【作者】 王伟章；

【导师】 闫相祯；

【作者基本信息】 中国石油大学 ， 机械设计及理论， 2008， 博士

【摘要】 疏松砂岩油藏在我国分布范围广、储量大,出砂是疏松砂岩油藏开采中经常遇到的难题之一。在国内外各油田生产中均广泛存在着出砂问题,而油井出砂已成为目前制约油田稳产上产的重要因素之一。目前各油田针对油井出砂问题较多采用的工艺方法是高压挤压充填技术。但长期以来疏松砂岩高压挤压理论体系未能得到有效建立,理论与实际应用的脱节,导致工艺技术和施工参数不甚合理,影响了高压挤压防砂技术的进一步发展。文章从疏松砂岩的岩石特性以及施工工艺角度分析了影响高压挤压砾石充填效果的各种可能因素。在此基础上,认为高压挤压充填压实过程为高压浆液挤压目标岩层使它发生弹塑性变形,然后携砂液占领这些空隙,达到近井压实充填的目的。随着施工压力的不断增大,塑性区内的岩层持续被压实,当压实到一定程度,携砂液无法挤入到岩层的孔隙中去时,携砂液积聚的能量会快速增加,当目标岩层附近井底压力增大到一定程度,岩体就会开始沿一定方向发生启裂。文章在对砾石在携砂液中运动进行力学分析的基础上,借鉴泥沙运动力学的成果,研究了高压挤压过程中砾石的运移规律。针对目前高压砾石充填后近井地带形态认识不清以及现有理论没有考虑井底岩层压实的情况,首次根据摩尔-库仑准则和平面应变轴对称问题的基本理论,推导得出了疏松砂岩高压挤压时近井地带的应力场、应变场和位移场等参数同压实区半径之间的关系,并通过算例分析了疏松砂岩岩体的内摩擦角、杨氏模量等参数对高压挤压结果的影响。以离散元理论为基础,利用二维颗粒流模拟软件PFC2D,针对疏松砂岩油藏,进行了数值模拟。模拟结果显示:当施加均匀地应力时,井眼产生均匀扩张现象,近井砾石充填体形状近似为圆形,井眼周围目标层被压密压实,岩层孔隙明显减小;模型被施加非均匀地应力时,井眼亦产生扩张现象,但其扩张沿最小地应力方向幅度较大,沿最大地应力方向较小,近井砾石充填体形状为近似椭圆形,井眼周围目标层被压密压实。模拟结果还显示,胶结强度不同的地层在高压挤压后,其地层形态差别较大。胶结较强的疏松砂岩地层,高压挤压后地层的形态接近于低渗油藏,胶结弱的疏松砂岩地层,高压挤压后井眼周围岩层被压散,沿最大主应力方向地层会出现数条裂缝。为正确确定地层软硬程度,为高压挤压砾石充填技术提供理论指导,本文首次提出疏松砂岩挤压模量概念,并在挤压模量计算公式推导的基础上提出疏松砂岩岩层挤压指数概念。采用推导的挤压模量计算公式对胜利油田防砂中心提供的具有完整测井资料的多口施工井进行编程计算,将各施工井挤压模量等相关参数加权平均后进行拟合得到两组拟合公式。研究了施工参数和地应力等因素对单位油层管外填砂量的影响,在此基础上对前面所拟合的公式进行了修正。文章最后对高压挤压施工过程中,套管最薄弱位置—射孔段的强度利用有限元法进行了分析研究,认为射孔孔密和相位相同时,随着孔径的增大,套管抗压强度降低;孔径和相位相同时,随着孔密的增大,套管抗压强度降低;孔密和孔径相同时,当相位在90度至180度区间内时,套管内的应力随着相位的增大而增大;当套管内施加内压时,套管射孔段的应力状况得到改善。根据推导得出的理论模型,开发了高压挤压充填优化设计软件。更多还原

【Abstract】 Loose sand reservoirs are suffering from sand production seriousely, which are distributed widely all around our country. Sand production problem can be found in many oil fields home and abroad and it is one of the important factor that confine the oil fields production increase. High pressure gravel packing is a popular sand control technology used by many oil fields at present. However, the theoretical system about high pressure gravel packing is not established effectively in a long period, disjunction of theory and practice, leads to the technology and construction parameters are not so reasonable, and the further development of high pressure gravel packing is blocked.The thesis analyzed the factors influencing the effect of high pressure gravel packing from the angle of the character of loose sand and the construction technology. Above this, the procedure of high pressure gravel packing could be described by the following words. Near well-bore area was compacted under grout pressure, elastoplastic deformation took place, and the gravels in carrier fluid filled the space, so the purpose for compacting and packing the near well-bore area was achieved. With the increasing of construction pressure, the stratum in the plastic area is compacted continuancely until carrier fluid could not be pushed into the space of the stratum, and the energy of carrier fluid gathered rapidly at this time, fractures emerging in certain directions when the pressure around aim stratum reached a certain degree.Based on the mechanics analysis of gravel moving in the carrier fluid, the thesis applies to the result of sediment movement, studied the migration mechanism of gravel during high pressure packing.Considering the fact that the configuration of near well-bore area after the construction was not understood rather clearly and the present mathematical model of frac-packing did not consider the near well-bore area might be compacted, firstly based on the Mohr-Coulomb criterion and the basic theory of plane strain axisymmetric problem, developed the relationship between the radius of compacted area and the stress, strain and displacement of near well-bore area, and the influence of rock parameters such as internal friction angel and young modulus was studied by some examples.On the basis of discrete element theory, numerical stimulation for loose sand reservoir was carried out by the software PFC2D, and some conclusions were attained. The results provided some recognitions about the near well-bore area configuration. The well bore had a uniform extension under uniform in-situ stress, the packed area was a proximate circle, the target stratum was compacted, and the porosity decreased significantly. It still had an extension under nonuniform in-situ stress, and the extension magnitude in the minimum stress direction was bigger compared with the maximum stress direction. In addition, different cementation strength made different near well-bore configuration after construction. The configuration of the loose sand reservoir with high cementation strength approximated to the low permeability reservoirs, but as to the weak consolidation reservoir, the rock near well bore was compacted with some fractures in the maximum stress direction.In order to determine the hardness of the stratum and provide theoretical guidance to high pressure gravel packing technology, rock compaction modulus was proposed creatively which was defined as the ratio of compression stress to compression strain under vertical restraint condition. On the basis of the deduction of compaction modulus, the concept of rock compressibility was put forward.With the deduced formulas, several oil wells offered by ShengLi oil field sandcontrol center with complete logging data were calculated. Two fitting formulas are attained according to some parameters such as compaction modulus, and some corrections to the fitting formulas were performed according to construction parameters and in-situ stress condition.Perforation section as the weak part of casing during high pressure gravel packing, was simulated through finite element method. With fixed perforation phase angel and density, the compressive strength decrease with the perforation diameter increase. With fixed perforation phase angel and diameter, the compressive strength decrease with the perforation density. With fixed perforation phase diameter and density, the casing stress increased with the perforation phase angel when the phase angel was located between 90 and 180 degree. Stress condition in the casing perforation improves when internal pressure is applied in the casing.An optimum design software for high pressure gravel packing was developed based on the theoretical model.更多还原