【摘要】：隨著我國經(jīng)濟(jì)的發(fā)展,對能源的需求量日益增大,且國內(nèi)頁巖氣具有良好形成及富集的地質(zhì)條件,因此頁巖氣的開采受到廣泛的關(guān)注。頁巖氣藏儲層具有典型的低孔、低滲特征,并隨著埋深加大,物性變差,導(dǎo)致開采難度大,采收率低。但通過人工增透的方法改變儲層的滲透性可以有效地提高采收率。水力壓裂是人工增透的重要方法之一,但在實(shí)際實(shí)施過程中也發(fā)現(xiàn)了水力壓裂的不足之處,壓裂液的摩阻較大,易滯留在孔道的裂縫里,易產(chǎn)生水鎖、賈敏效應(yīng),使儲層滲透率降低;壓裂結(jié)束后,壓裂液反排困難,會對儲層造成二次傷害,降低壓裂效果;而且頁巖礦物成分中含有較多的伊利石、高嶺石、伊蒙混層等粘土礦物,這些礦物極易吸水膨脹,使裂隙閉合,采收率下降。最重要是我國頁巖氣豐富的地方大多又缺水,所以無水壓裂技術(shù)得到大家的廣泛關(guān)注,利用氣體進(jìn)行儲層壓裂改造有望取得進(jìn)展。本文通過試驗(yàn)室試驗(yàn)、理論分析和數(shù)值模擬的方法系統(tǒng)地研究了利用水和氣體壓裂時裂縫啟裂的差異,主要取得以下進(jìn)展:(1)利用斷裂力學(xué)、滲流力學(xué)和滲流應(yīng)力耦合理論建立了基于水、氣滲透差異的破裂壓力準(zhǔn)則模型。在氣體滲流場計(jì)算中,考慮氣體密度在空間上的變化對氣體質(zhì)量守恒方程的影響,推導(dǎo)出了新的氣體滲流場計(jì)算方程。(2)設(shè)計(jì)了破裂壓力的數(shù)值計(jì)算方法,并通過Comsol with Matlab編寫了能夠?qū)崿F(xiàn)滲流邊界隨時間擴(kuò)展的滲流應(yīng)力耦合計(jì)算程序。(3)設(shè)計(jì)了不同水壓和氣壓加載速率下紅砂巖的水和氣體壓裂試驗(yàn),試驗(yàn)發(fā)現(xiàn)在一定加載速率范圍內(nèi)加載速率對水和氣體的破裂壓力及試樣的體積應(yīng)變增量影響都較小,且氣體壓裂的破裂壓力比水力壓裂的破裂壓力小40%左右;氣體壓裂后的試樣破壞的更為嚴(yán)重,形成兩條或三條主裂紋,裂縫會貫穿整個試樣,且裂紋寬度較大,主裂紋周圍有很多分岔裂紋;而水力壓裂后的試樣破壞的程度較小,只形成了兩條對稱裂紋,且裂紋沒有貫穿整個試樣,裂紋寬度較小。將數(shù)值計(jì)算出的水和氣體的破裂壓力和破裂時間與試驗(yàn)值比較,發(fā)現(xiàn)該計(jì)算模型可以較好地預(yù)測破裂壓力與破裂時間。(4)利用數(shù)值計(jì)算的方法,模擬并分析水壓和氣壓加載速率、儲層的滲透率、孔壁裂縫長度和不同深度的地應(yīng)力對水氣壓裂的影響,發(fā)現(xiàn)由于氣體粘度小,易于滲透,所以在不同條件下氣體壓裂都有著明顯的優(yōu)勢。
[Abstract]:With the development of economy in our country, the demand for energy is increasing day by day, and the shale gas in China has good geological conditions of formation and enrichment, so the exploitation of shale gas has received extensive attention. Shale gas reservoir has typical characteristics of low porosity and low permeability, and with the increase of buried depth, the physical properties become worse, which leads to the difficulty of exploitation and low recovery. However, the oil recovery can be effectively improved by changing the permeability of the reservoir by means of artificial penetration enhancement. Hydraulic fracturing is one of the important methods of artificial penetration enhancement, but in the actual implementation process, it has also found the shortcomings of hydraulic fracturing. The friction of fracturing fluid is large, it is easy to stay in the cracks in the channel, and it is easy to produce water lock and Jia Min effect. Reduce reservoir permeability; After fracturing, it is difficult to reverse the fracturing fluid, which will cause secondary damage to the reservoir and reduce the fracturing effect. Moreover, shale minerals contain more clay minerals such as Illite, Kaolinite, Yimeng mixed layer and so on, which are easy to absorb water and expand, closing fissures and decreasing oil recovery. The most important thing is that most of the places where shale gas is rich in China are lack of water, so the anhydrous fracturing technology has been widely concerned, and progress is expected to be made in reservoir fracturing transformation by using gas. In this paper, the difference of fracture initiation between water and gas fracturing is systematically studied by means of laboratory test, theoretical analysis and numerical simulation. The main progress is as follows: (1) using fracture mechanics, Based on the coupling theory of seepage mechanics and seepage stress, a fracture pressure criterion model based on the difference between water and gas permeability is established. In the calculation of gas seepage field, considering the influence of gas density on the conservation equation of gas mass, a new equation for calculating gas seepage field is derived. (2) the numerical calculation method of fracture pressure is designed. The coupling calculation program of seepage stress which can realize the expansion of seepage boundary with time is compiled by Comsol with Matlab. (3) the water and gas fracturing tests of red sandstone under different water pressure and pressure loading rates are designed. It is found that the loading rate has little effect on the fracture pressure of water and gas and the volume strain increment of the sample in a certain loading rate range, and the fracture pressure of gas fracturing is about 40% lower than that of hydraulic fracturing. After gas fracturing, the specimen is destroyed more seriously, forming two or three main cracks, the cracks will run through the whole sample, and the crack width is large, and there are many bifurcation cracks around the main cracks. However, the failure degree of the specimen after hydraulic fracturing is small, only two symmetrical cracks are formed, and the crack does not penetrate the whole sample, and the crack width is small. By comparing the fracture pressure and fracture time of water and gas calculated by numerical method with the experimental values, it is found that the model can predict the fracture pressure and fracture time well. (4) the numerical calculation method is used. The effects of water pressure and pressure loading rate, reservoir permeability, fracture length of pore wall and ground stress of different depths on water-gas fracturing are simulated and analyzed. It is found that the gas viscosity is small and easy to permeate. Therefore, gas fracturing has obvious advantages under different conditions.
【學(xué)位授予單位】：中國礦業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TE377

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