【摘要】：低溫致裂技術是一種潛在改造煤儲層,促進煤層氣增產的有效方法。低溫致裂技術通常是指在煤層中注入液氮、液態(tài)二氧化碳等低溫介質改造煤儲層,提高煤層滲透性。1998年Mc Daniel B W等人在美國肯塔基州采用液氮作為壓裂液對4口煤層氣井和1口致密砂巖氣井進行了重復壓裂施工,獲得了良好的增產效果。目前國內外對于煤層低溫致裂的研究集中于低溫流體注入煤層氣井后的地應力、溫度場、裂隙分布等模擬研究,對煤體本身的凍融損傷破壞研究較少。對于凍融作用下的煤體破壞、孔隙結構、滲透性能的研究,還不盡完善。凍融損傷后與煤層氣產出密切相關的煤體瓦斯放散特性還未有人開展相關的研究。針對上述問題,文本采用理論分析和實驗相結合的方法測量了凍融損傷對煤體的孔隙結構、力學性能和瓦斯放散能力等煤體特性的影響。首先以低溫致裂技術為研究背景,凍融損傷為研究切入點,筆者在查閱相關資料的基礎上,分析了凍融作用下煤體損傷破壞機制,形成了煤體凍融破壞機理,以此來指導后續(xù)的研究內容和實驗設計。同時限制了以下若干實驗條件:含水量,煤體均為飽和試樣;凍融溫度,范圍為-20℃-20℃。本文采用焦煤和貧煤兩種煤體主要考察了凍融次數(shù)的影響。開展了凍融作用對煤體宏觀破壞的研究。文中分析了不同凍融循環(huán)次數(shù)后的煤體表面破壞特征,采用單軸壓縮和聲發(fā)射技術測量了煤體抗壓強度和聲發(fā)射信號的形式特征。此外,我們通過室內超生波波速的測量計算,獲得了不同凍融循環(huán)次數(shù)煤體的泊松比、楊氏模量等動力學參數(shù)變化。開展了凍融作用對煤體孔滲特性的研究。實驗中主要采用核磁共振和掃描電鏡技術對焦煤和貧煤兩種煤體的孔滲特征開展了相關研究。主要測試了煤體總孔隙度、可動孔隙度(PP)、束縛孔隙度(IP)、滲透率、以及煤體內吸附孔和滲流孔的比例變化。這些測試有助于深入討論凍融損傷對煤體微觀結構的改變。最后,開展了凍融對煤體瓦斯放散特性影響的研究,分析了凍融前后煤體的瓦斯放散參數(shù)(放散量、放散速度、放散系數(shù))的變化。結果表明煤體凍融損傷有助于簡化煤的孔隙結構,減少擴散阻力,增擴煤體的滲流通道,減少滲流阻力,有利于瓦斯(煤層氣)從煤層中運移出來。
[Abstract]:Low temperature fracturing technology is an effective method to potentially transform coal reservoir and promote coalbed methane production. Low temperature cracking technology usually refers to the injection of liquid nitrogen, liquid carbon dioxide and other low temperature media into coal seams to transform coal reservoirs. Improve the permeability of coal seam. In 1998, Mc Daniel B W et al used liquid nitrogen as fracturing fluid to repeatedly fracturing 4 coal seam gas wells and 1 tight sandstone gas well in Kentucky, USA, and achieved good results of increasing production. At present, the research on low temperature cracking of coal seam at home and abroad focuses on the simulation of ground stress, temperature field and fracture distribution after low temperature fluid injection into coal seam gas well, but the research on freeze-thaw damage and failure of coal body itself is less. The research on coal failure, pore structure and permeability under freeze-thaw is not perfect. The gas emission characteristics of coal body which are closely related to the production of coalbed methane after freeze-thaw damage have not been studied. In order to solve the above problems, the effects of freeze-thaw damage on the pore structure, mechanical properties and gas release capacity of coal are measured by means of theoretical analysis and experiment. First of all, taking the low temperature cracking technology as the research background and freeze-thaw damage as the starting point, the author analyzes the damage and failure mechanism of coal body under freeze-thaw action on the basis of consulting the relevant data, and forms the freeze-thaw failure mechanism of coal body. To guide the follow-up research content and experimental design. At the same time, the following experimental conditions are limited: water content, coal is saturated sample, freeze-thaw temperature, range of-20 鈩，

本文編號：2495094