Implication of Water-Rock Interaction for Enhancing Shale Gas Production

Horizontal well drilling and multi-stage hydraulic fracturing technologies are at the root of commercial shale gas development and exploitation.During these processes,typically,a large amount of working fluid enters the formation,resulting in widespread water-rock interaction.Deeply understanding such effects is required to optimize the production system.In this study,the mechanisms of water-rock interaction and the associated responses of shale fabric are systematically reviewed for working fluids such as neutral fluids,acid fluids,alkali fluids and oxidative fluids.It is shown that shale is generally rich in water-sensitive components such as clay minerals,acidsensitive components(like carbonate minerals),alkali-sensitive components(like quartz),oxidative-sensitive components(like organic matter and pyrite),which easily lead to change of rock fabric and mechanical properties owing to water-rock interaction.According to the results,oxidizing acid fluids and oxidizing fracturing fluids should be used to enhance shale gas recovery.This study also indicates that an aspect playing an important role in increasing cumulative gas production is the optimization of the maximum shut-in time based on the change point of the wellhead pressure drop rate.Another important influential factor to be considered is the control of the wellhead pressure considering the stress sensitivity and creep characteristics of the fracture network.

Groundwater monitoring of an open-pit limestone quarry:Water-rock interaction and mixing estimation within the rock layers by geochemical and statistical analyses

Water-rock interaction and groundwater mixing are important phenomena in understanding hydrogeological systems and the stability of rock slopes especially those consisting largely of moderately watersoluble minerals like calcite. In this study, the hydrogeological and geochemical evolutions of groundwater in a limestone quarry composed of three strata: limestone layer(covering), interbedded layer under the covering layer, and slaty greenstone layer(basement) were investigated. Water-rock interaction in the open-pit limestone quarry was evaluated using PHREEQC, while hierarchical cluster analysis(HCA)and principal component analysis(PCA) were used to classify and identify water sources responsible for possible groundwater mixing within rock layers. In addition, Geochemist's Workbench was applied to estimate the mixing fractions to clarify sensitive zones that may affect rock slope stability. The results showed that the changes in Ca2+and HCO3àconcentrations of several groundwater samples along the interbedded layer could be attributed to mixing groundwater from the limestone layer and that from slaty greenstone layer. Based on the HCA and PCA results, groundwaters were classified into several types depending on their origin:(1) groundwater from the limestone layer(LO),(2) mixed groundwater flowing along the interbedded layer(e.g., groundwater samples L-7, L-11, S-3 and S-4), and(3) groundwater originating from the slaty greenstone layer(SO). The mixing fractions of 41% LO: 59% SO, 64% LO: 36% SO, 43%LO: 57% SOand 25% LO: 75% SOon the normal days corresponded to groundwaters L-7, L-11, S-3 and S-4,respectively, while the mixing fractions of groundwaters L-7 and L-11(61% LO: 39% SOand 93% LO: 7% SO,respectively) on rainy days became the majority of groundwater originating from the limestone layer.These indicate that groundwater along the interbedded layer significantly affected the stability of rock slopes by enlarging multi-breaking zones in the layer through calcite dissolution and inducing high water pressure, tension cracks and potential sliding plane along this layer particularly during intense rainfall episodes.

Test of subcritical crack growth and fracture toughness under water-rock interaction in three types of rocks

The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on subcritical crack growth. With water-rock interaction, the crack velocity increases, while the stress intensity factor declines, which illustrates that water-rock interaction can decrease the strength of rocks and accelerate the subcritical crack growth. Based on Charlse theory and Hilling & Charlse theory, the test data were analyzed by regression and the correlation coefficients were all higher than 0.7, which shows the correlation is significant. This illustrates that both theories can explain the results of tests very well. Therefore, it is believed that the subcritical crack growth attributes to the breaking of chemical bond, which is caused by the combined effect of the tensile stress and the chemical reaction between the material at crack tip and the corrosive agent. Meanwhile, water-rock interaction has a vital effect on fracture toughness. The fracture toughness of samples under atmospheric environment is higher than that of samples immersed in water. And water-rock interaction has larger influence on fracture toughness in amphibolite than that in peridotite and lherzolite.

Triggering mechanism and dynamic process of water-rock flow in Nanfen waste dump in 2010

Water-rock flow is a kind of debris flow with more coarse particles and low viscosity, which occurs in many areas of the world. In this work, the water-rock flow that occurred on May 24, 2010, at Nanfen’s open-pit mine of China was investigated by combining field investigation, meteorological and hydrological survey with numerical simulation to understand its triggering mechanism and dynamic process. The field data shows that the short-term high-intensity rainfall is the most direct inducement to trigger water-rock flow in the waste dump. The loose shallow gravel soil and the V-shaped valley with a certain slope provide the necessary conditions of the occurrence of water-rock flow in the waste dump. Moreover, the possibility criterion of water-rock flow is presented by analyzing the historical rainfall data. In addition, the smoothed particle hydrodynamics(SPH) method was employed to simulate the waterrock flow under the conditions of Newtonian fluid with uniform distribution of water and coarse-grained materials. The simulating results show that the flow distance, velocity, shape, and deposition profile of water-rock flow are in good agreement with the field observation. The present work is beneficial to the risk assessment and mitigation design of water-rock flow disaster in the waste dump.

Hydrogen and Oxygen Isotope Study on the Water-Rock Interaction of the Yinshan (Cu-) Pb-Zn-Ag Ore Deposit, Jiangxi Province

The δ18O values of vein quartz of different stages from the Yinshan ore deposit are constant around 16‰ and the calculated δ18OH2O values attain 8‰± ; the δDH2O values of fluid inclu-sions in vein quartz are constant at about-60‰. From the surface down to 1200 m below the δ18O values of altered rocks gradually decrease from 15‰± to 11‰± . Various water-rock inversion calculations indicate that the ore fluids were formed by the interaction between meteoric water and phyllite at 350℃ and the effective W/ R value of around 0.1. When the water-rock exchange in the upper mineralization system took place, the effective W / R value increased to 5.0 or more. As a result, an evolution and mineralization model of a buffered open system with two-stage water-rock interactions is proposed in this study.

Studies on the Inversion Phenomenon of Physical Properties Observed in the Huagang Formation Reservoir in the Xihu Sag Based on the Water-Rock Reaction Experiments

In the Xihu Sag,the reservoirs of the Paleogene Huagang formation have entered the middle diagenetic stage A and the rock physical properties of the water layer are considerably more suitable for the gas migration and storage than those of the present gas layer,indicating the inversion of the physical properties.In this study,core samples were collected from the corresponding reservoir to conduct water-rock reaction experiments in acidic,alkaline,and neutral systems under the specific temperature and pressure.The reasons for the inversion of physical properties were investigated based on the experiment results in reservoir diagenetic environments.The inversion of physical properties can be attributed to the fact that the diagenetic environment around the gas-water interface controls the water-rock reaction effect.With different types of acidic substances,two different situations corresponding to inverted physical properties were analyzed along with the corresponding mechanisms.When the pore fluid is acidic,the physical properties make the overall water layer a better reservoir space than the gas layer,which can be referred to as the overall inversion of physical properties.When the fluid were generally neutral or weakly alkaline and the gas layer was rich in CO2,only the physical properties of the water layer adjacent to the gas-water interface were more favorable for the gas migration than those of the gas layer.This phenomenon can be referred to as the near-interface inversion of physical properties.

Differences in CO_(2)-Water-Rock Chemical Reactions among ’Sweet Spot’ Reservoirs:Implications for Carbon Sequestration

The Lucaogou Formation,located in the Jimsar Sag,Junggar Basin,NW China,has great potential for shale oil resources.In the process of CO_(2)-EOR(CO_(2) enhance oil recovery),mineral dissolution,precipitation and transformation,leading to the local corrosion or blockage of reservoirs,have a significant influence on recovery.In this study,a combination of high-temperature and high-pressure laboratory experiments and coupled temperature/fluid-chemistry multifield numerical simulations are used to investigate CO_(2)-water-rock reactions under various reservoir conditions in the upper and lower ’sweet spots’,to reveal the mechanisms underlying CO_(2)-induced mineral dissolution,precipitation and transformation.In addition,we quantitatively calculated the evolution of porosity over geological timescales;compared and analyzed the variability of CO_(2) transformation in the reservoir under a variety of temperature,lithology and solution conditions;and identified the main factors controlling CO_(2)-water-rock reactions,the types of mineral transformation occurring during long-term CO_(2) sequestration and effective carbon sequestration minerals.The results demonstrate that the main minerals undergoing dissolution under the influence of supercritical CO_(2) are feldspars,while the main minerals undergoing precipitation include carbonate rock minerals,clay minerals and quartz.Feldspar minerals,especially the initially abundant plagioclase in the formation,directly affects total carbon sequestration,feldspar-rich clastic rocks therefore having considerable sequestration potential.

EXPERIMENTAL GEOCHEMISTRY STUDY ON GOLD IN WATER-ROCK REACTION UNDER THERMAL FLUID SYSTEM AT MESO-LOW TEMPERATURE

Based on the knowing geochemical characteristics of wall rock in the Mobin gold deposit and composition of fluid inclusion in ore,water rock experiments were carried out, important achievements are acquired as following: Gold is mainly derived from the ore bearing wall rock,i.e., a series of epimetamorphic clastic gritstone, sandy slate, and tuffaceous slate in the Wuqiang Banxi Formation, Wuqiangxi Group. In thermal system with middle low temperature chlorine gold may be derived form stable complex ions, so it is quite important in gold metallogenic process. Sulphur and chlorine perform as the major negative ions throughout the gold activation and migration movement. The concentration of sulphur and chlorine ions, pH value and temperature are of deciding significance for gold activation, migration and precipitation.

Temporal and spatial variations hydrochemical components and driving factors in Baiyangdian Lake in the Northern Plain of China

Understanding the temporal and spatial variation of hydrochemical components in large freshwater lakes is crucial for effective management and conversation.In this study,we identify the temporalspatial characteristics and driving factors of the hydrochemical components in Baiyangdian Lake using geochemical methods(Gibbs diagram,Piper diagram and End-element diagram of ion ratio)and multivariate statistical techniques(Principal component analysis and Correlation analysis).16 sets of samples were collected from Baiyangdian Lake in May(normal season),July(flood season),and December(dry season)of 2022.Results indicate significant spatial variation in Nat,ci,SO and NO,,suggesting a strong influence of human activities.Cation concentrations exhibit greater seasonal variation in the dry season compared to the flood season,while the concentrations of the four anions show inconsistent seasonal changes due to the combined effects of river water chemical composition and human activities.The hydrochemical type of Baiyangdian Lake is primarily HCO,Cl-Na.Ca,Mg*and HCO,originate mainly from silicate and carbonate rock dissolution,while Kt,Nat and CI originate mainly from sewage and salt dissolution in sediments.SO42 may mainly stem from industrial wastewater,while NO,primarily originates from animal feces and domestic sewage.Through the use of Principal Component Analysis,it is identified that water-rock interaction(silicate and carbonate rocks dissolution,and dissolution of salt in sediments),carbonate sedimentation,sewage,agricultural fertilizer and manure,and nitrification are the main driving factors of the variation of hydrochemical components of Baiyangdian Lake across three hydrological seasons.These findings suggest the need for effective control of substandard domestic sewage discharge,optimization of agricultural fertilization strategies,and proper management of animal manure to comprehensively improve the water environment in Baiyangdian Lake.

基于各向异性高分辨地震处理的煤层顶板含水性风险评价

随着矿井水防治在煤矿开采中的重要性与日俱增,对地震精细勘探的方法也提出了更高要求,常规基于各向同性的地震勘探已无法满足对复杂条件下煤层及其顶底板的高精度勘探要求。根据煤系地层正交各向异性特征,综合其周期性薄互层各向异性和裂隙诱导型各向异性,针对具有垂直对称轴的横向各向同性(Transverse Isotropy Medium with Vertical Symmetry Axis,VTI)介质特性提出基于高阶动校正的广角成像方法拉平同相轴,提高远、近偏移动校正精度,针对方位各向异性(Trans-verse Isotropy with Horizontal Axis of Symmetry,HTI)介质特性应用炮检距向量片(Offset Vector Tile,OVT)域处理消除煤系地层构造裂隙下不同方位各向异性,在地震资料处理阶段提高成像精度及分辨率。在宽方位高保真成像基础上,岩性解释基于岩石物理特征的拟声波方法,通过对声波时差测井曲线进行重构,在速度曲线中融入地层岩性信息,通过反演迭代可分析地层岩性空间展布特征;裂隙解释基于OVT道集所包含的方位角偏移距信息椭圆拟合,得到地震波在不同方位衰减梯度,由方位衰减梯度数据拟合得到裂缝密度及方位推出地层裂缝密度分布特征,实现对影响矿井水灾两大关键参数煤层顶板含水层以及导水裂隙带的精细探查。在此基础上对煤层顶板产水危险区进行综合评估。将所提方法应用于研究区,实际资料含水风险评价与生产井情况吻合度较好,结果验证了所提出的风险评价方法的可行性及适用性,为煤层开采中矿井水灾危险区预测提供了有益参考。

基于地下水化学特征的水封油库水幕系统有效性评价

水幕系统有效性是地下水封油库安全稳定运行的重要基础条件,然而目前评价水幕系统有效性的方法并不高效便捷。以我国首个大型地下水封油库工程为背景,采集油库运行期现场水样和岩样进行水质检测分析和电镜扫描试验,获取库址区地下水水化学类型和岩石的矿物成分组成特征。采用数理统计方法,基于地下水水化学特征获得了不同部位地下水之间的水力联系,开展水幕系统有效性评价。研究表明:油库运行初期库址区地下水主要为HCO^(3)—Na•Ca型水,围岩中的钾长石、钠长石和钙长石发生水化学反应,地下水中的K^(+)、Na^(+)、Ca^(2+)和HCO_(3)^(-)浓度总体呈上升趋势,pH值总体呈下降趋势;Cl^(-)浓度低于造成钢筋腐蚀的浓度,地下水对洞库支护系统无明显腐蚀作用;洞库周边监测孔地下水与水幕供水的水化学特征相似,说明水幕系统与油库围岩之间存在较好的水力联系,形成良好的水封效果。该研究可为判断地下水封油库运行情况提供重要依据,并为评价水幕系统有效性提供了一种科学方法。

自适应接地电阻的本安型电法监测场源信号发射装置设计

电法监测技术因其对煤岩电阻率变化的高灵敏特点而逐步在突水风险较高的矿井进行推广应用,然而由于井下工作面两巷工况环境复杂,不同场源发射监测电极间的接地条件差异较大且随时间变化,难以在整个监测周期内提供稳定的场源信号。设计了一种基于STM32F407的负反馈式本安型电法监测场源信号发射装置,该装置可自适应调节不同发射电极间的接入电阻,具备双重可靠本安保护电路,实现了本安限制条件下场源信号的最大功率稳定发射,既而使场源能量最大化加载至目标监测地质体来获得尽可能强的场源响应信号,提升电法监测系统数据采集质量,提高反演解释的准确性。

全自动凯氏定氮仪测定水系沉积物、土壤、岩石全氮含量方法的优化探索

本文通过改变硫酸钾(K_(2)SO_(4))和五水硫酸铜(CuSO4·5H2O)两个联合消化催化剂比例,以及消化催化剂加入量、辛醇滴入量和浓硫酸加入量等条件,探究KII60型全自动凯氏定氮仪在测定水系沉积物与土壤中全氮含量方法的优化以及对比。该方法得出在加入硫酸钾(K_(2)SO_(4))与五水硫酸铜(CuSO4·5H2O)质量比为9:1,加入浓硫酸量为6mL,辛醇最佳滴入量2滴为最佳条件。方法检出限低至25μg/g,相对标准偏差小于2.2%,相对误差小于0.65%,测定结果与传统方法无显著性差异。该方法简便、快捷、准确度高、精密度好,环境友好型,适用于水系沉积物、土壤和岩石中全氮含量的批量测定。

微震监测在矿井突水预警中的研究进展及展望

面对日益严峻的矿井水害问题,在水害防治中实时动态监测突水通道的存在及发育过程是国内外水文科学领域研究的热点。微震监测技术具有全空间、大范围、实时、连续、动态的探测功能,能够对突水通道进行时空定位。新实施的《煤矿防治水细则》着重强调完善煤矿监测监控系统,微震监测系统因其独特优势已经发展成为矿井安全生产的重要保障手段之一。通过对微震监测与矿井突水的研究进展的总结,分析了微震监测的应用优势,提出了突水预警中微震监测技术未来的发展方向。

“古地理学术论坛”第1—17期评述

以《古地理学报》中文版、英文版编辑部为主,联合中国矿物岩石地球化学学会岩相古地理专业委员会、国际古地理学会和中国石油大学(北京)共同举办的“古地理学术论坛”,是促进古地理学创新发展、倡导开展公益学术讲座的学术交流平台。从2022年9月论坛开始至2024年1月共举办了17期,共计邀请21位专家学者(包括外国专家4位)在论坛作报告。报告内容紧密结合生产实践和科技前沿,既有高屋建瓴的沉积古地理学综述,也有与油气勘探关系密切的沉积体系与沉积环境、源汇系统、层序地层学、深水沉积研究,以及与深时古环境重建有关的事件沉积、遗迹化石、古野火、碳酸盐沉积、构造古地理学研究,还包括铝土矿成因等矿产沉积学研究。总体看来,系列报告理论联系实践,既立足基础又关注前沿,受到学者们较高的关注。

铀在北山地下水中的种态分布及溶解度分析

为了解铀酰离子在北山地下水中的吸附、扩散和迁移行为,利用地球化学计算软件PHREEQC,采用由OECD/NEA发布的最新铀的热力学数据,计算了铀在我国高放废物地质处置库重点研究区甘肃北山地下水中的种态分布,并分析了围岩中存在的方解石对铀溶解度的影响。计算结果表明,在北山地下水组成不变的前提下,在偏酸性条件下,铀主要以UO2F+、UO2SO4、UO22+、UO2F2和UO2(SO4)22-的形式存在,而在中性至弱碱性条件下,主要以UO2(CO3)43-、UO2(CO3)22-、UO2(OH)3-和UO2(OH)24-的形式存在。我国计划建造的高放废物处置库的设计深度为地下500～1 000m,其水岩体系一般呈弱碱性。在这样的弱碱性水岩体系中,以阴离子形式存在的铀酰配合物具有较强的可移动性。当地下水的pH=7.56时,在Eh<24mV的条件下,铀主要以沥青铀矿的形式存在,而在更高的Eh条件下,则主要以UO22+与CO23-和OH-形成的阴离子配合物的形式存在。当地下水与空气接触时,O2的存在会使Eh升高,此时铀的主要存在种态为UO22+及其各种配合物。当围岩体系中存在方解石时,在pH<8.0的条件下,铀在地下水中的溶解度会显著提高,而在更高pH条件下,方解石对铀的溶解度无明显影响。

水岩体系E_h-pH法在砂岩型铀矿层间氧化带划分中的应用——以新疆伊犁盆地512铀矿床为例

512铀矿床层间氧化带水岩体系Eh 和 pH值的研究结果表明 ,层间氧化带内相同亚带的水岩体系Eh 和 pH平均值极为接近 ,而不同亚带的水岩体系Eh 值具有明显差异 ,即从氧化带到还原带 ,水岩体系Eh 值明显下降 ;层间氧化带内不同亚带的水岩体系 pH值也有所不同 ,氧化带和还原带处于弱碱性介质环境 ,而氧化还原过渡带则处于中性介质环境 ;水岩体系Eh 和 pH值可以作为划分层间氧化带和圈定铀矿体位置的依据。

贵阳市地表水地下水化学组成:喀斯特水文系统水-岩反应及污染特征

为了解喀斯特地区水-岩相互作用特征和辨别地下水污染物的来源,为揭示人类活动对喀斯特地下水文地球化学环境的影响,研究了贵州省贵阳市不同岩性含水层地下水和地表水的化学特征。结果发现,地表和地下水主要有HCO3型和SO4型以及这两种化学类型的混合型。地下水地表水化学溶解物质主要来源于碳酸盐岩和碎屑沉积岩的化学风化作用,硫酸盐矿物的溶解和硫化物氧化形成的硫酸对岩石矿物的化学风化是导致水体富集硫酸盐的主要因素。区内地表水和地下水的主要污染物质为K+、Na+、Cl-、SO42-和NO3-。这一研究成果为评价地表/地下水环境的质量现状,为喀斯特地区地表水地下水资源的保护和利用提供了科学依据。

莺歌海盆地底辟带热流体突破的地层水化学证据

地层水化学特征往往反映出盆地流体的成因和演化信息。莺歌海盆地地层水样品分析表明地层水矿化度可划分3个带,即非底辟带、底辟带上方常压段和超压段。非底辟带地层水矿化度接近于正常海水,而超压带为具有较低矿化度的NaHCO_3型水,底辟带上方常压段地层水矿化度变化极大,与垂向断裂距离有关,越靠近垂向断裂的井往往具有更低的矿化度和更高的 HCO_3^-和 CO_3^(2-)离子浓度。在远离垂向断裂的底辟带侧翼或较浅地层(<1200m)孔隙水接近正常海水,以 MgCl_2型地层水为主:而在毗邻于垂向断裂的浅部储层具有明显低的矿化度,与超压带流体相似,也具有较高的 HCO_3^-和 CO_3^(2-)离子浓度这些观察结果反映垂向断裂为深部超压热流体突破的主通道,底辟带上方成为地层原生孔隙水(海水)与超压带内低矿化度热流体混合场所,地层水矿化度越低,说明来自深部超压热流体所占比例越大。不同压力地层中的水化学特征可以很好地用来识别流体运移路径和可能的水-岩反应。

确定砂岩型铀矿体定位新方法——水岩体系Eh-pH法

水岩体系EhpH方法是根据水岩相互作用原理,来确定砂岩型铀矿体定位的一种新方法。研究结果表明:从氧化带到还原带,水岩体系Eh值明显下降,同一氧化还原环境水岩体系Eh平均值极为接近;不同氧化还原环境,其水岩体系pH值亦有所不同,氧化带和还原带处于弱碱性介质环境,过渡带(矿化地段)处于中性介质环境;水岩体系Eh和pH值可以作为划分含矿层氧化还原环境分带及圈定铀矿体位置的重要依据。