Numerical analysis of hydraulic fracture propagation in deep shale reservoir with different injection strategies

Deep shale reservoirs are characterized by elevated breakdown pressures,diminished fracture complexity,and reduced modified volumes compared to medium and shallow reservoirs.Therefore,it is urgent to investigate particular injection strategies that can optimize breakdown pressure and fracturing efficiency to address the increasing demands for deep shale reservoir stimulation.In this study,the efficiency of various stimulation strategies,including multi-cluster simultaneous fracturing,modified alternating fracturing,alternating shut-in fracturing,and cyclic alternating fracturing,was evaluated.Subsequently,the sensitivity of factors such as the cycle index,shut-in time,cluster spacing,and horizontal permeability was investigated.Additionally,the flow distribution effect within the wellbore was discussed.The results indicate that relative to multi-cluster simultaneous fracturing,modified alternating fracturing exhibits reduced susceptibility to the stress shadow effect,which results in earlier breakdown,extended hydraulic fracture lengths,and more consistent propagation despite an increase in breakdown pressure.The alternating shut-in fracturing benefits the increase of fracture length,which is closely related to the shut-in time.Furthermore,cyclic alternating fracturing markedly lowers breakdown pressure and contributes to uniform fracture propagation,in which the cycle count plays an important role.Modified alternating fracturing demonstrates insensitivity to variations in cluster spacing,whereas horizontal permeability is a critical factor affecting fracture length.The wellbore effect restrains the accumulation of pressure and flow near the perforation,delaying the initiation of hydraulic fractures.The simulation results can provide valuable numerical insights for optimizing injection strategies for deep shale hydraulic fracturing.

Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NOx) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NOx and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions.

Optimum development options and strategies for water injection development of carbonate reservoirs in the Middle East

Through the research on several carbonate reservoirs developed in the Middle East, the basic characteristics of different types of carbonate reservoirs are determined, and a set of high-efficiency water injection development options and strategies are presented. Hidden baffles and barriers exist in carbonate reservoirs in the Middle East, so the reservoirs could be divided into different separated development units based on the baffles and barriers characteristics. Flexible and diverse profile control techniques such as high angle wells and simple and applicative zonal water injection have been introduced to improve the control and development degree of reservoirs. Three principal water injection development methods suitable for different carbonate reservoirs in the Middle East are proposed, including the combination of crestal gas injection and peripheral water injection, bottom interval injection and top interval production(buoyancy underpinning), and "weak point and strong plane" area well pattern. Based on the characteristics of very low shale content, fast and far pressure transmission in the Middle East carbonate reservoirs, a large well-spacing flood pattern is recommended, and reasonable development strategies have been made such as moderate water injection rate and maintaining reasonable production pressure drawdown and voidage replacement ratio, so as to maximize the recovery of reservoirs in the none or low water cut period.

The Tenth Anniversary of Free Trade Pilot Zones in China:Fundamental Experiences and Enhancement Strategies

Since the 18th National Congress of the Communist Party of China,the country has established 21 Free Trade Pilot Zones(FTZs),achieving significant pioneering results in reform and opening up and creating a strong demonstrative effect nationwide.The basic experience from a decade of FTZs includes:adhering to the centralized and unified leadership of the CPC Central Committee;combining top-level design with encouragement of grassroots innovation;leveraging the distinct characteristics and strengths of FTZs to form a differentiated development pattern;maintaining the integration of opening up with domestic reforms;using openness to drive reforms;and organically combining openness with national security assurance.Under the current and future new circumstances,China’s FTZs face new challenges and tasks.In accordance with the directives of the 20th National Congress of the Communist Party of China,an enhancement strategy for the FTZs needs to be implemented.This involves the following:First,accurately understanding and responding to the changing situation to create strategic opportunities.Second,shifting paradigms to implement innovation-driven strategies,using the new development pattern concept to guide the reform experiments and construction of the FTZs.Third,granting more autonomy to FTZs for reforms,pursuing progress while maintaining stability,and solidly advancing the reform experiments in the FTZs.Fourth,orderly expanding the opening up of the service sector and cautiously advancing the internationalization of the renminbi.Fifth,promoting innovative development in trade to build a strong trade nation.Sixth,establishing synergy with bilateral FTZs,Belt and Road cooperation,and national diplomatic strategies to enhance the linkage effect.

A fault injection model-oriented testing strategy for component security

A fault injection model-oriented testing strategy was proposed for detecting component vulnerabilities.A fault injection model was defined,and the faults were injected into the tested component based on the fault injection model to trigger security exceptions.The testing process could be recorded by the monitoring mechanism of the strategy,and the monitoring information was written into the security log.The component vulnerabilities could be detected by the detecting algorithm through analyzing the security log.Lastly,some experiments were done in an integration testing platform to verify the applicability of the strategy.The experimental results show that the strategy is effective and operable.The detecting rate is more than 90%for vulnerability components.

Mechanism and optimization of fuel injection parameters on combustion noise of DI diesel engine

Combustion noise takes large proportion in diesel engine noise and the studies of its influence factors play an important role in noise reduction. Engine noise and cylinder pressure measurement experiments were carried out. And the improved attenuation curves were obtained, by which the engine noise was predicted. The effect of fuel injection parameters in combustion noise was investigated during the combustion process. At last, the method combining single variable optimization and multivariate combination was introduced to online optimize the combustion noise. The results show that injection parameters can affect the cylinder pressure rise rate and heat release rate, and consequently affect the cylinder pressure load and pressure oscillation to influence the combustion noise. Among these parameters, main injection advance angle has the greatest influence on the combustion noise, while the pilot injection interval time takes the second place, and the pilot injection quantity is of minimal impact. After the optimal design of the combustion noise, the average sound pressure level of the engine is distinctly reduced by 1.0 d B(A) generally. Meanwhile, the power, emission and economy performances are ensured.

Investigation of flue gas water-alternating gas (flue gas–WAG) injection for enhanced oil recovery and multicomponent flue gas storage in the post-waterflooding reservoir

Flue gas fooding is one of the important technologies to improve oil recovery and achieve greenhouse gas storage.In order to study multicomponent fue gas storage capacity and enhanced oil recovery(EOR)performance of fue gas water-alternating gas(fue gas-WAG)injection after continuous waterfooding in an oil reservoir,a long core fooding system was built.The experimental results showed that the oil recovery factor of fue gas-WAG fooding was increased by 21.25%after continuous waterfooding and fue gas-WAG fooding could further enhance oil recovery and reduce water cut signifcantly.A novel material balance model based on storage mechanism was developed to estimate the multicomponent fue gas storage capacity and storage capacity of each component of fue gas in reservoir oil,water and as free gas in the post-waterfooding reservoir.The ultimate storage ratio of fue gas is 16%in the fue gas-WAG fooding process.The calculation results of fue gas storage capacity showed that the injection gas storage capacity mainly consists of N_(2) and CO_(2),only N_(2) exists as free gas phase in cores,and other components of injection gas are dissolved in oil and water.Finally,injection strategies from three perspectives for fue gas storage,EOR,and combination of fue gas storage and EOR were proposed,respectively.

Optimization of operational strategies for rich gas enhanced oil recovery based on a pilot test in the Bakken tight oil reservoir

Horizontal well drilling and multistage hydraulic fracturing have been demonstrated as effective approaches for stimulating oil production in the Bakken tight oil reservoir.However,after multiple years of production,primary oil recovery in the Bakken is generally less than 10%of the estimated original oil in place.Gas huff‘n’puff(HnP)has been tested in the Bakken Formation as an enhanced oil recovery(EOR)method;however,most field pilot test results showed no significant incremental oil production.One of the factors affecting HnP EOR performance is premature gas breakthrough,which is one of the most critical issues observed in the field because of the presence of interwell fractures.Consequently,injected gas rapidly reaches adjacent production wells without contacting reservoir rock and increasing oil recovery.Proper conformance control is therefore needed to avoid early gas breakthrough and improve EOR performance.In this study,a rich gas EOR pilot in the Bakken was carefully analyzed to collect the essential reservoir and operational data.A simulation model with 16 wells was then developed to reproduce the production history and predict the EOR performance with and without conformance control.EOR operational strategies,including single-and multiple-well HnP,with different gas injection constraints were investigated.The simulation results of single-well HnP without conformance control showed that a rich gas injection rate of at least 10 MMscfd was needed to yield meaningful incremental oil production.The strategy of conformance control via water injection could significantly improve oil production in the HnP well,but injecting an excessive amount of water also leads to water breakthrough and loss of oil production in the offset wells.By analyzing the production performance of the wells individually,the arrangement of wells was optimized for multiple-well HnP EOR.The multiwell results showed that rich gas EOR could improve oil production up to 7.4%by employing conformance control strategies.Furthermore,replacing rich gas with propane as the injection gas could result in 14%of incremental oil production.

Optimization of Combustion Characteristics and Fuel Injection Timing of a New Type Dual-Pit Combustor Rotary Engine

In order to improve the performance of the rotary engine,this paper has designed a new type of dual-pit rotary engine combustion chamber structure,and compares the combustion and emission characteristics with the rotary engine with a traditional combustion chamber.The existence of the dual-pit combustion chamber strengthens the overall vortex intensity in the cylinder,effectively promotes the mixing process of fuel and air in the cylinder,the maximum combustion pressure in the cylinder increased by 8.6%,significantly increases the diffusion combustion speed,and significantly improves the dynamic performance of the rotary engine.On this basis,the effects of fuel injection timing parameters on fuel distribution,combustion and emission characteristics were studied.Fuel distribution is more even and dispersed during injection in the later stage of compression.When the fuel injection timing was 105°BTDC in the middle of the compression phase,the matching effect of fuel distribution law and ignition scheme was the best.When the injection timing was 75°BTDC and 85°BTDC in the late compression stage,the mass fraction of NOx remained at a low level.The correlation between soot generation and the change of fuel injection timing was weak.When the injection time was 85°BTDC,the soot generation remained at a relatively high level.

STRESSING THE PILOT RESEARCH FOR THE NATIONAL S&T DEVELOPMENTAL STRATEGY

How to put forward advisory suggestions regarded as feasible, workable and acceptable by the State leaders through the integration of the goodwill cherished by our scientists with the blueprint masterminded by the hosts of various R&D projects? It seems to me a problem worthy of our serious consideration. Here I would like to suggest that under the leading group of national S&T affairs, a new organ functionally similar to the State R&D Center be set up. Acting as a counselling team to the group, it must be small in payroll and include by strategists spe-

Investigation on combustion and emission characteristics of diesel polyoxymethylene dimethyl ethers blend fuels with exhaust gas recirculation and double injection strategy

As a kind of renewable and high oxygen content fuel,polyoxymethylene dimethyl ether(PODE)can be added in diesel to realize energy saving and emissions reduction.To evaluate the combustion and emission characteristics of a diesel engine fueled with diesel and diesel/PODE mixtures,exhaust gas recirculation(EGR)and main-pilot injection strategies with various injection timings were applied.PODE was blended with diesel by volume to form mixtures which were marked as D100(pure diesel),D90P10(90%diesel+10%PODE),and D80P20(80%diesel+20%PODE).The results showed that the ignition delay(ID)and combustion duration(CD)of D80P20 were the shortest because of the highest cetane number(CN)and high oxygen content of PODE,indicating more concentrated heat release.At low and medium loads,D80P20 achieved the highest peak heat release ratio(PHRR)and peak combustion temperature(PCT)among the three fuels,and it was 14.3%and 3.6%higher than those of D100.PODE blending with diesel can significantly reduce particulate matter(PM)and D80P20 has the lowest PM emissions at all loads.Compared with D100,both PM and nitrogen oxide(NO_(x))emissions of PODE blends decreased simultaneously with 20%EGR at all loads.With the increase of pilot-main interval,the ID and CD of all test fuels increased,while the NO_(x)and PM emissions decreased.The conclusions of the present research provide a state of the application in light-duty engines fueled with diesel/PODE blends in future work.

以制度型开放创新为核心 高标准高质量推进中国(新疆)自贸试验区建设

在我国自贸试验区建设十周年之际,2023年10月国务院印发了《中国(新疆)自由贸易试验区总体方案》,正式批准设立中国(新疆)自由贸易试验区,使新疆成为我国第22个自贸试验区,也是我国西北边境地区首个自贸试验区。文章深入研究分析了新疆自贸试验区设立的重大意义,并就自贸试验区在拉动我国经济增长和实现高质量发展中的作用,制度创新在自贸试验区打造一流营商环境、提升现代产业国际竞争力等方面所发挥的作用和影响,以及制度型开放创新与逆全球化背景下深入实施自贸试验区提升战略的关系等问题进行了全面分析与思考。在此基础上,就如何以高水平开放为引领,以制度创新为核心,高标准高质量建设新疆自贸试验区提出了思路与对策建议。

新发展格局下中国自贸试验区建设的现实约束、演进逻辑与政策取向

在构建新发展格局背景下,我国自贸试验区建设面临泛安全化倾向挤压开放合作空间、国际经贸规则重构抬高开放标准和要求、深层次体制机制障碍亟待突破等现实约束,需要处理好供需动态平衡、内外开放平衡、区域发展平衡,遵循由“效率优先兼顾安全”转向“效率与安全并重”、由“商品和要素流动型开放”转向“制度型开放”、由“产业演化路径依赖”转向“产业链协同创新”的演进逻辑。实施自贸试验区提升战略,要着力提升自贸试验区的平台能级,强化质量与安全导向,聚焦打造多点多极的双循环节点枢纽、提升国际经贸规则制定话语权、扩大产业高质量发展的示范带动效应“三向发力”。实施自贸试验区提升战略的政策取向为:坚持高水平对内对外开放,有效应对“脱钩断链”;对接高标准国际经贸规则,推进高水平制度型开放;破解深层次体制机制障碍,塑造高质量发展新优势。

自动飞行员复诵指令生成方法研究

为了提高效率,降低培训成本并推广使用计算机来取代管制模拟机中的飞行员席位,采用集成学习的策略来生成飞行员复诵指令。选用5个大规模预训练语言模型进行微调,并使用K折交叉验证来筛选出性能较好的4个模型作为基础模型来构建集成学习模型。所构建的集成学习模型在管制指令数据集上取得在本领域中的最优效果。在通用的ROUGE(recall-oriented understudy for gisting evaluation)评价标准中,取得R_(OUGE-1)=0.998,R_(OUGE-2)=0.995,R_(OUGE-L)=0.998的最新效果。其中,R_(OUGE-1)关注参考文本与生成文本之间单个单词的匹配度,R_(OUGE-2)则关注两个连续单词的匹配度,R_(OUGE-L)则关注最长公共子序列的匹配度。为了克服通用指标在本领域的局限性,更准确地评估模型性能,针对生成的复诵指令提出一套基于关键词的评价标准。该评价指标准基于管制文本分词后的结果计算各个关键词指标来评估模型的效果。在基于关键词的评价标准下,所构建模型取得整体准确率为0.987的最优效果,对航空器呼号的复诵准确率达到0.998。

二冲程半直喷航空发动机喷油策略研究

基于自主研发的二冲程低压半直喷航空发动机及控制系统,开展喷油控制策略及对发动机性能影响规律的研究。结果表明:对于不同的发动机运行工况,需要采取不同的喷油策略组合。在起动和怠速工况,采用进气道喷射的独立供油方式;在部分负荷及高负荷工况,采用进气道喷射和缸内直喷协同供油方式,随着发动机直喷比例的提高,燃油消耗率相应减小;与采用进气道喷射供油相比较,采用低压半直喷供油可以获得较理想的燃油经济性。

喷射策略对RCCI燃烧影响的试验

为了分析不同喷油策略对反应活性控制压燃(reactivity controlled compression ignition,RCCI)燃烧着火性能与燃烧性能的影响,使用汽油和柴油/加氢催化生物柴油(hydrocatalytic biodiesel,HCB)在光学发动机内进行了试验研究.结果表明:柴油/汽油RCCI燃烧较HCB/汽油需要的进气温度高,着火延迟期也较高,随着进气温度的增加,燃烧相位提前,着火延迟期减小;当柴油所含能量与燃料循环总能量之比从30%提高至40%时,缸内压力升高,进气温度对燃烧的影响减小;在HCB/汽油RCCI燃烧模式下,HCB喷油时刻从进气上止点后的曲轴转角-30.0°延迟至-20.0°后,燃烧过程对进气温度的敏感度降低;在光学发动机试验中,采用较高的进气温度有利于更好地实现RCCI稳定燃烧,但进气温度低于30℃时,可以通过推迟高活性燃料喷射时刻或提高高活性燃料质量分数来实现稳定着火燃烧,达到控制燃烧相位的目的.

川渝自贸试验区协同开放空间策略研究

川渝自贸试验区协同开放示范区是成渝地区双城经济圈和西部陆海新通道建设的重要支撑平台。从空间角度研究川渝自贸区协同开放的问题并提出规划策略,是优化配置成渝地区双城经济圈空间资源要素的重要手段。梳理相关政策,明确协同开放的空间内涵及空间要素,从平台要素、通道要素、产业要素入手,分析川渝自贸试验区空间发展现状,总结川渝自贸试验区空间要素存在的问题。以重庆自贸区为例,从优化区域协同布局、促进互联互通共享、增存联动差异引导、创新规划管控方法等方面提出协同开放的空间规划策略。

不同海拔下压燃式航空活塞发动机预喷的燃烧与排放特性

针对不同海拔下压燃式航空活塞发动机预喷的影响作用,在发动机台架试验验证的基础上进行了海拔2~4 km,不同预喷策略下的燃烧与排放仿真分析。结果表明:在中转速巡航工况下,随着预喷油量占比增加,放热率峰值降低,缸内压力峰值升高,燃烧始点与燃烧重心提前,燃烧持续期延长,CO,HC与NO_(x)排放均呈升高的趋势;当预喷间隔角增加时,放热率峰值略有升高,缸内压力峰值降低,尽管CO,NO_(x)排放降低,HC排放却是升高的。巡航高度为2 km,3 km,4 km时,采用预喷油量占比4%,预喷间隔角14°CA的方案,相比于单次喷射CO,HC与NO_(x)排放值分别平均降低约7.83%,25.63%与17.04%。在高转速爬升工况下,采用较小的预喷油量占比可以提升发动机输出功率并改善排放,但当预喷油量占比和间隔角增加时,最大燃烧温度、缸内压力与压力升高率均逐渐升高。总之,4%预喷油量占比和14°CA预喷间隔角的方案在不同海拔下均能保持较好的发动机功率输出,还能有效降低CO,HC与NO_(x)的排放。

柴油微引燃双燃料发动机燃烧及排放特性研究

为改善柴油微引燃双燃料发动机的燃烧过程、经济性及排放特性,通过数值仿真方法研究了大负荷工况下喷油策略、废气再循环(Exhaust Gas Recirculation,EGR)及进气门晚关(Late Intake Valve Closing,LIVC)对柴油微引燃双燃料发动机缸内燃烧及排放特性的影响。结果显示:随着预喷时刻提前,缸压和放热率峰值降低,NO_(x)排放量降低,但预喷时刻过早导致缸内燃烧状况恶化,热效率下降。随着主喷时刻提前,缸压和放热率峰值先升高后逐渐降低,碳烟、碳氢化合物(Hydrocarbon,HC)和CO排放量先逐渐降低后略微升高,NO_(x)排放量先增多后减少;燃烧相位受主喷时刻的影响较大,合理调节主喷时刻可有效控制天然气/柴油反应活性控制压燃(Reactivity Controlled Compression Ignition,RCCI)燃烧相位和污染物排放。随着EGR率增加,缸压及放热率峰值减小,缸内温度降低,燃烧相位推迟,有利于发动机向更高负荷范围拓展。当进气门晚关角度为0时,EGR率从32%增至48%,NO_(x)排放量下降66.21%;当EGR率大于40%后,碳烟、HC和CO排放量随EGR率增加而急剧升高。随着LIVC增大,缸压峰值和放热率峰值显著下降,指示热效率和NO_(x)排放量逐渐降低,碳烟、HC和CO排放量增加。在大负荷工况下,采用合适的主喷时刻、较小的LIVC耦合较低的EGR率可提高发动机的热效率,维持NO_(x)排放量较低的同时能有效减少碳烟、HC和CO排放量。

预燃室点火式汽油机稀薄燃烧特性试验研究

基于测试试验台架对被动预燃室增压直喷汽油机在不同工况下的效率特性、燃烧特性、燃油经济性以及排放特性进行了研究。采用3次喷射策略形成稀薄燃烧环境(过量空气系数为1.3),发动机转速为2800 r/min,2000 r/min。结果表明:同一转速条件下,增压预燃室发动机在负荷增加时,有效热效率和有效机械效率呈上升趋势,但超过一定范围,有效热效率下降;CA10,CA50,CA75,CA90和最大爆震指数随负荷增大呈上升趋势,同时燃烧循环变动率也可以控制在0.35%以下;发动机转速为2800 r/min,较小负荷时的燃油消耗率最低可达242.1 g/(kW·h);NO_(x),HC和CO排放与发动机运行工况密切相关,随负荷增加呈现减少趋势,Soot排放可控制在0.13 mg/m^(3)。