Characteristics and control factors of feldspar dissolution in gravity flow sandstone of Chang 7 Member,Triassic Yanchang Formation,Ordos Basin,NW China

To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.

Experimental Study on Gold Dissolution from Hosting Minerals of the Hadamengou Gold Deposit and the Implications

The Hadamengou gold deposit is located in western part of the northern margin of the North China craton. It is a hydrothermal deposit related to alkaline magmatism. Dissolution of Au, Fe from pyrite and iron oxide （including magnetite and hematite） individual minerals in the three main types of ore shows： in iron oxides （magnetite and hematite）, Au and Fe were dissolved simultaneously and their solubilities are positively correlated, which means Au is mainly chemical-bonded （lattice gold） and/or colloidal-adsorbed in iron oxides; while in pyrite, on the contrary, Au dissolution obviously lags behind Fe and the solubility of Au shows negative relationship with that of Fe, which indicates Au is mainly hosted as grains of elemental gold （or native gold） within pyrite. Previous studies revealed that the Hadamengou gold deposit is characterized by intensive K-feldspathization and holds high content of iron oxides occasionally replaced by sulfides, which was caused by oxidizing K-enriched alkaline fluids under a stretching geodynamic setting. These geological features, together with the high Au-content in iron oxides, comparable with that of the Olympic Dam deposit in South Australia, suggest that this deposit is the first example of iron oxide-type gold deposits in China.

Experimental Simulation of Dolomite Dissolution Under Burial Diagenesis Conditions and Thermodynamic Interpretation

Simulating experiments on dolomite dissolution by acetic acid were made under burial diagenesis conditions, at temperatures ranging from 75℃ to 130℃ and pressures from 20 MPa to 30 MPa. The results show that the dissolution rate of dolomite increased rapidly with increasing temperature and pressure. From 75℃/20 MPa to 130℃/30 MPa, the total amount of released Ca and Mg increased from 32.98 mg/L to 337.9 mg/L, over one order of magnitude in difference. Thermodynamic calculation indicates that the increment of Gibbs free energy (△G) of the chemical reaction decreases with increasing temperature and pressure. This thermodynamic result is consistent with the experimental result. Based on the experimental results, it is suggested that secondary porosities formed by dolomite dissolution under conditions of deep burial diagenesis should be more common than those under epigenesis and shallow burial conditions, and therefore dolomite reservoirs in the formations that have been deeply buried should be more abundant than in the formations that have only been shallowly buried.

Experimental study on interaction between simulated sandstone and acidic fluid

In order to investigate the controlling mechanism of temperature, fluid and other factors on water-rock interaction in the diagenetic process, we performed a series of simulated experiments on the interaction between two kinds of fluids with different salinity and a composite mineral system （simulated sandstone）, which contains albite, K-feldspar and other minerals. The experimental results showed that acidity was the most important factor that affected the dissolution of minerals in the composite mineral system. The lower the pH value, the more easily the minerals dissolved. At the same pH value, the dissolution abilities of different acids for various mineral components were also different. Compared to hydrochloric acid （inorganic acid）, oxalic acid （organic acid） was more able to dissolve aluminosilicate minerals. However, the dissolution ability of oxalic acid for carbonate minerals was lower than that of hydrochloric acid. In the process of fluid-rock interaction, dissolution of feldspar was relatively complicated. Increase of temperature would accelerate the dissolution of feldspar. Under acidic conditions, albite had a higher dissolution rate than K-feldspar. K-feldspar could dissolve and convert into montmorillonite and kaolinite, while albite could dissolve and convert into kaolinite both at 40℃ and 80℃. Presence of organic acid, and decrease of pH value and water salinity were all favorable for the dissolution of feldspar, but weakened the ability to form clay minerals.

Simulation for the dissolution mechanism of Cambrian carbonate rocks in Tarim Basin, NW China

Carbonate dissolution during the process of burial and evolution by percolating acid fluid was simulated using core plugs to analyze the characteristics and controlling factors of Cambrian carbonate rock dissolution in the Tarim Basin. The results showed that mineral composition and reservoir space type control selective dissolution. In the carbonate rock strata with high calcite content, the calcite is likely to dissolve first to form secondary dissolution pores; gypsum and anhydrite in the carbonate rock can be dissolved to form mold pores in contemporaneous and penecontemporaneous stages. Porous carbonate has mainly enlargement of matrix pores, with porosity and permeability increasing correspondingly, but not obviously. In comparison, dominant channels for fluid are likely to occur in fractured carbonate or porous carbonate forming cracks under high pressure, resulting in a relative reduction in the dissolution volume, but great increase of permeability. With the rise of temperature and pressure, corrosion ability of acid fluid to carbonate rock increases first and then decreases, there exists an optimum range of temperature and pressure for dissolution, which corresponds to the buried depth of 2 250-3 750 m of the Cambrian. Considering reservoir characteristics of the study area, it is concluded that calcite in the penecontemporaneous period is the material basis for the development of dissolution pore, and carbonate rock were mainly dissolved by early atmospheric fresh water, superimposed and reformed to form high quality reservoirs by multiple acid fluids including deep hydrothermal fluid and acid fluid generated during the process of organic thermal evolution under burial condition.

鄂尔多斯盆地长7段重力流砂岩长石溶蚀特征及控制因素

基于岩心薄片、扫描电镜、能谱分析、X射线衍射全岩分析及溶蚀实验,研究鄂尔多斯盆地三叠系延长组7段(简称长7段)重力流砂岩中长石溶孔发育特征及控制因素,明确长石溶孔的形成与分布,为预测优质储集层分布提供依据。研究表明:(1)研究区长7段砂岩中的长石经历3类成岩作用:长石次生加大、黏土以及方解石的交代、长石碎屑的溶蚀作用。(2)长7段致密砂岩中的长石溶蚀主要源于有机酸溶蚀,此外还受长石类型、长石早期蚀变程度以及砂岩中云母碎屑对有机酸的缓冲作用影响。(3)不同长石的溶蚀程度不同,表现为钾长石较斜长石易溶蚀,钾长石中正长石较微斜长石易溶,未蚀变的长石较早期高岭土或绢云母化的长石易溶蚀。(4)溶蚀实验显示云母的存在会抑制长石溶蚀,相同质量的云母对有机酸的消耗能力明显强于长石。(5)在云母含量低的情况下,长7段砂岩长石溶孔较为发育,储集层物性得以改善,而云母含量较高的地区长石溶孔则明显减少。

砂岩储层中凝灰质溶蚀效应的物理模拟实验研究——以珠江口盆地惠州—陆丰地区古近系文昌组为例

为认识埋藏过程中酸性流体对碎屑岩储层中凝灰质的溶蚀改造效应及控制因素,选取珠江口盆地珠一坳陷惠州—陆丰地区古近系文昌组凝灰质砂岩储层,设计开展了岩心尺度的流体—岩石相互作用模拟实验。通过显微镜下观察、流体成分分析、物性表征等方法,对比分析了实验前后不同流体流速、不同凝灰质含量条件下砂岩储层的溶蚀作用和物性响应特征。结果表明,酸性流体环境中凝灰质溶蚀现象普遍,但不同实验条件下,凝灰质溶蚀强度及储层物性响应不同:成岩体系的开放性与封闭性决定凝灰质的溶蚀作用强弱。相同岩石和相同酸性流体条件下,高流速开放体系中凝灰质溶蚀量高于封闭体系,且低流速相对封闭体系中溶蚀产物趋于沉淀,溶蚀作用增孔效应有限。凝灰质含量显著影响溶蚀效应,富凝灰质砂岩中溶蚀作用有限,含凝灰质砂岩和贫凝灰质砂岩能够溶蚀增孔,且含凝灰质砂岩的溶蚀增孔效率更高。凝灰质含量相对中等—较低的储层中,中浅层埋藏阶段的开放成岩流体体系最有利于粒间凝灰质溶孔的发育。经历晚期酸性流体溶蚀改造后,较易形成次生溶蚀型优质储层,这一认识有助于不同地区的溶蚀型储层甜点预测。

临兴气田井筒堵塞机理及现场解堵工艺研究

临兴区块自投产以来,井筒堵塞问题日益严重,导致气井生产测试、措施作业等无法正常开展。文章结合区块堵塞物的粒径分析、无机成分XRD、红外等分析结果,明确了堵塞物成分主要包括石英、石盐、难溶盐垢(以硅铝酸盐垢为主)及少量的铁垢和固体砂砾等,主要堵塞类型为砂堵、腐蚀结垢及结盐堵塞等。通过解堵实验,优选出HYJD-10和CAWF两种解堵剂体系,静态溶蚀实验最高溶解率分别可达25.3%及18.3%,驱替实验最优渗透率的提高率分别可达105.9%及91.3%。现场结合注解堵剂、气举及泡沫流体等方式进行解堵作业,单井平均增产不小于9 000 m3/d,最高增产25 000 m3/d。本研究为致密气井井筒解堵试验提供了参考。

四川盆地北部中二叠统茅口组碳酸盐岩溶蚀模拟实验与岩溶层组特征

四川盆地北部中二叠统茅口组岩溶储层发育,是该区重要储层类型之一。基于野外露头、钻井岩心资料,采用宏观与微观结合的方法,根据薄片鉴定、扫描电镜、主微量元素等资料、辅于溶蚀模拟实验等技术方法,对四川盆地北部茅口组岩溶层组特征进行了研究。该区茅口组一段以泥质灰岩、生屑泥晶灰岩为主,酸不溶物含量较高;茅二段、茅三段以泥晶生屑灰岩、亮晶生屑灰岩为主,酸不溶物含量较低。溶蚀模拟实验结果表明,碳酸盐矿物类型、化学成分等是影响茅口组岩石可溶性的主要因素,样品溶蚀速率、溶液离子浓度及微观溶蚀变化特征均表现为生屑灰岩>泥晶灰岩>白云岩>泥质灰岩。茅口组岩溶层组类型可划分为2类3型9亚型,不同岩溶层组类型岩溶作用条件、岩溶化程度不同,缝洞型岩溶储层发育规模也存在差异。

四川盆地高石梯-磨溪地区震旦系灯影组白云岩溶蚀差异实验研究

近年来,高石梯—磨溪地区灯影组天然气勘探取得重要发现,其含气储层主要位于灯四段,储层岩石类型以藻凝块白云岩、藻砂屑白云岩、藻叠层白云岩为主。为了研究该地区灯影组白云岩的溶蚀差异,本文采用岩石切片和薄片同时进行溶蚀实验的方法,实验过程中定时记录实验数据,对灯影组白云岩的溶蚀速率、表面形貌和微观特征进行研究。实验结果既有溶蚀量化指标——溶蚀速率,又能直观掌握溶蚀特征及溶蚀后的孔隙结构变化。溶蚀实验结果表明:(1)所有样品的溶蚀启动速率均较高,随溶蚀时间增加,溶蚀速率呈现大幅度衰减并趋于稳定;(2)不同样品的溶蚀速率有明显差异,藻叠层白云岩、藻砂屑白云岩溶蚀速率最高,藻凝块白云岩次之,藻叠层硅质白云岩溶蚀速率最低;(3)通过观察比较不同反应时间内样品的微观溶蚀特征,发现沿粒间、晶间孔隙以及微裂隙溶蚀程度较高;(4)灯影组藻白云岩储层发育可能与藻间白云石的溶蚀作用有关。通过溶蚀实验,掌握了研究区不同白云岩的溶蚀差异,进而对预测优质储层分布、指导油气勘探具有重要意义。

基于Visual MINTEQ软件计算水环境中沉淀反应

在环境化学教学过程中,水环境化学中的沉淀-溶解计算是教学过程中的难点和重点。围绕采用地球化学平衡计算软件Visual MINTEQ计算相关沉淀的方法,介绍了在软件数据库中添加新沉淀相方法,举例说明单一和混合沉淀条件下沉淀生成计算方法以及含有沉淀相的lg C-pH图绘制方法。通过该软件的学习,不仅可提高学生计算效率和准确度,还可增加学生的学习兴趣,加深对水化学相关知识的理解。

雄安新区蓟县系雾迷山组地层水对白云岩溶蚀的模拟实验研究

为了研究雄安新区雾迷山组地层水对白云岩的溶蚀作用,文章以雾迷山组白云岩为研究对象,以井下雾迷山组地层水为实验流体,开展高温高压条件下溶蚀模拟实验。实验结果表明:(1)样品在地层水中的溶蚀速率随温度增加总体呈下降趋势,具有快速下降—缓慢增加—快速下降的特征,在100~140℃范围内明显增加。样品在地层水中的溶蚀速率随压力增加明显增大。反应溶液的Ca^(2+)、Mg^(2+)浓度增加量随温度、压力变化特征与样品溶蚀速率随温度、压力变化特征一致;(2)孔隙、微裂隙欠发育的样品仅在样品表面发生溶蚀,使得样品表面变模糊。孔隙、微裂隙发育的样品,沿粒间、晶间孔隙及各类裂隙溶蚀、扩展,最终呈一定程度连通;(3)埋藏成岩环境下,在100~140℃范围存在一个保持较高溶蚀能力的温度窗口,这可能是研究区雾迷山组白云岩岩溶储层形成的有利温度区间。

砂岩储层黏土矿物溶解实验研究

为了搞清砂岩储层黏土矿物溶解情况,提出效果较好的解堵体系;针对不同酸液与储层黏土矿物发生反应易造成储层堵塞等问题,开展了盐酸、氢氟酸、氟硼酸和乙酸单独溶蚀矿物实验;研究了反应温度和酸液浓度的影响以及矿物解除效果评价;在此基础上,进行了混合酸液以及混合碱盐溶液对矿物溶蚀实验研究。结果表明:1)盐酸、氢氟酸、氟硼酸和乙酸的最佳单酸溶液的矿物溶蚀浓度分别为6%~8%,2%~4%,4%~6%和1%~5%,4种酸均起到了降低岩心强度的作用,盐酸的影响最大,乙酸影响最小(5%)。2)4种酸液对石英、长石和黏土等矿物溶蚀的影响顺序为氢氟酸>氟硼酸>盐酸>乙酸。3)氢氧化钠和氢氧化钾对矿物的溶蚀效果较差,硅酸钠和氯化铵对矿物溶蚀后,岩心强度得到提高。4)提出黏土矿物解除体系为(2%~4%)氢氟酸+(6%~8%)盐酸+(4%~6%)氟硼酸+(1%~5%)乙酸,系统的酸液浓度可在浓度范围内调节。以上成果认识,对解除储层黏土矿物时保护储层骨架有一定的指导意义。

青海马海盐湖低品位固体钾矿室内溶矿实验研究

柴达木盆地马海盐湖浅部赋存有储量可观的低品位固体钾盐资源,通过水溶开采即固液转化的方法为企业10万吨/年的钾肥生产提供了资源保障。随着水溶开采工作的持续进行,目前马海钾矿区北部浅部固体钾矿的品位进一步降低,给盐田和选矿工艺的调整带来极大挑战。为使这部分资源得以充分利用,本文以马海盐湖钻孔9-13和9-3附近埋深0~3m的固体钾矿样品为研究对象,系统开展了室内溶矿模拟实验。实验结果表明:(1)在固体钾矿KCl品位较低时,适当提高溶剂的波美度,有利于K^(+)的溶出,提高溶出液中K^(+)的浓度。(2)溶剂中Na^(+)的浓度太低会溶解盐层骨架,而Na^(+)的浓度太高会导致结盐,生产中应根据钾矿层的实际情况,以满足溶出液K^(+)浓度含量达标为准调整溶剂的波美度。(3)随着马海矿区固体钾矿品位持续降低,当K^(+)的浓度达到盐田生产要求时,钠盐池卤水中Na^(+)的浓度会明显增加,卤水中SO42-相对浓度也相应增加,钠盐池阶段析出的石盐将明显增加,进入成矿池中卤水的组分也会发生明显变化,这可能会对盐田生产产生较大的影响。上述实验结果可为盐田生产时溶剂的优化提供参考。

高钛焊丝钢保护渣吸收TiN的研究

在高钛焊丝钢的连铸过程中,钢液中生成的TiN夹杂物容易诱发“结鱼”物的形成,从而引发连铸坯表面缺陷,甚至漏钢。针对以上问题,采用热力学计算、旋转柱法和高温共聚焦法实验对高钛焊丝钢连铸保护渣对TiN夹杂物的吸收进行了研究。热力学计算结果表明:CaO-SiO_(2)保护渣中的SiO_(2)和Al_(2)O_(3)均能与TiN发生反应,且SiO_(2)与其反应的能力更强;旋转柱实验表明:保护渣对柱状TiN的溶解能力有限,TiN和保护渣的界面处有反应发生;高温共聚焦实验表明:TiN很容易被空气所氧化,从反应前后试样总量的变化来看,TiN能够被保护渣所氧化。因此,采用保护渣氧化组分氧化TiN来减小结鱼有一定的可行性。

长石溶解模拟实验研究综述

在综合分析前人研究成果基础上,对长石溶解模拟实验研究进行了综述。研究表明,长石溶解与其成分、结构、反应的温压条件以及流体性质等有关。在相同的温压条件下,3种长石的稳定性依次为:钾长石>钠长石>钙长石,且温度升高可加强长石的溶解能力,促进长石的溶解,而压力的变化对长石的溶解影响不大。长石的溶解速率在酸性区域随pH值增大而减小、在中性区域溶解速率低且受影响小、在碱性区域随pH值增大而增大。有机酸通过提供H+、络合金属元素来提高长石的溶解度。长石的溶蚀速率与颗粒的总表面积大小以及颗粒表面粗糙度有关,总表面积越大,表面越粗糙,则反应速率越快,而且溶液的矿化度越低越有利于长石的溶解。长石的溶解过程由表面反应和扩散反应所控制,描述长石溶蚀机理的模型主要包括:表面反应模型和淋滤层扩散模型。

塔里木盆地寒武系碳酸盐岩溶蚀作用机理模拟实验

以岩心柱样为实验样品,通过酸性流体渗流方式进行溶蚀模拟实验,模拟地层埋藏演化过程中的溶蚀作用,以分析塔里木盆地寒武系碳酸盐岩溶蚀作用特征及控制因素。研究表明:塔里木盆地寒武系碳酸盐岩的矿物成分及储集空间类型控制选择性溶蚀,方解石含量高的过渡型碳酸盐岩中方解石易优先溶蚀形成次生孔洞,而碳酸盐岩中的石膏、硬石膏在同生期、准同生期易溶蚀形成膏模孔。孔隙型碳酸盐岩以基质孔隙的扩溶为主,溶蚀后孔隙度、渗透率相应增加,但增幅不明显;裂缝型碳酸盐岩或者高压下形成裂缝的孔隙型碳酸盐岩易形成流体运移的优势通道,导致溶蚀量相对减少,但极大地提高了渗透率。随着温压的增加,酸性流体对碳酸盐岩的溶蚀能力先增强后减弱,存在最佳溶蚀温压范围,对应于寒武系的2 250~3 750 m埋深段。结合研究区储集层特征,认为准同生期方解石是溶蚀孔洞发育的物质基础,以早期大气淡水溶蚀为主,埋藏条件下受与有机质热演化有关的酸性流体、深部热流体等多种酸性流体溶蚀叠加改造形成规模优质储集层。

不同温度条件下CO_2水溶液对碳酸盐岩的溶蚀作用

普遍认为酸性流体的溶蚀作用是碳酸盐岩储层形成的重要制约因素。本文以一个全新的模拟实验方式对不同类型碳酸盐岩在CO2水溶液中的相对溶蚀能力进行了研究，结果发现随温度从常温至200℃，碳酸盐岩的溶蚀能力由弱变强再变弱，在60—90℃区间内溶蚀能力最强。白云岩不管在低温还在高温环境下，总比灰岩更难溶蚀，过渡类型的岩类介于二者之间，当温度大于150℃后，CO2对碳酸盐岩的溶蚀能力变得越来越弱。灰岩与白云岩的溶蚀差异也变得越来越小。这暗示碳酸盐岩在早成岩晚期一中成岩早期，CO2水溶液对灰岩的溶蚀作用有重要影响，而对白云岩的溶蚀作用影响较小，白云岩优质储层的形成可能与碳酸盐岩中钙质的流失或白云岩化作用有关。

碳酸盐岩溶蚀窗的形成及地质意义

设计了温度压力同时变化的溶蚀模拟实验,得到了一组近似箱状曲线的溶蚀率变化曲线。溶蚀作用在开始阶段随温度、压力的上升,溶蚀率上升,在60～120℃(13～31MPa)形成一个高峰箱顶。该曲线表明,在一定深度(溶蚀窗)范围内,CO_2对碳酸盐岩的溶蚀能力保持在较高的水平。而当深度进一步增加时,溶蚀能力急剧下降,当埋深相当于4 000 m左右时,溶蚀能力达到最低,此时的溶蚀能力仅比常温下略高一些。该溶蚀试验结果对于深埋溶蚀作用的理解及有利储层的预测有着重要的意义。

贵州施秉白云岩溶蚀特性及孔隙特征实验研究

以贵州施秉白云岩为研究对象,从宏观和微观角度分析白云岩的溶蚀特性及孔隙特征,结果显示:(1)在众多影响施秉喀斯特发育的因素中,矿物成分是最基本的内因,水是最关键的外因,孔隙结构起辅助作用。(2)极细晶白云岩的单位表面积溶蚀量一般大于细晶白云岩的,在晶粒相同的情况下,白云岩的溶蚀量与Ca O和Mg O的含量分别成正比,且Mg O的含量影响较Ca O大。(3)施秉白云岩溶蚀速率不仅受岩石矿物颗粒粒径大小的控制,还受岩石内部孔隙结构特征的影响,颗粒粒径越大,孔隙度越高,连通性越好,越有利于水溶液进入,溶蚀量也就越大。(4)施秉白云岩的溶蚀特性是多种因素综合作用的结果,必须把各个因素分离开来,从宏观和微观角度逐个作详细的分析研究,然后综合起来,才能对喀斯特发育规律有更深入的了解。