裂缝性致密气藏压裂裂缝参数研究

发布时间：2018-03-09 21:11

本文选题：致密气　切入点：缝网压裂　出处：《西南石油大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着常规油气资源日益减少,非常规油气藏逐渐转变为目前勘探开发的重点。致密气藏资源量丰富,有着巨大的开发潜力。致密气藏具有天然裂缝发育、基质渗透率低的特点,在对其进行开采时,通常需要对储层进行压裂改造。针对不同的储层条件,压裂裂缝各个参数对产能的影响不同,针对某一储层特征,应选择怎样的压裂裂缝形态,以及各压裂裂缝参数如何影响压裂效果,是对致密气藏实现合理、高效开发亟需解决的问题之一。本文基于离散裂缝网络模型,利用有限元方法建立了裂缝性致密气藏压裂气井生产动态预测数值模型,并以此为基础开展了对压裂裂缝参数的研究。首先,采用Monte-Carlo模拟方法建立了随机分布的天然裂缝网络模型。然后采用树状分叉结构表征不规则的压裂裂缝形态,并将其嵌入天然裂缝网络模型中,得到裂缝性致密气藏压后离散裂缝网络模型。接着按照有限元理论对气体渗流数学模型离散化处理:分别对基质系统采用三角形单元、裂缝系统采用线单元对区域进行离散,并对其选用了二次拉格朗日插值函数。采用等效积分原理和变分原理得到原渗流微分方程的泛函,进而分别对基质系统和裂缝系统进行单元特性分析。最后对整体特性进行分析建立了气体渗流的有限元数值模型,并对模型进行求解及验证。本文基于裂缝性致密气藏压裂气井产能预测模型开展压裂裂缝参数优化研究,得到以下结论:(1)储层基质渗透率较低时,宜采用缝网压裂来达到较好的改造效果。当基质渗透率相对较高时,可以考虑采用常规单缝压裂来达到与缝网压裂几乎相同的改造效果。(2)开采初期,缝网主裂缝导流能力成为制约产量的关键因素,开采后期,缝网分支缝导流能力和储层改造体积的大小成为影响产量的主要因素。(3)在不同储层渗透率条件下,主裂缝导流能力、分支缝导流能力存在最优值,分支缝导流能力的最优值受基质渗透率影响较主缝大。(4)相同压裂规模下,生产前期,储层改造体积越小,压裂裂缝密度越大,累计产气量越高;但随着生产年限的增长,储层改造体积越大,稳产能力越好,累计产气量越高。本文基于离散裂缝网络模型,通过以裂缝为网格限定条件来表征树状分叉结构压裂裂缝网络,实现了对压裂复杂缝网不规则性的刻画,为较为真实地描述压裂复杂裂缝提供了新的方法,同时模拟研究结果为致密气藏压裂工艺的优选提供了理论依据,同时为缝网压裂裂缝参数的优化提供了思路和手段。
[Abstract]:With the decrease of conventional oil and gas resources, unconventional reservoirs gradually become the focus of exploration and development. Dense gas reservoirs are rich in resources and have great potential for development. Dense gas reservoirs are characterized by natural fractures and low matrix permeability. For different reservoir conditions, each parameter of fracturing fracture has different influence on productivity, according to the characteristics of a certain reservoir, what kind of fracturing fracture form should be selected. And how the fracturing fracture parameters affect the fracturing effect is one of the problems that need to be solved to achieve reasonable and efficient development of the tight gas reservoir. This paper is based on the discrete fracture network model. The finite element method is used to establish a numerical model for predicting the production performance of fractured gas wells in fractured tight gas reservoirs, and based on this model, the fracture parameters are studied. The random distributed natural fracture network model is established by using Monte-Carlo simulation method, and then the tree bifurcation structure is used to characterize the irregular fracturing fracture shape, which is embedded in the natural fracture network model. The discrete fracture network model of fractured tight gas reservoir after compression is obtained. Then the mathematical model of gas seepage is discretized according to the finite element theory: triangular element is used for matrix system and line element is used for discrete area in fracture system. The quadratic Lagrangian interpolation function is selected. The functional of the original seepage differential equation is obtained by using the equivalent integral principle and the variational principle. Then the element characteristics of matrix system and fracture system are analyzed respectively. Finally, the finite element numerical model of gas seepage is established. Based on the model of fractured tight gas reservoir fracturing gas well productivity prediction model, this paper studies the optimization of fracturing fracture parameters, and obtains the following conclusion: 1) when the reservoir matrix permeability is low, When the matrix permeability is relatively high, the conventional single fracture fracturing can be used to achieve the same revamping effect as fracture mesh fracturing. The main fracture conductivity of fracture net becomes the key factor to restrict the production. In the later stage of exploitation, the permeability of branch fracture and the volume of reservoir reconstruction become the main factors that affect the production. (3) under different reservoir permeability conditions, the main fracture conductivity. At the same fracturing scale, the smaller the volume of reservoir reconstruction, the greater the fracture density and the higher the cumulative gas production. However, with the increase of production years, the larger the volume of reservoir reconstruction, the better the stable production capacity and the higher the cumulative gas production. Based on the discrete fracture network model, this paper describes the tree-branched fracturing fracture network by taking the fracture as the grid qualification condition. The irregularity of fracturing complex fracture network is described, which provides a new method to describe the complex fracturing fracture, and the simulation results provide a theoretical basis for the optimization of fracturing technology in tight gas reservoir. At the same time, it provides the train of thought and means for optimizing fracture parameters of fracture mesh fracturing.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE377

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