Fracture propagation law of temporary plugging and diversion fracturing in shale reservoirs under completion experiments of horizontal well with multi-cluster sand jetting perforation

This study conducted temporary plugging and diversion fracturing(TPDF)experiments using a true triaxial fracturing simulation system within a laboratory setting that replicated a lab-based horizontal well completion with multi-cluster sand jetting perforation.The effects of temporary plugging agent(TPA)particle size,TPA concentration,single-cluster perforation number and cluster number on plugging pressure,multi-fracture diversion pattern and distribution of TPAs were investigated.A combination of TPAs with small particle sizes within the fracture and large particle sizes within the segment is conducive to increasing the plugging pressure and promoting the diversion of multi-fractures.The addition of fibers can quickly achieve ultra-high pressure,but it may lead to longitudinal fractures extending along the wellbore.The temporary plugging peak pressure increases with an increase in the concentration of the TPA,reaching a peak at a certain concentration,and further increases do not significantly improve the temporary plugging peak pressure.The breaking pressure and temporary plugging peak pressure show a decreasing trend with an increase in single-cluster perforation number.A lower number of single-cluster perforations is beneficial for increasing the breaking pressure and temporary plugging peak pressure,and it has a more significant control on the propagation of multi-cluster fractures.A lower number of clusters is not conducive to increasing the total number and complexity of artificial fractures,while a higher number of clusters makes it difficult to achieve effective plugging.The TPAs within the fracture is mainly concentrated in the complex fracture areas,especially at the intersections of fractures.Meanwhile,the TPAs within the segment are primarily distributed near the perforation cluster apertures which initiated complex fractures.

Propagation law of shock waves and gas flow in cross roadway caused by coal and gas outburst

In order to study the propagation law of shock waves and gas flow during coal and gas outburst,we analyzed the formation process of outburst shock waves and gas flow and established the numerical simulation models of the roadways with 45°intersection and 135°intersection to simulate the propagation of outburst gas flow and the process of gas transport.Based on the analysis of the simulation results,we obtained the qualitative and quantitative conclusions on the characteristics and patterns of propagation and attenuation of outburst shock waves and gas flow.With the experimental models,we investigated the outburst shock waves and gas flow in the roadways with the similar structures to the simulated ones.According to the simulation results,when the angle between the driving roadway and the adjacent roadway increased,the sudden pressure variation range in adjacent roadway and the influencing scope of gas flow increased and the sudden pressure variation duration decreased.The intersection between the driving roadway and the adjacent roadway has no effect on airflow reversal induced by the shock waves and gas flow.

Research on propagation law of AE wave in coal seam

Based on mechanism of AE creation, put forward sphere cavity model, and deduced wave Equation of AE wave radiated by the AE source in detail, and analyzed the propagation attenuation law of AE stress wave in coal （rock） strata. Displacement function of AE wave indicates that displacement field can be divided into two parts. Firstly, displacement of particle is approaching to the source intensity function in zone near the AE source. Secondly, in zone far away from the AE source, displacement of particle is approaching to the derivative of source intensity function. AE wave changes gradually in the spreading process, and notable change of the wave form happens when wave propagates far away from the AE source.

Study on the Propagation Law of Shock Wave Pressure in Tunnels with Different Materials

The propagation of shock wave pressure in the tunnel is greatly affected by the tunnel structure,shape,material and other factors,and there are great differences in the propagation law of shock wave pressure in different kinds of tunnels.In order to study the propagation law of shock wave pressure in tunnels with different materials,taking the long straight tunnel with the square section as an example,the AUTODYN software is used to simulate the explosion of TNT in the concrete,steel and granite tunnel,and study on the variation law of shock wave pressure in tunnels with different materials.By using dimensional analysis and combined with the results of numerical simulation,a mathematical model of the propagation law of shock wave pressure in the tunnel is established,and the effectiveness of the mathematical model is verified by making the explosion test of the warhead in the reinforce concrete tunnel.The results show that the same mass of TNT explodes in the tunnel with different materials,and the shock wave overpressure peak at the same measuring point is approximate in the near field.However,there is a significant difference in the middle-far fields from the explosion center,the shock wave overpressure peak in the steel tunnel is 20.76%and 34.82%higher than that of the concrete and the granite tunnel respectively,and the shock wave overpressure peak in the concrete tunnel is 24.91%higher than that in the granite tunnel.Through the experimental verification,getting the result that the maximum relative deviation between the measured value and the calculated value of the shock wave overpressure peak is 11.85%.Therefore,it is proved that the mathematical model can be used to predict the shock wave overpressure peak in the tunnel with different materials,and it can provide some reference for the power evaluation of warhead explosion in the tunnel.

Mechanism of chain propagation for the synthesis of polyoxymethylene dimethyl ethers

Polyoxymethylene dimethyl ethers(PODE)were synthesized from the reaction of paraformaldehyde with dimethoxymethane(DMM)over different acid catalysts at different conditions.Products were found to follow the Schulz-Flory distribution law.The chain propagation proceeds through the insertion of an individual segment of CH2O one by one,while the simultaneous insertion of a few CH2O segments or their assembly is unlikely.Due to the restriction of this law,it is difficult to increase the selectivity to the desired products(e.g.,PODE3 4).

Vibration characteristics of FGM circular cylindrical shells filled with fluid using wave propagation approach

The vibration characteristics of a functionally graded material circular cylindrical shell filled with fluid are examined with a wave propagation approach. The shell is filled with an incompressible non-viscous fluid. Axial modal dependence is approximated by exponential functions. A theoretical study of shell vibration frequencies is analyzed for simply supported-simply supported, clamped-simply supported, and clamped-clamped boundary conditions with the fluid effect. The validity and the accuracy of the present method are confirmed by comparing the present results with those available in the literature. Good agreement is observed between the two sets of results.

Numerical simulation of hydraulic fracture propagation in laminated shale reservoirs

The main area of the Jiaoshiba anticline of the Fuling shale gas field was taken as the research object,laboratory rock mechanical experiments and direct shear experiments were conducted to clarify the mechanical anisotropy characteristics and parameters of rock samples with rich beddings.Based on the experimental results,a 3D fracture propagation model of the target reservoir taking mechanical anisotropy,weak bedding plane and vertical stress difference into account was established by the discrete element method to analyze distribution patterns of hydraulic fractures under different bedding densities,mechanical properties,and fracturing engineering parameters(including perforation clusters,injection rates and fracturing fluid viscosity).The research results show that considering the influence of the weak bedding plane and longitudinal stress difference,the interlayer stress difference 3–4 MPa in the study area can control the fracture height within the zone of stress barrier,and the fracture height is less than 40 m.If the influence of the weak bedding plane is not considered,the simulation result of fracture height is obviously higher.Although the opening of high-density bedding fractures increases the complexity of hydraulic fractures,it significantly limited the propagation of fracture height.By reducing the number of clusters,increasing the injection rate,and increasing the volume and proportion of high-viscosity fracturing fluid in the pad stage,the restriction on fracture height due to the bedding plane and vertical stress difference can be reduced,and the longitudinal propagation of fractures can be promoted.The fracture propagation model was used to simulate one stage of Well A in Fuling shale gas field,and the simulation results were consistent with the micro-seismic monitoring results.

Near-wellbore fracture propagation physical simulation based on innovative interlaced fixed perforation

An innovative perforation method of interlaced fixed perforation was put forward based on the analysis of the characteristics of fractures in various periods of perforation and conventional perforation modes.By conducting a large-scale perforation shooting experiments,we investigated the morphology,propagation mechanism and propagation law of the near-wellbore fractures generated during perforating processes under different fixed angle and interlaced angle combinations,and discussed the control method of near-wellbore fractures in different types of unconventional oil and gas reservoirs.The experimental results show that:(1)The interlaced fixed perforation strengthens the connectivity between the perforation tunnels not only in the same fixed plane but also in adjacent fixed planes,making it likely to form near-wellbore connected fractures which propagate in order.(2)Three kinds of micro-fractures will come up around the perforation tunnel during perforation,namely typeⅠradial micro-fracture,typeⅡoblique micro-fracture and typeⅢdivergent micro-fracture at the perforation tip,which are interconnected into complex near-wellbore fracture system.(3)Different types of perforation bullets under different combinations of fixed angles and interlaced angles result in different shapes of near-wellbore fractures propagating in different patterns.(4)By using the interlaced perforation on fixed planes,arranging fixed planes according to the spiral mode or the continuous"zigzag"shape,the desired near-wellbore fractures can be obtained,which is conducive to the manual control of main fractures in the fracturing of unconventional or complex conventional reservoirs.

Dynamic models of pest propagation and pest control

This paper proposes a pest propagation model to investigate the evolution behaviours of pest aggregates. A pest aggregate grows by self-monomer birth, and it may fragment into two smaller ones. The kinetic evolution behaviours of pest aggregates are investigated by the rate equation approach based on the mean-field theory. For a system with a self-birth rate kernel I（k） = Ik and a fragmentation rate kernel L（i,j） = L, we find that the total number MoA（t） and the total mass of the pest aggregates MA （t） both increase exponentially with time if L ≠ 0. Furthermore, we introduce two catalysis-driven monomer death mechanisms for the former pest propagation model to study the evolution behaviours of pest aggregates under pesticide and natural enemy controlled pest propagation. In the pesticide controlled model with a catalyzed monomer death rate kernel J1 （k） ---- J1 k, it is found that only when I 〈 J1 B0 （B0 is the concentration of catalyst aggregates） can the pests be killed off. Otherwise, the pest aggregates can survive. In the model of pest control with a natural enemy, a pest aggregate loses one of its individuals and the number of natural enemies increases by one. For this system, we find that no matter how many natural enemies there are at the beginning, pests will be eliminated by them eventually.

煤岩介质对水压裂隙扩展的影响机理

为研究不同煤岩介质压裂条件下水压钻孔裂隙起裂压力、起裂位置的变化规律,通过梳理现有理论,对连续介质弹性理论和非连续介质断裂理论2种经典模型进行比较。以王家岭煤矿等9个矿井为研究对象,针对不同介质岩石钻孔的压裂条件,开展室内试验并对结果进行比较,采用比较分析法进一步研究围岩压力、抗压强度对裂隙起裂压力、起裂位置的影响规律。结果表明:不同应力环境中,侧压系数越大,2种介质岩石钻孔开裂所需的起裂压力越大,相差越大,差值(2种压力差与连续介质岩石起裂压力的比值)越小,当侧压系数大于2时,差值无限接近于0;不同介质岩石的抗压强度具有差异性,抗压强度越大,2种介质岩石钻孔起裂压力越大;连续介质理论中起裂位置与围岩压力、抗压强度呈正相关,非连续介质理论中起裂位置始终沿水平应力方向。岩石介质对水压裂隙扩展规律的影响,可以为理论模型的优选提供参考,同时有助于裂隙起裂扩展行为预测。

深层页岩气井拉链式压裂裂缝扩展及窜通规律

针对深层页岩气井工厂开发模式下拉链式压裂裂缝扩展及窜扰规律认识不清的问题,基于有限元-离散元方法,建立了考虑天然裂缝带影响的拉链式压裂裂缝扩展流-固耦合模型,采用实验数据与现场监测压力涨幅数据验证了模型的可靠性,并以川南深层页岩气储层为例,研究了不同特征天然裂缝带影响下压裂裂缝的扩展及窜扰规律。结果表明:大逼近角裂缝带对压裂裂缝正向扩展及井间窜通具有阻挡作用,停泵期间水力裂缝在净压力驱动下存在继续扩展行为;高应力差下,随裂缝带逼近角增加,响应井压力涨幅、压裂裂缝总长度分别呈先减小再增加及先增加再减小的趋势;与小逼近角裂缝带相比,大逼近角天然裂缝带发生窜通所需时间更长,窜通难度更大;响应井压力涨幅与裂缝带带宽负相关,与天然裂缝长度正相关;窜通时间、压裂裂缝总长及压裂效率则与裂缝带带宽正相关,与天然裂缝长度负相关;随布孔错位距离增加,裂缝窜通概率减小,但错位距离与响应井压力涨幅、裂缝总长度之间的规律性不明显。

浅埋隧道爆破施工近接建筑结构动力响应规律

为了研究上覆建筑物在浅埋隧道爆破施工时的动力响应规律,该文以福州某城市隧道为工程背景,采用现场监测和Ansys/LS-DYNA模拟相结合的方法对上覆建筑群结构响应进行分析。监测结果表明:建筑结构在竖直方向上受爆破影响最为明显且具有高程放大效应,最大振速值为2.45 cm/s;各向振速随爆心距的增大而逐渐减小并趋于稳定,在爆心距较小时衰减较快;竖向振动主频更接近于建筑结构自身频率,主要分布在25~35 Hz区间。数值模拟结果与监测结果相吻合,进一步分析得到:同一测点在Ⅲ~Ⅴ级围岩下最大峰值振速分别为2.29 cm/s、2.51 cm/s和2.79cm/s,地表建筑物振动响应随围岩等级提高而增强;建筑物柱体和板等结构的力学响应与振速变化密切相关,建筑物保护要充分考虑爆破在建筑物中引起的各方向振速。

致密油储层压裂裂缝扩展规律分析及影响研究

以鄂尔多斯延长组长7裂缝性致密油储层为例,开展致密油储层裂缝扩展实验研究,分析裂缝扩展的影响因素,并对裂缝扩展规律进行模拟分析,实验结果表明:长7致密油储层岩石杨氏模量、泊松比和抗压强度波动范围广,造成数值差异较大;矿物组成分布差异为3%~46%,平均值为16.85%左右;该区块储层岩石发育部分的天然裂缝,储层最大水平主应力和最小水平主应力差异较大,储层水平和垂直方向上的孔、渗、饱等物性差异较大。天然裂缝的形成和发展受自然裂缝存在与地应力场差异这两个关键因素的显著影响,长7储层原始状态下裂缝的形态呈现低角度。

诱导下岩体裂隙扩展规律研究存在问题及对策

大部分地下工程的失稳都是岩体在长期的“诱导”作用下裂隙扩展、贯通从而改变岩体本身的强度特征导致的结果,因此,研究岩体中裂隙的扩展演化规律,对进一步揭示岩体工程失稳、岩石破坏现象的机理和本质具有重要意义。本文从物理实验、数值模拟和力学理论三个方面介绍了目前对于裂隙岩体扩展的研究现状,并结合地下工程的演化过程和工程需求分析了目前裂隙扩展研究中存在的问题,提出了更适应工程问题需求的研究思路:以相似材料、3D打印和声发射技术为手段,首先通过小试样压缩实验确定适用于声发射技术监测的相似材料成分及配比范围,然后采用3D打印的方法制作成交叉裂隙的拉、剪实验试件并开展拉、剪蠕变试验,研究裂隙扩展致裂规律,裂隙岩体拉、剪蠕变声发射特征及破坏的前兆特征,分析岩体强度随蠕变时间的变化规律,在此基础上建立裂隙岩体的大型相似材料模型,研究开挖诱导下随裂隙参数、时间等因素的预测模型和岩体冒落触发时间与裂隙参数、开挖空间的关系模型,揭示裂隙岩体冒落演化机制,预测岩体冒落时间和范围,为地下工程长期稳定性和岩体冒落调控提供理论支撑。

致密砂岩裂缝时空演化特征规律

摸清层理对致密砂岩断裂规律的影响,对于客观评价致密油气储层压裂裂缝延展规律具有实际意义。对不同层理方向上致密砂岩半圆弯曲试样(SCB)开展三点弯加载,借助数字图像相关技术(DIC)对试样表面位移、应变演化和裂纹扩展进行记录,得到砂岩裂纹扩展演化情况。研究表明:加载位移载荷曲线显示致密砂岩断裂裂缝发展包括缺陷压缩、弹性压缩、破裂失效、快速断裂、缓慢破裂这5个阶段,整体上致密砂岩塑性较为显著;致密砂岩在层理角0°、90°时横向位移最大,表明裂缝开度大,岩石断裂为纯张型断裂形式,对于深部致密油气储层高导流压裂有利;在层理角45°时位移最小而x轴方向应变最大,表明试样为剪切断裂,裂缝两侧岩石基质变形严重,制约基质孔隙油气流体进入压裂裂缝。试验发现,层理组构影响裂缝延展方位,随着层理夹角的增大,裂缝偏斜角先增大后减小,层理角45°时裂缝与最大载荷方向夹角最大。

吉木萨尔页岩油井区CO_(2)前置压裂工艺参数优化及现场实践

吉木萨尔凹陷芦草沟组页岩油具有原始渗透率极低,原油黏度高等特点,自然条件下无经济产能。通过现场实践,证明密切割+高强度体积压裂,是实现页岩油规模开发的最有效手段之一,但现阶段如何延缓油井递减率,提高单井采收率仍是亟待解决的问题。2019—2022年,在吉木萨尔页岩油区块,开展了CO_(2)前置压裂辅助提产技术研究和现场试验,系统地研究分析CO_(2)前置蓄能压裂和CO_(2)吞吐在吉木萨尔页岩油区块的应用效果。结果表明,超临界态CO_(2)具有混相增能、溶蚀改善储层条件、提高渗吸置换效率、提高缝网复杂程度等作用,并明确最优注入量、注入速度、注入方式等关键工艺参数,初步形成了一套页岩油藏CO_(2)前置压裂的工艺技术体系。根据生产数据预测,CO_(2)前置压裂工艺可将最终采收率提升20%左右,对实现页岩油效益开发,为其他类型页岩油藏提高开发效果提供参考。

高斯光束湍流大气传输远场扩展半径快速计算方法研究

高斯光束湍流大气传输的远场有效半径是工程中较为关注的远场光斑特征,文中研究其快速计算方法。基于多场景下高斯光束湍流大气传输波动光学仿真数据,建立了定标规律模型和3种人工智能模型LightGBM(Light Gradient Boosting Machine)、MLP(Multilayer Perceptron)、MFTT(Modified Feature Tokenizer Transformer),比较了不同模型的精度、泛化能力、样本量的影响和计算速度。结果表明:4种模型的精度受训练集样本量的影响,小样本量下定标规律模型精度最高,大样本量下MFTT模型精度最高;数据分为70%的训练集和30%的测试集时,MFTT在测试集上的平均相对偏差为1.36%;MFTT泛化能力最强,定标规律模型计算速度最快。希望为激光大气传输评估快速计算方法的选择和应用提供参考。

初始环境压力对RDX基温压炸药冲击波超压和温度的影响

为分析初始环境压力对温压炸药的冲击波超压峰值和温度的影响,在2.6 m^(3)的爆炸罐内开展不同初始环境下不同质量温压炸药的内爆试验,研究初始环境压力对温压炸药冲击波超压峰值与温度的影响.试验结果显示,初始环境压力对冲击波的影响明显,在海拔5 km处产生的冲击波超压峰值衰减率最大.借助Sachs比定律量纲一参数和Hopkins-Brown公式,构建了一个将平原数据推广至不同海拔高度的冲击波入射超压关联模型.进一步分析表明,在相同初始压力下,爆炸温度峰值与炸药量成正比,且随初始压力降低而下降,大药量炸药温度峰值下降程度大于小药量.这些发现对评估温压炸药在高海拔或低气压地区爆炸威力和温度效应评估有着一定的参考价值.

鄂尔多斯盆地黄土塬区地震波场数值模拟及传播规律

为研究鄂尔多斯盆地黄土塬区地震波的传播规律和噪声的产生机理,根据庆城北三维工区实际地表高程和速度结构,建立准确反映黄土塬区近地表结构的三维数字模型(速度和品质因子Q),以基于Q显式表达的黏滞声波方程为基础,采用坐标变换法实现起伏地表条件下的三维黏滞声波方程数值模拟。该方法可以将复杂近地表引起的近炮点强能量噪声和强衰减效应较客观地模拟出来,模拟结果与实际资料的吻合度较高。通过不同复杂程度模型的三维数值模拟和波场分析,厘清了黄土塬区地震资料近炮点强能量噪声和多次反射、多次折射的产生机理,并结合实际资料分析了黄土塬区不同位置(塬、梁、坡、沟)及不同炮点深度的波场特征差异,认为:沟中激发时,近炮点强能量噪声较弱,资料品质相对较好;随着炮点深度增大,信号的高频端成分逐步增加;黄土塬地区野外地震采集时,应避免在干黄土层中激发,尽可能选择胶泥层或更深层激发。波场分析结论对黄土塬区实际资料采集和处理具有一定的指导意义。

钢桥面板顶板-U肋焊缝裂纹萌生特征及扩展规律

【目的】研究轮载作用下钢桥面板顶板-U肋焊缝裂纹的萌生特征及扩展规律。【方法】通过有限元方法建立钢桥面板节段模型,分析了不同轮载位置下构造的变形特征,明确了轮载位置与典型变形特征的对应关系,相应建立了3种局部简化模型。在局部模型的基础上根据应力分布确定了裂纹萌生特征,并基于断裂力学进行裂纹扩展三维数值模拟。【结果】模拟结果表明,在以顶板为主的变形条件下,顶板焊趾和顶板焊根的最大主应力明显大于U肋焊趾处,裂纹产生后Ⅰ型应力强度因子远高于Ⅱ型和Ⅲ型;在以U肋为主的变形条件下,顶板焊根和U肋焊趾处的最大主应力垂直于U肋厚度方向,裂纹产生后Ⅱ型和Ⅲ型应力强度因子占Ⅰ型应力强度因子K的20%~30%。【结论】实桥中轮载偏离焊缝正上方时,疲劳裂纹易从顶板焊根和顶板焊趾处萌生且沿顶板厚度方向扩展,以Ⅰ型裂纹为主;当轮载位于焊缝正上方时,疲劳裂纹易从顶板焊根和U裂焊趾处萌生并大致垂直U肋腹板扩展,属于Ⅰ-Ⅱ-Ⅲ复合型裂纹,且扩展速率较快。