【摘要】：在頁巖氣藏的開發(fā)過程中,水力壓裂是頁巖氣藏開發(fā)的重要手段,壓裂產(chǎn)生的大尺度壓裂裂縫流動特性與天然微裂縫明顯不同,頁巖氣藏基質(zhì)孔隙、天然裂縫人工壓裂裂縫中的流動尺度相差懸殊�？紤]多尺度流動效應(yīng),本文提出基于雙重介質(zhì)的離散裂縫模型,作為描述頁巖氣藏開發(fā)過程中的滲流數(shù)學模型。 通過數(shù)值算例,將本文模型和滲透率粗化方案的雙重介質(zhì)模型及基于壓裂裂縫導流能力無窮大假設(shè)的等壓模型進行對比分析。結(jié)果顯示,本文模型與采用精確滲透率粗化方案的雙重介質(zhì)模型具有相同的計算精度。在實際的地質(zhì)條件下,水力壓裂裂縫會具有復雜的形態(tài),滲透率粗化模型的等效滲透率計算將會變得非常復雜,同時滲透率粗化問題本身也是國際上的熱點和難點問題,本文模型可以有效避免該難題,且較容易推廣到多相流動。等壓模型是一種簡單的易于分析和計算的模型,該模型假設(shè)壓裂裂縫的導流能力無窮大,在計算中將高估氣井的產(chǎn)氣速率,從而在模擬真實氣藏的開采過程時會帶來一定的誤差 本文還分析研究了計算區(qū)域大小及不同邊界條件對數(shù)值模擬結(jié)果的影響,研究結(jié)果表明,當計算區(qū)域選取的不夠大時,計算結(jié)果受邊界條件的影響較大。因此,在模擬計算過程中,應(yīng)選取足夠大的計算區(qū)域。 將本文模型應(yīng)用到頁巖氣藏的開發(fā)中,通過分析計算地質(zhì)參數(shù)與水力壓裂的工藝參數(shù)對產(chǎn)量的影響,以期望為頁巖氣藏的開發(fā)提供參考。在地質(zhì)參數(shù)中,分別研究了基質(zhì)孔隙度、天然微裂縫孔隙度、基質(zhì)的擴散系數(shù)、天然微裂縫的滲透率對氣井產(chǎn)氣速率的影響。在水力壓裂工藝參數(shù)方面,分別研究了壓裂裂縫的導流能力、長度、數(shù)目對氣井產(chǎn)氣速率的影響。計算結(jié)果表明天然裂縫滲透率及基質(zhì)孔隙擴散系數(shù)對產(chǎn)氣速率有著重要影響,產(chǎn)氣速率伴隨著人工壓裂裂縫導流能力、長度以及數(shù)目的增加而增加,但是增加幅度會逐步趨緩。 綜上所述,本文提出了基于雙重介質(zhì)的離散裂縫模型。對于頁巖氣藏開發(fā)的數(shù)值模擬,本文的模型可以描述頁巖氣藏基質(zhì)孔隙、天然裂縫、人工壓裂裂縫中的多尺度效應(yīng)且計算量較小,易應(yīng)用于實際工程計算。我們期望該模型的建立能夠為頁巖氣藏的實際開發(fā)提供參考。
[Abstract]:In the development of shale gas reservoir, hydraulic fracturing is an important means of shale gas reservoir development. The flow characteristics of large-scale fracturing fracture produced by fracturing are obviously different from those of natural micro-fracture. The flow scales of natural fractures in artificial fracturing are very different. Considering the multi-scale flow effect, this paper presents a discrete fracture model based on dual media, which is used as a mathematical model to describe the seepage flow in the development of shale gas reservoir. A numerical example is given to compare this model with the dual medium model of permeability coarsening scheme and the isobaric model based on the infinite assumption of fracture conductivity. The results show that this model has the same calculation accuracy as the dual medium model with accurate permeability coarsening scheme. Under the actual geological conditions, hydraulic fracturing fracture will have a complex shape, the equivalent permeability calculation of permeability coarsening model will become very complicated, and the permeability coarsening problem itself is also a hot and difficult problem in the world. This model can effectively avoid this problem and is easy to be extended to multiphase flow. The isobaric model is a simple model which is easy to analyze and calculate. The model assumes that the flow conductivity of fracturing fractures is infinite and the gas production rate of gas wells will be overestimated in the calculation. Thus, there will be some errors in simulating the production process of real gas reservoirs. In this paper, the influence of the size of the calculation area and the different boundary conditions on the numerical simulation results is also analyzed. The results show that, When the calculation area is not large enough, the calculation results are greatly affected by the boundary conditions. Therefore, in the process of simulation, a large enough calculation area should be selected. The model is applied to the development of shale gas reservoir and the influence of geological parameters and hydraulic fracturing parameters on the production is analyzed and calculated in order to provide a reference for the development of shale gas reservoir. Among the geological parameters, the effects of matrix porosity, natural microfracture porosity, matrix diffusion coefficient and permeability of natural microfracture on gas production rate were studied respectively. In terms of hydraulic fracturing process parameters, the effects of flow conductivity, length and number of fracturing fractures on gas production rate of gas wells are studied respectively. The results show that natural fracture permeability and matrix pore diffusion coefficient have important influence on gas production rate, and the gas production rate increases with the increase of fracture conductivity, length and number of artificial fracturing fractures, but the increase range will gradually slow down. To sum up, a discrete fracture model based on dual media is proposed in this paper. For the numerical simulation of shale gas reservoir development, the model in this paper can describe the multi-scale effect in shale gas reservoir matrix pore, natural fracture and artificial fracturing fracture, which is easy to be applied to practical engineering calculation. We hope that the establishment of the model can provide a reference for the actual development of shale gas reservoirs.
【學位授予單位】：中國科學技術(shù)大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TE319

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