压裂液黏度对循环水力压裂影响的试验研究

中国石油大学（北京）石油天然气工程学院,北京 102249     

The effect of phosphorus on the iron redox ratio,viscosity, and density of an evolved ferro-basalt

Despite the abundant evidence for the enrichment of phosphorus during the petrogenesis of natural ferro-basalts, the effect of phosphorus on the physical properties of these melts is poorly understood. The effects of phosphorus on the viscosity, density and redox ratio of a ferro-basaltic melt have been determined experimentally. The viscosity measurements were obtained using the concentric cylinder method on a ferro-basaltic melt above its liquidus, at 1 atm, in equilibrium with air and with CO₂. The density measurements were performed using the double Pt-bob Archimedean method at superliquidus conditions under 1 atm of air. The redox ratio was obtained by wet chemical analysis of samples collected during physical property measurements. Phosphorus pentoxide reduces ferric iron in ferro-basaltic melt. The reduction due to P₂O₅ is much larger than that for most other oxide components in basaltic melts. A coefficient for the reduction of ferric iron has been generated for inclusion in calculation schemes. The effect of P₂O₅ on the viscosity is shown to be complex. The initial reduction of ferric iron with the addition of P₂O₅ results in a relatively small change in viscosity, while further addition of P₂O₅ results in a strong increase. The addition of phosphorus to a ferro-basaltic melt also reduces the density. A partial molar volume of 64.5±0.7 cm³/mol for P₂O₅ in this melt has been obtained at 1300° C, yielding a volume of 12.9 cm³/mol per oxygen, consistent with a tetrahedral coordination for this high field strength cation. The effects of P₂O₅ on redox state, density and viscosity provide constraints on the structural role of phosphorus in these melts. The results suggest a complex interaction of phosphorus with the aluminosilicate network, and tetrahedral ferric iron. In light of the significant effects of phosphorus on the physical and chemical properties of ferro-basaltic liquids, and the extreme enrichments possible in these liquids in nature, the role of phosphorus in these melts should, in future, be considered more carefully.     

地下水在引发边坡病害中的作用

人们普遍认为由于地下水的浸泡降低滑带土的抗剪强度值是导致边坡失稳的内部机制.文章以云南元磨公路边坡为实例,对其进行了探究,发现病害边坡主要滑带土的天然含水量与其剪切试验所得的内聚力和内摩擦角之间并没有明显的线性关系.于是,文章采用极限平衡方程从理论上论述了地下水在边坡失稳过程中的力学作用,并对比边坡开挖前后入渗系数值的变化幅度,揭示出工程活动与降雨共同对边坡破坏的作用机制.     

地下水系统对鄂尔多斯低阻油层成因的控制作用

鄂尔多斯西缘广泛发育低电阻率油层,其形成原因与地下水系统关系密切。地下水对电阻率的影响主要表现在以下几个方面:高束缚水饱和度、高地下水矿化度、岩石润湿性、钻井液侵入等。深入研究低电阻率油层,不仅在储层电性研究中具有很高价值,对油气勘探开发也有重大意义。     

Sensitivity assessment of strontium isotope as indicator of polluted groundwater for hydraulic fracturing flowback fluids produced in the Dameigou Shale of Qaidam Basin

Hydrogeochemical processes that would occur in polluted groundwater and aquifer system, may reduce the sensitivity of Sr isotope being the indicator of hydraulic fracturing flowback fluids(HFFF) in groundwater. In this paper, the Dameigou shale gas field in the northern Qaidam Basin was taken as the study area, where the hydrogeochemical processes affecting Sr isotope was analysed. Then, the model for Sr isotope in HFFF-polluted groundwater was constructed to assess the sensitivity of Sr isotope as HFFF indicator. The results show that the dissolution can release little Sr to polluted groundwater and cannot affect the εSr(the deviation of the 87 Sr/86 Sr ratio) of polluted groundwater. In the meantime, cation exchange can considerably affect Sr composition in the polluted groundwater. The Sr with low εSr is constantly released to groundwater from the solid phase of aquifer media by cation exchange with pollution of Quaternary groundwater by the HFFF and it accounts for 4.6% and 11.0% of Sr in polluted groundwater when the HFFF flux reaches 10% and 30% of the polluted groundwater, respectively. However, the Sr from cation exchange has limited impact on Sr isotope in polluted groundwater. Addition of Sr from cation exchange would only cause a 0.2% and 1.2% decrease in εSr of the polluted groundwater when the HFFF flux reaches 10% and 30% of the polluted groundwater, respectively. These results demonstrate that hydrogeochemical processes have little effect on the sensitivity of Sr isotope being the HFFF indicator in groundwater of the study area. For the scenario of groundwater pollution by HFFF, when the HFFF accounts for 5%(in volume percentage) of the polluted groundwater, the HFFF can result in detectable shifts of εSr(ΔεSr=0.86) in natural groundwater. Therefore, after consideration of hydrogeochemical processes occurred in aquifer with input of the HFFF, Sr isotope is still a sensitive indicator of the Quaternary groundwater pollution by the HFFF produced in the Dameigou shale of Qaidam Basin.     

Impact of water and nitrogen fracturing fluids on fracturing initiation pressure and flow pattern in anisotropic shale reservoirs

A numerical model is proposed to investigate the impact of water and nitrogen fracturing fluids on the fracturing initiation pressure and the flow pattern in anisotropic shale reservoirs. This model considers the anisotropy of shale deformation and permeability, the compressibility of fracturing fluid, and the fluid moving front. A crack initiation criterion is established with the stress intensity factor of mode I crack. Both crack initiation pressure and seepage area are verified and analyzed. These results show that shale deformation and permeability anisotropy, fracturing fluid compressibility, viscosity, and pressurization rate have significant impacts on fracturing initiation pressure and seepage area.     

The effect of topography on the formation of groundwater recharge

Analysis of the influence of a gently sloping relief on groundwater recharge was made by a surface and vadose-zone water-balance simulation for different slope (gradient and exposure) and landscape (type of soil and vegetation) characteristics for humid climate conditions. The model results show that the main feature of the relief is slope exposure and the greatest differences in recharge in comparison with flat surface are manifested at the foot of a hill. For northern slope exposures there are local zones that exceed recharge, but for southern exposures the foot of a hill may be the area of groundwater evapotranspiration discharge, which is subject to landscape conditions.     

Experimental and theoretical study on the effect of unsteady flow on the fracturing pressure in hydraulic fracturing test

Reasonable determination of formation fracturing pressure concerns the stable operation of underground fluid injection projects. In this work, we studied the effect of unsteady flow on fracturing pressure. Hydraulic fracturing tests on low permeable sandstone were conducted with the injection rate between 0.1 and 2.0 ml/min. Then, the fracturing pressure prediction models for hollow cylinder under both unsteady flow and steady flow conditions were deduced. Finally, the effect of unsteady flow on the fracturing pressure was studied based on the experimental result and several influence factors. It was shown that fracturing pressure increased with the elevated pressurization rate in the tests, while the slope of the variation curve decreases. The model considering unsteady flow can reflect the variation tendency of fracturing pressures in experiments, while fracturing pressures from the model considering steady flow are invariant with different pressurization rates. Fracturing pressure decreases with the elevated rock permeability and increases with the elevated fluid viscosity, and these two effects are actually generated by the unsteady flow. Whether to consider the unsteady flow has no significant influence on the effect of rock tensile strength on fracturing pressure when the tensile strength is very low. However, when the tensile strength is high, the effect of unsteady flow cannot be neglected.     

The effect of chemicals on the viscosity and stability of coal water slurries

In this study, the effects of different chemicals that were used as dispersing agent and stabiliser on the stability and viscosity of coal–water slurries have been investigated. In the experiments, anionic type of chemicals—polyisoprene sulphonic acid soda (Dynaflow-K), a derivative of carboxylic acid (AC 1320) and naphthalenesulfonate–formaldehyde condensate (NSF)—were used as dispersing agents and the stabiliser was the sodium salt of carboxymethyl cellulose (CMC-Na). The coal sample used was a bituminous coal (thermal code no. 434) of Turkish origin, with medium volatile matter. The results of the experiments showed that polymeric anionic dispersing agents such as Dynaflow have much greater effect on the viscosity and the stability of coal water slurry.     

Rheological behaviour effects of non-Newtonian fracturing fluids on propagation of a vertical hydraulic fracture

This communication investigates the effects fo the non-Newtonian behaviour of the fracturing fluids in the hydraulic fracturing mechanism. These effects are illustrated on the propagation of a vertical hydraulic fracture into an oil reservoir, in which the fracturing fluid is of power law and of pseudo-plastic type. The analytical solutions for evaluating the fracture lengrhs are presented for the cdases of large fluid loss and for no fiuid loss. The results obtained should be useful in the design of fracture treatments, permitting the finding of the rheological properties of the injected fluid for obtaining the desired fracture length and width.     

The effect of CO ratio on the condensation of planetary material

The condensation temperatures of refractory silicates and oxides in a gas of cosmic composition are strongly dependent on the $\text{C}\text{O}$ ratio. As the ratio increases from 0.4 to 0.9 (solar ~ cosmic ~ 0.6), condensation temperatures of compounds such as A1₂O₃, Ca₂Al₂SiO₇, MgAl₂O₄, Mg₂SiO₄ and MgSiO₃ decrease by 50–100°. As $\text{C}\text{O}$ increases from 0.9 to 1.0, these temperatures drop an additional 300–400°. Other chemical differences result when $\text{C}\text{O}\text{\$}\text{?}\text{0.9}$ include: a new suite of high temperature minerals appears (graphite, CaS, Fe₃C, SiC and TiN); the reaction CO + 3H₂ → CH₄ + H₂O proceeds to the right at higher temperatures; and iron, whose condensation temperature is unaffected, condenses at higher temperatures than any silicate or oxide.     

海底地下水排泄对海洋锶储库的影响

海底地下水排泄（ submarine groundwater discharge, SGD）不仅是全球水循环的重要组成部分,也是各种溶解化学物质由陆向海输送的重要而隐蔽通道。笔者等在分析全球海洋锶来源的基础上,综述了多种岩性含水层条件下SGD锶的地球化学行为及其控制因素,并利用已有的SGD通量和高分辨率全球岩性数据,计算出更为保守和精确的SGD锶通量及同位素组成,确认了SGD是海洋贫放射成因锶的重要来源之一,起到平衡河流输入的富放射成因锶的作用。     

海底地下水排泄对海洋锶储库的影响

海底地下水排泄（submarine groundwater discharge,SGD）不仅是全球水循环的重要组成部分,也是各种溶解化学物质由陆向海输送的重要而隐蔽通道。本文在分析全球海洋锶来源的基础上,综述了多种岩性含水层条件下SGD锶的地球化学行为及其控制因素,并利用已有的SGD通量和高分辨率全球岩性数据,计算出更为保守和精确的SGD锶通量及同位素组成,确认了SGD是海洋贫放射成因锶的重要来源之一,起到平衡河流输入的富放射成因锶的作用。     

The interplay of groundwater and magmatic fluids in the formation of the cassiterite-sulfide deposits of western Tasmania

The cassiterite-sulfide deposits of western Tasmania are spatially and temporally related to Devonian granitoids. The stable isotope and fluid inclusion data of these deposits are best explained by a genetic model in which Sn is leached from the granites by reduced, non-magmatic fluids mixed with late-stage magmatic fluids. These fluids mineralize the overlying dolomite horizons and subjacent faults by a combination of wallrock and boiling induced reactions. The model requires co-incidental release of volatiles and ingress of groundwaters to sustain the leach mechanism. This implies some specific structural/deformational controls on the process and an intimate association between cassiterite-sulfide deposits and volatile-rich granites.The sulfur isotope data show a wide range in values, from about −2 to 20 per mil, and are explained in terms of a near-zero magmatic component and three heavier country-rock sources: the Precambrian Oonah Formation, the Crimson Creek Formation and the Mount Read Volcanics. Following this interpretation, the heavy sulfur isotope values from the Heemskirk Granite (Hajitaheri, 1985) and the Federal-Bassett Fault at Renison (Kitto, 1994) indicate ingress of groundwater into the granites. Salinities of fluid inclusions from the deposits show a restricted range (around 5 to 15 weight percent NaCl equivalent) compared with the range shown by inclusions from alteration zones within the granites (around 5 to 40 weight percent NaCl equivalent). It is suggested that the wide range of salinities in the granites is generated in the critical region of the NaCl---H₂O system at temperatures around 400 to 500°C and pressures around 400 to 500 bars. The limited range of salinities in the deposits reflects cooling to sub-critical conditions. Cooling through the critical region promotes homogenization of groundwater and magmatic vapor and brine. Condensation of magmatic volatiles within this zone of mixing maintains acidity and promotes fluid-rock reaction.The geochemistry of the granites underlying the Renison Bell area (Bajwah et al., 1995) is interpreted in terms of two granites. The geological relationships indicate the more mafic phase, the Renison Granite, was intruded by the more fractionated Pine Hill Granite. Fluids from the Pine Hill Granite sericitised and tourmalinized both the Renison Granite and Pine Hill Granite along their mutual contact, generating a broad north-east trending zone of alteration. This contact may have been offset by the Federal-Bassett Fault before the Renison deposit was formed. It is suggested that groundwater flow was essentially constrained within this NW-SE trending structure and subsidiary structures. Magmatic volatiles, emanating from deep within the Pine Hill Granite, acidified the reduced groundwater and promoted leaching of the granite. The siting of the Renison deposit on the margin of the Pine Hill Granite is consistent with a strong up-flow zone on the margin of a cooling pluton. The very constant S-isotope signature in the deposit is consistent with a large-scale homogenization process operating over a sustained period. The very large size of the Renison deposit is accounted for by a long-lived groundwater system maintained by the high heat flow from a fractionated granite.     

含水层层状非均质对地下水流系统的影响

区域尺度上含水层非均质具有复杂的结构性和随机性,难以准确刻画,造成非均质对区域地下水流系统的影响机制研究不够深入。本文以鄂尔多斯盆地白垩系地下水流系统为研究实例,选择典型剖面,采用剖面二维随机数值模拟方法,通过对比不同非均质刻画方法下地下水流场的变化,探讨含水层层状非均质对地下水流系统的影响机制。结果显示,均质条件下模型各向异性（含水层水平和垂向渗透系数比值Kh/Kv）取值为1000时,地下水流场与实际条件较为接近;非均质条件下,渗透系数方差取值0.91,水平相关长度取值5000 m,Kh/Kv取值150时,接近实际条件。研究表明,在大尺度地下水流模拟研究中,采用水平相关长度、渗透系数方差和各向异性值三个变量生成的随机场能很好地刻画含水层的层状非均质特征及其对水流系统的影响控制作用。由于含水层不同尺度层状非均质的叠加效应,采用均质各向异性介质等效概化含水层层状非均质性会造成等效各向异性值偏大失真的效应。     

鄂尔多斯盆地白垩系含水层系统分析

从地下水含水层系统的角度对鄂尔多斯盆地白垩系地下水系统进行了划分和分析。由于下白垩系统保安群为一套陆相碎屑岩建造,岩性复杂,由砂岩、粉砂岩和泥岩组成的频繁交替、重复叠置的多层层状结构,决定了鄂尔多斯白垩系自流水盆地是多层结构的地下水系统。这种重复叠置的多层层状地质结构,决定了地下水含水层系统的多层性、承压性及层与层之间的相对封闭性。根据沉积旋回和含水介质的性质,在全盆地范围内把白垩系地下水系统从上向下划分为:罗汉洞含水岩组、环河含水岩组和洛河含水岩组。通过对这3大含水岩组分别进行了分析认为,洛河含水岩组和环河含水岩组分布范围广、含水层厚度大、天然资源丰富,是盆地区具供水意义的主要含水岩组。罗汉洞含水岩组因分布面积小,含水层厚度差异大、水质变化大,除陇东地区外,大部分地区供水价值较小。     

Modeling the effects of the variability of temperature-related dynamic viscosity on the thermal-affected zone of groundwater heat-pump systems

Thermal perturbation in the subsurface produced in an open-loop groundwater heat pump (GWHP) plant is a complex transport phenomenon affected by several factors, including the exploited aquifer’s hydrogeological and thermal characteristics, well construction features, and the temporal dynamics of the plant’s groundwater abstraction and reinjection system. Hydraulic conductivity has a major influence on heat transport because plume propagation, which occurs primarily through advection, tends to degrade following conductive heat transport and convection within moving water. Hydraulic conductivity is, in turn, influenced by water reinjection because the dynamic viscosity of groundwater varies with temperature. This paper reports on a computational analysis conducted using FEFLOW software to quantify how the thermal-affected zone (TAZ) is influenced by the variation in dynamic viscosity due to reinjected groundwater in a well-doublet scheme. The modeling results demonstrate non-negligible groundwater dynamic-viscosity variation that affects thermal plume propagation in the aquifer. This influence on TAZ calculation was enhanced for aquifers with high intrinsic permeability and/or substantial temperature differences between abstracted and post-heat-pump-reinjected groundwater.

     

基于煤储层水力压裂动态渗透率变化的压裂效果评价方法及其应用

压裂施工曲线是反映压裂效果的重要依据,而压裂阶段储层渗透率的动态变化能够更直观地反映造缝效果。借鉴试井渗透率测试原理,建立一种压裂阶段储层动态渗透率定量评价方法,并将该方法应用到准南某区块2口煤层气井水力压裂效果评价中,获得压裂阶段储层动态渗透率曲线;同时采用G函数对压裂效果进一步评价。结果表明:动态渗透率曲线所反映压裂效果与G函数分析和基于排量、井底流压关系的评价结果吻合较好,能够反映储层内裂缝开启、延伸效果;其中,CMG-01井通过实施煤储层与围岩大规模缝网改造,压裂阶段储层渗透率最高达到2.5 μm2,造缝效果良好;而CBM-02井实施煤储层常规水力压裂,储层渗透率保持在1.8 μm2之下,显示出煤储层常规水力压裂与煤储层?围岩大规模缝网改造的差异性。动态渗透率定量评价方法弥补前期压裂改造效果缺乏量化评价的不足,为煤层气/煤系气储层水力压裂工艺的优化提供依据。      

地下水位变化对透—阻型岩溶塌陷影响的分析

文章从一维地下水运动和渗透力学的角度,分析比较潜水位上升与承压水位下降对岩溶地区透—阻型盖层中阻水层渗透稳定性的影响,重点讨论了承压水位下降速度(降速)与下降深度（降深）对阻水层中渗透坡降的影响,结果表明:地下水位变化（潜水位上升或承压水位下降）产生的非稳定渗流不利于岩溶洞穴开口上方阻水层的稳定,承压水位的下降对岩溶开口附近处阻水层中渗透力的影响远大于潜水位的变化;在承压层水位最大降深确定的条件下,承压水位下降速度愈快,岩溶开口附近处阻水层中向下渗透力愈大。因此,在覆盖型岩溶地区抽取地下水时,为了减缓或避免覆盖型塌陷的发生,应同时控制好最大降深和最大开采速度。