered in rock engineering, such as oil & gas drilling process. The rock indentation represents the fundamental process for mechanical rock breaking. Therefore, it is necessary to research the failure mechanism during the rock indentation process. For this purpose, the Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests are performed to calibrate the relations between micro-properties and macro-properties of the rock specimens. The rock indentation process and crack propagation with the effects of lateral pressure, hydraulic pressure, ledge, wedge angle and joint are researched by PFC2D in this paper. The results show that: with the indenter penetrating into rock, the sub-vertical crack is formed from the damaged zone and it will extend to bottom edge of the rock at last; the initiation and propagation of the sub-vertical crack is mostly driven by the tensile contact force. The development of sub-vertical crack and damaged zone are restrained with increasing lateral pressure, the lateral pressure increases led to an increase in the critical penetration depth and the size of the damaged zone decreases and its shape flattens with the lateral pressure increasing. On the contrary, the development of sub-vertical crack and damaged zone are promoted with increasing hydraulic pressure. With the wedge angle increases the size of crushed zone underneath the indenter increases, it promotes the formation of sub-vertical crack; larger wedge angle causes a larger indentation force. The existence of a ledge leads to crack initiation and propagation towards the free surface and the presence of the joint also promotes crack initiation and propagation towards the joint; when the crack propagates to the joint, the crack will no longer propagate towards the intact rock mass but along the joint.

Core–shell ZIF-67(Co) wrapped CuO as high efficient peroxymonosulfate catalyst for the degradation of methylene blue

Zhu Wenjun,Zuo Xiaohua,Deng Xiangyi,Zhang Xinhao,Yao Chuang,Wang Xiaobo 한국탄소학회 2023 Carbon Letters Vol.33 No.2

Core–shell ZIFs wrapped CuO hybrid materials (CuO@ZIF-67(Co)) were designed, synthesized, characterized, and employed as peroxymonosulfate (PMS) activators to degrade methylene blue (MB). It demonstrated outstanding catalytic activity on account of the unique structure and the synergistic effect between CuO cores and ZIF-67(Co) shells, resulting in complete degradation of MB (10 mg/L) in 1 min. Reactive oxygen species (ROSs) research showed that both SO4− and OH were responsible for the removal of MB. The synergistic activation mechanisms in the CuO@ZIF-67(Co)/PMS system were investigated, which mainly involved the effective electron transfer of CuO and ZIF-67(Co) for accelerating the cycle of CuII/CuI and CoIII/CoII. This study broadens the application of MOF-derived materials for wastewater treatment.

Prognostic value of programmed death-ligand 1 (PD-L1) expression in ovarian clear cell carcinoma

Jun Zhu,Hao Wen,Rui Bi,Yong Wu,Xiaohua Wu 대한부인종양학회 2017 Journal of Gynecologic Oncology Vol.28 No.6

Objective: Programmed death-ligand 1 (PD-L1) was expressed in various tumors andantibodies targeting its receptor programmed cell death-1 (PD-1) are emerging cancertherapeutics. This study was designed to evaluate the expression of PD-L1 and its correlationwith clinicopathologic features and clinical outcomes in ovarian clear cell carcinoma (OCCC). Methods: The PD-L1 expression was measured by tissue-microarray-basedimmunohistochemistry from 122 eligible patients diagnosed with OCCC. The associations ofclinicopathologic features with progression-free survival (PFS) and overall survival (OS) wereanalyzed by Kaplan-Meier method and multivariate analysis was further performed by Coxregression model. Results: Overall, high PD-L1 expression (PD-L1high) was observed in 44.7% (55/123) ofOCCC patients, and was strongly associated with advanced stages (p=0.020), positive asciticfluid (p=0.016), platinum-resistant (PR) disease (p=0.045), and recurrence (p=0.038). Moreover, patients with PD-L1high were associated with poorer OS (hazard ratio [HR]=2.877;p=0.001) and PFS (HR=1.843; p=0.021) than those with low PD-L1 expression (PD-L1low). In subgroup analysis, PD-L1high patients experienced a poorer PFS (HR=1.926; p=0.044)and OS (HR=2.492; p=0.021) than PD-L1low cases among advanced stages (III–IV), but thisdifference was not observed in stage I–II patients. Meanwhile, PD-L1high was associated withpoorer prognosis than PD-L1low in PR patients (OS, HR=2.253; p=0.037; PFS, HR=1.448;p=0.233). Multivariate analysis revealed that PD-L1high and advanced stages (III–IV) wereadverse independent prognosticators for both PFS (HRPD-L1=2.0; pPD-L1=0.038; HRstage=10.2;pstage<0.001) and OS (HRPD-L1=3.0; pPD-L1=0.011; HRstage=14.3; pstage<0.001). Conclusion: PD-L1high might serve as a risk factor for PFS and OS in patients with OCCC. It ispossible that immunotherapy targeting PD-L1 pathway could be used in OCCC.

Clinicopathological characteristics, treatment and outcomes in uterine carcinosarcoma and grade 3 endometrial cancer patients: a comparative study

Jun Zhu,Hao Wen,Rui Bi,Xiaohua Wu 대한부인종양학회 2016 Journal of Gynecologic Oncology Vol.27 No.2

Objective: Uterine carcinosarcoma (UCS) shared the same staging system with endometrial carcinoma in the International Federation of Gynecology and Obstetrics 2009. The aim of the present study was to compare the clinicopathological and prognostic characteristics between UCS and grade 3 endometrioid endometrial carcinoma (G3EC). Methods: A retrospective analysis of 60 UCS and 115 G3EC patients with initial treatment at the Department of Gynecology in the Fudan University Shanghai Cancer Center between February 2006 and August 2013. Chi-square analysis was used to compare differences between variables. Prognostic factors were determined using univariate/multivariate analysis, and the survival rates were assessed using the Kaplan-Meier method. The Cox regression model was used to assess the independent prognostic factor. Results: UCS had significantly worse overall survival (OS) compared with G3EC. Carcinosarcoma subtype was an independent factor (hazard ratio [HR], 2.4; 95% confidence interval [CI], 1.0 to 5.8; p=0.039), stratified based on stage. Compared with G3EC, UCS patients had a greater incidence of ascites fluid (55.0% vs. 15.7%, p<0.001) and adnexal involvement (20.0% vs. 8.7%, p=0.048) and larger median tumor volume (4.6 cm vs. 4.0 cm, p=0.046). Subgroup analysis of the prognostic factors revealed that UCS patients exhibited worse OS than G3EC patients in such specific subgroups as patients at younger ages, with postmenopausal status, without ascites fluid, with early stage diseases, without vagina invasion, without lymph node metastases and receiving adjuvant chemo/radiotherapy. Adjuvant radiotherapy with chemotherapy was predictive of better survival in UCS patients compared with chemotherapy or radiotherapy alone (5-year OS, 71.0% vs. 35.8%, p=0.028). Multivariate Cox regression revealed that tumor mesenchymal component (HR, 4.6; 95% CI, 1.4 to 15.8; p=0.014) was an independent prognostic factor for UCS, whereas advanced stages (HR, 5.9; 95% CI, 1.0 to 33.9; p=0.046) and ascites fluid (HR, 5.1; 95% CI, 1.1 to 22.7; p=0.032) were independently correlated with poor prognosis for G3EC patients. Conclusion: The distinctions in both clinicopathological and prognostic characteristics between UCS and G3EC suggest that this subtype should be treated separately from high-risk epithelial endometrial carcinoma.

Bonded-cluster simulation of tool-rock interaction using advanced discrete element method

Weiji Liu,Xiaohua Zhu,Yun-Lai Zhou,Tao Li,Xiangning Zhang 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.72 No.4

The understanding of tool-rock interaction mechanism is of high essence for improving the rock breaking efficiency and optimizing the drilling parameters in mechanical rock breaking. In this study, the tool-rock interaction models of indentation and cutting are carried out by employing the discrete element method (DEM) to examine the rock failure modes of various brittleness rocks and critical indentation and cutting depths of the ductile to brittle failure mode transition. The results show that the cluster size and inter-cluster to intra-cluster bond strength ratio are the key factors which influence the UCS magnitude and the UCS to BTS ratio. The UCS to BTS strength ratio can be increased to a more realistic value using clustered rock model so that the characteristics of real rocks can be better represented. The critical indentation and cutting depth decrease with the brittleness of rock increases and the decreasing rate reduces dramatically against the brittleness value. This effort may lead to a better understanding of rock breaking mechanisms in mechanical excavation, and may contribute to the improvement in the design of rock excavation machines and the related parameters determination.