气井二次压裂裂缝轨迹模拟

发布时间：2018-01-22 01:26

本文关键词： 二次压裂转向压裂诱导应力裂缝轨迹数值模拟　出处：《西南石油大学》2015年硕士论文　论文类型：学位论文

【摘要】：对于采用压裂投产的油气井而言,由于老裂缝控制的油气已接近全部采出,必须实施转向二次压裂,才能有效开采出老裂缝控制区以外的油气,提高油气产量和油气田最终采收率。本文针对垂直裂缝气井二次压裂前应力场的分布特征、新裂缝的重定向以及新裂缝延伸轨迹等问题开展了系统的、深入的研究,取得了如下主要研究成果： (1)应用弹性力学理论,建立并求解了气井初次人工裂缝的诱导应力数学模型,进而完成了人工裂缝诱导应力的影响因素分析,分析表明：人工裂缝诱导应力和诱导应力差随作用于裂缝壁面的净压力的增大和缝高的增加而增大；人工裂缝诱导应力随泊松比的增加而增大,诱导应力差却随之减小。 (2)综合应用渗流力学和岩石力学理论,建立了流—固耦合应力场计算模型。该模型中的耦合渗流方程考虑了储层渗透率各向异性,采用有限差分法求解,而对岩土变形方程则采用有限元法求解,并采用显式交替求解方式将它们结合起来整体求解,实现了对垂直裂缝气井二次压裂前由长期生产活动产生的诱导应力场的定量分析和模拟。 (3)根据建立的流-固耦合计算模型,对影响气井生产诱导应力的因素进行了分析,分析表明：生产时间越长,井底流压越小以及渗透率各向异性越强都有利于井周围各点产生更大的诱导应力差值,使得应力重定向区域越大；缝长、泊松比和弹性模量对生产诱导应力的影响相对较小,泊松比和弹性模量的增大不利于应力重定向,而缝长主要影响裂缝远处应力重定向。 (4)采用最大周向拉应力起裂判据分析了新缝延伸轨迹,完成了新缝延伸轨迹的影响因素分析,分析表明：生产时间、井底流压、渗透率各向异性和原始水平主应力差是影响新裂缝转向的主要因素,且生产时间越长,井底流压越小,渗透率各向异性越强和原始水平主应力差越小都有利于二次压裂新裂缝具有更大的转向距离,进而尽可能地沟通储层的未动用区域。 (5)在理论推导的基础上,通过VB6.0语言编制了气井二次压裂前应力场分布及新裂缝延伸轨迹计算程序,实现了二次压裂气井应力场变化及新裂缝延伸轨迹的定量分析。本文的研究可以为气井二次压裂优化设计提供一定的理论基础,以及指导二次压裂施工,提高其工艺可行性和经济可行性,这对老油气田综合治理、稳产增产具有较为重要的意义。
[Abstract]:For oil and gas wells with fracturing production, since the oil and gas controlled by old fractures have been nearly all produced, it is necessary to implement secondary fracturing in order to effectively produce oil and gas outside the control area of old fractures. Aiming at the distribution characteristics of stress field before secondary fracturing of vertical fractured gas wells, the reorientation of new fractures and the trajectory of new fractures, etc., this paper has carried out a systematic study on the improvement of oil and gas production and the final recovery of oil and gas fields. The main research results are as follows: 1) based on the theory of elasticity, a mathematical model of induced stress of primary artificial fracture in gas well is established and solved, and the factors influencing the induced stress of artificial fracture are analyzed. The results show that the induced stress and induced stress difference increase with the increase of net pressure and crack height. The induced stress increases with the increase of Poisson's ratio, but the induced stress difference decreases with the increase of Poisson's ratio. (2) based on the theory of seepage mechanics and rock mechanics, a computational model of fluid-solid coupling stress field is established. The coupled seepage equation in this model takes account of reservoir permeability anisotropy and is solved by finite difference method. The deformation equations of rock and soil are solved by finite element method, and they are solved by alternating explicit solution. The quantitative analysis and simulation of induced stress field produced by long-term production activities before secondary fracturing of vertical fractured gas wells are realized. 3) according to the fluid-solid coupling calculation model established, the factors influencing the induced stress in gas well production are analyzed. The analysis shows that the longer the production time is, the longer the production time is. The smaller the bottom hole flow pressure and the stronger the permeability anisotropy are, the greater the induced stress difference is, and the larger the stress reorientation area is. The effect of joint length, Poisson's ratio and elastic modulus on the induced stress is relatively small. The increase of Poisson's ratio and elastic modulus is not conducive to the stress reorientation, while the joint length mainly affects the stress reorientation in the distance of the crack. 4) using the criterion of maximum circumferential tensile stress to analyze the trajectory of new fracture extension, the factors influencing the trajectory of new crack extension are analyzed. The analysis shows that: production time, bottom hole flow pressure. The anisotropy of permeability and the difference of primary horizontal principal stress are the main factors affecting the new fracture turn, and the longer the production time is, the smaller the bottom hole flow pressure is. The stronger the permeability anisotropy and the smaller the primary horizontal principal stress difference are, the greater the turning distance of the new fracture is, and then the unproduced area of the reservoir can be communicated as much as possible. 5) on the basis of theoretical derivation, a program for calculating stress field distribution and new fracture extension trajectory before secondary fracturing in gas wells is compiled by VB6.0 language. The quantitative analysis of stress field change and new fracture extension trajectory of secondary fracturing gas well is realized. The research in this paper can provide a certain theoretical basis for the secondary fracturing optimization design of gas wells, and guide the secondary fracturing operation to improve its technological and economic feasibility, which can comprehensively control the old oil and gas fields. It is of great significance to stabilize production and increase production.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE357

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