【作者】 刘冰；

【导师】 李继志； 徐兴平；

【作者基本信息】 中国石油大学 ， 机械设计及理论， 2011， 博士

【摘要】 水平井的产能评价和完井参数优化设计是水平井技术研究中的热点问题。水平井具有泄油面积大和生产压差小的特点,已经成为提高单井产量、延迟底水或顶气锥进、改善开发效果和提高采收率的重要途径。本文以顶底封闭无限大板状油藏中的裸眼和射孔水平井为研究对象,系统研究了水平井油藏渗流和水平井筒压降模型,建立了水平井油藏渗流与井筒变质量流动耦合模型,进行了影响水平井产能的完井参数敏感性分析;将最优化理论应用于油藏渗流与井筒流动耦合模型,在完井参数敏感性分析的基础上,建立了射孔水平井的参数优化模型,并采用序列二次规划(SQP)算法对其进行优化分析。通过研究和分析,得到以下主要研究成果:针对顶底封闭边界的均质各向异性无限大板状油藏中的单相渗流问题,采用Green函数和源函数法、Newman乘积法、Laplace变换与反变换、叠加原理、镜像法等数学物理方法,并考虑地层损害和非Darcy流所产生的附加压降,得到了时域中裸眼和射孔水平井井筒表面处压力响应方程的长时间渐近解;将该压力响应方程与考虑摩擦损失、加速损失和壁面入流影响产生的井筒压降模型进行耦合,建立了水平井油藏渗流与井筒流动耦合模型,为水平井产能评价、敏感性参数分析和参数优化设计提供了理论基础。裸眼水平井产能影响的完井参数敏感性分析表明,水平井位于油藏中部时产能指数最大,偏离中部时其产能指数均呈下降趋势。产能指数随水平井长度的增加而增大且存在一个最优长度。同一污染程度条件下,产能指数随地层污染厚度的增加而减小;同一地层污染厚度下,产能指数随污染程度的增大而明显减小;污染程度较小时,产能指数随地层污染厚度的增加而减小缓慢;污染程度较大时,产能指数随地层污染厚度的增加而明显减小。非Darcy流在流量较大时对产能指数有显著的影响。射孔水平井产能影响的完井参数敏感性分析表明,相位角对产能指数有显著的影响且180o相位角性能最好,相位角对产能指数的影响在孔密较大时差别较小而在孔密较小时差别较大。产能指数随射孔密度的增大而增大,但当射孔密度超过6孔/m时,增加射孔密度对产能指数的影响不大。增加孔眼深度可以提高水平井的产能,而且孔密较小时的孔深对产能影响尤为显著。射孔能否穿过钻井污染带对产能非常重要,钻井污染带厚度大于射孔深度时,产能指数随钻井污染带厚度的增加而缓慢减小,随钻井污染带渗透率的减小而减小,钻井污染在孔眼未穿过污染带时严重影响产能,钻井污染程度小于0.5时将导致产能显著减小,而钻井污染程度大于0.5时将保证水平井有较高的产能,在较低的钻井污染程度下进行深穿透射孔可以获得更高的产能。射孔损害程度大于0.4时,射孔损害对产能指数的影响并不严重。非Darcy流在流量较大时对产能指数有显著的影响。基于油藏渗流与井筒流动耦合模型,在完井参数敏感性分析的基础上,结合最优化理论,以提高产能和改善沿井入流剖面为目的,建立了以孔眼位置为决策变量、以沿井入流量为约束条件、以产能指数为目标函数的射孔水平井优化数学模型,为射孔水平井的参数优化提供了研究基础。编程实现了SQP算法程序,对几个典型非线性约束优化问题进行了数值试验,所得结果基本与文献结果一致,验证了该算法的正确性。通过SQP算法对射孔水平井完井参数优化分析表明,射孔水平井位于油藏中部,采用180o相位螺旋布孔,孔深穿过钻井污染带,沿井射孔密度呈“∪”形分布时,产能指数最大,沿井射孔密度呈“∩”形分布时,沿井入流剖面均匀、产能指数有所降低但不明显。采用全井段变密度射孔对产能的提高并不明显。采用选择性完井射孔时,每个射孔段孔密的增加都将提高水平井的产能,但增加端部处的孔密可显著提高水平井的产能。建立了射孔水平井的参数优化策略,对射孔水平井的优化设计具有理论指导意义。更多还原

【Abstract】 Productivity evaluation and completion parameter optimization of the horizontal well has been the highlight of horizontal well technology. Horizontal wells are one of the most important strategic tools in increasing productivity significantly, delaying water or gas coning, enhancing oil recovery and improving exploitation effect by enhancing the reservoir contact area and creating smaller drawdown. As result of advantages and widespread application of horizontal wells in field development, the state of applications of horizontal well technology require better completion designs to optimize production rate. Concentrating on an openhole or a perforating completed horizontal well in a homogeneous anisotropic infinite slab reservoir confined by top and bottom no-flow boundaries, a comprehensive semi-analytical model coupling the flow equations in the reservoir and wellbore is developed to investigate the effect of well completion on horizontal well performance. Based on the coupling model, the sensitivity analysis performed for a perforating completed horizontal well and optimal theories, mathematical optimization models for completion parameters are established and solved by sequential quadratic programming (SQP) algorithm to maximize production and obtain uniform inflow rate along the wellbore.Openhole completion horizontal well or perforations for perforating completed horizontal well are modeled as line sources in a homogeneous anisotropic infinite slab reservoir with no-flow at both top and bottom boundaries. The method of source and Green’s functions, Newman’s product method, Laplace and its inverse transform, the method of images and principle of superposition are used to derive the long-time asymptotic solutions of the pressure response in real time domain for single-phase flow in the reservoir along the well surface. The additional pressure drop due to formation damage and non-Darcy flow are addressed and incorporated into long-time asymptotic equations of pressure response. The wellbore flow model considers the pressure losses inside the well due to friction and acceleration and the effect of influx from the reservoir into the horizontal well. A comprehensive semi-analytical model which couples the reservoir and wellbore flow equations and takes into account formation damage, non-Darcy flow is presented and can be used to evaluate the productivity, perform sensitivity analysis and optimize perforating completed parameters. This study will provide the knowledge of basic theory for production rate, sensitivity analysis and optimization for completion parameters of a horizontal well.Sensitivity analysis performed for completion parameters of an openhole completed horizontal well shows, the productivity index is maximum when the well is located at the center of the reservoir; increasing well length increases the productivity index but there exists an optimum length; the productivity index decreases with increment of drilling damage thickness for same ratio of damamge permeability to formation permeability; increment of ratio of damamge permeability to formation permeability for same damage thickness results in significant reduction of productivity index; increment of damage thickness results in less reduction of productivity index for less ratio of damage permeability to formation permeability; reduction of productivity index with increment of damage thickness becomes severe for larger ratio of damage permeability to formation permeability; the impact of non-Darcy flow upon productivity index becomes obvious for higher flow rate.Sensitivity analysis performed for completion parameters of a perforating completed horizontal well indicates, perforation phase angle has significant effect on productivity index, 180o phasing angle is the best, and the difference in effect of phase angle on productivity index becomes unconspicuous for higher perforation density but obvious for low perforation density; perforation density has significant impact on productivity index, increasing perforation density enhances productivity index but the gain in productivity index becomes negligible beyond the density of 6 shot/m; the increment of perforation penetration improves productivity of the well and perforaton length has more important influence on productivity index especially for low perforating density; whether perforations terminated inside or extended beyond damaged zone has more important influence on productivity of the well, the reduction of productivity index due ot the further increase of damage zone thickness becomes moderate for damaged zone penetrated by perforations; the smaller the damage zone permeability, the smaller the well productivity, damage zone has more severe influence on well productivity for perforations terminated inside the damaged zone; drilling damage leads to significant reduction of well productivity when the ratio of damage permeability to formation permeability is smaller than 0.5, however, the ratio beyond 0.5 guarantees relatively high well productivity; when the ratio of perforating crushed zone permeability to formation permeability is larger than 0.4, perforating damage impact on well productivity is not severe; the influence of non-Darcy flow has obvious influence on productivity index for higher flow rate.On the basis of the comprehensive semi-analytical model, the sensitive analysis of the performance of perforating completed horizontal well and optimal theories, mathematical optimization models in which the productivity index is treated as an objective function, the perforation locations as decision-making variables and the inflow profile as constraints are presented to maximize the productivity index or lead to uniformity of specific inflow along the wellbore. The establishment of optimization models provides the theoretical basis of optimizing perforating parameters of horizontal wells.A program based on SQP algorithm in optimal theories is developed and verified by some typical nonlinear programmings with constraints. Then, the program is used to solve optimization models assisting in investigating how perforation distribution affects the performance of a horizontal well under infinite and finite conductivity. The results shows the perforating completed horizontal well is located at the center of the reservoir and perforated by 180o phasing angle, perforations are penetrated drilling damages zone, and the perforation density with a shape of“U”curve is distributed along the wellbore, the well productivity becomes maximum; the perforation density with a shap of“∩”curve will result in a uniform inflow rate along the wellbore; the variable perforation density along full length of the wellbore does not significantly improve the well productivity; increasing perforation density in each open segment for selective completion of the well improves well productivity but using high perforation density near the heel end of the well significantly enhance the well productivity. Last, the guidelines of perforating parameters optimization are developed.更多还原