Natural gas hydrate is a potential unconventional energy resource. Understanding the mechanical behavior of gas hydrate-bearing sediments (GHBS) is important to ensure the safe and efficient exploitation of natural gas hydrate and prevent geohazard problems. This study employs discrete element method to investigate the me-chanical properties of GHBS with different hydrate saturations under various vertical stresses, and a series of direct shear tests, which requires less computational consumption than triaxial or biaxial tests. Comprehensive analyses of macroscopic and microscopic mechanical behaviors, including shear strength, internal friction angle, cohesion, shear band, average coordination number, and crack number evolution, are carried out, as an effort for understanding the shear strength breakpoint, which is recognized in laboratory experiments, probably caused by the transition in hydrate morphology in sediment pores. The results obtained reveal that: (1) the way of hydrate in strengthening GHBS is to enhance cohesion; (2) the increasing rate of the strength difference between the sediment matrix with and without hydrate remarkably increases when the hydrate saturation is over certain value at which the shear strength breakpoint is observed, and this rate decreases with the increase in median particle diameter (D50) of host sediments; (3) the transition in hydrate morphology in sediment pores is recognized when the hydrate saturation increases at microscale; and (4) the shear strength breakpoint in the curve of strength difference versus hydrate saturation is explained based on the micromechanical properties of GHBS, including shear bandwidth, average coordination number, average normal force, and crack number evolution.

In the process of CO2 geological sequestration, there is a risk that CO2 will leak into groundwater, resulting in a series of physical and chemical reactions, with influence on chemical compositions of groundwater. In this work, numerical simulation is conducted to study the influence of CO2 migration on the chemical composition of groundwater. The modeling results indicated that when CO2 leaks into groundwater, gaseous CO2 will migrate upward and diffuse laterally under the effect of buoyancy. The acidity of groundwater is enhanced and the pH is significantly reduced, leading to dissolution of calcite, illite, oligoclase, K-feldspar, chlorite and hematite, and precipitation of quartz, kaolinite, smectite-Na, siderite and smectite-Ca. The porosity of the formation increases. The concentrations of K+ and Fe2+ in groundwater gradually increase, the concentrations of Ca2+ and HCO3− basically remain unchanged after increasing to a certain value, the concentrations of Mg2+ and AlO2− first increase and then decrease, and the concentrations of Na+, Cl− and SO42− first decrease slightly and then gradually increase, but the change in concentration is small. Therefore, Fe2+, Mg2+, Ca2+ and pH can be used as important monitoring indicators of whether CO2 leakage into groundwater during geological storage.

在CO2驱油封存过程中,封存的CO2可能通过盖层泄漏到浅层含水层.以延长油田杏子川化子坪试验区白垩系洛河组砂岩含水层为例,采用数值模拟软件TOUGHREACT研究地层各向异性对CO2在浅层含水层中迁移转化的影响.结果表明:溶解矿物为方解石、钾长石、绿泥石、奥长石、赤铁矿和伊利石,其中伊利石从第10年开始沉淀,沉淀矿物为钠蒙脱石、高岭石和石英,次生矿物为钙蒙脱石和菱铁矿.地层垂向与水平渗透率比值kv/kh(kv保持不变)越大,CO2在水平方向上的迁移扩散距离越小,含水层中溶解态CO2浓度越高,pH越低,CO2突破浅层含水层的时间越短.通过研究地层各向异性对CO2在浅层含水层中迁移转化的影响,为驱油封存CO2泄漏监测和风险预警提供科学依据.

现有微观孔隙结构研究手段多局限于在微尺度提供孔喉尺寸、孔喉比等孔隙结构参数,所得结果无法直接应用于岩心尺度及矿场尺度等宏观尺度的研究中,其研究结果与储层实际结合具有一定困难.为此,从多尺度评价角度出发,以碳酸盐岩岩心数据体为研究对象建立孔隙网络模型分析碳酸盐岩微观孔隙结构,在此基础上,根据分布函数及分形函数对其进行尺度升级,获得岩心尺度评价参数.结果表明:尺度升级后的岩心表现出明显低渗、致密特性,与孔隙网络模型分析结果相符.可见,对微观孔隙结构分析结果进行尺度升级具有一定可行性,并且升级结果对于宏观尺度的评价工作具有一定的理论意义.

运用场发射扫描电镜(FE-SEM)和N2/CO2等温吸附方法,文中对黔北地区不同构造区五峰组—龙马溪组页岩的孔隙特征进行表征,并且基于构造差异深入分析了其孔隙结构及甲烷吸附能力.研究表明:相比于高陡构造区,低缓构造区孔径以双峰分布为主,并且发育较多的微裂隙有机质孔隙、与黏土矿物紧密结合的有机质孔隙以及粒间孔隙,而刚性矿物格架内的有机质微孔几乎不受构造条件影响,其发育特征仅随总有机碳质量分数(TOC)改变.低缓构造区微孔、中孔、大孔的体积均大于高陡构造区,表明低缓构造区具有更大的孔隙空间和游离气储存能力.另外,甲烷等温吸附实验表明,构造差异对甲烷吸附能力无显著影响,有机质丰度和保存条件是储层高产的先决条件.

滑溜水体积压裂是非常规致密储层的主要经济增产措施,支撑剂的运移与分布规律决定着复杂裂缝网络内支撑剂的最终分布形态和导流能力.文中采用PIV(粒子成像测速)系统捕捉支撑剂颗粒在主裂缝中的瞬时运移状态,研究了不同压裂液黏度、排量、砂比和支撑剂筛 目条件下支撑剂铺置后的砂堤平衡状态,揭示了砂堤前缘与末端流场的变化规律.结果表明:随着排量、砂比和支撑剂筛目的增大,以及压裂液黏度的降低,支撑剂颗粒在砂堤前缘入口处和离开砂堤峰部时的运移速度更快,湍流强度更大,形成的有效裂缝更长;砂堤处于平衡状态时的高度和时间随着排量增加而减小,砂堤整体形态变得平缓;砂比越大,砂堤峰部出现位置越靠近裂缝入口处;优化的排量为10～12m3/min、砂比控制在20％以下、压裂液黏度在6～16mPa·s、支撑剂筛目为40/70目时,形成的砂堤高度和长度最大.该研究成果可以为滑溜水体积压裂设计和施工提供有效的技术指导.

酸化压裂是碳酸盐岩油气藏增产的主要措施和手段,即使采用较大规模施工,酸蚀缝长一般不超过120 m,而水力压裂技术能够实现大规模造长缝的目的.为此,开展水力压裂与酸携砂压裂相结合的复合酸化压裂技术研究及现场实验,以探索碳酸盐岩增产措施的新工艺技术.实验采用塔里木盆地奥陶系碳酸盐岩岩心,模拟高温高压地层条件,通过测试水力加砂压裂裂缝、酸化压裂酸蚀缝、酸携砂压裂裂缝、水力压裂与酸携砂复合酸压裂缝的短期导流能力,探索评价了碳酸盐岩地层增产改造的新工艺技术,实验结果表明了碳酸盐岩地层实施复合酸化压裂可以实现较好的导流能力.基于导流能力实验评价结果,优化设计了4口井的复合酸化压裂方案并进行现场施工,增产效果良好,为碳酸盐岩地层实施复合酸化压裂提供了有力的理论支持.

TOUGHREACT has been widely used as a chemical reaction simulation program for non-isothermal multiphase flow in pore and fracture media. By analyzing the comprehensive research results, the application status of TOUGHREACT in CO2 geological storage, geothermal energy development, nuclear waste disposal, mineral recovery and silica fouling and environmental pollution remediation are summarized. Finally, the future development trend of TOUGHREACT is also analyzed. It can be used as a reference for the future application of TOUGHREACT in the field of energy and environment.

针对裂缝型储层的不同裂缝类型,分别设计和进行了5种裂缝贯穿程度和4种裂缝充填模式的致密岩心渗透率应力敏感性实验,并分析了各种裂缝贯穿程度和裂缝充填模式的岩心渗透率应力敏感性差异.结合一维产能解析模型,分析了裂缝贯穿程度和裂缝充填模式对裂缝型油藏产油量的影响.研究结果表明:裂缝贯穿程度较小时,岩心渗透率应力敏感性主要体现为基质压缩,而随着裂缝贯穿程度增大,岩石应力敏感过程主要包括裂缝闭合和基质压缩2个阶段;岩心流量并不一定随着实验压差增大而简单增大,而是生产压差和岩心渗透率的综合函数.

We investigated the performance of viscoelastic surfactant (VES) solution when applied in treatment on the uninvaded matrix using core flooding tests to analyze the impact of VES/CaCl2 concentration on fluid viscosity. In this paper, core samples from Tahe carbonate reservoir, with an average permeability less than 0.02 × 10−3 μm−2 and a small average porosity in the range of approximately 0.04–5.24% are used in the experiments. Computed tomography (CT) scanning is used to provide a detailed description of inner structure variation of cores after the acid system treatment. The results confirmed that a large pressure difference contributed to fracture propagation and the relative permeability of water increased significantly after the treatment. It was also found that higher concentrations of VES and/or Ca2+ induced higher viscosity and a stronger fracturing effect, while a lower concentration improved the reaction rates and etching effect, generating small worm holes inside the core. Foam in-situ produced during the etching process is the major contributor to the fluid viscosity enhancement. The permeability of fracture formed on the surface of the core is more sensitive to the confining pressure. These findings can help better understand the rheological properties of the acid system and etching and fracturing mechanisms during acid treatment, and which provides instructions for field implementation.

采用塔里木盆地奥陶系碳酸盐岩岩心,在不考虑酸液滤失的情况下,用Nierode-Kruk方法,通过室内实验评价了酸液用量、温度、酸液体积分数、组合酸等因素对长效酸(高温胶凝酸、变黏酸和自转向酸)酸蚀导流能力的影响规律,分析了闭合压力对导流能力的影响程度.研究表明:酸蚀导流能力和刻蚀强度由强至弱依次为高温胶凝酸、自转向酸、变黏酸,且随酸液体积分数和用量的增加,酸蚀导流能力逐渐增加,但裂缝导流能力保持率的变化趋势有所不同;高温胶凝酸在高温状态的酸蚀导流能力较高;高温胶凝酸和自转向酸的组合产生的裂缝导流能力最大.现场应用长效酸进行酸化压裂施工取得了良好的效果,该研究成果在优化酸化压裂施工设计和提高现场施工效果方面具有一定的参考价值.

With the progress of the exploration and development technologies ,the number of fracturing wells in volcanic reservoirs gradually increases .Since there are large changes in lithological characters ,poor heterogeneity ,and high fracture pressure in volcanic reservoir ,it is difficult to reach a good stimulation effect by conventional fracturing techniques .There-fore,aiming at the geological characteristics and fracturing difficulties of volcanic reservoir in Chagan area ,based on the a-nalysis experiments of reservoir sensitivity and rock mechanics property ,a low residue and damage fracturing fluid was se-lected .And then it was carried out studies on the temporary plugging agent and the entire process assisted liquid nitrogen injection technology .Finally,it was formed a more effective hydraulic fracturing technology system for volcanic reservoir . The field application obtained obvious stimulation effect .Thus,the technology can provide an effective stimulation method for high efficient development of volcanic reservoir .

针对查干凹陷苏一段储层的地质特征和压裂改造难点，结合部分前期压裂井的效果分析，开展储层伤害及岩石力学特征分析评价，优选出了低残渣、低伤害、易返排的压裂液体系，并进行了降破压实验评价；在压裂工艺技术方面，进行了酸化预处理技术、全程伴注液氮技术、多裂缝技术和压后返排优化设计的研究，初步形成了一套较为有效的适用于该地区储层的水力压裂工艺技术体系。经现场应用后取得了显著的增产效果，对该地区储层勘探开发提供了一套有效的储层改造技术。

塔里木盆地奥陶系碳酸盐岩油藏产层厚度大,完井井段长,非均质性严重.分别运用均值和均方差方法优选酸压井段物性参数,运用最优BP神经网络结构编制酸压决策软件,对塔里木盆地酸压施工的20井次进行酸压前决策模拟.实例应用对比分析表明,均值方法符合率75％,均方差方法符合率90％.对于长裸眼非均质碳酸盐岩储层,采用均方差方法优选储层物性参数,可以较准确地描述不同深度的物性差异给酸压造成的影响,定量地指导酸压选井选层工作及增产措施的制定.

粘弹性颗粒驱油剂B-PPG是一种全新的驱油剂,具有部分交联、部分支化的分子结构,分散于水中形成非均相的B-PPG悬浮液.采用稳态剪切和动态振荡实验,研究了不同质量分数、不同交联度的B-PPG在不同矿化度盐水中的流变特性,并分析其产生机理.结果表明,B-PPC悬浮液具有优异的粘弹性、耐盐性和增粘性.随着B-PPG交联度的增加,B-PPG悬浮液粘度呈下降趋势,B-PPG悬浮液粘性与弹性模量交点处频率(Fc)逐渐趋向低频;高矿化度使部分水解聚丙烯酰胺(HPAM)溶液的弹性减弱,而对B-PPG悬浮液模量影响较小,表明B-PPG较HPAM具有更优异的耐盐性;随着B-PPG质量分数的增大,B-PPG悬浮液线性粘弹区范围增大,且粘度明显增大,B-PPG悬浮液更加偏离牛顿流体,Fc值逐渐趋向低频;通过对其动态振荡曲线的线性拟合数据发现,B-PPG悬浮液表现出弱凝胶特性.

塔河油田是典型的缝洞型碳酸盐岩油藏,储集体非均质性强,油水界面不清楚,出水量大,堵水效果整体较差.现有堵水工艺堵水有效率仍较低,需要进行技术集成.根据缝洞型碳酸盐岩油藏的储层特征,建立堵水井生产概念模型,从油藏地质因素、油藏开发状况和工程工艺三方面总结影响堵水效果的11个因素,对影响堵水效果的各类因素采用均值和均方差的处理方法,优选出影响堵水效果的主要因素.采用支持向量机方法建立塔河油田奥陶系油井堵水效果预测模型,并对8口井进行实例预测,符合率达到87％.对于塔河油田有限的堵水样本,利用支持向量机方法进行堵水决策具有较高的精度,可以用来指导塔河油田的堵水选井选层工作.

The Ordovician fissure-cavern carbonate reservoirs of Tarim Basin have relatively large production thickness, long completion intervals and serious heterogeneity problems, former studies about physical parameters for fractured intervals of acid fracturing cannot be well presented through mean algorithm method. This paper uses mean square deviation method to acquire the values of the main influencing factors of acid fracturing, then optimizes the physical characteristics of the fractured intervals. The BP neural network simulation has been adopted to get the optimal BP neural network structure model. In Tarim, this study has simulated 20 wells before acid fracturing using the decision software which compiled by the optimum neural network construction. Comparative analysis has been made through application examples, the coincident rate of mean algorithm is 75%, compared with the 90% of mean square deviation method. Therefore, during the target selection for acid fracturing of heterogeneous carbonate reservoirs with long open hole intervals, it’s significant to use mean square deviation method to optimize physical parameters of reservoirs.

The frequency of fracturing practice in glutenite reservoir has increased gradually with the progress of exploration and development technology. Glutenite, which has properties like fast transformation in phase, great change in lithology, permeability and dip angle, irregular fracture face, disturbed flow phenomenon, severity in heterogeneity and complex pressure system,explains the low efficiency and success rate of hydraulic fracture's utilization in glutenite reservoir exploration and development. This paper features the glutenite reservoir in Songnan area, using PT software, with data of artificial fracture monitoring and well temperature etc. combined, to deal with construction curve, further explores the artificial fracture propagation mechanism. What's more, effect of in-situ stress on fracture propagation mechanism is determined and the fracturing technical measures in glutenite reservoir is also proposed with acoustic emission Kaiser experiment, both of which can effectively channel fracturing well and layer selection and design optimization, improve efficiency and success rate of hydraulic fracturing.

一般水平井压裂的破裂压力比直井的破裂压力要高得多,存在裂缝压不开而导致压裂施工失败的问题,反映了水平井的裂缝起裂机理与垂直井及普通定向井有显著差别,研究水平井裂缝起裂机理和裂缝延伸规律,对水平井水力压裂优化设计具有重要的意义.以黄陵地区三叠统延长组长6油层组裂缝性储层为例,利用测井资料处理了地应力剖面,采用岩心的岩石力学性质和地应力试验分析方法、压裂施工参数和净压力处理分析方法,结合裂缝监测及区域构造特征,将室内试验与数值分析方法相结合,明确了该类储层水平井人工裂缝起裂特征,揭示了水平井裂缝延伸规律,为该类储层水平井压裂方案和设计优化提供理论依据,从而有效地提高了施工效率和成功率.