本文關(guān)鍵詞：含水煤層中氣體吸附、解吸-擴(kuò)散的分子模擬研究　出處：《西南石油大學(xué)》2015年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 煤層氣 含水率 吸附 擴(kuò)散 壓裂液 分子模擬

【摘要】：煤層氣儲(chǔ)層通常飽和著大量地層水,水的存在會(huì)對(duì)氣體的吸附和擴(kuò)散產(chǎn)生影響。為了提高煤層氣的產(chǎn)量,壓裂成為主要的增產(chǎn)措施,而壓裂液的適用性是決定煤層氣井壓裂效果好壞的關(guān)鍵因素之一。因此,本文針對(duì)含水煤層中氣體吸附和擴(kuò)散時(shí)的特征以及活性水壓裂液和泡沫壓裂液對(duì)CH4擴(kuò)散的影響,利用分子模擬方法和實(shí)驗(yàn)手段展開(kāi)如下研究：(1)煤層氣儲(chǔ)層具有非均質(zhì)性,所以采用Fuchs煤化學(xué)結(jié)構(gòu)模型構(gòu)建煤分子狹縫孔模型。在干燥煤的氣體吸附研究中,采用蒙特卡羅法模擬了不同溫度和孔徑下H2O、CO2和CH4的吸附特征；在含水煤的氣體吸附研究中,則分別考慮了單組分CO2和CH4以及雙組分CH4/CO2在不同溫度、孔徑、含水率和摩爾比下的吸附特征。(2)通過(guò)分子動(dòng)力學(xué)方法分別模擬計(jì)算了單組分CO2和CH4以及雙組分CH4/CO2在不同溫度、壓力、孔徑、含水率和摩爾比下的擴(kuò)散系數(shù)、分子平均自由程和等勢(shì)而分布等參數(shù),揭示了氣體在含水煤中的擴(kuò)散規(guī)律。(3)利用分子模擬方法分別建立了泡沫壓裂液中起泡劑十二烷基磺酸鈉、十二烷基硫酸鈉、十二烷基苯磺酸鈉和甜菜堿以及穩(wěn)泡劑聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、聚乙二醇(PEG)和羧甲基纖維素鈉(CMC)的分子結(jié)構(gòu)模型。通過(guò)分子動(dòng)力學(xué)方法分別模擬計(jì)算了不同起泡劑和穩(wěn)泡劑與煤、水和含水煤之間的相互作用能和泡沫壓裂液影響下CH4的擴(kuò)散系數(shù),并與實(shí)驗(yàn)測(cè)定出的飽和泡沫壓裂液煤粉的CH4有效擴(kuò)散系數(shù)進(jìn)行了對(duì)比,揭示了泡沫壓裂液對(duì)煤層CH4擴(kuò)散的影響規(guī)律。(4)通過(guò)分子模擬方法分別研究了KCl對(duì)水分子在煤表面吸附的影響以及鉀離子含量的多少對(duì)助排劑(十二烷基硫酸鈉和十二烷基苯磺酸鈉)分子在煤表面吸附的影響。利用分子動(dòng)力學(xué)方法模擬計(jì)算了活性水壓裂液影響下CH4的擴(kuò)散系數(shù),并與實(shí)驗(yàn)測(cè)定¨的飽和活性水壓裂液煤粉的CH4有效擴(kuò)散系數(shù)進(jìn)行了對(duì)比,揭示了活性水壓裂液對(duì)煤層CH4擴(kuò)散的影響規(guī)律。在上述的研究工作中,,吸附和擴(kuò)散規(guī)律總體歸納起來(lái)主要體現(xiàn)在以下幾方面：(1)在干燥煤中氣體的吸附強(qiáng)弱為H2OCO2CH4;溫度的升高對(duì)水分子吸附的影響程度大于CO2和CH4；孔徑的增大使水的吸附量逐漸增大,而C02和CH4則呈現(xiàn)出相反的趨勢(shì)；水因氫鍵和范德華勢(shì)的共同作用使其在煤狹縫中的吸附熱高于CO2和CH4的吸附熱；水在狹縫孔中吸附時(shí)密度均勻分布,而CO2和CH4的密度分布集中在壁面。(2)含水煤中,含水率的增大、溫度的升高和孔徑的增大會(huì)使單組分CO2和CH4的吸附量降低。雙組分CH4/CO2也有類似結(jié)論,但當(dāng)溫度逐漸升高和逸度逐漸增大時(shí),CO2和CH4的絕對(duì)吸附量曲線和過(guò)剩吸附量曲線均出現(xiàn)交錯(cuò)區(qū)；孔徑的增大有利于CH4絕對(duì)吸附量的增加,但無(wú)論是在哪種孔徑下CO2的過(guò)剩吸附量始終大于CH4的過(guò)剩吸附量；CO2摩爾含量的增大使CO2的過(guò)剩吸附量曲線逐漸出現(xiàn)峰值、開(kāi)闊區(qū)和交錯(cuò)區(qū)；孔徑的增大使高摩爾含量CO2的過(guò)剩吸附量驟減程度逐漸增大；在大孔徑下,當(dāng)CH4/CO2摩爾比小于1且壓力較高時(shí),CO2在競(jìng)爭(zhēng)吸附中處于劣勢(shì)。(3)含水煤中,溫度的升高、壓力的降低、孔徑的增大和含水率的降低會(huì)促進(jìn)單組分CO2和CH4在煤狹縫孔中的擴(kuò)散,使擴(kuò)散系數(shù)增大。雙組分CH4/CO2也有類似結(jié)論,當(dāng)CH4/CO2的摩爾比逐漸減小時(shí),CO2的擴(kuò)散系數(shù)逐漸增大,而CH4的擴(kuò)散系數(shù)僅在0.35×10-8m2/s左右變化,可見(jiàn)不管CO2的摩爾含量是否占優(yōu)勢(shì),CH4的擴(kuò)散過(guò)程始終處于劣勢(shì)。雖然影響因素不斷變化,但氣體擴(kuò)散始終以分子擴(kuò)散和Knudsen擴(kuò)散為主。(4)起泡劑和穩(wěn)泡劑分子雖然會(huì)吸附于煤分子表面,但不同起泡劑和穩(wěn)泡劑分子的吸附性能有較大差異；與無(wú)起泡劑時(shí)CH4的擴(kuò)散系數(shù)對(duì)比可知,起泡劑的加入會(huì)使CH4的擴(kuò)散系數(shù)顯著降低,造成CH4從煤基質(zhì)微孔向裂縫的擴(kuò)散受阻；與僅加入起泡劑時(shí)CH4的擴(kuò)散系數(shù)對(duì)比可知,穩(wěn)泡劑的加入大大降低了CH4的擴(kuò)散系數(shù),大分子聚合物型穩(wěn)泡劑會(huì)對(duì)煤層帶來(lái)極大的傷害,顯著降低CH4的擴(kuò)散速度。(5)活性水壓裂液中KCl的存在可減少水分子和助排劑分子在煤表面的吸附；因鉀離子有效干擾了水分子占據(jù)煤表面的吸附位,減緩了水分子吸附引發(fā)的煤基質(zhì)膨脹效應(yīng),所以2%KCl水溶液影響下含水煤層中CH4的擴(kuò)散系數(shù)稍大于水影響下的擴(kuò)散系數(shù),而因助排劑分子與煤表面發(fā)生了吸附,所以活性水壓裂液影響下的擴(kuò)散系數(shù)最小。綜上,本文完成了含水煤層中氣體吸附擴(kuò)散的分子模擬研究,揭示了單組分和雙組分氣體的吸附和擴(kuò)散規(guī)律以及泡沫壓裂液和活性水壓裂液影響下煤層CH4的擴(kuò)散規(guī)律,取得研究手段和結(jié)論認(rèn)識(shí)的突破。
[Abstract]:Coalbed gas reservoir is usually saturated with lots of formation water, the water would gas adsorption and diffusion effect. In order to improve the gas production, fracturing has become the main measures to increase, and the applicability of the fracturing fluid is the key factor to determine the quality of the CBM well fracturing effect. Therefore, this paper according to the characteristics of gas water coal seam in the adsorption and diffusion of active water fracturing fluid and the effect of CH4 foam fracturing fluid diffusion, simulation method and experimental method is studied as following: (1) the use of molecular CBM reservoir heterogeneity, so the chemical structure model of Fuchs coal slit pore model. The coal molecular adsorption on coal gas drying in the simulation, different temperature and different aperture H2O by Monte Carlo method. The adsorption characteristics of CO2 and CH4; adsorption on coal gas water, were considered the single component and CH4 and CO2 Two component CH4/CO2 in different temperature, pore size, adsorption characteristics of water content and molar ratio. (2) simulated single component CO2 and CH4 and two-component CH4/CO2 in different temperature, pressure, pore size was calculated by molecular dynamics method, the diffusion coefficient of water content and the molar ratio of the molecular mean free path and etc. the potential distribution parameters, reveals the law of gas diffusion in coal in water. (3) were established for foaming agent twelve sodium dodecyl sulfate foam fracturing fluid using molecular simulation method, twelve sodium dodecyl sulfate, twelve sodium and beet alkali and foam stabilizing agent of polyacrylamide (PAM), polyvinyl alcohol (PVA), polyethylene glycol (PEG) Suo Jiaji (CMC) and cellulose molecular structure model. To simulate different foaming agent and foam stabilizing agent and coal by the method of molecular dynamics, the interaction between water and water content of coal and foam fracturing fluid. Sound diffusion coefficient CH4, the saturation of foam fracturing fluid and pulverized coal and experimental determination of the effective diffusion coefficient of the CH4 were compared to reveal the influence of coal seam fracturing fluid of CH4 diffusion. (4) the KCl of water molecules on the surface of coal adsorption and the influence of the number of rows of potassium ion content to help agent were studied by molecular simulation methods (twelve sodium dodecyl sulfate and twelve sodium) molecules in the influence of coal surface adsorption. Using the molecular dynamics simulation of the diffusion coefficient of liquid crack under the influence of the activity of CH4 hydraulic calculation, and experimental measurement of saturated hydraulic fracturing fluid. The activity of pulverized coal CH4 effective diffusion coefficient were compared, revealing the active water fracturing fluid influence law of coal seam CH4 diffusion. In this research work, adsorption and diffusion, summed up the general law mainly reflected in the following aspects: (1) in dry coal gas The adsorptive body is H2OCO2CH4; the rise of temperature influence on the adsorption of water molecules is greater than CO2 and CH4; the diameter increases the absorption capacity of water increases gradually, while C02 and CH4 showed the opposite trend; the adsorption heat water by interaction of hydrogen bonds and Fan Dehua potential the heat of adsorption in slit in coal higher than that of CO2 and CH4; the water adsorption in slit pores in the uniform density distribution, while the CO2 and CH4 density distribution concentrated in the wall. (2) water content in coal, the increase of the water content, temperature and pore size increases with single component CO2 and CH4 adsorption amount decreased. Two component CH4/CO2 has a similar conclusion, but when the temperature rises gradually and fugacity increases gradually, the absolute adsorption curves of CO2 and CH4 and the excess adsorption curves were ecotone; pore size increased CH4 absolute adsorption, but no matter in which CO2 had left suction aperture The amount of CH4 is always greater than the excess adsorption; increasing the CO2 molar content of the excess adsorption curve of CO2 gradually peak, open area and transitional area; the aperture increases the excess adsorption degree and the content of CO2 was sharply increased gradually; in large aperture, when the CH4/CO2 molar ratio is less than 1 and the pressure is higher. In the competitive adsorption of CO2 at a disadvantage. (3) water content in coal, the increase of temperature, the pressure decreases, the diameter increases and the lower moisture content will promote the diffusion of single component CO2 and CH4 in coal slot Kong Zhong, the diffusion coefficient increased. Two CH4/ CO2 has a similar conclusion, when CH4/CO2 the molar ratio is gradually reduced, the diffusion coefficient of CO2 increases gradually, and the diffusion coefficient of CH4 changes only around 0.35 * 10-8m2/s visible, regardless of whether the CO2 molar content is dominant, the diffusion process of CH4 is always at a disadvantage. Although the influence factors of changing, But the gas diffusion has always been to molecular diffusion and the diffusion of Knudsen. (4) foaming agent and foam stabilizer molecules adsorbed on the surface while the coal molecule, but different adsorption properties of foaming agent and surfactant molecular foam had great difference; and comparing the diffusion coefficient of CH4 foaming agent, foaming agent with the the diffusion coefficient of CH4 decreased significantly, resulting in CH4 blocked from coal matrix to crack the micropore diffusion; diffusion coefficient compared with only adding CH4 foaming agent, adding foam agent greatly reduces the diffusion coefficient of CH4, high molecular polymer foam stabilizing agent will bring great harm to the coal layer, significantly reduce diffusion the speed of CH4. (5) active water fracturing fluid in the presence of KCl can reduce the adsorption of water molecules and help row agent molecules on the surface of coal; due to the adsorption of potassium ion effectively interfere with water molecules and coal surface, slowing the water molecular adsorption caused by coal The matrix expansion effect, so 2%KCl solution under the influence of diffusion coefficient of water in coal seam CH4 is slightly larger than the diffusion coefficient of water under the influence, and because of additive molecules and coal surface adsorption, so the active water fracturing fluid under the influence of the diffusion coefficient minimum. To sum up the molecular simulation study of gas containing water in coal seam the adsorption and diffusion, reveals the single and binary component gas adsorption and diffusion and foam fracturing fluid and active water diffusion in CH4 coal seam fracturing fluid under the influence of research methods and conclusions achieved breakthrough.

【學(xué)位授予單位】：西南石油大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TE377

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