發(fā)布時間：2018-07-06 18:41

  本文選題：復合加卸載 + 有效應力�。� 參考：《中國礦業(yè)大學(北京)》2015年博士論文

【摘要】：瓦斯抽采作為礦井瓦斯治理的基本技術手段之一,在突出礦井、高瓦斯礦井以及瓦斯礦井的深部采區(qū)發(fā)揮著至關重要的作用。煤層受采動影響后,煤層應力重新分布,煤體局部發(fā)生損傷甚至破壞變形,煤體孔隙一裂隙結構和滲透能力發(fā)生改變,孔隙率和滲透性的改變不僅會導致瓦斯?jié)B流速度和孔隙壓力分布的變化,而且會引起煤層應力和位移的改變。對于水力擴孔后的抽采鉆孔而言,其周圍煤體中同樣存在著采動應力場和瓦斯?jié)B流場的耦和效應,水力擴孔形成的鉆孔開挖效應對煤體滲透性的影響比較明顯。為了深入探討水力擴孔開挖效應對鉆孔周圍煤體滲透率的影響,本文以本煤層水力擴孔工藝技術為工程背景,開展復合加卸載條件下含瓦斯煤樣滲流特性試驗,建立抽采鉆孔周圍煤體流固耦合模型,進行普通抽采鉆孔和水力擴孔鉆孔周圍煤體應力場分析及瓦斯?jié)B流規(guī)律數(shù)值模擬,最后運用體現(xiàn)工作面瓦斯抽采效果的煤層殘余瓦斯含量和鉆孔瓦斯流量等數(shù)據(jù),與數(shù)值模擬結果進行對比驗證。首先,基于鉆孔周圍煤體切向應力由原巖應力先升高至峰值強度而后減小至殘余強度、徑向應力由原巖應力逐步遞減直至破壞卸荷的演變特征,以受載含瓦斯煤體滲流特性試驗裝置為實驗平臺,開展了常規(guī)三軸加載和復合加卸載應力路徑下含瓦斯煤樣滲流特性試驗,研究了圍壓、軸壓、應力路徑、孔隙壓力與煤樣滲透率之間的定性定量關系。常規(guī)三軸加載應力路徑為固定圍壓的同時,持續(xù)增加軸壓直至煤樣進入殘余強度階段；復合加卸載應力路徑為持續(xù)增加軸壓的同時,減小圍壓直至煤樣進入殘余強度階段,尤其是復合加卸載應力路徑與鉆孔周圍煤體應力變化過程極為相似。常規(guī)三軸加載含瓦斯煤樣和復合加卸載含瓦斯煤樣的全應力-應變曲線均可以分為煤樣壓密階段、線彈性階段、屈服階段、峰后軟化階段和殘余強度階段等五個階段；在固定軸壓和圍壓的條件下,常規(guī)三軸加載煤樣滲透率隨著孔隙壓力的升高呈現(xiàn)先減小而后增大的“V”字形變化規(guī)律；在固定軸壓和孔隙壓力的條件下,常規(guī)三軸加載煤樣滲透率隨著圍壓的增大而呈現(xiàn)指數(shù)函數(shù)規(guī)律性下降；在屈服強度前后,常規(guī)三軸加載煤樣體積應變與滲透率均呈指數(shù)函數(shù)關系變化。復合加卸載含瓦斯煤樣的峰值強度較常規(guī)三軸加載含瓦斯煤樣的峰值強度更低；復合加卸載煤樣峰值強度時的軸向變形均小于常規(guī)三軸加載煤樣峰值強度時的軸向變形,復合加卸載煤樣峰值強度時的徑向變形均大于常規(guī)三軸加載煤樣峰值強度時的徑向變形；隨著軸向應變的持續(xù)增大,復合加卸載煤樣滲透率呈現(xiàn)先減小后增大的變化規(guī)律；復合加卸載條件下卸載圍壓引起煤樣屈服后滲透率的增加量較常規(guī)三軸加載煤樣屈服后滲透率的增加量更大；卸載起始軸壓的改變可引起加卸載階段煤樣滲透率差異性演變；卸載起始時刻煤樣滲透率隨著卸載起始圍壓的增大呈現(xiàn)指數(shù)函數(shù)規(guī)律性下降；相同的卸載起始軸壓和卸載起始圍壓時,隨著孔隙壓力的升高,復合加卸載煤樣峰值強度呈線性降低,從而導致煤樣失穩(wěn)破壞的加速出現(xiàn),進而縮短了煤樣滲透率發(fā)生劇烈改變的時間。接著,開展了復合加卸載應力路徑下煤樣孔隙率測定實驗,在分析復合加卸載煤樣有效應力作用機制的基礎上,從孔隙率的基本定義出發(fā),同時考慮煤樣吸附膨脹變形、孔隙氣體壓縮變形和熱膨脹變形等影響因素,建立復合加卸載條件下煤樣孔隙率演化模型；對比國內(nèi)外各類滲透率演化模型,以立方定律和受載煤體應力-應變本構方程為橋梁,建立復合加卸載條件下煤樣滲透率演化模型；考慮瓦斯流動克林伯格效應、瓦斯吸附-解吸-擴散過程的傳質特征、煤體的吸附膨脹效應等影響因素,建立復合加卸載含瓦斯煤體非線性滲流場方程；通過對鉆孔周圍煤體彈塑性分析,求解得到鉆孔周圍煤體應力場、位移場的解析表達式；通過耦合變量,實現(xiàn)應力場、變形場、滲流場等多物理場耦合,并最終實現(xiàn)鉆孔周圍含瓦斯煤體流固耦合模型的建立。其中,不同卸載起始軸壓條件下,復合加卸載煤樣的孔隙率演變規(guī)律表現(xiàn)為沿著加卸載應力路徑的逐步推進,煤樣內(nèi)孔隙率均呈現(xiàn)先減小而后增大的變化規(guī)律,但平均有效應力與煤體孔隙率的關系曲線卻存在較大差異；復合加卸載煤樣在外界應力和孔隙壓力的共同作用下,煤樣在不同的受載階段均受到有效應力的約束,區(qū)別之處在于不同受載階段時三類有效應力各自所占的比重存在著差異；對于復合加卸載煤樣而言,在壓密階段和線彈性階段有α→φ,在屈服階段和峰后軟化階段有φ≤α≤φd,在殘余強度階段有φd≤α≤φc；復合加卸載煤樣孔隙率演化方程及滲透率演化方程可以分別表述為然后,以復合加卸載應力路徑下含瓦斯煤樣的軸向應力-軸向應變-滲透率演變規(guī)律為理論基礎,結合鉆孔開挖后周圍煤體應力重分布規(guī)律,分析了抽采鉆孔周圍煤體的滲透率演變特征,將抽采鉆孔周圍煤體視為黏彈塑性介質,從而將抽采鉆孔周圍煤體從鉆孔孔壁到煤體深處依次劃分為殘余強度區(qū)、塑性軟化區(qū)、黏彈性區(qū)和原始應力區(qū),其中殘余強度區(qū)和塑性軟化區(qū)內(nèi)的煤體經(jīng)歷過峰值應力的作用,共同組成了極限應力區(qū),該區(qū)域的范圍大小決定了鉆孔抽采效果的好壞；建立了考慮煤體流變、剪切擴容和塑性軟化特性的鉆孔周圍煤體黏彈塑性模型,并推導了抽采鉆孔周圍不同區(qū)域內(nèi)煤體應力-應變解；在考慮克林伯格效應、瓦斯吸附-解吸-擴散過程的傳質特征、煤體吸附膨脹效應和孔隙率、滲透率動態(tài)演變規(guī)律等影響因素的基礎之上,建立了包括鉆孔周圍煤體內(nèi)瓦斯流動非線性滲流方程,滲透率演變方程和鉆孔周圍不同區(qū)域煤體的切向應力-徑向應力-體積應變方程等方程的抽采鉆孔周圍含瓦斯煤體流固耦合模型；運用數(shù)值模擬軟件COMSOL,引入鉆孔周圍含瓦斯煤體流固耦合模型,以工作面瓦斯抽采為背景,分析了普通抽采鉆孔周圍煤體應力、應變變化規(guī)律和抽采后煤層瓦斯含量、煤層滲透率變化規(guī)律及影響因素。其中,沿著遠離鉆孔方向,鉆孔周圍煤體切向應力整體上表現(xiàn)為先增高至峰值、而后下降至原巖應力的演變特征,鉆孔周圍煤體徑向應力則表現(xiàn)為逐漸升高至原巖應力的演變規(guī)律；相同應力環(huán)境和煤層賦存條件下,隨著鉆孔孔洞半徑的增加,鉆孔卸壓范圍不斷增大；不同抽采時刻條件下,鉆孔周圍煤體滲透率沿著遠離鉆孔方向大致呈現(xiàn)先減小而后又有所恢復的規(guī)律；隨著抽采時間的延長,鉆孔周圍一定范圍內(nèi)煤體殘余瓦斯含量均呈現(xiàn)逐漸下降的趨勢；此外,模擬得到鉆孔抽采30天時的有效影響半徑為2.77m,與現(xiàn)場實測值差別較小最后,針對水力擴孔工藝技術的特點,選取試驗礦井典型工作面,對水力擴孔技術應用效果進行現(xiàn)場考察,重點考察工作面水力擴孔后鉆孔瓦斯抽采效果,建立順層擴孔鉆孔開挖模型,借助鉆孔周圍含瓦斯煤體流固耦合模型,分析了順層擴孔鉆孔周圍煤體應力分布規(guī)律和瓦斯?jié)B透率變化規(guī)律,并和普通抽采鉆孔周圍煤體應力分布規(guī)律和瓦斯?jié)B透率變化規(guī)律進行了對比,同時利用現(xiàn)場考察結果驗證數(shù)值模擬所得到的擴孔鉆孔周圍煤體滲透率演變規(guī)律的正確性。其中,鉆孔擴孔完成之后,擴孔鉆孔周圍煤體的徑向應力峰值有所降低,鉆孔周圍煤體所受切向峰值應力向遠離鉆孔的方向轉移；水力擴孔技術的實施擴大了抽采鉆孔的有效卸壓范圍,普通抽采孔和擴孔鉆孔在抽采一段時間后,其周圍煤層殘余瓦斯含量均發(fā)生不同程度的下降,但擴孔鉆孔較普通抽采孔的下降程度更大、下降范圍更廣；擴孔鉆孔瓦斯抽采量相對于普通抽采鉆孔無明顯提高,但抽采鉆孔經(jīng)水力擴孔之后,鉆孔瓦斯流量衰減系數(shù)減小,鉆孔瓦斯有效抽采時間增長；水力擴孔影響范圍內(nèi)鉆孔月瓦斯抽采量相比未經(jīng)擴孔影響的普通抽采鉆孔有顯著提高。本論文的創(chuàng)新點主要體現(xiàn)在：(1)依據(jù)鉆孔開挖效應對鉆孔周圍煤體應力變化的影響,設計了復合加卸載條件下含瓦斯煤滲流特性實驗,實驗得到了卸載起始軸壓、卸載起始圍壓、孔隙壓力和應力路徑對煤體滲透率演變的影響規(guī)律；(2)設計了復合加卸載應力路徑下煤樣孔隙率測定實驗,并建立了考慮煤樣有效應力作用機制、煤樣吸附膨脹變形、孔隙氣體壓縮變形和熱膨脹變形等因素的復合加卸載下煤樣孔隙率及滲透率演化模型：(3)在考慮克林伯格效應和瓦斯吸附-解吸-擴散過程的傳質特征、煤體吸附膨脹效應、熱膨脹效應、孔隙氣體壓縮效應等影響因素的基礎上,建立了抽采鉆孔周圍含瓦斯煤體非線性瓦斯?jié)B流控制方程,通過抽采鉆孔周圍煤體瓦斯流動規(guī)律數(shù)值模擬結果和現(xiàn)場實測抽采鉆孔周圍煤層殘余瓦斯含量的對比分析,對非線性瓦斯?jié)B流控制方程的正確性進行了驗證。
[Abstract]:In order to study the influence of coal seam stress redistribution on the permeability of coal body around the borehole , the influence of gas seepage velocity and gas seepage field on the permeability of coal body is studied .
The stress path of composite loading and unloading is to increase the axial pressure continuously , the confining pressure is reduced until the coal sample enters the residual strength stage , especially the stress change process of composite loading and unloading stress path is similar to that of the coal body stress change process around the borehole .
Under the condition of fixed axial pressure and confining pressure , the normal triaxial loading coal sample permeability decreases with the increase of pore pressure and then increases the variation rule of " V " shape .
Under the condition of fixed axial pressure and pore pressure , the normal three - axis loading coal - like permeability decreases with the increase of confining pressure and the regularity of exponential function decreases ;
Before and after the yield strength , the volumetric strain and permeability of the conventional triaxial loading coal sample varied with exponential function . The peak intensity of the composite loading and unloading gas - containing coal sample was lower than that of the conventional triaxial loading gas - containing coal sample .
the axial deformation of the composite loading and unloading coal sample peak intensity is less than that of the conventional triaxial loading coal sample peak strength , and the radial deformation when the peak intensity of the composite loading and unloading coal sample is greater than that of the conventional triaxial loading coal sample peak strength ;
With the sustained increase of axial strain , the permeability of composite loading and unloading coal sample decreased first and then increased .
Under the condition of compound loading and unloading , the increase of permeability after loading coal sample under the condition of unloading confining pressure is much larger than that of the conventional triaxial loading coal sample yield .
The variation of coal sample permeability in the loading and unloading stage can be caused by the change of unloading initial axial pressure .
The coal sample permeability decreases with the increase of unloading initial confining pressure and the regularity of exponential function decreases .
On the basis of analyzing the effective stress action mechanism of the composite loading and unloading coal sample , the coal sample porosity evolution model is established based on the analysis of the effective stress action mechanism of the composite loading and unloading coal sample , the influence factors of the coal sample adsorption expansion deformation , the pore gas compression deformation and the thermal expansion deformation are taken into consideration , and the coal sample porosity evolution model is established under the condition of composite loading and unloading .
The permeability evolution model of coal sample under the condition of complex loading and unloading is established by using cubic law and the stress - strain constitutive equation of the coal - loaded coal body as the bridge in comparison with the various models of permeability evolution at home and abroad .
Considering the influence factors such as the mass transfer characteristics of the gas flow Klingberg effect , the gas adsorption - desorption - diffusion process , the adsorption expansion effect of the coal body and the like , a nonlinear seepage field equation of the gas - containing coal body is established and unloaded ;
Through the elastic - plastic analysis of the coal body around the borehole , the analytical expression of the stress field and displacement field of the coal body around the borehole is obtained .
The coupling variables are coupled to realize the coupling of multiple physical fields such as stress field , deformation field , seepage field and so on .
Under the combined action of external stress and pore pressure , the coal samples are subject to effective stress at different loading stages . The difference lies in the difference of the specific gravity of three types of effective stress at different loading stages .
For composite loading and unloading coal samples , there is 偽 鈫，

本文編號：2103750