页岩储层渗吸过程中水的微观分布及其气测渗透率动态响应特征

在页岩油气储层水力压裂过程中,压裂液的滤失行为会增加储层的含水饱和度、降低储层渗透率。研究压裂液侵入对储层渗透率的影响,对于页岩油气的高效开发具有重要意义。为此,针对渤海湾盆地沾化凹陷沙河街组三段下亚段灰质页岩和混合质页岩岩相样品,通过自发渗吸实验获得了样品不同含水饱和度行为,利用核磁共振表征水在孔隙中的动态运移,结合覆压渗透率定量表征气测渗透率动态变化。实验结果表明：①在含水饱和度为5%~40%的渗吸过程中,以微孔（核磁共振T₂<1 ms）吸水为主,T₂谱累积信号呈上升趋势,占比逐渐增加,而中孔和大孔的T₂累积信号呈缓慢上升和波动状态且占比逐渐降低。当含水饱和度达到40%时,微孔累积信号占比高达87%以上。②水化改善作用与水锁和水敏损害相互制约,影响渗透率的动态变化,主要分为3种制约状态（水化远大于、大于、小于水锁和水敏）。结合矿物组分和孔隙结构分析发现,在黏土矿物含量为25%~43%的页岩中,渗透率损害率与黏土矿物和石英含量呈正相关,与脆性指数和碳酸盐矿物含量呈负相关性,灰质页岩水化改善作用优于混合质页岩,且大于1 μm孔喉的发育既能促进水化改善作用,又能降低水锁和水敏对孔喉的损害。     

Effect of porosity on rehydration of dry food particulates

Rehydration of food particulates is a complex phenomenon affected by numerous factors that typically include pre‐drying treatments, mode of dehydration, structure, composition and medium viscosity. Freeze drying (FD), air drying (AD) and their combinations, were utilized to produce an array of porosities, ranging from very high to very low values for FD and AD carrots, respectively. Bulk porosity correlated significantly with open, but not with closed, porosity. Bulk and open porosities decreased with AD time. Scanning electron micrographs of the FD samples verified their organized and more open structure in comparison with the AD carrots. Rehydration ratio increased with bulk and open porosity, and was not affected by the closed porosity. The effective moisture diffusivity, derived from fitting the normalized Weibull distribution, increased with bulk and open porosity and was about two orders of magnitude higher for the FD, than for the AD, carrots. The Weibull shape parameter, β, was inversely related to porosity. Its values indicated that water uptake of only the AD carrots followed a Fickian diffusion. A critical porosity value above which water mechanism changed from a Fickian diffusion to imbibition into a porous medium is suggested. Copyright © 2004 Society of Chemical Industry     

Numerical simulation of liquid absorption in paper‐like swelling porous media

The work is built on a previous research by Wiryana and Berg, in which wicking into four wet‐formed paper stripes, consisting of cellulose fibers and four different percentages of the powdered carboxymethyl cellulose (CMC) superabsorbent, was studied experimentally. Because of the swelling of cellulose fibers and CMC powder on contact with water, the wicking was accompanied by a swelling of the matrix. A finite element/control volume (FE/CV)‐based computer program is used for the first time to model the wicking in such swelling porous medium. The simulation used a novel form of continuity equation, which included the effects of liquid absorption and matrix swelling, in conjunction with the Darcy's law to model the single‐phase flow behind a clearly defined liquid‐front. A new method of estimating the time‐varying permeability of the paper, based on the absorbed liquid‐mass vs. time plots, is also proposed. Later, this time‐dependent permeability is used in the numerical simulation to change the permeability in elements behind the moving liquid‐front as a function of the time that the element has been wetted by the liquid, since the passage of the liquid‐front. The numerical prediction of the wicking‐front location as a function of time compares well with the reported experimental data. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2536–2544, 2012     

Effect of Capillary Pressure on Wetting Film Imbibition Ahead of Main Liquid–Gas Displacement Front in Porous Media

Abstract

The effect of capillary pressure on wetting film imbibition along the edges of pores in porous media is investigated experimentally. It is found that the capillary pressure at the main liquid–gas front (the main displacement front) plays a major role, among other factors, in determining the imbibition rate of a wetting liquid along pore edges. The measured velocities of the wetting film in a two-dimensional consolidated glass bead model and the imbibed volumes of the wetting liquid into the mode ahead of the main front are found to be proportional to 1/P^1/2 _C and 1/P^5/2 _C, respectively, where P_C is the capillary pressure at the main liquid–gas front. The effect of capillary pressure on wetting film imbibition along the edges of pores is also illustrated by the experiments in a periodically constricted capillary where different film imbibition rates were obtained when the main liquid–gas meniscus is kept at a throat and a pore. Both theoretical analysis and experimental results show that the length of the wetting film ahead of the main meniscus increases greatly as the injection rate is decreased.     

Wettability Alteration of Low-permeable Carbonate Reservoir Rocks in Presence of Mixed Ionic Surfactants

Abstract

Altering the wettability of the carbonate reservoir rocks from oil-wet to water-wet has figured prominently as one of the enhanced oil recovery methods in recent years. The authors measured the effect of different ionic surfactants on the wettability alteration of the rock, saturated with crude oil, and the consequent improvement in oil production was investigated by spontaneous imbibitions of solutions containing cationic, anionic, and cationic-anionic surfactant mixtures. A very low-permeable carbonate rock from one of the Iranian oil reservoirs was selected for this study. The results of imbibition tests were furthermore supported by measuring IFT, taking pictures of producing oil drops from different exterior core plug surfaces and also observing the distribution of the remaining oil in cores at the end of experiments. The results show that cationic surfactants at concentrations higher than CMC can cause a remarkable oil production through alteration of wettability and, moreover, the extent of oil production increases with temperature. In contrast, it is observed that the anionic surfactants are not able to change the wettability of an oil-wet surface and their combination with the cationic type would reduce the oil production potential of cationic surfactants.     

三塘湖盆地芦草沟组页岩自吸特征

页岩储集层压裂后,存在压裂液返排率低、产能差异大的特点,大量的压裂液长期滞留井下并被储集层自发吸入,对油气开发及有效动用具有很大影响。以页岩油可动性、页岩静态自吸和润湿性等多项实验为基础,通过页岩自吸压裂液驱油实验和恒压水驱油实验,认识到页岩独具的自吸特征。基于静态自吸实验,从页岩基本吸水物理现象入手,通过自吸饱和度和自吸速率2个自吸特征参数来反映页岩的自吸能力,分析现场压裂后生产排液曲线,认为室内实验结果对页岩压裂后生产排液有一定的预测作用。通过液—岩铺展性实验,分析了三塘湖盆地二叠系芦草沟组页岩润湿性特征及其对自吸能力和特征的影响,认识到页岩既有亲油性又具有亲水性的混合润湿特征,结合相关资料综合分析认为,页岩的自吸能力和特征主要受微观孔隙结构和润湿性的共同控制和影响。     

鄂尔多斯盆地延长组7段凝灰质页岩油层的润湿性及自发渗吸特征

页岩油源-储体系内通常发育大量凝灰质泥岩层,由于大量火山凝灰质的沉积导致页岩层系内页岩油储层结构发生变化,因此,凝灰质泥岩层内烃类物质的流动性引起广泛关注。为研究页岩体系内凝灰质泥岩成分对烃类流体流动行为的影响,利用储层润湿性接触角实验表征凝灰质泥岩样品的亲油性,利用轻质油自发渗吸实验的渗吸率表征储层流体流动性。结合生烃热解实验和放射性Th、U元素测试,探讨火山凝灰质成分和残留有机质对页岩油自发渗吸作用的影响,并将这两项关键因素引入凝灰质泥岩层流体自发渗吸刻度模型,半定量刻画了火山凝灰质成分对页岩油流动能力的控制作用。研究结果表明：对于页岩油源-储体系,几乎所有凝灰质泥岩层段都是亲油性的。岩层内流体自发渗吸率随着凝灰质主控孔和残留烃覆盖孔的增加而增加,大量凝灰质沉积物自生的多孔沸石有利于提高页岩油的流动性。     

页岩气井压裂后焖排模式

页岩气井水力压裂过程中注入液量大,但压裂后返排率往往较低,滞留压裂液对储层的影响仍不清晰。针对该问题,选取永川新店子构造YY1井龙马溪组的岩心,开展压裂液渗吸实验,并对比渗吸前后岩心物性、孔隙结构特征及电子显微镜下微观结构等参数的变化规律。实验结果表明：永川新店子构造岩心压裂液渗吸后,岩心平均孔隙度增大了50%,平均渗透率增大了25%,气体吸附量减少了35%,比表面积降低了40%;岩心沿层理方向产生了新的裂缝,并随着渗吸的持续进行,裂缝发生扩展和延伸,逐步沟通裂缝网络,增大了液体的渗吸面积;通过YY1HF井的现场试验发现,焖井30 d后再控产（6万m³/d）试采,产液量大幅度降低,气井生产稳定。研究认为,压裂后焖井有利于改善储层物性,增加渗流通道,压裂后返排应由小到大逐级控制油嘴排液,以提高气井采收率。     

不同渗透率砂岩岩心在纳米流体中的渗吸特征

针对目前渗吸岩心移位核磁成像实验存在表面油相损耗与空气吸附,进而影响实验结果精度的问题,改进设计出原位核磁成像渗吸实验方法,采用该方法开展砂岩岩心在纳米流体中的渗吸实验,记录了整个纳米流体渗吸过程中原油的实际运移图像,同时结合砂岩岩心的物性、渗吸过程中的驱动力变化,分析了不同渗透率砂岩岩心在纳米流体中的渗吸特征.研究表...