多段压裂水平井压力计算及分析方法

发布时间：2018-10-26 09:26

【摘要】：在致密油气及页岩气等低渗透和特低渗透油田的开采中,其储层自然产能低,必须通过储层改造才可能达到工业油气流的标准。水平井及其分段压裂作为一种致密油气藏开发的有力手段,能有效增大油气接触面积进而提高油气产能,因此近几年来在低渗透油气田中得到迅速发展和广泛应用。由于低渗透储层的致密性,其压裂改造难度很大,成本很高,因而对压裂施工方案进行优化设计是致密储层高效和经济开采的关键,如根据储层的特征进行水平井的布井,以及对水平井压裂段数和裂缝半长的优化。同时本文的研究涉及到渗流方程解析和数值方法,对计算渗流力学方法,有一定的指导意义。本文的研究如下：首先,针对油井多段压裂水平井建立方程,运用Newman乘积法得到了直井和水平井的单裂缝解析解。为了将单裂缝解推广到多段压裂井,我们建立了二维模型,并假设各个裂缝的流量并不等于其长度比,建立多段压裂水平井方程,求解各裂缝流量和井底压力随时间的变化。求解的结果表明,在流动的前期,裂缝长度与其流量基本成正比；而在流动的后期,裂缝流量基本与长度无关,影响裂缝流量的主要是裂缝分布位置。因此,建议水平井压裂应尽可能使裂缝长度一致,位置均匀分布。其次,本文考虑了真实气体状态方程对页岩气状态进行描述,用Langmuir吸附对页岩气体吸附和解析吸附现象进行描述,并考虑了气体压敏效应,定义了页岩气标准压力,最终得到了页岩气多段压裂水平井的解析解。在计算过程中,为了加快计算速度,采用了GPU加速计算技术,从而得到页岩气井底压力及其导数随时间的变化并讨论了吸附系数,储容比等参数对于页岩气开采中的井底压力的影响。再次,为了克服上述解析方法的局限即必须矩形边界并且井与边界必须平行的限制,提出了复杂油气储层水平井多段压裂非结构PEBI网络划分方法及有效裂缝半长,并在此基础上实现了渗流方程的有限体积离散。针对离散后线性方程组具有稀疏性、不规则性、大规模性及非对称性的特点,采用预处理的GMRES进行求解,并研发了相应的数值模拟程序。通过与数值解相对比,验证了解析解的正确性。最后将本文的结论运用到某油田,并对一口井例在不同裂缝半长和角度下进行模拟,同时给出了具体的优化建议。在实际应用中发现,当水平井较长且裂缝较多时,水平井多段压裂井底压力可近似为带有负表皮的水平井。
[Abstract]:In the production of low permeability and ultra-low permeability oil fields such as tight oil and gas and shale gas, the natural productivity of its reservoir is low, so it must be reformed in order to meet the standard of industrial oil and gas flow. Horizontal well and its fracturing, as a powerful means to develop a tight reservoir, can effectively increase the contact area of oil and gas and increase the productivity of oil and gas, so it has been rapidly developed and widely used in low permeability oil and gas fields in recent years. Because of the compactness of low permeability reservoir, it is very difficult and expensive to reconstruct fracturing, so the optimization design of fracturing operation scheme is the key to high efficiency and economic exploitation of tight reservoir, such as well layout of horizontal well according to reservoir characteristics. And the optimization of fracturing section number and fracture half length of horizontal well. At the same time, the research of this paper involves the analytical and numerical methods of seepage equation, which has certain guiding significance for the calculation of seepage mechanics method. The research in this paper is as follows: firstly, the analytical solutions of single fracture of straight well and horizontal well are obtained by using Newman product method to establish the equation for multi-stage fracturing horizontal well. In order to extend the single fracture solution to multistage fracturing wells, a two-dimensional model is established, and assuming that the flow rate of each fracture is not equal to its length ratio, the multistage fracturing horizontal well equation is established to solve the variation of fracture flow rate and bottom hole pressure with time. The results show that in the early stage of flow, the crack length is proportional to the flow rate, but in the later stage of flow, the crack flow is basically independent of the length, and the crack distribution is mainly affected by the crack flow. Therefore, it is suggested that the fracture length should be consistent and the position should be uniformly distributed in horizontal well fracturing as far as possible. Secondly, the state of shale gas is described by the equation of state of real gas, the phenomenon of adsorption and desorption of shale gas is described by Langmuir adsorption, and the pressure sensitive effect of gas is considered, and the standard pressure of shale gas is defined. Finally, the analytical solution of multistage fracturing horizontal well of shale gas is obtained. In order to speed up the calculation process, the GPU accelerated calculation technique is used to obtain the variation of the bottom hole pressure and its derivative of shale gas with time, and the adsorption coefficient is discussed. The effect of reservoir capacity ratio and other parameters on bottom hole pressure in shale gas production. Thirdly, in order to overcome the limitation of the above analytical method, that is, the rectangular boundary must be restricted and the well and the boundary must be parallel, the method of dividing the unstructured PEBI network and the effective fracture half length of the multi-section fracturing in horizontal wells of complex oil and gas reservoir are proposed. On this basis, the finite volume discretization of seepage equation is realized. Aiming at the characteristics of sparse, irregular, large-scale and asymmetric linear equations after discretization, the preprocessing GMRES is used to solve the problem, and the corresponding numerical simulation program is developed. The correctness of the analytical solution is verified by comparison with the numerical solution. Finally, the conclusion of this paper is applied to a certain oil field, and a well example is simulated under different fracture half-length and angle, and some specific optimization suggestions are given at the same time. In practical application, it is found that when the horizontal wells are longer and have more fractures, the bottom pressure of multi-section fracturing wells in horizontal wells can be similar to that of horizontal wells with negative skin.
【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】：TE357

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