海底甲烷滲漏背景下自生礦物形成控制條件數(shù)值模擬研究
發(fā)布時間：2018-08-12 18:24
【摘要】：甲烷厭氧氧化反應(yīng)是海底厭氧沉積物的重要生物地球化學(xué)過程,該反應(yīng)顯著地調(diào)控著全球甲烷收支平衡,在全球碳、硫循環(huán)中發(fā)揮著重要作用,同時與甲烷厭氧氧化反應(yīng)伴生的生物地球化學(xué)特征也成為天然氣水合物找礦的標(biāo)志。已有的研究多是針對生物作用和生物能量學(xué)對甲烷厭氧氧化反應(yīng)的控制,缺少綜合考慮甲烷厭氧氧化反應(yīng)、成巖作用和溶質(zhì)運移來研究海底甲烷滲漏背景下自生礦物的形成。本文依托天然氣水合物相關(guān)自生礦物形成項目,以南海北部陸坡臺西南盆地為研究區(qū),結(jié)合研究區(qū)的物性參數(shù)、生物地球化學(xué)條件,采用TOUGHREACT模擬軟件,研究海底甲烷滲漏背景下自生礦物形成的控制條件。依據(jù)研究區(qū)實際物性參數(shù),通過設(shè)置不同的模擬方案,研究不同的甲烷泄漏速率、水文地球化學(xué)條件情況下,硫酸鹽-甲烷界面以及自生礦物形成的時間、空間變化特征。研究發(fā)現(xiàn),甲烷泄漏速率對自生礦物的形成具有顯著影響。甲烷泄漏速率越大,硫酸根-甲烷界面越淺,界面處甲烷厭氧氧化反應(yīng)越劇烈,方解石沉淀量越大,界面處方解石的沉淀主要受控于甲烷厭氧氧化反應(yīng);當(dāng)甲烷泄漏速率比基礎(chǔ)方案增大20倍時(7.60×10-2 mmolcm-2 a-1),有文石的沉淀,甲烷泄漏速率越大,文石出現(xiàn)沉淀時間越早,沉淀位置越淺,沉淀量也越大,甲烷泄漏速率是文石生成的主要控制因素;硫酸根離子濃度對鐵白云石的沉淀具有顯著影響,硫酸根濃度越低,鐵白云石的沉淀量越大,當(dāng)硫酸根離子濃度減小3倍時,鐵白云石的沉淀量能增大到3個數(shù)量級以上;鈣離子濃度主要影響方解石、菱鎂礦的沉淀,鈣離子濃度比基礎(chǔ)方案增大5倍時,方解石沉淀量比基礎(chǔ)方案增大了0.16%,鈣離子濃度比基礎(chǔ)方案減小5倍時,菱鎂礦沉淀量比基礎(chǔ)方案增大約5個數(shù)量級,因此,低鈣離子環(huán)境有利于菱鎂礦沉淀;溫度主要是從反應(yīng)速率和平衡常數(shù)兩個方面進行控制的,溫度升高,奧長石、鉀長石、鈉蒙脫石、鈣蒙脫石、綠泥石的溶解量增加,方解石、菱鎂礦、黃鐵礦的沉淀量增加。綜上所述,在綜合考慮生物作用、成巖作用和溶質(zhì)運移來研究甲烷滲漏背景下自生礦物形成過程中,不同自生碳酸鹽巖以及硫化物的形成能夠指示不同的沉淀環(huán)境,因此在實際工作中結(jié)合沉積層礦物沉淀情況能夠更好的指示底部存在天然氣水合物的可能。
[Abstract]:Methane anaerobic oxidation is an important biogeochemical process of submarine anaerobic sediments, which significantly regulates the balance of global methane budget and plays an important role in the global carbon and sulfur cycle. At the same time, the biogeochemical characteristics associated with the anaerobic oxidation of methane have also become the indicators of gas hydrate prospecting. Most of the previous studies have focused on the control of methane anaerobic oxidation by biological action and bioenergy, and lack of comprehensive consideration of methane anaerobic oxidation, diagenesis and solute migration to study the formation of autogenous minerals under the background of methane leakage. In this paper, based on the natural gas hydrate related autogenic mineral formation project, taking the southwest basin on the northern slope of the South China Sea as the study area, and combining the physical parameters and biogeochemical conditions of the study area, the TOUGHREACT simulation software is used. The control conditions for the formation of autogenous minerals under the background of methane leakage on the sea floor are studied. According to the actual physical parameters of the study area, by setting different simulation schemes, the characteristics of the time and space variation of the sulfate methane interface and the formation of the autogenous minerals under different methane leakage rates and hydrogeochemical conditions are studied. It is found that methane leakage rate has a significant effect on the formation of authigenic minerals. The larger the rate of methane leakage, the shallower the interface between sulfate and methane, the more intense the anaerobic oxidation of methane at the interface, and the larger the amount of calcite precipitation. The calcite precipitation at the interface is mainly controlled by the anaerobic oxidation of methane. When the methane leakage rate is 20 times higher than that of the basic scheme (7.60 脳 10 ~ (-2) mmolcm-2 a ~ (-1), the larger the methane leakage rate is, the earlier the precipitation time is, the lighter the precipitation position is and the larger the precipitation amount is. Methane leakage rate is the main controlling factor for the formation of dolomite, and the concentration of sulfate ion has a significant effect on the precipitation of dolomite. The lower the concentration of sulfate is, the greater the precipitation amount of dolomite is, and when the concentration of sulfate ion decreases by 3 times, The precipitation capacity of dolomite can be increased to more than 3 orders of magnitude, and the calcium ion concentration mainly affects the precipitation of calcite and magnesite, when the calcium ion concentration is 5 times higher than that of the basic scheme. Calcite precipitation is 0.16% higher than that of base scheme. When calcium concentration is 5 times lower than base scheme, magnesite precipitation is increased by about 5 orders of magnitude. Therefore, low calcium ion environment is favorable for magnesite precipitation. The temperature is controlled mainly from two aspects: reaction rate and equilibrium constant. With the increase of temperature, the amount of precipitate of ordoclase, potassium feldspar, sodium montmorillonite, calcium montmorillonite, chlorite, calcite, magnesite and pyrite increase. In conclusion, the formation of different authigenic carbonate rocks and sulphides can indicate different precipitation environments in the study of the formation of authigenic minerals in the context of methane leakage, taking into account biological processes, diagenesis and solute migration, Therefore, the combination of sedimentary mineral precipitation in practical work can better indicate the existence of natural gas hydrate at the bottom.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：P736.3
本文編號：2179910
[Abstract]:Methane anaerobic oxidation is an important biogeochemical process of submarine anaerobic sediments, which significantly regulates the balance of global methane budget and plays an important role in the global carbon and sulfur cycle. At the same time, the biogeochemical characteristics associated with the anaerobic oxidation of methane have also become the indicators of gas hydrate prospecting. Most of the previous studies have focused on the control of methane anaerobic oxidation by biological action and bioenergy, and lack of comprehensive consideration of methane anaerobic oxidation, diagenesis and solute migration to study the formation of autogenous minerals under the background of methane leakage. In this paper, based on the natural gas hydrate related autogenic mineral formation project, taking the southwest basin on the northern slope of the South China Sea as the study area, and combining the physical parameters and biogeochemical conditions of the study area, the TOUGHREACT simulation software is used. The control conditions for the formation of autogenous minerals under the background of methane leakage on the sea floor are studied. According to the actual physical parameters of the study area, by setting different simulation schemes, the characteristics of the time and space variation of the sulfate methane interface and the formation of the autogenous minerals under different methane leakage rates and hydrogeochemical conditions are studied. It is found that methane leakage rate has a significant effect on the formation of authigenic minerals. The larger the rate of methane leakage, the shallower the interface between sulfate and methane, the more intense the anaerobic oxidation of methane at the interface, and the larger the amount of calcite precipitation. The calcite precipitation at the interface is mainly controlled by the anaerobic oxidation of methane. When the methane leakage rate is 20 times higher than that of the basic scheme (7.60 脳 10 ~ (-2) mmolcm-2 a ~ (-1), the larger the methane leakage rate is, the earlier the precipitation time is, the lighter the precipitation position is and the larger the precipitation amount is. Methane leakage rate is the main controlling factor for the formation of dolomite, and the concentration of sulfate ion has a significant effect on the precipitation of dolomite. The lower the concentration of sulfate is, the greater the precipitation amount of dolomite is, and when the concentration of sulfate ion decreases by 3 times, The precipitation capacity of dolomite can be increased to more than 3 orders of magnitude, and the calcium ion concentration mainly affects the precipitation of calcite and magnesite, when the calcium ion concentration is 5 times higher than that of the basic scheme. Calcite precipitation is 0.16% higher than that of base scheme. When calcium concentration is 5 times lower than base scheme, magnesite precipitation is increased by about 5 orders of magnitude. Therefore, low calcium ion environment is favorable for magnesite precipitation. The temperature is controlled mainly from two aspects: reaction rate and equilibrium constant. With the increase of temperature, the amount of precipitate of ordoclase, potassium feldspar, sodium montmorillonite, calcium montmorillonite, chlorite, calcite, magnesite and pyrite increase. In conclusion, the formation of different authigenic carbonate rocks and sulphides can indicate different precipitation environments in the study of the formation of authigenic minerals in the context of methane leakage, taking into account biological processes, diagenesis and solute migration, Therefore, the combination of sedimentary mineral precipitation in practical work can better indicate the existence of natural gas hydrate at the bottom.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：P736.3
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