The Negative Thermal Expansion Property of NdMnO_(3) Based on Pores Effect and Phase Transition

A novel negative thermal expansion(NTE) material NdMnO_(3) was synthesized by solid-state method at 1 523 K. The crystal structure, phase transition, pores effect and negative expansion properties of NdMnO_(3) were investigated by variable temperature X-ray diffraction(XRD), scanning electron microscope(SEM) and variable temperature Raman spectra. The compound exhibits NTE properties in the orderly O' phase crystal structure. When the temperature is from 293 to 759 K, the ceramic NdMnO_(3) shows negative thermal expansion of-4.7×10^(-6)/K. As temperature increases, the ceramic NdMnO_(3) presents NTE property range from 759 to 1 007 K. The average linear expansion coefficient is-18.88×10^(-6)/K. The physical mechanism of NTE is discussed and clarified through experiments.

Free radicals trigger the closure of open pores in lignin-derived hard carbons toward improved sodium-storage capacity

The chemical activation of various precursors is effective for creating additional closed pores in hard carbons for sodium storage.However,the formation mechanism of closed pores under the influence of pore-forming agents is not well understood.Herein,an effective chemical activation followed by a high-temperature self-healing strategy is employed to generate interconnected closed pores in lignin-derived hard carbon(HCs).By systematic experimental design combined with electron paramagnetic res-onance spectroscopy,it can be found that the content of free radicals in the carbon matrix influences the closure of open pores at high temperatures.Excessively high activation temperature(>700 C)leads to a low free radical concentration,making it difficult to achieve self-healing of open pores at high tempera-tures.By activation at 700°C,a balance between pore making and self-healing is achieved in the final hard carbon.A large number of free radicals triggers rapid growth and aggregation of carbon microcrys-tals,blocking pre-formed open micropores and creating additional interconnected closed pores in as-obtained hard carbons.As a result,the optimized carbon anode(LK-700-1300)delivers a high reversible capacity of 330.8 mA h g^(-1) at 0.03 A g^(-1),which is an increase of 86 mA h g^(-1) compared to the pristine lignin-derived carbon anode(L-700-1300),and exhibits a good rate performance(202.1 mA h g^(-1) at 1 A g^(-1)).This work provides a universal and effective guidance for tuning closed pores of hard carbons from otherprecursors.

Maceral evolution of lacustrine shale and its effects on the development of organic pores during low mature to high mature stage:A case study from the Qingshankou Formation in northern Songliao Basin,northeast China

Organic matter(OM)hosted pores are crucial for the storage and migration of petroleum in shale reservoirs.Thermal maturity and macerals type are important factors controlling the development of pores therein.In this study,six lacustrine shale samples with different thermal maturities from the first member of the Qingshankou Formation in the Songliao Basin,of which vitrinite reflectance(R_(o))ranging from 0.58% to 1.43%,were selected for a comparative analysis.Scanning electron microscopy(SEM)and reflected light microscopy were combined to investigate the development of organic pores in different macerals during thermal maturation.The results show that alginite and liptodetrinite are the dominant primary macerals,followed by bituminite.Only a few primary organic pores developed in the alginite at the lowest maturity(R_(o)=0.58%).As a result of petroleum generation,oil-prone macerals began to transform to initial-oil solid bitumen at the early oil window(R_(o)=0.73%)and shrinkage cracks were observed.Initial-oil solid bitumen cracked to oil,gas and post-oil bitumen by primary cracking(R_(o)=0.98%).Moreover,solid bitumen(SB)was found to be the dominant OM when R_(o)>0.98%,which indicates that SB is the product of oil-prone macerals transformation.Many secondary bubble pores were observed on SB,which formed by gas release,while devolatilization cracks developed on migrated SB.Additionally,at the late oil window(Ro?1.16%),migrated SB filled the interparticle pore spaces.With further increase in temperature,the liquid oil underwent secondary cracking into pyrobitumen and gas,and spongy pores developed on the pyrobitumen at higher levels of maturity(Ro=1.43%),which formed when pyrobitumen cracked into gas.Vitrinite and inertinite are stable without any visible pores over the range of maturities,verifying their low petroleum generation potential.In addition,it was concluded that clay minerals could have a catalytic effect on the petroleum generation,which may explain why organicclay mixtures had more abundant pores than single OM particles.However,after R_(o)>0.98%,authigenic minerals occupied the organic pore spaces on the organic-clay mixtures,resulting in fewer pores compared to those observed in samples at the early to peak oil window.

Preparation of Chiral Silica Nanostructures with Radial Pores through Single-templating Approach

A chiral low-molecular-weight gelator(LMWG) L-16Ala5PyPF6 was synthesized from L-alanine, which can cause physical gel in n-propanol, ethyl acetate, butylene oxide, water, benzene, 1,4-dioxane and chloroform. The sol-gel reactions were carried out in a mixture of stronger ammonia water and n-propanol at the volume ratio of 2:8. Single-handed twisted silica nanostructures with pore channels vertical to the wall surfaces were first prepared through a single-templating approach comparing with the reported double template method. The formation mechanism of radial pore structure was studied by transmission electron microscopy at different reaction time intervals, which indicated that the radial pore structure was formed via a structural transition in the sol-gel transcription process.

Organic matter pores in the chang 7 lacustrine shales from the Ordos Basin and its effect on reflectance measurement

To quantify the pore characteristics of various macerals in Chang 7 lacustrine shales,macerals were effectively identified according to their optical and morphological characteristics,and the nanoscale pore structure of macerals was observed by scanning electron microscope.Meanwhile,the reflectances of different positions in the same pieces of vitrinite or solid bitumen with heterogeneous pores development were measured.The results showed that the average contents of sapropelinite,liptinite,vitrinite,inertinite and solid bitumen are 42.7%,8.7%,13.6%,13.8% and 21.2%,respectively,which suggests that the source of the organic matter of the Chang 7 shales is a mixed source input.The organic pores of Chang 7 shales are enriched,and the pore shapes are mostly round or elliptical.The pore size of organic pores has a wide distribution,mainly concentrate in the range of 100-400 nm,and the average plane porosity of organic pores is 10.13%.The size order of the organic pores in various macerals is:solid bitumen<bituminite<alginite<vitrinite<fusinite<liptinite.The abundance order of organic matter pores of each maceral is as follows:alginite>fusinite>bituminite>solid bitumen>vitrinite>liptinite.OM pores are mainly contributed by bituminite,solid bitumen and fusinite.The plane porosity of bituminite increases with maturity.In the process of thermal evolution,the plane porosity of fusinite is distributed in the two ranges of 20%-28% and 1%-7%.The former is mainly the primary pores of the fusinite itself,and the latter is the secondary pores formed in the thermal evolution.As for the organic pores of other macerals,no obvious thermal evolution law was found.Meanwhile,the surface imperfections of vitrinite or solid bitumen is enhanced by the enrichment of organic pores(an increase in pore size or pore number),which may result in the underestimation of their reflectances.

Types and microstructures of pores in shales of the Ordovician Wulalike Formation at the western margin of the Ordos Basin, China

Shale samples from the Ordovician Wulalike Formation at the western margin of the Ordos Basin are studied to define the types, microstructures and connectivity of pores as well as the relationships between the pore structures and gas content of the samples by using experimental techniques such as high-resolution field emission scanning electron microscopy (FESEM), mercury injection capillary pressure (MICP), low-temperature nitrogen adsorption (LTNA), CO_(2) adsorption, and focused ion beam scanning electron microscopy (FIB-SEM). The results show that the shale has 10 different lithofacies, typical mixed sedimentary characteristics, and poorly developed pores. The reservoir space mainly consists of intercrystalline pores, dissolution pores, intergranular pores, and micro-fissures, with organic pores occasionally visible. The pore size is mostly within 0.4–250 nm range but dominated by micropores and mesopores less than 20 nm, with pore numbers peaking at pore sizes of 0.5 nm, 0.6 nm, 0.82 nm, 3 nm, and 10 nm, respectively. The pores are poorly connected and macropores are rarely seen, which may explain the low porosity and low permeability of the samples. Samples with high content of organic matter and felsic minerals are potential reservoirs for oil and gas with their favorable physical properties and high connectivity. The pores less than 5 nm contribute significantly to the specific surface area and serve as important storage space for adsorbed gas.

煅烧凝灰岩对水泥水化产物和硬化体孔结构的影响

为探明煅烧凝灰岩对水泥水化产物的影响,借助X射线衍射(XRD)、热重分析(TG)、傅里叶变换红外光谱(FTIR)等测试方法,分析了700℃下煅烧不同时间后凝灰岩的矿物组成及其对水泥水化产物和硬化体孔结构的影响.结果表明:煅烧后凝灰岩中的沸石水、结构水和吸附水被脱除,斜发沸石等沸石矿物架状结构发生破坏,形成无定形的SiO_(2)和Al_(2)O_(3);煅烧凝灰岩有助于水泥中的水化硅酸钙(C-S-H)、钙矾石(AFt)和单硫型水化硫铝酸钙(AFm)形成,且降低了C-S-H的钙硅比(n(Ca)/n(Si)),消耗了Ca(OH)_(2),水泥更易发生碳化;水化28 d后,煅烧凝灰岩水泥的孔隙率降低,孔径分布更细,从而提高了水泥强度.

川东地区侏罗系大安寨段页岩储层特征及发育控制因素

为探究陆相页岩储层特征及页岩储集空间发育的控制因素,文中以四川盆地东部大安寨段页岩为例,基于页岩岩心的分析化验资料,对页岩储层孔隙发育控制因素进行了研究,明确了优势岩相及甜点储层特征。研究结果表明:1)川东地区大安寨段页岩岩相类型包括硅质页岩、混合质页岩以及黏土质页岩,其中黏土质页岩总有机碳质量分数最高,其次为混合质页岩。2)页岩孔隙类型以片状黏土矿物晶间孔与有机质孔为主,裂缝以页理缝为主。3)页岩储集空间的发育主要受矿物组分、成岩作用以及构造因素的共同控制。4)基于页岩生烃潜力与储集能力,认为混合质页岩为大安寨段的优势页岩岩相。大安寨段页岩甜点储层段主要分布于大二亚段a小层,主要为混合质页岩与介壳灰岩的薄夹层。

海砂超高性能混凝土试验

采用未淡化的海砂制备超高性能混凝土(UHPC)和普通混凝土,研究了不同氯离子含量的海砂对UHPC抗压强度、孔结构、快速氯离子渗透性以及内置钢筋耐久性的影响,并与普通混凝土进行分析比较。结果表明,海砂中的氯离子含量对UHPC抗压强度并不会产生较大的消极影响;海砂UHPC的临界孔半径约为2 nm,与海砂普通混凝土不同,孔隙率随海砂中氯含量的增加而增加;即使海砂氯离子含量高达0.636%,海砂UHPC的氯离子渗透性仍可忽略不计;海砂UHPC中钢筋在28 d后处于钝化状态并趋于稳定。

页岩基质孔隙油微观赋存及可动性定量表征——以东营凹陷沙河街组为例

页岩基质孔隙油微观赋存特征及可动性是制约陆相页岩油高效开采的关键要素。本文针对页岩基质孔隙内不同相态油的含量、比例、分布及可动性开展定量化表征研究,从理论上提出了页岩油吸附量、游离量、可动量评价模型以及吸附油占比评价模型(即吸附比例方程),建立了基于饱和—离心—核磁共振联合实验的孔隙油微观赋存及可动性评价方法。上述模型与方法在渤海湾盆地济阳坳陷东营凹陷沙河街组页岩油储层中进行了应用,揭示了实验条件(20℃、常压)下页岩基质孔隙中轻质油(正十二烷)微观赋存与可动性特征。结果显示:(1)富有机质页岩吸附油、游离油含量普遍大于含有机质页岩,吸/游比主体介于1~2,不同类型页岩中吸附油、游离油赋存空间具有差异性。(2)富有机质页岩吸附油平均密度(0.8331 g/cm^(3))略大于含有机质页岩(0.8067 g/cm^(3)),富有机质页岩吸附油平均厚度(1.7475 nm)约为含有机质页岩(0.5734 nm)的3倍,富有机质页岩具有更强的油—岩相互作用。(3)游离油赋存孔隙直径下限(d_(min))数值上等于吸附油平均厚度与孔隙形状因子的乘积,富有机质页岩d_(min)介于3.5~10.5 nm,开始主要富集游离油的孔隙直径约为100 nm;含有机质页岩d_(min)介于1.1~3.4 nm,开始主要富集游离油的孔隙直径约为30 nm。(4)富有机质页岩孔隙油可动性相对更好,其可动性指数(平均6.24 mg·g^(-1)·MPa^(-1))高于含有机质页岩(平均5.20 mg·g^(-1)·MPa^(-1)),孔隙油吸/游比约为1.5时具有较好可动性。(5)以油—岩相互作用为纽带,构建了页岩含油性、储集性及页岩油可动性之间的耦合关系,并数学描述了它们之间的内在联系,为寻找优质页岩油储层奠定了理论基础。

基于形态学开运算的浸矿体系孔隙结构及其演化特征

立足堆浸体系的偏析分层复杂结构,结合X-ray CT无损探测、形态学开运算处理、MATLAB和OsiriX可视化软件等手段,引入颗粒间孔隙的当量孔隙尺寸、面积、数量等关键表征参量,如从二维量化和三维可视化层面揭示浸矿体系中颗粒间孔隙结构特征及其演化规律.研究发现,细颗粒夹层呈“包裹体”状且均位于粗矿石颗粒的内部,分析认为其是造成堆浸体系颗粒偏析和分层的重要致因;浸矿作用下微细颗粒迁移导致矿堆内部发生沉积压实作用,由197 mm降至180 mm以下;浸矿21 d后,矿堆上部孔隙呈增大趋势,下部孔隙率呈减小趋势,此外,纵向当量孔隙的直径由2.81 mm减小至2.18 mm,其变化趋势和程度要显著大于横向颗粒间孔隙的当量直径;对比浸矿0 d和21 d的柱浸体系三维颗粒间孔隙结构,证实了细颗粒夹层所处区域的粘结聚集以及细颗粒夹层周边区域形成溶液绕流、溶液优势流动路径.

基于电成像的孔洞型碳酸盐岩储层连通性评价

碳酸盐岩储层非均质性强,孔隙结构复杂,相较于常规碎屑岩储层,其孔隙度、渗透率关系的规律及特征不明显。碳酸盐岩储层的连通性与孔洞特征具有强相关性,且连通性是影响储层渗透率的重要因素,因此,对碳酸盐岩孔洞连通性的评价是孔洞型碳酸盐岩储层评价的关键问题。以伊拉克东南部B油田FQ-1井M组MB21亚油组孔洞型碳酸盐岩储层为例,基于地层微电阻率扫描成像(FMI)测井的高分辨率动态图像,利用最大类间方差算法(OTSU)进行二次迭代分割,识别电成像图像孔洞;根据8连通域标记法标记连通孔洞;提取每个连通孔洞的特征孔径、内部最长通道距离、内部最长通道与水平方向夹角、平均通道宽度这4个几何参数,最终构建孔洞型碳酸盐岩储层连通指数。连通指数在伊拉克东南部B油田FQ-1井M组MB21亚油组孔洞型碳酸盐岩储层的应用表明,利用此方法建立的连通指数与FQ-1井碳酸盐岩储层岩心渗透率相关系数达0.8437,并且连通指数曲线的趋势符合岩心渗透率在储层不同深度的分布情况,证明了连通指数可以指示储层孔隙结构较好、溶蚀孔洞发育的深度段,并可以划分储层中连通性较好的深度区间,该参数对于寻找碳酸盐岩储层渗透层具有重要意义。

计算注水开发不同阶段体积波及系数的新方法

体积波及系数是油田评价开发效果、制定开发调整方案的重要依据。为了研究注水开发不同阶段体积波及系数的变化规律,从注入孔隙体积倍数角度出发,根据油水相对渗流理论与油藏工程原理,提出了驱油效率与注入孔隙体积倍数的计算模型,建立了体积波及系数计算方法,并以胜利油田3个试验区为例进行了计算与分析。结果表明:驱油效率与注入孔隙体积倍数之间满足指数方程,二者关系曲线呈上凸型;随着注入孔隙体积倍数的增大,驱油效率由最小驱油效率逐渐增大,并趋近于最大驱油效率;对驱油效率计算模型进行验证,预测值与实测值的平均相对误差仅为1.90%;水驱开发过程中体积波及系数与注入孔隙体积倍数关系曲线整体呈快升-缓升-近平台状演变趋势,计算结果能够指导开发调整措施的效果评价;3个试验区目前体积波及系数接近90%,波及区内存在大量剩余油,亟需开展波及区内主体剩余油的描述与启动方法研究。

流固耦合作用下深部岩石动态力学响应研究进展

深部岩石处于高地应力、高渗透压和强动态扰动的复杂地质环境之中,3者作用下岩石体更加容易发生损伤破裂,诱发突涌水、渗漏、井喷等工程地质灾害,因而探究流固耦合作用下岩石的动态力学响应是开展岩石工程建设的前提之一。近年来,国内外众多学者在考虑水和不同应力状态下的岩石动态力学实验研究方面取得了显著的成果。为给工程建设提供更加全面的指导并为后续研究奠定基础,从实验装置、测试结果以及围压与水的作用机理层面,对上述工作进行了回顾与总结。首先介绍了分离式霍普金森压杆测试装置的基本原理,以及用于模拟深部岩石赋存环境所进行的装置改进,包括围压分离式霍普金森压杆实验系统和孔压(渗透压)耦合的分离式霍普金森压杆实验系统,简要分析了各类装置在研究流固耦合作用下岩石动力学问题时的优势和不足。其次,总结了考虑不同应力状态(单向加载、三向围压加载)的流固耦合作用下岩石的动态力学响应特性。详细介绍了固定预设孔压、渗透压耦合作用下深部岩石的动态力学响应及其随孔隙水压、渗透压变化的规律。随后,概述了围压对岩石动力学性质的影响机理,分析了不同围压条件下的影响规律;总结了水对岩石动态力学性质的强化、弱化微观机制和定量表达。最后,对流固耦合作用下深部岩石的动态力学响应进行了概括总结,并对未来实验研究工作和深部赋存条件下岩石动态力学的研究方向进行了展望。

页岩无机孔和有机孔的渗透率计算方法

针对页岩储层无机孔隙和有机孔隙共存的问题,运用双重连续介质方法,结合油相和水相在页岩无机孔隙和有机孔隙中的润湿性和渗流特征,得到油相和水相在页岩中的渗流数学模型。基于该模型拟合页岩油水自吸实验结果,分别得到了页岩的无机孔渗透率和有机孔渗透率,实现了对页岩储层含油量的准确计算,研究了页岩渗流过程的动态特征和影响规律。结果表明:无机孔渗透率为10^(-8)~10^(-5)D,有机孔渗透率为10^(-10)~10^(-7)D;随无机孔渗透率、有机孔渗透率的增加,页岩自吸速率加快;当有机孔渗透率与无机孔渗透率比值小于10^(-3)时,有机孔渗透率对自吸速率的影响不显著。研究成果对页岩储层渗透率和储量的精细评价具有重要指导意义。

聚酯纤维泡沫混凝土力学性能及孔结构研究

纤维的掺加可有效地改善泡沫混凝土抗压强度低、脆性特征显著的缺陷,增强其工程适用性。本工作针对聚酯纤维对泡沫混凝土力学性能的改善开展试验研究,选定密度等级为700 kg/m3的泡沫混凝土,考虑不同纤维体积掺量(0.1%、0.2%、0.3%和0.4%)对其抗压强度、抗折强度、劈裂抗拉强度以及延性的影响。结果表明:纤维掺量为0.1%时,材料表现出较优的抗压和劈裂抗拉性能,28 d强度分别增加了86.4%和91.3%;纤维掺量为0.2%时,材料表现出较优的抗折性能,28 d抗折强度提升了39.1%。试样破坏形态和应力-应变曲线表明,聚酯纤维可有效地提升泡沫混凝土的延性。最后,运用图像分析处理法分别获得了五组试件的孔结构参数,从细观孔结构的角度讨论了聚酯纤维对泡沫混凝土抗压强度的影响机理。

甲烷裂解双分散孔催化剂颗粒积碳行为模拟

【目的】为了更好地理解催化剂颗粒的积碳行为,分析积碳效应下催化剂颗粒界面反应传质特性,实现对催化剂颗粒的优化设计与调控。【方法】采用颗粒解析模型,考虑积碳引起的孔隙结构动态演变以及反应性能的衰减,分别探讨单分散孔和双分散孔颗粒积碳形成及所引起的孔隙结构演变规律。【结果】积碳失活从多孔颗粒表层向内部核心移动,扩散主导机制转向反应主导机制;相较于单分散孔颗粒,双分散孔颗粒具备更强的抗积碳性能;固定床反应器中催化剂颗粒分布影响积碳行为,壁面处积碳更加严重,更容易导致失活。【结论】选择双分散孔催化剂颗粒对于积碳行为具有改善作用,同时应选择合适的长径比反应器,削弱壁面效应对积碳行为的影响。

页岩储层应力敏感性的时间效应

有效应力及其作用时间是控制岩石孔隙和裂缝变形的重要外部因素。页岩储层的多尺度孔隙结构特征及孔缝配置关系使得其应力敏感时间效应具有特殊性,然而,以往研究尚未考虑有效应力加载及卸载时间对页岩应力敏感行为的影响。以川南威荣气田龙马溪组页岩气藏为研究对象,钻取不同孔缝发育程度的页岩样品,设计并测试了变有效应力状态下变加载及卸载持续稳定时间对岩样渗透率的影响实验。结果表明:1)有效应力从5 MPa升至35 MPa时,微裂缝岩样和基块岩样渗透率分别降低了66.82%和27.19%,卸载过程中渗透率恢复率为74.73%和79.82%。页岩渗透率越低,有效应力滞后效应越显著;2)恒定有效应力加载持续稳定时间从2.5 h延长至10.0 h,应力敏感系数增加3.76%∼80.17%,且当有效应力较小时的时间效应更显著。研究认为,页岩组分及多尺度孔缝结构是导致其孔缝变形行为差异性的主因。基于实验研究结果,推荐页岩样品老化处理为6.0 h,提出了优化页岩储层敏感性评价实验方案和优化气井工作制度的建议。

下扬子地区荷塘组细粒沉积岩岩相划分及微观孔隙发育特征

下扬子地区下寒武统荷塘组细粒沉积岩岩相微观孔隙发育特征不清楚制约了页岩气的勘探开发。基于普通薄片观察、氩离子抛光扫描电镜(SEM)分析、物性测试、X射线衍射全岩矿物及黏土矿物含量分析、N_(2)及CO_(2)等温吸附实验、聚焦离子束扫描电镜(FIBSEM)分析等实验资料,建立了荷塘组细粒沉积岩岩相划分方案,分析了不同岩相的微观孔隙结构特征。研究表明:①荷塘组细粒沉积岩主要发育块状硅质泥岩相、纹层状硅质页岩相、块状含黏土硅质泥岩相、块状硅/灰混合质泥岩相和块状混合灰质泥岩相5种岩相类型。②荷塘组不同细粒沉积岩岩相孔隙度和渗透率差异较大。孔隙类型主要为粒间孔、晶间孔、粒内孔、有机质孔和微裂缝,以微米-纳米级孔隙为主。介孔孔径为2.0~10.0 nm,微孔孔径为0.4~0.9 nm。③块状硅/灰混合质泥岩相有机质和脆性矿物含量高,粒间孔与微裂缝发育,孔隙度和渗透率较大、孔隙连通性较好、比表面积较大,为荷塘组最有利的页岩气勘探开发细粒沉积岩岩相。块状含黏土硅质泥岩相孔隙比表面积和孔体积较高,脆性指数、孔隙度和渗透率低于块状硅/灰混合质泥岩相,为次要的有利岩相。

鄂尔多斯盆地长7_(3)亚段储层微观孔隙结构和固液作用力

针对鄂尔多斯盆地长7_(3)亚段页岩储层孔隙结构和固液作用力问题,首先,通过聚焦离子束电子显微镜、计算机断层扫描技术和原子力显微镜对纯页岩储层样品开展研究;其次,结合Avizo软件建立页岩多尺度三维重构模型,定量分析页岩孔隙结构特征;最后,提出页岩储层固液相互作用黏附力测试方法,测定原油与孔隙壁面之间的黏附力。研究结果表明:长7_(3)储层发育有粒间孔、粒内孔和有机质孔隙,有机质孔隙形状主要有条状、弯月状和椭圆状;在微米尺度下,可以清晰看到层理缝;在纳米尺度下,不同页岩结构的样品孔隙结构特征无明显差异,孔喉形态多为片状和条状;有机质与原油之间的黏附力最大,长英质与原油之间的黏附力次之,层理面与原油之间的黏附力最小,3种平均黏附力分别为0.098、0.063和0.041μN,长7_(3)页岩储层中壁面原油启动难度较大,这从力学角度解释了该区为原位转化重点区域的原因。