本文選題：頁巖酸損傷 + 巖石力學(xué)��； 參考：《西南石油大學(xué)》2017年博士論文

【摘要】：頁巖氣資源開發(fā)技術(shù)發(fā)展對解決我國常規(guī)天然氣產(chǎn)量不足和緩解能源對外依存度高的現(xiàn)狀具有重大意義。與北美主要頁巖氣儲層相比,四川盆地龍馬溪組頁巖儲層壓裂工程地質(zhì)條件相對較差。高地應(yīng)力差(15～20 MPa)、低脆性指數(shù)(50)及天然裂縫相對不發(fā)育的特點使得常規(guī)壓裂施工后難以保證形成復(fù)雜裂縫網(wǎng)絡(luò),導(dǎo)致該地區(qū)頁巖氣增產(chǎn)改造難度大、單井開發(fā)成本高�？梢酝ㄟ^酸處理改變頁巖力學(xué)特征提高壓后形成復(fù)雜縫網(wǎng)的可能。然而酸損傷頁巖內(nèi)部微孔隙和微裂縫結(jié)構(gòu)復(fù)雜,水力壓裂過程中儲層巖體變形破壞特征對復(fù)雜裂縫擴展影響機理不明確。本文以川南地區(qū)龍馬溪組儲層頁巖為對象,基于室內(nèi)試驗手段研究酸處理后頁巖礦物組分、微觀結(jié)構(gòu)和力學(xué)性質(zhì)變化。綜合運用塑性力學(xué)和損傷力學(xué)理論,建立龍馬溪組頁巖酸損傷彈塑性本構(gòu)模型。通過引入酸損傷彈塑性本構(gòu)方程建立龍馬溪組頁巖壓裂裂縫擴展數(shù)值模型,研究考慮酸損傷效應(yīng)的頁巖裂縫擴展規(guī)律及影響因素。主要研究工作及取得的認識如下:(1)鹽酸溶蝕頁巖中的碳酸鹽礦物后改變巖石顆粒膠結(jié)強度和微觀孔隙結(jié)構(gòu),在宏觀上表現(xiàn)為酸損傷頁巖孔滲特征和力學(xué)特征改變。由于裂縫擴展受儲層巖體應(yīng)力-滲流耦合過程的影響,因此酸損傷頁巖孔滲特征和力學(xué)特征的改變將引起頁巖復(fù)雜裂縫擴展機理的改變。有必要開展酸損傷效應(yīng)對頁巖壓裂裂縫擴展的影響規(guī)律研究,明確回答頁巖酸處理是否能為形成復(fù)雜裂縫網(wǎng)絡(luò)服務(wù)。(2)針對研究區(qū)頁巖開展加壓飽和酸處理實驗,分析酸處理對頁巖礦物組分、微觀結(jié)構(gòu)及孔滲特征的影響。龍馬溪組頁巖碳酸鹽含量隨著酸處理時間增加而減少。酸處理過程中,酸對巖石膠結(jié)物的溶蝕作用破壞了巖石固有結(jié)構(gòu),削弱巖石骨架顆粒之間的膠結(jié)作用。測試結(jié)果表明頁巖內(nèi)部碳酸鹽礦物被酸溶蝕后形成許多次生孔隙和微裂隙,導(dǎo)致龍馬溪組頁巖孔隙度和滲透率增加。(3)針對酸處理前后頁巖巖樣開展了三軸壓縮試驗測試,分析酸損傷效應(yīng)對頁巖力學(xué)特征的影響。結(jié)果表明:隨酸反應(yīng)時間的增加頁巖峰值抗壓強度和楊氏模量明顯降低,力學(xué)性質(zhì)參數(shù)與孔滲參數(shù)之間的關(guān)系滿足線性回歸擬合。分析酸處理前后頁巖的變形特征和破壞特征,認為龍馬溪組頁巖酸損傷后具有塑性變形特征,且破裂形態(tài)復(fù)雜,是壓裂后地層形成復(fù)雜裂縫網(wǎng)絡(luò)的有利條件。(4)根據(jù)酸損傷頁巖破壞的物理過程分析變形破壞特征。運用塑性力學(xué)理論,建立基于Drucker-Prager屈服準則的頁巖彈塑性本構(gòu)模型。利用損傷力學(xué)理論,基于酸損傷后頁巖孔隙度增加的現(xiàn)象提出考慮孔隙度變化的損傷因子和損傷演化方程。將損傷變量引入彈塑性本構(gòu)模型中建立酸損傷彈塑性本構(gòu)模型,編寫Fortran程序?qū)δＰ颓蠼�。對不同酸反�?yīng)時間下的酸損傷頁巖三軸壓縮試驗進行了數(shù)值驗證,結(jié)果表明酸損傷彈塑性本構(gòu)模型能夠比較準確地模擬經(jīng)過酸處理后頁巖的受載荷變形過程和峰后應(yīng)變軟化特征。(5)本文提出利用粘性區(qū)單元建立二維裂縫相交擴展模型,模擬不同天然裂縫展布和不同地應(yīng)力狀態(tài)下的裂縫擴展結(jié)果。通過真三軸水力壓裂物模實驗結(jié)果與數(shù)值模擬結(jié)果對比驗證了該方法的正確性。引入酸損傷彈塑性本構(gòu)方程研究頁巖酸損傷效應(yīng)下的裂縫擴展規(guī)律。通過與彈性巖體模型結(jié)果對比分析,認為考慮酸損傷的裂縫擴展數(shù)值模型計算誘導(dǎo)應(yīng)力場更復(fù)雜、地層水平應(yīng)力比更低,是形成復(fù)雜縫網(wǎng)的有利條件。(6)根據(jù)川南龍馬溪組某口井工程地質(zhì)特征建立考慮酸損傷效應(yīng)的頁巖三維多裂縫相交擴展數(shù)值模型,模擬不同施工參數(shù)下縫網(wǎng)擴展的形態(tài)�；趽p傷力學(xué)理對酸處理后的天然裂縫和層理面損傷進行模擬,基于酸損傷彈塑性本構(gòu)模型模擬儲層巖體變形。分析施工參數(shù)對多裂縫擴展復(fù)雜程度的影響,對比分析該井現(xiàn)場微地震監(jiān)測結(jié)果,認為考慮酸損傷效應(yīng)的多裂縫擴展模型能反映龍馬溪組頁巖酸處理壓裂擴展規(guī)律。本文通過試驗測試和理論模型相結(jié)合,建立酸損傷頁巖本構(gòu)模型并引入龍馬溪組頁巖儲層水力壓裂裂縫擴展數(shù)值模型,研究考慮酸損傷效應(yīng)下的多裂縫擴展機理。相比常規(guī)壓裂,在高應(yīng)力差條件下酸損傷頁巖儲層壓裂后裂縫更容易擴展,裂縫復(fù)雜程度更高。本文通過建立描述龍馬溪組酸損傷頁巖力學(xué)性質(zhì)特征的本構(gòu)關(guān)系,分析考慮酸損傷效應(yīng)下龍馬溪組頁巖儲層裂縫擴展機理,為該類通過常規(guī)壓裂不易形成復(fù)雜縫網(wǎng)的頁巖儲層提供增產(chǎn)改造思路和理論支撐。
[Abstract]:The development of shale gas resources development technology is of great significance to solving the current situation of the shortage of conventional natural gas production and the high dependence of energy on energy. Compared with the main shale gas reservoirs in North America, the fracturing engineering geological conditions of the Sichuan basin Long Maxi formation shale reservoir are relatively poor. The high geostress difference (15~20 MPa), low brittleness index (50) and The characteristics of natural fractures are relatively undeveloped, which makes it difficult to guarantee the formation of complex fracture network after conventional fracturing, which leads to the difficulty of shale gas production and transformation in this area, and high cost of single well development. The energy of shale mechanics can be changed by acid treatment to improve the ability to form complex seams after pressure. However, acid damage shale internal pore gap and microcrack are damaged by acid. In the process of hydraulic fracturing, the mechanism of the deformation and failure of the reservoir rock in the process of hydraulic fracturing is not clear. In this paper, the shale of the long Ma Creek Reservoir in South Sichuan Province is taken as the object. Based on the laboratory test, the mineral composition, microstructure and mechanical properties of the shale after acid treatment are studied. Plastic mechanics and damage mechanics are used synthetically. The theory is to establish the elastoplastic constitutive model of shale acid damage in the Long Maxi formation. Through the introduction of the elastoplastic constitutive equation of acid damage, the numerical model of the fracture expansion of the shale fracture in the long Maixi formation is established, and the law and the influence factors of shale fracture considering the effect of acid damage are studied. The main research work and the knowledge obtained are as follows: (1) in the hydrochloric acid dissolved shale After carbonate minerals, the cementation strength and micropore structure of the rocks are changed, and the pore and permeability characteristics and mechanical characteristics of the shale are changed in macroscopic view. Because the fracture expansion is influenced by the stress seepage coupling process of the reservoir rock, the change of pore and permeability characteristics and mechanical characteristics of acid damaged shale will cause the expansion of the shale complex crack. It is necessary to carry out the study of the effect of acid damage effect on the fracture expansion of shale fracturing, and clearly answer whether shale acid treatment can serve as a network service for the formation of complex fractures. (2) the effects of acid treatment on shale mineral composition, microstructure and pore and permeability characteristics are analyzed by pressure saturated acid treatment experiments on shale in the study area. The shale carbonate content in the long Ma Creek formation decreases with the increase of acid treatment time. In the process of acid treatment, the corrosion of acid to rock cementation destroys the natural structure of rock and weakens the cementation between the rock skeleton particles. The test results show that the carbonate minerals in the shale are corroded by acid and form many secondary pores and micro cracks. The porosity and permeability of shale in the long Ma Creek formation increase. (3) three axial compression tests were carried out for shale samples before and after acid treatment, and the effect of acid damage effect on shale mechanical characteristics was analyzed. The results showed that the peak compressive strength and Yang Shimo quantity of shale decreased obviously with the increase of acid reaction time, and the mechanical properties and pore permeability parameters were observed. The relationship between the shales is satisfied with the linear regression fitting. The deformation characteristics and damage characteristics of shale before and after the acid treatment are analyzed. It is considered that the shale acid after the damage of the shale is characterized by plastic deformation and complex fracture morphology, which is a favorable condition for the formation of complex fracture network after fracturing. (4) analysis of deformation and damage according to the physical process of acid damaged shale damage. Characteristics. Using the theory of plastic mechanics, the elastoplastic constitutive model of Shale Based on Drucker-Prager yield criterion is established. Based on the damage mechanics theory, the damage factor and the damage evolution equation with the porosity change are proposed based on the increase of shale porosity after the acid damage. The damage variable is introduced into the elastoplastic constitutive model to establish the acid damage. The elastoplastic constitutive model and the Fortran program are compiled to solve the model. The three axial compression tests of acid damaged shale under different acid reaction time have been verified. The results show that the acid damage elastoplastic constitutive model can accurately simulate the deformation process of the shale after acid treatment and the strain softening characteristics after the peak. (5) this paper is proposed in this paper. A two-dimensional fracture propagation model is established by using the viscous region element to simulate the fracture propagation of different natural fractures and different stress states. The correctness of the method is verified by the results of real three axis hydraulic fracturing experiment and numerical simulation. The acid damage elastoplastic constitutive equation is introduced to study shale acid loss. The crack propagation law under the injury effect is compared with the results of the elastic rock mass model. It is considered that the calculation of the induced stress field is more complex and the horizontal stress ratio of the stratum is lower. (6) considering the acid damage according to the engineering geological characteristics of a certain well in the Long Ma Creek formation in South Sichuan, the calculation of the induced stress field is more complex and the horizontal stress ratio of the stratum is lower. A three-dimensional multi fracture propagation numerical model of shale is used to simulate the expansion of seams under different construction parameters. The damage of natural fractures and bedding surfaces after acid treatment is simulated on the basis of damage mechanics, and the deformation of the reservoir rock is simulated based on the acid damage elastoplastic constitutive model. The complexity of the construction parameters for multiple fracture expansion is analyzed. The results of the field microseismic monitoring in this well are compared and analyzed. It is believed that the multi fracture expansion model considering the acid damage effect can reflect the fracture expansion law of the shale acid treatment in the Long Maxi formation. In this paper, an acid damaged shale constitutive model is established by combining the experimental test and the theoretical model, and the fracture expansion of the shale reservoir of the Long Maxi formation is introduced. The numerical model is used to study the mechanism of multiple crack propagation under the effect of acid damage. Compared with conventional fracturing, the fracture is more easy to expand and the fracture complexity is higher after the acid damaged shale reservoir under the high stress difference. This paper establishes the constitutive relation of the mechanical properties of the acid damaged shale of the Long Maxi group, and analyzes the effect of acid damage. The fracture expansion mechanism of the shale reservoir of the maxi formation in Xialong is provided for the shale reservoir which is not easily formed by the conventional fracturing.

【學(xué)位授予單位】：西南石油大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TE377

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