本文選題：煤層氣　切入點(diǎn)：氣水兩相　出處：《太原理工大學(xué)》2015年博士論文

【摘要】：煤層氣作為與煤伴生、共生的氣體資源,以其清潔、熱值高、開(kāi)發(fā)利用前景廣闊的特點(diǎn),已經(jīng)成為非常規(guī)天然氣勘探開(kāi)發(fā)的重點(diǎn)。我國(guó)煤層氣形成的地質(zhì)條件和賦存環(huán)境條件復(fù)雜,其開(kāi)發(fā)受到地應(yīng)力、含壓地下水及溫度等多場(chǎng)耦合作用。本文以煤層氣熱力開(kāi)采為背景,采用實(shí)驗(yàn)與模擬相結(jié)合的方法,對(duì)煤體常溫及高溫應(yīng)力作用下氣水兩相滲流規(guī)律做了研究,本文的主要研究?jī)?nèi)容及結(jié)果如下:1)從煤層氣產(chǎn)出機(jī)理出發(fā),分析了煤層氣的開(kāi)采是氣體“解吸-擴(kuò)散-滲流”的運(yùn)動(dòng)過(guò)程。根據(jù)汽化和凝聚的動(dòng)力學(xué)平衡原理、Fick定律、Darcy定律,得到了煤層氣氣水兩相滲流模擬的數(shù)值模型。在一般的求解過(guò)程中,根據(jù)不同情況對(duì)毛細(xì)管力及重力進(jìn)行分析,得到了簡(jiǎn)化的滲流微分方程。2)采用自行研制的氣水兩相高精度滲透系統(tǒng),進(jìn)行了大量非穩(wěn)態(tài)氣水兩相滲流實(shí)驗(yàn),結(jié)果表明:非穩(wěn)態(tài)全過(guò)程包含三個(gè)階段,即水滲流階段、氣水混合階段、含束縛水的氣體滲流階段,并得到了各階段的滲流特性。煤體含水飽和度降低到0.5以下會(huì)發(fā)生“突變”,隨后含水飽和度急劇減小,只存在氣體滲流區(qū)域,該飽和度的變化可對(duì)產(chǎn)氣進(jìn)行預(yù)測(cè)。3)進(jìn)行了不同應(yīng)力條件下的單相滲流及非穩(wěn)態(tài)兩相滲流實(shí)驗(yàn),結(jié)果表明:在同一軸壓σ1、圍壓σ2(σ1σ2)條件下,增加孔隙壓P1,氣、水滲透率均隨之非線(xiàn)性增加,孔隙壓持續(xù)增大會(huì)有滲透率突增情況,且在相對(duì)低應(yīng)力下,孔隙壓對(duì)滲透率的作用更明顯。對(duì)比注氣前后水相滲透率可以看出:氣相的存在不同程度增加了水的滲流阻力,且氣體驅(qū)替壓力越高,阻力越大,滲透率的差值越大。煤體相對(duì)滲透率的曲線(xiàn)形態(tài)特征為:隨含氣飽和度增大,氣相相對(duì)滲透率曲線(xiàn)會(huì)急劇上升,液相相對(duì)滲透率則在較低值范圍內(nèi)緩慢減小,在氣體突破后很快下降到零,煤樣有較高的束縛水飽和度。4)煤試樣在17種壓力組合實(shí)驗(yàn)過(guò)程中,水測(cè)滲透率與氣測(cè)滲透率均隨有效應(yīng)力的增加而減小,在相對(duì)較低有效應(yīng)力范圍內(nèi)(小于4~5mpa),滲透率減小幅度較大。隨著有效應(yīng)力增加,后期滲透率變化幅度則較小。無(wú)論是選擇水相作為流體還是氣相作為流體,對(duì)試樣進(jìn)行的滲透率測(cè)量經(jīng)歸一化處理后,結(jié)果趨勢(shì)一致。對(duì)實(shí)驗(yàn)數(shù)據(jù)數(shù)學(xué)擬合表明,煤體歸一化滲透率與有效應(yīng)力之間具有良好的冪函數(shù)關(guān)系。相比于常溫下有效應(yīng)力與滲透率關(guān)系曲線(xiàn),加熱后的曲線(xiàn)下降更加平緩,經(jīng)過(guò)熱作用后的煤應(yīng)力敏感性下降,在煤層氣熱力開(kāi)采過(guò)程中,煤應(yīng)力敏感性下降會(huì)使排水產(chǎn)氣過(guò)程更加平緩,避免了傳統(tǒng)降壓開(kāi)采中遇到的氣體突然大量產(chǎn)出的情況。5)采用氣水兩相滲透裝置及控溫試驗(yàn)臺(tái),進(jìn)行了30℃~180℃范圍內(nèi)等溫度間隔變化的煤體單相滲透實(shí)驗(yàn)及非穩(wěn)態(tài)氣水兩相滲流實(shí)驗(yàn)。研究了在溫度的影響下,兩相流動(dòng)過(guò)程的變化規(guī)律及流體滲流的特性。隨溫度的增加,各壓力下產(chǎn)液量均為增加的趨勢(shì)。產(chǎn)量增加在高溫階段(120℃以后),增幅更為明顯。說(shuō)明溫度120℃~180℃范圍內(nèi),溫度越高,煤體孔隙裂隙連通性更好,同時(shí),水分子在高溫下所獲的熱能越大,越有利于煤體中液體產(chǎn)出,束縛水飽和度變小。相反,在相同溫度條件下,增加圍壓軸壓使有效應(yīng)力改變,煤體內(nèi)部的孔隙裂隙被壓縮,部分液體無(wú)法被排出,束縛水增多,產(chǎn)水量減少。6)在溫度作用下非穩(wěn)態(tài)兩相滲流全過(guò)程的三個(gè)階段變化為:第一階段以產(chǎn)水為主的液體線(xiàn)性滲流階段,隨溫度升高,液體產(chǎn)量占總產(chǎn)液量百分比緩慢減小,溫度高于120℃后變化幅度加大;第二階段氣水混合流動(dòng)階段,液體流速急速線(xiàn)性增加,氣體流速平穩(wěn)加快。隨溫度升高,該階段液體產(chǎn)量占總產(chǎn)液量百分比逐漸減小,溫度高于90℃后減小幅度更大。第三階段束縛水下的氣體滲流,該階段受溫度影響比較明顯,液體產(chǎn)量占總產(chǎn)液量百分比提升較大。溫度低于60℃該階段液體產(chǎn)量?jī)H占總產(chǎn)液量10%左右,產(chǎn)液量以第一、二階段為主。當(dāng)溫度達(dá)到150℃左右,該階段百分比達(dá)到50%左右,比例均超過(guò)了一、二階段。7)溫度在30℃到180℃的變化范圍內(nèi),滲透率變化分為兩個(gè)階段:相對(duì)低溫段(30℃至120℃),該階段溫度對(duì)流體影響占主導(dǎo),對(duì)比氣、水相滲透率,在該溫度變化階段,液體粘度變化顯著,減小幅度較大,而氣體粘度略有增加,滲透率測(cè)量結(jié)果與粘度的變化趨勢(shì)一致。高溫段(120℃至180℃),溫度對(duì)多孔介質(zhì)結(jié)構(gòu)的改變成為主要影響因素,在此溫度變化范圍,液體、氣體粘度變化均較平緩,而滲透率的變化卻有大幅度的提高,說(shuō)明受高溫影響,煤樣的孔隙裂隙發(fā)生了較大變化,滲流通道比低溫段連通性更好,有利于流體的流動(dòng)。同時(shí),隨著溫度的升高,束縛水飽和度減小,氣水兩相滲流區(qū)變寬,水相相對(duì)滲透率隨含水飽和度的降低而減小趨勢(shì)變緩,溫度越高,對(duì)氣水兩相相對(duì)滲透率曲線(xiàn)的影響逐漸減小。為客觀地反映由于溫度變化而引起的壓降變化,提出了溫度敏感性系數(shù),該系數(shù)與溫度較好的服從對(duì)數(shù)函數(shù)關(guān)系。8)采用歐拉觀點(diǎn)和拉格朗日觀點(diǎn),對(duì)氣水流動(dòng)界面進(jìn)行分析,將擬壓力函數(shù)p=2∫PP0p/μdgZdp引入兩相滲流方程。對(duì)壓力函數(shù)分為三種情況討論:①pμgZ為常數(shù)時(shí),pg=pg;②μgZ為常數(shù)時(shí), pg=pg2;③μgZ為壓力p的一次線(xiàn)性函數(shù)時(shí),p=2∫PP0p/ap+bdp。由此得到氣水兩相流動(dòng)界面的不考慮壓縮性驅(qū)替模型、考慮壓縮性驅(qū)替模型及擬壓力線(xiàn)性函數(shù)方程驅(qū)替模型。對(duì)三種模型的滲流方程及邊界條件進(jìn)行了詳細(xì)推導(dǎo),獲得流體流量與位置函數(shù)的關(guān)系式。用Matlab軟件分別對(duì)三種模型進(jìn)行了求解計(jì)算,選取相同應(yīng)力條件下的實(shí)驗(yàn)參數(shù),得到了累計(jì)產(chǎn)出水量隨時(shí)間變化曲線(xiàn)及不同時(shí)間下的氣水流動(dòng)界面位置。對(duì)比了三種模型的實(shí)驗(yàn)結(jié)果和誤差,得到了三種模型的適用性。為實(shí)際工程中排水預(yù)測(cè)產(chǎn)氣提供了較為可靠的模型選擇依據(jù)。
[Abstract]:Coal seam gas is associated with coal, gas resources symbiosis, with its clean, high calorific value, wide utilization foreground features, has become the focus of natural gas exploration and development of unconventional. The formation of coalbed gas geological conditions and geological environment condition is complicated, and its development is affected by stress, pressure and temperature of groundwater containing multi-physics. Based on coalbed gas thermal recovery as the background, using the method of combination of experiment and simulation, the coal body at room temperature and high temperature should be the seepage law of gas water two-phase force to do the research, the main research contents and results of this paper are as follows: 1) starting from the production of coalbed gas mechanism analysis of coal seam gas mining is a process of gas desorption, diffusion and percolation ". According to the dynamic balance principle, vaporization and condensation of Fick law, Darcy law, the numerical simulation of coalbed methane gas water two-phase flow in the general solution. In the process, according to the different situation to analyze the capillary force and gravity, the seepage differential equation.2 simplified) using high precision gas water two-phase infiltration system developed by ourselves, a lot of unsteady gas water two-phase flow experiments, the results show that the unsteady process includes three stages, namely water seepage stage. The gas water mixing stage, gas seepage stage of bound water, and the seepage characteristics of each stage. The coal water saturation is reduced to less than 0.5 will happen "mutations", then the water saturation decreases sharply, there is only the gas seepage area, the change of saturation can be predicted for.3 gas production) were different under the condition of single-phase seepage force and unsteady two-phase flow experiment, the results showed that in the same axial pressure and confining pressure of 2 sigma 1, sigma (sigma 1 sigma 2) under the condition that the increase of pore pressure P1 gas, increase the water permeability were also nonlinear, continuous pore pressure There will be a sudden increase of permeability increases, and the relatively low stress, pore pressure on permeability effect is more obvious. Compared before and after gas injection water permeability can be seen: the gas phase there are different degrees of increased flow resistance of water, gas and the displacement pressure is higher, the greater the resistance, the greater the difference in permeability morphological characteristics of relative permeability curve. Coal is: with gas saturation increases, the gas phase relative permeability curve will be a sharp rise in liquid phase relative permeability is slow in the lower range decreases in gas after the break quickly drops to zero, the coal samples have higher irreducible water saturation) of coal samples in 17.4 a combination of pressure in the experimental process, increase the permeability with effective stress of water and gas permeability decreases, at a relatively low effective stress range (less than 4~5mpa), the permeability decreases greatly. With the increase of effective stress, permeability of late Change range is smaller. Whether it is the choice of water as the fluid or gas phase as fluid permeability measurement of samples after normalization, the results showed the same trend. The experimental data fitting, a good power function relationship between normalized coal permeability and effective stress. Compared to the normal temperature effective relation curves between stress and permeability, after heating curve decreased more gently, after the action of coal after heat stress sensitivity decreased in the thermal recovery process of coalbed methane in coal, the stress sensitivity will decrease the drainage gas production process more gentle, to avoid the traditional gas encountered depressurization in sudden and large output situation of gas and water by.5) two-phase osmosis device and temperature control test bench, the 30 DEG ~180 DEG range and temperature interval changes of coal single-phase permeability test and unsteady gas water two-phase flow was studied in the experiment. Under the influence of temperature variation and fluid flow characteristics of two-phase flow process. With the increase of temperature, the pressure of liquid production was increased. Yield increased at high temperature (120 C), rate of increase is more obvious. The temperature of 120 DEG C within the range of ~180 DEG C, the higher the temperature, crack coal pore connectivity is better, at the same time, the energy of water molecules at high temperature is larger, more conducive to the production of liquid in the coal body, irreducible water saturation decreases. On the contrary, at the same temperature, increasing the axial pressure and confining pressure so that the effective stress, pore fracture of coal body inside is compressed, part liquid can not be discharged, bound water increased, the water yield reduced.6) under the action of temperature changes in the whole process of three stages of non steady two-phase flow for liquid phase to produce linear seepage water of the first stage, with the increasing of temperature, the liquid yield of the total liquid yield percentage slow Reduced temperature higher than 120 DEG C after the amplitude of variation increases; second stage gas water mixture flow stage, the rapid increase of liquid velocity linear gas velocity smooth speed. With the increase of temperature, the liquid yield the total liquid yield percentage decreases, temperature higher than 90 DEG C after the reduction of slightly greater. Third stage bound gas seepage water next, the stage is affected by temperature obviously, liquid yield the total liquid yield percentage improved greatly. A temperature below 60 DEG C in the liquid phase output accounted for only about 10% of total liquid production, liquid production in first, second phases. When the temperature reaches 150 degrees Celsius, the percentage reached 50%, the proportion of more than the two stage,.7) at a temperature of 30 DEG C to 180 DEG C within the range, the change of permeability is divided into two stages: the period of relatively low temperature (30 DEG to 120 DEG), the temperature influence on fluid dominated, contrast gas, water permeability The change of temperature, phase, liquid viscosity changes significantly, decreased greatly, while the gas viscosity increased slightly, the same trend of permeability and viscosity measurements. The high temperature (120 DEG C to 180 DEG C), the change of temperature on the structure of porous media has become the main influencing factors, changes in the scope of the temperature of liquid, gas viscosity change are relatively flat, and the variation of permeability has greatly improved, that affected by high temperature, great changes have taken place in pore and fracture of coal samples, seepage channel connectivity is better than the low temperature section, facilitates fluid flow. At the same time, with the increase of temperature, the irreducible water saturation decreases, gas water two-phase flow zone broadening the water relative permeability, water saturation decreases with decreasing trend slowed down, the higher the temperature, the effect of gas water two-phase relative permeability curve decreased gradually. To objectively reflect due to temperature change The pressure drop, the temperature sensitivity coefficient, the temperature coefficient and good logarithmic function relationship with Euler and Lagrange.8) point of view, the flow of gas and water interface were analyzed, the pseudo pressure function p=2 PP0p/ dgZdp formula introduced the two-phase flow equations. The stress function is divided into three types: the P discussion gZ is a constant, pg=pg; the gZ is constant, pg=pg2; the gZ is a linear function of pressure P, p=2 formula PP0p/ap+bdp. obtained from the gas water two-phase flow interface without considering the compression displacement model, considering the compression displacement model and quasi linear function equation of pressure displacement model. The seepage equation of the three models and boundary conditions are deduced in detail, relationship between fluid flow and position function through the Matlab software. The three models are calculated, the experimental parameters should select the same stress condition, get The time curves of cumulative output and the location of gas and water flow at different time intervals are compared. The experimental results and errors of the three models are compared, and the applicability of the three models is obtained. It provides a reliable model selection basis for drainage prediction in practical engineering.

【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TD841

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本文編號(hào)：1685282