Numerical Analysis of Perforation during Hydraulic Fracture Initiation Based on Continuous-Discontinuous Element Method

Perforation is a pivotal technique employed to establish main flow channels within the reservoir formation at the outset of hydraulic fracturing operations.Optimizing perforation designs is critical for augmenting the efficacy of hydraulic fracturing and boosting oil or gas production.In this study,we employ a hybrid finite-discrete element method,known as the continuous–discontinuous element method(CDEM),to simulate the initiation of post-perforation hydraulic fractures and to derive enhanced design parameters.The model incorporates the four most prevalent perforation geometries,as delineated in an engineering technical report.Real-world perforations deviate from the ideal cylindrical shape,exhibiting variable cross-sectional profiles that typically manifest as an initial constriction followed by an expansion,a feature consistent across all four perforation types.Our simulations take into account variations in perforation hole geometries,cross-sectional diameters,and perforation lengths.The findings show that perforations generated by the 39g DP3 HMX perforating bullet yield the lowest breakdown pressure,which inversely correlates with increases in sectional diameter and perforation length.Moreover,this study reveals the relationship between breakdown pressure and fracture degree,providing valuable insights for engineers and designers to refine perforation strategies.

Study on orientation fracture blasting with shaped charge in rock

On the basis of the theories of mechanics of explosive and rock fracture mechanics, the mechanism of crack initiation and its expansion of directional fracture controlled blasting with shaped charges in rock were studied, then the blasting parameters were designed and tested by a model test in laboratory and field experiment. The experimental and test results showed that the energy from blasting is directionally concentrated for the cumulative action. The directional expansion of cracks is satisfactory, the results of the model test and field test suggested that the orientation fracture blasting with shaped charge is a good means of excavating tunnels or cutting rock.

Lumbopelvic Fixation and Sacral Decompression for U-shaped Sacral Fractures： Surgical Management and Early Outcome

U-shaped sacral fractures are rare and often difficult to diagnose primarily due to the difficulty in obtaining adequate imaging and the severe associated injuries. These fractures are highly unstable and frequently cause neurological deficits. The majority of surgeons have limited experience in management of U-shaped sacral fractures. No standard treatment protocol for U-shaped sacral fractures has been available till now. This study aimed to examine the management of U-shaped sacral fractures and the early outcomes. Clinical data of 15 consecutive patients with U-shaped sacral fracture who were admitted to our trauma center between 2009 and 2014 were retrospectively analyzed. Demographics, fracture classification, mechanism of injury and operative treatment and deformity angle were assessed. All the patients were treated with lumbopelvic fixation or （and） sacral decompression. EQ-5d score was applied to evaluate the patients＇ quality of life. Of the 15 consecutive patients with U-shaped sacral fracture, the mean age was 28.8 years （range： 15-55 years） at the time of injury. There were 6 females and 9 males. The mean follow- up time was 22.7 months （range： 9-47 months） and mean full weight-bearing time was 9.9 weeks （range： 8-14 weeks）. Ten patients received lumbopelvic fixation and sacral decompression, one lombosacral fixation, and 4 merely sacral decompression due to delayed diagnosis or surgery. The post-operation deformity angle （mean 27.87°, and range： 8°-90°） of the sacrum was smaller than that pre-operation （mean 35.67; range： 15-90） with no significance difference noted. At the latest follow-up, all patients obtained neurological recovery with different extents. Visual analogue score （VAS） was reduced from preoperative 7.07 （range： 5-9） to postoperetive 1.93 （range： 1-3）. All patients could walk without any aid after treatment. Eight patients were able to care for themselves and undertook some daily activities. Five patients had returned to work full time. In conclusion, lumbopelvic fixation is an effective method for stabilization of U-shaped sacral fractures with fewer complications developed. Effective reduction and firm fixation are the prerequisite of early mobilization and neurological recovery. Sacral decompression effectively promotes neurological recovery even in patients with old U-shaped sacral fractures.

Formation of X-shaped hydraulic fractures in deep thick glutenite reservoirs:A case study in Bohai Bay Basin,East China

Tight glutenite reservoirs are widely developed in Bohai Bay Basin,East China.They are mostly huge thick and rely on hydraulic fracturing treatment for commercial exploitation.To investigate the propagation behavior of hydraulic fractures in these glutenite reservoirs,the geological feature of reservoirs in Bohai Bay Basin is studied firstly,including the reservoir vertical distribution feature and the heterogeneous lithology.Then,hydraulic fracturing treatments in block Yan 222 are carried out and the fracturing processes are monitored by the microseismic system.Results show the hydraulic fractures generated in the reservoirs are mostly in X shape.The cause of X-shaped hydraulic fractures in this study is mainly ascribed to(I)the reservoir heterogeneity and(II)the stress shadow effect of two close hydraulic fractures propagating in the same orientation,which is confirmed by the following numerical simulation and related research in detail.This study can provide a reference for the research on the fracturing behavior of the deep thick glutenite reservoirs.

Design of a test structure based on chevron-shaped thermal actuator for in-situ measurement of the fracture strength of MEMS thin films

A novel test structure to characterize the fracture strength of MEMS(Micro-electro-Mechanical Systems)thin films is presented.The test structure is comprised of a micro fabricated chevron-shaped thermal actuator and test specimen.The test structure is capable of producing large displacement and stresswhile keeping a relatively low temperature gradient across the test specimen.A voltage is applied across the beams of the chevron-shaped actuator,producing thermal expansion force to fracture the test specimen.Actuator deflection is computed based on elastic analysis of structures.To verify the test structure,simulations have been implemented using COMSOL Multiphysics.A 620μmlong,410μm wide,10μm thick test structure produced stress of 7.1 GPawhile the applied voltage is 5 V.The results indicate that the test structure is suitable for in-situ measurement of the fracture strength of MEMS thin films.

Fracture behavior and microstructure of as-cast NiTi shape memory alloy

The as-cast ingot of equiatomic nickel-titanium shape memory alloy （NiTi SMA） was prepared by vacuum consumable arc melting. The tensile tests and the compressive tests with respect to as-cast NiTi SMA were performed to study its mechanical properties of fracture. The microanalysis of as-cast NiTi SMA as well as its fractured samples was performed so as to better understand microstructure evolution and fracture behavior of NiTi SMA. Under tensile loading, the as-cast NiTi SMA shows higher plasticity and is characterized by ductile fracture at 750℃, but it demonstrates poorer plasticity and is characterized by cleavage fracture as well as transcrystalline fracture at room temperature and -100 ℃. Under compressive loading at -100 ~C, the as-cast NiTi SMA is characterized by shear fracture where the normal to the shearing fracture surface inclines about 45° to the compressive axis, and belongs to cleavage fracture where the cracks exoand via transcrvstalline fracture.

Shape factor for regular and irregular matrix blocks in fractured porous media

Describing matrix–fracture interaction is one of the most important factors for modeling natural fractured reservoirs.A common approach for simulation of naturally fractured reservoirs is dual-porosity modeling where the degree of communication between the low-permeability medium(matrix)and high-permeability medium(fracture)is usually determined by a transfer function.Most of the proposed matrix–fracture functions depend on the geometry of the matrix and fractures that are lumped to a factor called shape factor.Unfortunately,there is no unique solution for calculating the shape factor even for symmetric cases.Conducting fine-scale modeling is a tool for calculating the shape factor and validating the current solutions in the literature.In this study,the shape factor is calculated based on the numerical simulation of fine-grid simulations for single-phase flow using finite element method.To the best of the author’s knowledge,this is the first study to calculate the shape factors for multidimensional irregular bodies in a systematic approach.Several models were used,and shape factors were calculated for both transient and pseudo-steady-state(PSS)cases,although in some cases they were not clarified and assumptions were not clear.The boundary condition dependency of the shape factor was also investigated,and the obtained results were compared with the results of other studies.Results show that some of the most popular formulas cannot capture the exact physics of matrix–fracture interaction.The obtained results also show that both PSS and transient approaches for describing matrix–fracture transfer lead to constant shape factors that are not unique and depend on the fracture pressure(boundary condition)and how it changes with time.

FRACTURE LIMIT LOAD OF CONE SHAPE PART IN DRAWING PROCESS

The deformation characters and load status of the blank＇s potential fracture zone are analyzed at the moment when blank is approaching to punch comer in drawing process of cone shape part. Based on tension instability theory, the formula for calculating fracture limit load of cone shape part in drawing process is derived. Also, the formula is analyzed and verified by experiment.

STUDY OF THE STRESS INTENSITY FACTOR OF PREFORMED V SHAPE FRACTURE TIP

In order to make the fracture cross-section of rock smooth in controlled cutting-blast, generally, two V-shape-notches on the inner wall of a shot hole are notched in symmetry along the design direction. A V-shape notch approximately be considered as V-shape-fracture under certain condition. This paper gave the complex stress function of preformed V-shape-fracture under a blasting load. The stress field and displacement field at the tip of a preformed V-shape-fracture were derived with Westergaard's method, hence its stressintensity factor was obtained. To verify the derived results, blasting tests were made with concrete samples of 400mm×400mm×300mm, and all having, in the center, a drilled hole of 25mm in diameter and 200mm in height. The test result showed that the formulas derived are correct and effective.

Study on linear shaped charge in penetrating rock

Based on the action mechanism of linear shaped charge（ LSC ）, penetration performance of LSC on rock was studied. The optimal standoff and the vertex angle of LSC were studied and determined by lab experiments. Through cutting sand-cement grout samples, the spacing interval of boreholes can approach 17.5 times of the bore-hole＇ s diameter, and the result of the directional expansion of crack is satisfactory. The result of field experiment indicates cutting effect is very good, the ruggedness in fracture plane is less than 50 mm, the rate of half-hole marks is nearly 100 % , and the crack inspection shows that there is no damage in the internal of the cutting part. All these suggest that the orientation fracture blasting with LSC is a good means in directional fracture controlled blasting and is worth popularizing widely.

Hydraulic fracture geometry and proppant distribution in thin interbedded shale oil reservoirs

Small-scale true triaxial sand fracturing experiments are conducted on thin interbedded shale samples made from cores of Permian Lucaogou Formation shale oil reservoir in Jimsar sag, Junggar Basin, NW China. Combined with high-precision CT scanning digital core model reconstruction technology, hydraulic fracture geometry and proppant distribution in thin interbedded shale oil reservoirs are studied. The research shows that: In thin interbedded shale oil reservoir, the interlayer difference of rock mechanics and the interlayer interface near the wellbore cannot restrain the growth of fracture height effectively, but has a significant impact on the fracture width distribution in the fracture height direction. Hydraulic fractures in these reservoirs tend to penetrate into the adjacent layer in “step-like” form, but have a smaller width at the interface deflection, which hinders the transport of proppant in vertical direction, resulting in a poor effect of layer-crossing growth. In shale layers with dense laminae, hydraulic fractures tend to form “丰” or “井” shapes. If the perforated interval is large in rock strength and high in breakdown pressure, the main fracture is fully developed initially, large in width, and supported by enough sand. In contrast, if the perforated interval is low in strength and rich in laminae, the fracturing fluid filtration loss is large, the breakdown pressure is low, the main fracture will not open wide initially, and likely to have sand plugging. Proppant is mainly concentrated in the main hydraulic fractures with large width near the perforated layer, activated laminae, branch fractures and fractures in adjacent layers contain only a small amount of(or zero) proppant. The proppant is placed in a limited range on the whole. The limit width of fracture that proppant can enter is about 2.7 times the proppant particle size.

FRACTAL DIMENSION AS MORPHOLOGY AND SIZE PARAMETERS OF FRACTURED PARTICLES OF ROCK

Semi-automatic image analysis system was used for the surface fractal dimension measurement of 15 kinds of rock-fractured particles. The results indicate that the surfaces of the particles that have a size of about 200 mesh are fractal, and that the fractal dimension is in the range of 2.07～2.11. Therefore, some definitions of particle size such as surface diameter, equivalent volumetricly surface diameter are equivocal without giving the step length and the drag diameter, free-fall diameter, and stokes’diameter may be modified by the fractal dimension.

基于自适应整形正则化的AVAz反演

高角度裂缝的存在导致地下介质呈现方位各向异性,具有水平对称轴的横向各向同性介质中反射系数随方位角的变化可以近似表示为傅里叶级数的形式.傅里叶系数的大小取决于背景介质和裂缝参数,傅里叶系数的相位角取决于裂缝对称轴方向.常规傅里叶级数分析利用逐个时间采样点的方位地震数据求和计算傅里叶系数,计算结果易受噪声影响.为了提高傅里叶系数估计的抗噪性和稳定性,将常规傅里叶级数分析与AVAz(振幅随方位角变化)反演方法相结合,提出一种基于整形正则化的AVAz二阶傅里叶系数反演方法.常规整形正则化约束中的整形算子形态固定,提出一种基于方位各向异性强度的自适应整形算子,利用基于常规傅里叶级数分析的二阶傅里叶系数初步估计结果计算阻尼因子,结合一阶差分矩阵构建自适应整形算子,达到在反演中自适应地调整整形算子形态的目的.理论测试表明,基于自适应整形正则化的AVAz反演方法具有较强的抗噪性,能够有效提高二阶傅里叶系数反演的稳定性.实际叠前地震数据应用结果显示裂缝预测结果与测井资料相吻合,证明了基于自适应整形正则化AVAz反演进行裂缝预测的有效性.

X形软钢阻尼器延性断裂的试验研究与数值模拟

为了研究X形软钢阻尼器在大变形状态下的耗能性能和损伤演化规律,设计了6组试件进行单向和循环荷载作用下延性断裂的试验研究,分析了软钢阻尼器的破坏过程和滞回曲线。采用Lemaitre-Chaboche混合强化模型,分别对各工况下包含与不包含基于应力三轴度的钢材微观损伤模型的软钢阻尼器进行了精细的有限元模拟。对比有限元模拟结果和试验结果,分析结果表明,颈部为X形耗能软钢阻尼器的薄弱位置,最容易发生集中损伤甚至破坏。考虑钢材损伤准则的有限元模拟的荷载-位移曲线与试验结果更加吻合,能够表征软钢阻尼器的承载力与刚度退化现象,并能较为准确地预测软钢阻尼器的损伤演化过程和断裂破坏位置。

跗骨窦小切口与经外侧“L”形切口术对跟骨骨折患者的疗效

目的 比较跗骨窦小切口与经外侧“L”形切口术治疗跟骨骨折的疗效及对足功能恢复情况的影响。方法 研究对象选取2020年10月至2022年10月收治的跟骨骨折患者88例,按照手术方法分为对照组43例,研究组45例,对照组采用经外侧“L”形切口术,研究组采用跗骨窦小切口手术。检测比较2组手术情况及并发症发生情况、足功能、跟骨解剖结构、骨代谢、炎性因子、应激反应指标水平。结果 与对照组比较,研究组术后引流量、术中出血量较少,手术、住院及骨折愈合时间较短,并发症发生率较低(P<0.05)。与术前比较,术后3个月2组AOFAS评分、Bohler角、Gissane角、跟骨长度、跟骨高度、P1NP、骨特异性碱性磷酸酶(BALP)水平升高,且研究组高于对照组,抗酒石酸酸性磷酸酶(TRAP)、环磷酰胺(CTX)水平降低,且研究组低于对照组(P<0.05)。与术前比较,术后3 d 2组CRP、IL-6、MDA水平升高,但研究组低于对照组,SOD水平降低,但研究组高于对照组(P<0.05)。结论 跗骨窦小切口术治疗跟骨骨折效果理想,可减少手术创伤,减轻炎症及应激反应,且可促进术后足功能、骨代谢恢复,并发症少。

前外侧入路联合胫骨远端L形钢板内固定治疗胫腓骨远端骨折的临床研究

目的探讨前外侧入路联合胫骨远端L形钢板内固定治疗胫腓骨远端骨折的临床疗效。方法选取2021年1月至2022年12月抚州市第一人民医院收治的60例胫腓骨远端骨折患者作为研究对象,根据治疗方案的不同分为对照组与研究组,每组30例。对照组采用传统术式入路治疗,研究组采用前外侧入路联合胫骨远端L形钢板内固定治疗。比较两组踝关节功能、术后引流量、术中出血量、手术时间、并发症发生情况。结果研究组踝关节功能恢复优良率高于对照组,差异有统计学意义(P<0.05)。两组术中出血量、手术时间、术后引流量比较差异无统计学意义。研究组并发症发生率低于对照组,差异有统计学意义(P<0.05)。结论前外侧入路联合胫骨远端L形钢板内固定治疗胫腓骨远端骨折疗效显著,可降低患者并发症发生风险,有利于恢复踝关节功能,明显提升患者恢复效果,临床应用价值较高。

煤矿“Y”型断层分支底板断裂力学判据及模拟研究

【目的】断层分支作为主断层的一部分普遍存在,不易引起人们重视,但断层分支是引起突水的主要因素之一。【方法】以安徽刘庄煤矿为工程地质背景,在考虑Mohr-Coulomb准则岩体压剪断裂判据基础上,建立断层分支渗流与应力双重影响下的断裂力学灾变模型,分析得出断层分支发生劈裂破坏时的临界水压及断层分支到底板破碎区最小安全距离,研究断层倾角、最小主应力、主断层长度和渗透水压对临界水压及最小安全距离的影响规律和主控影响因素,并模拟分析断层分支在采动影响下塑性区及渗流场的演化特征,开展现场压水试验的验证工作。【结果和结论】结果表明:(1)断层分支倾角越大越易发生突水;最小主应力越大,断层分支裂隙越不容易发生扩展;(2)当主断层倾角为60°且断层分支与主断层夹角为60°时,模拟分析结果显示在工作面推进至断层分支正上方位置时,断层导升通道整体活化贯通;当工作面推过断层分支正上方10 m后,断层分支尖端裂隙与工作面底板破坏带贯通并引起底板突水;(3)通过现场压水试验验证了理论计算的正确性,证实断层分支会造成底板裂隙提前与断层相互贯通,引起工作面出水。研究结果可为煤矿采场底板含此类断层分支时的防水煤柱留设提供一定参考。

不同断面泄流槽的堰塞坝溃决模型试验研究

以2018年“11·3”金沙江白格滑坡堰塞坝为原型,对所布设的泄流槽从断面形状、位置、尺寸等方面进行考虑,采用相同颗粒级配材料,设置7种试验工况,在控制上游来水量相同条件下,对各工况下试验溃决过程进行观察,进而揭示堰塞坝溃决演变机理及其影响因素。结果表明:溃决过程可分为初始孕育阶段、溯源坡面侵蚀阶段、溯源陡坎侵蚀阶段、河床稳定平衡阶段4个阶段;不同断面形状泄流槽的溃决过程中,冲蚀程度影响范围由强到弱排序为自然组、三角形槽、矩形槽、梯形槽。对于泄流槽断面形状尺寸及位置,当宽度相同且深度较低时,受约束影响溃决过程会较为提前;当泄流槽断面一致,布设位置位于一侧时,受一侧固定约束影响,溃口宽度扩展会小于布设位置位于中间的情况。研究结果可为堰塞坝溃决机理分析及堰塞坝应急救援处置提供参考。

基于循环孔洞扩张模型的X型圆管节点超低周疲劳寿命预测

海洋工程钢结构在服役过程中,受风、浪、流或地震等极端循环载荷的影响,易发生超低周疲劳断裂破坏,造成人员伤亡及财产损失,因此超低周疲劳断裂分析及寿命预测对于海工结构安全性评估至关重要。然而,现阶段基于累积损伤理论提出的多种超低周疲劳寿命预测模型无法对多尺度节点实现统一预测,造成了实际工程应用的不便。因此文中基于循环孔洞扩张模型开展X型圆管节点超低周疲劳寿命预测。首先,开发了基于循环孔洞扩张模型的VUSDFLD程序,实现ABAQUS与FORTRAN子程序联合应用,利用有限元分析验证循环孔洞扩张模型在X型圆管节点超低周疲劳断裂分析中的有效性;其次,根据多组X型圆管节点超低周疲劳断裂有限元分析结果,在宏观层面提出了一种基于Manson-Coffin公式的超低周疲劳寿命预测公式;最后,依据Miner理论,将适用于等幅加载的超低周疲劳寿命公式扩展至变幅加载情况,验证了多种节点尺寸下超低周疲劳公式的适用性,为工程应用提供了理论依据。

两种治疗方案对前十字韧带胫骨止点撕脱骨折患者术后膝关节功能及稳定性的影响研究

目的观察两种治疗方案对前十字韧带(ACL)胫骨止点撕脱骨折患者术后膝关节功能及稳定性的影响。方法回顾性分析2020年1月至2022年1月在四川省骨科医院就诊的ACL胫骨止点撕脱骨折患者临床资料,从接受关节镜下“8”字缝线治疗的患者中随机抽取71例纳入对照组,从接受关节镜下缝线桥固定治疗的患者中随机抽取71例纳入试验组,术后患者均已随访12个月。比较两组患者的临床治疗情况和术后并发症发生情况,记录其术后3个月时(T1)、术后6个月时(T2)和术后12个月时(T3)的膝关节功能[国际膝关节文献委员会膝关节评估表(IKDC)]、稳定性(KT-2000值)和膝关节活动度。结果试验组患者的手术时间高于对照组,而住院时间和骨折愈合时间低于对照组(P<0.05);两组术后并发症发生率差异无统计学意义(P>0.05);T1、T2和T3时,试验组患者的IKDC评分和膝关节活动度高于对照组(P<0.05);试验组患肢的KT-2000值低于对照组(P<0.05),且T3时试验组患者患肢和健肢的KT-2000值差异无统计学意义(P>0.05),对照组患肢的KT-2000值高于健肢(P<0.05)。结论采用关节镜下缝线桥固定治疗ACL胫骨止点撕脱骨折患者具有明显疗效,能够有效改善患者膝关节功能,提高膝关节稳定性和活动度,减少术后并发症发生情况。