页岩气藏的双重介质—离散裂缝模型研究

发布时间：2018-12-08 15:22

【摘要】：在页岩气藏的开发过程中,水力压裂是页岩气藏开发的重要手段,压裂产生的大尺度压裂裂缝流动特性与天然微裂缝明显不同,页岩气藏基质孔隙、天然裂缝人工压裂裂缝中的流动尺度相差悬殊。考虑多尺度流动效应,本文提出基于双重介质的离散裂缝模型,作为描述页岩气藏开发过程中的渗流数学模型。通过数值算例,将本文模型和渗透率粗化方案的双重介质模型及基于压裂裂缝导流能力无穷大假设的等压模型进行对比分析。结果显示,本文模型与采用精确渗透率粗化方案的双重介质模型具有相同的计算精度。在实际的地质条件下,水力压裂裂缝会具有复杂的形态,渗透率粗化模型的等效渗透率计算将会变得非常复杂,同时渗透率粗化问题本身也是国际上的热点和难点问题,本文模型可以有效避免该难题,且较容易推广到多相流动。等压模型是一种简单的易于分析和计算的模型,该模型假设压裂裂缝的导流能力无穷大,在计算中将高估气井的产气速率,从而在模拟真实气藏的开采过程时会带来一定的误差本文还分析研究了计算区域大小及不同边界条件对数值模拟结果的影响,研究结果表明,当计算区域选取的不够大时,计算结果受边界条件的影响较大。因此,在模拟计算过程中,应选取足够大的计算区域。将本文模型应用到页岩气藏的开发中,通过分析计算地质参数与水力压裂的工艺参数对产量的影响,以期望为页岩气藏的开发提供参考。在地质参数中,分别研究了基质孔隙度、天然微裂缝孔隙度、基质的扩散系数、天然微裂缝的渗透率对气井产气速率的影响。在水力压裂工艺参数方面,分别研究了压裂裂缝的导流能力、长度、数目对气井产气速率的影响。计算结果表明天然裂缝渗透率及基质孔隙扩散系数对产气速率有着重要影响,产气速率伴随着人工压裂裂缝导流能力、长度以及数目的增加而增加,但是增加幅度会逐步趋缓。综上所述,本文提出了基于双重介质的离散裂缝模型。对于页岩气藏开发的数值模拟,本文的模型可以描述页岩气藏基质孔隙、天然裂缝、人工压裂裂缝中的多尺度效应且计算量较小,易应用于实际工程计算。我们期望该模型的建立能够为页岩气藏的实际开发提供参考。
[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.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE319

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